origin of fayalitic olivine rims and lath shaped matrix olivine in the cv3 chondrite allende and its dark inclusions we have studied an allende dark inclusion by optical microscopy scanning electron microscopy electron microprobe analysis and transmission electron microscopy the inclusion consists of chondrules isolated olivines and matrix which as in the allende host is mainly composed of 5 20 m long lath shaped fayalitic grains with a narrow compositional range fa42 2 and nepheline olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5 10 m wide fayalitic rims fa39 2 and 100 1000 m wide translucent zones which consist of 5 20 m long lath shaped fayalitic grains fa41 1 intergrown with nepheline these fayalitic olivines like those in the matrix of the dark inclusion contain 10 20 nm sized inclusions of chromite hercynite and fe ni sulfides the fayalitic rims around remnant olivines are texturally and compositionally identical to those in allende host suggesting that they have similar origins chondrules are surrounded by opaque rims consisting of tiny lath shaped fayalitic olivines 1 3 m long intergrown with nepheline as in the allende host fayalitic olivine veins may crosscut altered chondrules fine grained chondrule rims and extend into the matrix indicating that alteration occurred after accretion we infer that fayalitic olivine rims and lath shaped fayalites in allende and its dark inclusions formed from phyllosilicate intermediate phases this explanation accounts for 1 the similarity of the replacement textures observed in the dark inclusion and allende host to aqueous alteration textures in cm chondrites 2 the anomalously high abundances of al and cr and the presence of tiny inclusions of spinels and sulfides in fayalitic olivines in allende and allende dark inclusions 3 abundant voids and defects in lath shaped fayalites in the allende dark inclusion which may be analogous to those in partly dehydrated phyllosilicates in metamorphosed cm ci chondrites we conclude that the matrix and chondrule rims in allende were largely converted to phyllosilicates and then completely dehydrated the allende dark inclusions experienced diverse degrees of aqueous hydrothermal alteration prior to complete dehydration the absence of low ca pyroxene in the dark inclusion and its significant replacement by fayalitic olivine in allende is consistent with the lower resistance of low ca pyroxene to aqueous alteration relative to forsteritic olivine hydro thermal processing of allende probably also accounts for the low abundance of planetary noble gases and interstellar grains and the formation of nepheline sodalite salite hedenbergite pyroxenes wollastonite kirschsteinite and andradite in chondrules and ca al rich inclusions

oxygen isotopic evolution of amoeboid olivine aggregates in the reduced cv3 chondrites efremovka vigarano and leoville amoeboid olivine aggregates aoas from the reduced cv chondrites efremovka vigarano and leoville consist of forsteritic olivine feni metal and a refractory component composed of spinel al diopside anorthite secondary ferrous olivine and alkali rich minerals nepheline and sodalite commonly observed in the oxidized cvs are rare mineralogy and chemical compositions of aoas are similar to those predicted by equilibrium thermodynamic condensation models suggesting that aoas formed primarily by gas solid condensation over a narrow temperature range slightly below the temperatures over which most ca al rich inclusions cais formed aoas in the reduced cvs preserve a 1st generation 16o rich signal 17 18o 40 similar to that observed in many cais suggesting that these refractory objects originated from a common source in the solar nebula in fact aoas and many fine grained cais may have formed by the same processes but at slightly different temperatures and can be considered a single class of refractory objects alteration of the aoas is manifested by differing extents of 16o depletion in original aoa minerals feo enrichment in olivine and formation of interstitial very fine grained na bearing phases from the six aoas and one fine grained melilite pyroxene rich cai examined in this study five distinct patterns of alteration were identified 1 one unaltered aoa from vigarano is characterized by 16o rich forsterite without feo rich rims and interstitial na bearing phases 2 weak alteration in the melilite pyroxene rich cai is characterized by incomplete 16o depletion in some melilite and precipitation of na bearing phases near the cai rim 3 oxygen isotopic composition and mineralogy are correlated in two aoas from leoville with 16o rich olivine 16o poor anorthite and a range of intermediate compositions in al diopside this pattern is consistent with model diffusion between original grains and a 16o poor reservoir during a relatively short term 60 yr high temperature 900 1100 c event 4 original forsterite has been enriched in feo but remained 16o rich in one aoa from vigarano this result is consistent with the slower rate of diffusion of o than fe and mg in olivine at least some interstitial phases are 16o rich and na bearing phases are abundant in this aoa 5 in contrast oxygen isotopic composition and fo content are correlated in two aoas from efremovka the olivine in these aoas tends to have forsteritic 16o rich cores and feo rich 16o depleted rims the general correlation between oxygen isotopic composition and fo content is difficult to model by diffusion and may have formed instead by aqueous dissolution and precipitation along the margins of preexisting olivine grains independent evidence for aqueous alteration of the efremovka aoas is provided by oh rich signals detected during ion beam sputtering of some of the 16o poor olivine elevated 16oh count rates and order of magnitude increases in 16oh detected during single analyses reflect trapping of an aqueous phase in 16o depleted olivine an elevated 16oh signal was also detected in one analysis of relatively 16o poor melilite in the melilite pyroxene cai from vigarano suggesting that this object also was altered by aqueous fluid

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

the impact of ancient civilization on the northeastern chinese landscape palaeoecological evidence from the western liaohe river basin inner mongolia the western liaohe river basin in northeastern china is one of the cradles of ancient chinese civilization archaeological records from this region indicate that human occupation began about 8000 y

fayalitic olivine in cv3 chondrite matrix and dark inclusions a nebular origin fayalitic olivine fa32 is the major component of the matrices and dark inclusions of cv3 and other unequilibrated chondrites it occurs most commonly as rims veins and halos in and around chondrule silicates in the allende type cv3oxa chondrites and to a much lesser extent in the reduced cv3r and bali type cv3oxb chondrites the olivines have distinctive platy tabular and lath or irregular shaped crystals with the ratio of the two types varying widely in cv3oxb chondrites matrix fayalitic olivines range up to fag99 9 whereas in the other cv3 chondrites the range is much smaller the platy and tabular anisotropic forms of the fayalitic olivines strongly suggest growth from a vapor and the nature of the occurrences suggests that cv3 matrices are unequilibrated mixtures of nebular materials we argue that the parent body hydration dehydration model has numerous inconsistencies that make this hypothesis highly unlikely these include 1 there is no direct evidence linking fayalitic olivine to precursor phyllosilicates 2 dehydration of phyllosilicates cannot explain the wide range of morphologies of the fayalitic olivines 3 fayalitic olivine clearly predates the formation of the hydrous phases in cv3 chondrites and is one of the phases that breaks down to form phyllosilicates keller et al 1994 4 the unequilibrated nature of the matrix including fine scale zoning in 10 m sized fayalitic olivine crystals would not survive the parent body metamorphism required in the dehydration model 5 a dark inclusion in the ningqiang chondrite contains fayalitic olivine rimmed by glassy and microcrystalline material zolensky et al 1997 which probably formed by radiation damage this indicates that the fayalitic olivine was exposed to solar radiation in a nebular setting 6 some allende chondrules contain unaltered primary anhydrous glassy mesostasis in contact with the host matrix e g ikeda and kimura 1995 chondrule mesostases would not have survived parent body hydration without becoming hydrated and would probably not survive the metamorphic heating required in the dehydration scenario 7 single platy and barrel shaped crystals of fayalitic olivine are present in accretionary rims in calcium aluminum rich inclusions cais macpherson and davis 1997 which developed in the nebula 8 matrix lumps completely encased in chondrules in ordinary chondrites contain mainly fayalitic olivine scott et al 1984 which indicates a nebular origin 9 oxygen isotopic compositions of allende matrix and dark inclusions strongly indicate little or no hydration for allende and its components clayton 1997 we favor a nebular vaporization recondensation model in which vaporization of chondritic dust produced a fayalite rich vapor followed by formation of the fayalitic olivine by direct recondensation from the vapor epitactic growth on surfaces of existing forsterite and enstatite in chondrules and replacement of existing forsterite and enstatite by gas solid exchange

climate change and cultural response around 4000 cal yr b p in the western part of chinese loess plateau new data suggest that dramatic environmental change in the western loess plateau of china corresponded with substantial changes in human demography ca 4000 cal yr b p these data demonstrate that a rapid climatic transition from wet to dry led to an ecologically devastated period between 4090 and 3600 cal yr b p the sudden reduction in the number of archaeological sites during this period namely a reduction in the total number of sites and a contraction of the areal distribution of sites points to declining agricultural productivity associated with widespread aridification beginning at 4000 cal yr b p 2005 published by university of washington

human environment interactions within the west liao river basin in northeastern china during the holocene optimum abstract cultural studies of neolithic china have focused on the social aspects and the human environment interactions associated with those cultures however the uneven spatial distribution of neolithic sites in northeastern china has not yet been explored this study traces the relationship between human settlement patterns and the agro ecological environment during the holocene optimum based on the spatial distribution of 4184 neolithic sites together with optically stimulated luminescence osl dating and pollen analysis of five profiles and 22 plant flotation samples from 10 of the archaeological sites in the west liao river basin the hub of neolithic cultures in northeastern china the overwhelming majority 96 7 of the neolithic sites are located south of 43o30 n latitude in the west liao river basin on the southern fringe of the horqin dunefield the dunefield which has been commonly hypothesized as vegetated during the holocene optimum was a typical steppe at that time and not suitable for growing millet the primary staple crop of neolithic cultures our results and other archaeological site records reveal that the 43 30 n latitude was a remarkable barrier for the dispersal of human settlements in northeastern china during the neolithic age the barrier was probably formed by the low frost tolerance of millet and the temperature gradient associated with the latitude making large scale agricultural production impossible in the regions north of this latitude at the time our findings provide evidence for the natural northern limit of neolithic cultures in northeastern china during the holocene optimum

mid infrared spectroscopy of refractory inclusions cais in cv and co chondrites we present laboratory mid infrared absorption spectra 2 5 m to 16 0 m of powdered calcium aluminum rich inclusions cais and matrix separated from the carbonaceous chondrites allende cv3 2 vigarano cv3 3 and ornans co3 3 two groups of spectra with different features were found for the cai in the first group spectra are dominated by spinel pyroxene and sodalite nepheline where main features occur at 9 3 m 10 3 m and 11 3 m in the second group characteristic minerals are spinel and melilite with typical band maxima at 11 0 m and 12 3 m and a broad feature between 14 0 m and 15 0 m the position of the broad spinel feature probably depends on its iron content comparison of band positions in spectra from the cai components to observed circumstellar emission spectra indicates the potential occurrence of cai like material pyroxene and spinel rich features could occur in spectra of dust around the herbig ae star hd104237 the t tauri star hen3 600 and the post agb star r sge melilite and spinel rich components possibly appear in the spectrum of hd104237 hen3 600 04187 1927 r sge and the planetary nebula hb 12 there is also indication for a spinel component in dust from the herbig ae be star hd179218 the spectra of the agb stars r cas and aps show no features of cai type spinel

mid holocene climate change and its effect on prehistoric cultural evolution in eastern qinghai province china abstract we studied the mid holocene climate change in eastern qinghai province china and its impact on the evolution of majiayao 3980 2050 bc and qijia 2183 1635 bc cultures near the important neolithic site of changning the investigation focused on analyses of grain size magnetic susceptibility ratios of elemental contents and pollen assemblage from a loess paleosol sequence the results indicate that the climate was wet during 5830 4900 cal yr bp which promoted the development of early mid majiayao culture in eastern qinghai province however 4900 4700 cal yr bp were drought years in the region responsible for the decline and eastward movement of prehistoric culture during the period of transition from early mid to late majiayao culture the climate turned wet again during 4700 3940 cal yr bp which accelerated the spread of qijia culture to the middle reaches of the huangshui river including the changning site

incompletely transformed serpentine type phyllosilicates in the matrix of antarctic cm chondrites abstract recent hrem high resolution electron microscopy investigation has shed light on the characterization of matrix phyllosilicates in cm chondrites in examining the antarctic cm chondrite yamato 793321 by hrem mineral grains which show an ed electron diffraction pattern consisting of both olivine and serpentine spots show disordered and defect structures in patchy hrem images these data are interpreted as representing an intermediate phase in the transformation from serpentine to olivine this is the first description of such an intermediate phase in belgica 7904 phyllosilicates seem to have been almost completely transformed to olivine it is suggested that it formed by heating of matrix phyllosilicates preliminary heating experiments on murchison also a cm chondrite showed that the matrix phyllosilicates transformed to a phase which gave an ed pattern and hrem image similar to those for yamato 793321 the results of these heating experiments support the formation of the intermediate phase by transformation from phyllosilicate to olivine during a heating event at a late stage

a 700 year history of groundwater recharge in the drylands of nw china a 700 year semi quantitative history of diffuse groundwater recharge in the badain jaran desert inner mongolia is proposed on the basis of solute data from multiple unsaturated zone groundwater profiles using mass balance of chloride to establish recharge rates and profile chronologies four relatively humid 1330 1430 1500 1620 1700 1780 and 1950 1990 and three relatively arid phases 1430 1500 1620 1700 and 1900 1950 are discernable across the profiles the recharge history broadly reflects multidecadal to centurial timescale precipitation changes in the northern tibetan plateau and suggests that variations in east asian summer monsoon intensity affect desert recharge rates uncertainties in the records owing to assumptions about the cl inputs are examined by comparing deterministic and stochastic cl input scenarios such records are valuable for assessing spatial aspects of climate changes in the region as well as for informing sustainable water resource management strategies for northwestern china s drylands

tracking millennial scale climate change by analysis of the modern summer precipitation in the marginal regions of the asian monsoon abstract the asian summer monsoon and the westerly winds interact in the mid latitude regions of east asia so that climate change there is influenced by the combined effect of the two climate systems the holocene millennial scale asian summer monsoon change shows the out of phase relationship with the moisture evolution in arid central asia although much research has been devoted to the long term climate change little work has been done on the mechanism summer precipitation in the marginal regions of the asian monsoon is strongly affected by the monsoon and the westerly winds the purpose of this paper is to examine the mechanism of the millennial scale out of phase relationship by modern summer precipitation analysis in the northwest margin of the asian monsoon 95 110 e 35 45 n first the method of empirical orthogonal function eof analysis was carried out to the 1960 2008 summer rainfall data from 64 stations in that region then the water vapor transportation and geopotential height field data were studied in order to explain and understand the factors that influence the summer precipitation lastly the east asian summer monsoon index easmi south asian summer monsoon index sasmi summer westerly winds index swi were compared with the eof time series the results indicate the complicated interannual scale interaction between the asian summer monsoon and the westerly winds which can result in the modern out of phase relationship in the study area this study demonstrates that the interaction between the two climate systems can be considered as a factor for the millennial scale out of phase relationship

some effects of viscosity on the dynamics of replenished magma chambers some aspects of the dynamical behavior of magma chambers replenished from below with hotter but denser magma have been modeled in a series of laboratory experiments in previously reported work the fluids used were aqueous solutions of comparable viscosity and thus the results should be applicable to basaltic magma chambers in which the magmas do not vary greatly in viscosity in that case the lower layer cools by convective heat transfer to the fluid above and crystallization causes the density of the residual liquid in the lower layer to decrease when the density becomes equal to that in the upper layer sudden overturning and intimate mixing take place the present paper reports experimental results that allow us to extend the application to systems in which there is a large viscosity ratio between the resident and the injected fluid for example to calcalkaline magmas where magma viscosity can vary by as much as 5 orders of magnitude the largest viscosity ratio in our experiments about 3000 was achieved using cold glycerine for the upper layer above a hot denser kno3 solution the most striking new feature with the very viscous upper layer is that now less dense fluid is released immediately and continuously from the interface and rises as plumes through the upper layer further crystallization occurs in the plumes and the crystals fall out but there is little mixing and a layer of depleted kno3 solution is eventually deposited at the top the transfer process between the layers is dominated by interfacial effects with the high viscosity upper layer acting as a nearly rigid lid that allows buoyant fluid to accumulate just below the interface and then rise in localized plumes across the interface into the viscous layer this physical picture is supported by a series of experiments in which the viscosity ratio is varied systematically the mixing behavior changes gradually between that described above for a large viscosity ratio and the sudden over turning characteristic of layers with comparable viscosity the importance of the viscosity ratio rather than just an increase in viscosity is confirmed by experiments in which both viscosities are increased by the same factor the overturning process is then slower but symmetrical other variations suggested by previous experiments are also described the release of gas by a chemical reaction to model the release of volatiles following an overturning event in a magma chamber the effect of a cold immiscible layer above the cooling crystallizing fluid the influence of two viscous layers with a density step between them and the constraining effects of a density with corresponding viscosity gradient in the upper region the experiments indicate that whatever the stratification whether it be in layers or continuous the form of the initial motion in the upper fluid is determined by the viscosity ratio between the two fluids immediately adjacent to the interface geological applications are not examined in detail in this paper but the experiments suggest that both sudden overturning characteristic of magmas of nearly equal viscosity and continuous release when the upper layer is much more viscous are viable mechanisms for magma mixing in the appropriate circumstances

late quaternary aeolian sand deposition sustained by fluvial reworking and sediment supply in the hexi corridor an example from northern chinese drylands abstract aeolian deposits are frequently used for palaeoenvironmental change studies their formation depends on an array of requirements the supply of material suitable for aeolian transport and favorable conditions of sediment availability and wind strength in order to infer palaeoenvironmental information from aeolian sand deposits these factors need to be carefully evaluated we present a study from northern chinese hexi corridor based on 11 optically stimulated luminescence osl dated sediment sections these represent interchanging aeolian and alluvial deposits under gravel surfaces and aeolian sand in dune fields interrupted by interdunal flood deposits investigations in two subareas reveal contrasting geomorphologic and sedimentary histories 1 sediment deposition during the pleistocene holocene transition 12 ka followed by deflation during the holocene and 2 frequent sediment recycling revealed by a wide spectrum of ages throughout the holocene the late glacial sediment pulse recorded in the western hexi corridor is attributed to high sediment supply generated by efficient peri glacial sediment production during glacial times in the adjacent qilian shan geomorphological and hydrological preconditions of the subareas are discussed and reveal the controlling influence of fluvial processes on sand supply for the aeolian system while a perennial drainage is missing in the drier western part the hei river drainage is fed by higher monsoonal precipitation in the central hexi corridor it maintains a sediment recycling system and has ensured a sufficient sediment supply throughout the holocene the study promotes closer consideration of the fluvial influence on aeolian archives in palaeoenvironmental studies from central asian and other drylands

grain size distribution of the matrix in the allende chondrite abstract hrtem atem and sem studies of the allende chondrite reveal that the matrix is composed of very fine grained iron rich olivine ca poor and iron rich clinopyroxene iron rich spinel and ni bearing troilite there are two types of very fine grained aggregates one is not sintered and the other is slightly sintered most 1 10 m olivine aggregates show the sintered microstructure but ultrafine grained aggregates 1 10 nm display little evidence of sintering this means that coarse grained olivine aggregates experienced a heating event but ultrafine grained aggregates underwent no heating event the size distribution of matrix grains were measured by sem and tem at magnifications of 570 000 to 2000 corresponding to grain sizes ranging from 1 nm to 10 m the frequency distribution shows a log normal pattern having a peak at 5 nm in the range from 1 to 10 nm and it has a long term tail with power law this distribution means that the fine grained matrix seems to be formed at conditions far from equilibrium in the protosolar cloud

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

a petrologic and ion microprobe study of a vigarano type b refractory inclusion evolution by multiple stages of alteration and melting abstract usnm 1623 8 is a type b vigarano inclusion 6 mm in diameter consisting of melilite ak12 72 fassaite 17 23 a12o3 5 17 tio2 anorthite and spinel secondary alteration is negligible and consists of diopside and sparse nepheline melilite is normally zoned and contains up to 0 35 wt na2o higher than generally seen in melilite from other refractory inclusions a strong correlation between akermanite content and na2o in 1623 8 melilite suggests that the na was present during igneous crystallization rather than introduced later by diffusion anorthite in 1623 8 is coarse grained but commonly has an irregular border with neighboring melilite crystals many spinel grains enclosed within anorthite have selvages of melilite around them which in places are continuous with melilite exterior to the anorthite the anorthite appears to be replacing melilite ion microprobe analyses of anorthite in 1623 8 show that there is no detectable excess 26mg in nine anorthite crystals that have 27 al 24 mg as high as 970 implying an upper limit of 26 al 27 al 0 7 one crystal was found that has excess 26mg consistent with 26 al 27 al 0 3 10 6 melilite in the outer portion of the inclusion 27 al 24 mg 2 7 11 5 contains excess 26mg that considered together with spinel and pyroxene defines an isochron consistent with the canonical early solar system value of 26 al 27 al 0 4 5 10 5 melilite near an anorthite 27 al 24 mg 1 6 5 9 has 26mg values in excess of those predicted from 26 al 27 al 0 4 5 10 5 presumably caused by redistribution of radiogenic 26mg from adjacent anorthite the high na2o inferred to have been present in the melt suggests that the precursor solids were na bearing such as for example refractory material having an allende like overprint of feldspathoid bearing secondary alteration the melting event must have been brief in order that not all of the na was vaporized during melting the isotopic composition of the anorthite relative to melilite indicates a subsequent much later after the decay of most or all 26a1 episode of partial melting or solidstate recrystallization that did not affect the al rich melilite but reset most of the anorthite and some mg rich melilite near anorthite because the inclusion is both rimmed and slightly altered this late resetting event appears to have been a nebular one an assumption of homogeneously distributed 26a1 in the regions of the nebula where the inclusion formed and was later modified implies a several millionyear interval between condensation of the precursors and final melting of 1623 8

mineralogy and petrology of amoeboid olivine inclusions in co3 chondrites relationship to parent body aqueous alteration petrographic and mineralogic studies of amoeboid olivine inclusions aois in co3 carbonaceous chondrites reveal that they are sensitive indicators of parent body aqueous and thermal alteration as the petrologic subtype increases from 3 0 to 3 8 forsteritic olivine fa0 1 is systematically converted into ferroan olivine fa60 75 we infer that the fe si and o entered the assemblage along grain boundaries forming ferroan olivine that filled fractures and voids as temperatures increased fe 2 from the new olivine exchanged with mg 2 from the original aoi to form diffusive haloes around low feo cores cations of mn 2 ca 2 and cr 3 were also mobilized the systematic changes in aoi textures and olivine compositional distributions can be used to refine the classification of co3 chondrites into subtypes in subtype 3 0 olivine occurs as small forsterite grains fa0 1 free of ferroan olivine in petrologic subtype 3 2 narrow veins of feo rich olivine have formed at forsterite grain boundaries with increasing alteration these veins thicken to form zones of ferroan olivine at the outside aoi margin and within the aoi interior by subtype 3 7 there is a fairly broad olivine compositional distribution in the range fa63 70 and by subtype 3 8 no forsterite remains and the high fa peak has narrowed fa64 67 even at this stage there is incomplete equilibration in the chondrite as a whole e g data for coarse olivine grains in isna co3 8 chondrules and lithic clasts show a peak at fa39 we infer that the mineral changes in aoi identified in the low petrologic types required aqueous or hydrothermal fluids whereas those in subtypes 3 3 largely reflect diffusive exchange within and between mineral grains without the aid of fluids

hydroclimatic changes in china and surroundings during the medieval climate anomaly and little ice age spatial patterns and possible mechanisms abstract investigating hydroclimatic changes during key periods such as the medieval climate anomaly mca 1000 1300 ad and the little ice age lia 1400 1900 ad is of fundamental importance for quantifying the responses of precipitation to greenhouse gas induced warming on regional and global scales this study synthesizes the most up to date and comprehensive proxy moisture precipitation records during the past 1000 years in china and surroundings the proxy data collected include 34 records from arid central asia aca and 37 records from monsoonal asia our results demonstrate a pattern of generally coherent regional moisture variations during the mca and lia in mid latitude asia north of 30 n monsoonal northern china north china and northeast china was generally wetter while aca northwest china and central asia was generally drier during the mca than in the lia a west east mode the boundary between wetter northern china and drier aca was roughly consistent with the modern summer monsoon boundary in monsoonal china to the east of 105 e the northern part was generally wetter while the southern part was generally drier during the mca than in the lia a north south mode with a boundary roughly along the huai river at about 34 n these spatial patterns of moisture precipitation variations are also identified by instrumental data during the past 50 years in order to understand the possible mechanisms related to the moisture variations during the mca and lia we investigate the major sst and atmospheric modes e g the el nino southern oscillation enso the atlantic multidecadal oscillation amo and the north atlantic oscillation nao which affect the moisture precipitation variations in the study region using both the instrumental data and the reconstructed time series it is found that the enso may play an important role in determining hydroclimatic variability over china and surroundings on a multi centennial time scale and that the foregoing spatial patterns could be attributed to the la nina like el nino like condition during the mca lia in addition amo and nao may also have their own contributions

the impact of early smelting on the environment of huoshiliang in hexi corridor nw china as recorded by fossil charcoal and chemical elements abstract recent research has greatly increased our knowledge of early human impacts on the environment records of fossil charcoal and chemical elements from a bronze smelting site at huoshiliang in the hexi corridor of northwest china provide material with which to estimate the extent of smelting activity and its impact on the environment analysis of the microstructure of wood fossil charcoal is used to identify the types of charred wood and to reconstruct the local vegetation present during the period of smelting four wood types were used as firewood for smelting tamarix populus salix and polygonaceae the assemblages of fossil charcoal showed that tamarix was the most dominant shrub and was widely used as firewood as a percentage of charcoal it increased from 89 to 97 over the smelting period populus polygonaceae and salix were much less common and finally disappeared completely when the trees and shrubs were used as fuel the vegetation cover was reduced and erosion rates increased this erosion increase was recorded in the higher values of the rb sr ratio in the lacustrine sediment of tiaohu lake located near the huoshiliang site the deforestation caused by smelting activity sharply reduced the vegetation coverage and had serious impacts on the environment when the available fuel wood ceased to meet the needs of smelting and human settlement the huoshiliang site was eventually abandoned in about 1860 bc

oasis evolution processes and mechanisms in the lower reaches of heihe river inner mongolia china since 1 ka ago two major oases in the lower reaches of heihe river inner mongolia of china the desertified ancient juyanze oasis ajo and the modern ejina oasis meo experienced dramatic environmental changes and human migrations as documented in historic records the processes and mechanisms of their evolution are the key for us to understand the environmental changes and human activities in this region yet are still unclear this study provides an evolution chronology of these two oases by analyzing the optical dating records from meo and c 14 dating records from ajo and discusses their evolution mechanisms based on drainage network analysis and field investigations the optical dating samples collected from aeolian sands below humus layers in populus euphratica woodlands on meo indicate that this oasis developed between 1 05 and 0 45ka ago while the c 14 dating samples collected from a number of dead p euphratica trees from ajo consistently suggest that the complete desertification of ajo occurred before similar to 400 cal a bp these new dating results imply that the two oases evolved simultaneously but in opposite directions that is ajo desertified while meo developed gradually in the last 1ka climate change occurring over the last 1ka in northern china cannot explain the opposite evolution directions of these two adjacent oases the drainage network analysis based on digital elevation models dems and field observations and the dates similar to 0 5ka of the top lacustrine layer from gaxunur lake north of meo suggest that the evolution of the two oases was mainly governed by heihe river migration

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

aqueous alteration of the bali cv3 chondrite evidence from mineralogy mineral chemistry and oxygen isotopic compositions abstract a petrographic geochemical and oxygen isotopic study of the bali cv3 carbonaceous chondrite revealed that the meteorite has undergone extensive deformation and aqueous alteration on its parent body deformation textures are common and include flattened chondrules a well developed foliation and the presence of distinctive 100 planar defects in olivine the occurrence of alteration products associated with the planar defects indicates that the deformation features formed prior to the episode of aqueous alteration the secondary minerals produced during the alteration event include well crystallized mg rich saponite framboidal magnetite and ca phosphates the alteration products are not homogeneously distributed throughout the meteorite but occur in regions adjacent to relatively unaltered material such as veins of altered material following the foliation the alteration assemblage formed under oxidizing conditions at relatively low temperatures oxygen isotopic compositions for unaltered regions in bali fall within the field for other cv3 wholerocks however the oxygen isotopic compositions of the heavily altered material lie in the region for the cm and cr chondrites the heavy isotope enrichment of the altered regions in bali suggest alteration conditions similar to those for the petrographie type 2 carbonaceous chondrites

correlated petrologic and geochemical characteristics of co3 chondrites many properties of co3 chondrites have been shown previously to have resulted from thermal metamorphism petrologic subtypes 3 0 3 7 have been assigned to members of the group additional properties that correlate with the metamorphic sequence but seem to have resulted from hydrothermal alteration include the modal abundance of amoeboid olivine inclusions aoi chondrule size the types of refractory inclusions and whole rock o isotopic composition the percentage of rimmed aoi increases with petrologic subtype the rims most likely formed during hydrothermal alteration the previously reported correlation between aoi abundance and chondrite subtype is probably an artifact due to the difficulty in recognizing small unrimmed aoi in the least metamorphosed co3 chondrites because large 200 micron size porphyritic chondrules have nearly the same mean size in all co3 chondrites it seems likely that the correlation between chondrule size and subtype is due to alteration of the smallest chondrules to the point of unrecognizability as complete objects in the more metamorphosed co3 chondrites the previously reported decrease in the proportion of melilite rich refractory inclusions with increasing petrologic subtype may have resulted from more extensive hydrothermal alteration in co3 4 3 7 chondrites that converted primary melilite into ca pyroxene andradite and nepheline alteration probably caused the preferential occurrence of o 16 poor oxygen isotopes in the more metamorphosed whole rock samples

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

aqueous alteration in the matrix of the vigarano cv3 carbonaceous chondrite the matrix of vigarano a meteorite which belongs to the reduced subgroup of the cv3 chondrites contains small amounts 10 of ferrihydrite and smectite these hydrous minerals occur together as fine fibrous intergrowths between anhydrous silicate and oxide grains coarser crystals of ferrihydrite fill fractures that cut matrix minerals and smectite also lines narrow channels within olivine grains these channels may have formed by preferential alteration of olivines along 100 parallel defects formation of ferrihydrite and smectite in the matrix of vigarano was the result of mild aqueous alteration in a low temperature 150 c oxidising parent body environment partial equilibration of matrix olivines indicates that alteration was followed by thermal metamorphism with a peak temperature of 400 500 c mineralogically similar alteration products which also were formed by parent body processes have previously been described from the matrices of four cv meteorites bali grosnaja kaba and mokoia all of which belong to the oxidised subgroup this discovery of the products of oxidative aqueous alteration in vigarano has important consequences for understanding the chemical and thermal history of the cv class of meteorites

fluid motions and compositional gradients produced by crystallization or melting at vertical boundaries the results of a continuing series of laboratory experiments designed to model the fluid motions which accompany crystallization are both described and related in a preliminary way to prototype flows in magma chambers previous experiments have demonstrated the importance of compositional inhomogeneity produced by crystallization and melting in a thermal gradient and coupled with double diffusive effects in driving convective flows which result in thermal and compositional stratification in an originally homogeneous fluid the present experiments examine effects produced in tanks cooled at the side by the upward flow of a less dense boundary layer depleted in the crystallizing component as crystals grow on the side wall these processes are examined in simple two and three component aqueous systems h2o na2co3 h2o na2co3 k2co3 h2o cuso4 na2so4 with one and two crystallizing phases in each of these systems an initially downward flow of a cooled boundary layer against the side wall is reversed as crystallization commences and depletes the boundary layer in the crystallizing component accumulation of this cooler but lighter depleted fluid at the top of the chamber produces thermal and compositional layering by a filling box mechanism partly modified by interchange between the boundary layer and the convecting layers outside when more than one component is present in the solution the crystallization process produces a differentiated fluid column i e one with compositional gradients which are different for each of the components the compositional and thermal distributions within the fluid change with time but finally appear to reach a steady state these distributions are the integrated result of compositional changes produced by crystallization from a thin boundary layer a small proportion of the bulk fluid which evolves in composition and temperature independently of the bulk fluid in a manner controlled by the dynamics of the system the paths of fluid evolution and the resulting sequence and abundance of crystalline products are very different from those predicted on the basis of simple thermally driven crystallization in the static system disequilibrium effects probably involving different kinetics of crystallization of different crystals in part determine crystallization in the experimental system these may or may not be important in real magmatic systems there is still much to learn before even the behaviour in these simple experimental systems is understood fully and the application of the results to the interpretation of the behaviour in real magma chambers in even further away however it is apparent that dynamic effects provide an additional degree of freedom in crystallization processes and allow evolution of small increments of solution to compositions much further along crystallization paths than that allowed in static equilibrium systems petrologists will have to free their thinking from classical constraints of static systems in order to interpret many magmatic phenomena

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

westerlies asia and monsoonal asia spatiotemporal differences in climate change and possible mechanisms on decadal to sub orbital timescales abstract the westerlies dominated climatic regime wdcr in the present interglacial period was proposed because precipitation moisture variations between arid central asia and mid latitude monsoonal asia are out of phase or anti phased on different timescales during the holocene in this study we first review the development of the theoretical framework of the wdcr and then outline the boundary of its core area from the caspian sea in the west to the western hexi corridor in the east with the northern and southern limits coinciding with the domain of arid central asia next we present a synthesis of multiple lines of evidence for the occurrence of the wdcr on multi millennial sub orbital herein to decadal timescales during the holocene finally we examine the possible physical mechanisms responsible for the wdcr we find that external factors insolation changes induced by orbital factors generated the wdcr on a sub orbital timescale whereas a circum global teleconnection silk road pattern was the most significant factor responsible for the wdcr on centennial and decadal timescales the study provides a comprehensive summary of the development of our knowledge of the wdcr over the past several decades together with a tentative theoretical framework for understanding climatic and environmental changes within its region of influence in addition it forms a scientific basis for environmental management and ecological restoration in this arid region in the context of global warming

disentangling nebular and asteroidal features of co3 carbonaceous chondrite meteorites abstract analyses of olivines and low ca pyroxenes in a suite of porphyritic chondrules of types ia and ii in each of ten co3 chondrites and comparisons with similar chondrules in ll chondrites suggest that the co3 chondrites may be divided into a metamorphic sequence of subtypes 3 0 to 3 7 chondrules in allan hills a77307 and colony which we classify as type 3 0 show only igneous zoning whereas in the other more metamorphosed type 3 1 3 7 co chondrites chondrule silicates are enriched in feo most markedly in olivine crystals near the rims of type ia chondrules and along cracks the feo enrichments in metamorphosed chondrules result largely from equilibration by solid state diffusion between chondrules and feo rich matrices type 3 1 3 7 co chondrites were formed from chondrites like colony and alh a77307 in heated asteroids or planetesimals we find no evidence for nebular condensation of fayalite rims around these chondrules as reported for cv3 chondrites or nebular modification of chondrule silicates as favored by some workers metallic fe ni in alh a77307 contains up to 0 1 1 wt cr si and p as in the least metamorphosed ordinary chondrites and cm2 chondrites and grains of cohenite fe3c and haxonite fe23c6 these carbides which are the first reported in carbonaceous chondrites are associated with pentlandite and magnetite as in certain ll3 chondrites we assign the following petrologic subtypes to other co chondrites kainsaz 3 1 felix 3 2 alh 82101 and ornans 3 3 lance and alh a77029 3 4 alh a77003 3 5 warrenton 3 6 and isna 3 7

phyllosilicate rich chondrule rims in the vigarano cv3 chondrite evidence for parent body processes abstract a petrographic and scanning electron microscopic study of the vigarano cv3 carbonaceous chondrite reveals that a small proportion 5 of the fine grained rims surrounding chondrules consist mainly of phyllosilicates saponite and serpentine and minor but variable amounts of ferrihydrite most of the rims consist mainly of fe rich olivine the phyllosilicate rich rims and the chondrules that they enclose show abundant evidence of aqueous alteration low ca pyroxene and olivine at chondrule margins have been partially replaced by phyllosilicate rich materials producing embayments on chondrule surfaces fe ni metal fe sulfide and magnetite in the chondrules have also been partially replaced by fe hydroxide due to preferential replacement of low ca pyroxene and olivine sulfide magnetite and fe hydroxide remain exposed at chondrule margins we discovered a clast 0 7 0 9 mm in size containing several chondrules embedded in a phyllosilicate rich matrix that is almost identical in mineralogy texture and composition to the rims we also found numerous small clasts 20 400 m in size consisting of a similar phyllosilicate rich material in the host vigarano meteorite many of the clasts include fragments of chondrules amoeboid olivine aggregates and ca al rich inclusions these clasts also show abundant evidence of aqueous alteration which is similar to that observed in the rims and their host chondrules from these observations we conclude that the chondrule rim assemblages and the clasts are a part of the same precursor chondrite which was fragmented during brecciation on the meteorite parent body we interpret that a portion or portions of the vigarano parent body was aqueously altered and the interchondrule matrix was largely converted to phyllosilicates and ferrihydrite this hydrated portion was later fragmented and brecciated by impacts as fragmentation occurred preferentially along the phyllosilicate rich porous matrix most of the ejected clasts consisted of a chondrule rimmed by remnant matrix the clasts were rounded by abrasion during brecciation and transportation and finally mixed into an anhydrous portion in the regolith from which the vigarano meteorite was derived some of the phyllosilicate rich rims show evidence for partial dehydration during heating before final incorporation into the regolith these results taken together suggest that the vigarano parent body was spatially heterogeneous in degree of aqueous alteration and thermal metamorphism and the host vigarano meteorite is a breccia consisting of numerous clasts from many different locations

oxygen isotopes in chondrule olivine and isolated olivine grains from the co3 chondrite allan hills a77307 we have measured o isotopic ratios in a variety of olivine grains in the co3 chondrite allan hills alh a77307 using secondary ion mass spectrometry in order to study the chondrule formation process and the origin of isolated olivine grains in unequilibrated chondrites oxygen isotopic ratios of olivines in this chondrite are variable from delta 17 o 15 5 to 4 5 parts per thousand and delta 18 o 11 5 to 3 9 parts per thousand with delta 17 o varying from 10 4 to 3 5 parts per thousand forsteritic olivines fa 1 are enriched in o 16 relative to the bulk chondrite whereas more feo rich olivines are more depleted in o 16 most ratios lie close to the carbonaceous chondrite anhydrous minerals ccam line with negative values of delta 17 o although one grain of composition fa 4 has a mean delta 17 o of 1 6 parts per thousand marked o isotopic heterogeneity within one feo rich chondrule is the result of incorporation of relic o 16 rich mg rich grains into a more o 16 depleted host isolated olivine grains including isolated forsterites have similar o isotopic ratios to olivine in chondrules of corresponding chemical composition this is consistent with derivation of isolated olivine from chondrules as well as the possibility that isolated grains are chondrule precursors the high o 16 in forsteritic olivine is similar to that observed in forsterite in cv and ci chondrites and the ordinary chondrite julesburg and suggests nebula wide processes for the origin of forsterite that appears to be a primitive nebular component

an experimental investigation of volatile exsolution in evolving magma chambers abstract previous laboratory experiments investigating the fluid dynamics of replenished magma chambers have been extended to model effects resulting from the release of gas turbulent transfer of heat between a layer of dense hot and volatile rich mafic magma overlying cooler more evolved magma can lead to crystallization and exsolution of volatiles in the lower layer small gas bubbles can cause the bulk density to decrease to that of the upper layer and thus produce sudden overturning and initiate mixing followed by further exsolution of gas and explosive eruption these processes have been modelled in the laboratory using a chemical reaction between sodium or potassium carbonate and nitric acid to release small bubbles of co 2 we have investigated both the initial overturning produced by gas release in the lower layer and the subsequent evolution of gas due to intimate mixing of the two layers the latter experiments in which the reactants remained isolated in the two layers until overturning occurred demonstrated unambiguously that the fluxes of chemical components across the interfaces between convecting layers are very slow compared to the flux of heat this shows that the evolution of layers of magma of different origins and composition can take place nearly independently of each other the magmas can coexist in the same stratified chamber until their bulk densities become equal and they mix together the processes illustrated in these experiments could occur in h 2 o bearing magmas such as in the calcalkaline association and in co 2 bearing mafic magmas such as in silica undersaturated suites

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

human impact on natural systems modeled through soil erosion in geowepp a comparison between pre hispanic periods and modern times in the teotihuacan valley central mexico abstract anthropogenic changes during the past 2000 years in the teotihuacan valley imply that intensity of soil degradation varies depending on the land management practices and the intensity of soil use as a part of a broader effort to reconstruct erosion dynamics in the teotihuacan valley through geoarchaeological approaches our study applies a process based watershed hydrology and upland erosion model the water erosion prediction project wepp the geo spatial interface for wepp geowepp was used to characterize locations of soil detachment and sediment deposition predicted in the watershed through time based on current and reconstructed conditions in the valley climate topography soil and land use were used as inputs to wepp to estimate surface runoff and soil loss rates for periods with different environmental and anthropogenic conditions the teotihuacan period 1 650 ce the aztec period 1325 1521 ce and for modern times after 1970 ce over a simulated and established timeframe for those periods surface runoff and rate of soil loss were estimated to be higher during the aztec period when the area devoted to agriculture dominated the landscape land use change had a major impact on soil erosion comparison of the pre hispanic periods with current conditions shows that wepp is useful in showing the roles of management and climate in environmental degradation the results contribute to the scientific debate about the antiquity and causes of erosion in central mexico the research shows that land use is one of the foremost factors affecting soil erosion both in ancient and modern periods with particular impact during the aztec period

the microstructure of semarkona and bishunpur abstract the ordinary chondrites semarkona and bishunpur appear to have experienced in situ hydrous alteration here we report the results of the first detailed tem examination of them which supports this conclusion in semarkona all but the most magnesian mafic minerals have been destroyed and primary sulphides most likely troilite have been partially altered to phyllosilicates and ni rich pyrrhotite in bishunpur alteration is confined to the production of smectite from an amorphous feldspathic material in the chondrule rims and interchondrule matrix during hydrous alteration of both meteorites the temperature probably did not exceed 260 c the equilibrium composition of the gas present during the alteration of semarkona was not solar but was dominated by h2o the formation of smectite does not require the presence of liquid water however evidence for the redistribution of elements such as ca zn and si over tens of microns or more implies that there was at least some transient grain boundary fluid present the alteration in semarkona and bishunpur is far from complete thermodynamic modelling suggests that more altered ordinary chondrites would be mineralogically similar to the cm and ci carbonaceous chondrites superficially the mineralogy mineral chemistry and bulk chemistry of semarkona matrix rims resemble those of some chondritic interplanetary dust particles cidps the ordinary chondrite parent bodies may therefore be a source of some cidps

an isotopic and petrologic study of calcium aluminum rich inclusions from co3 meteorites we have studied the mineralogy and petrology of 229 calcium aluminum rich inclusions cais from ten co3 meteorites of petrologic types 3 0 3 7 subsets of these inclusions were measured by ion probe for magnesium calcium and titanium isotopes and ree abundances most cais from co3 meteorites fall into three major types 1 melilite rich inclusions which also contain spinel hercynite perovskite and occasionally hibonite 2 spinel pyroxene inclusions and 3 hibonite hercynite inclusions in addition several isolated hibonite grains two grossite caal 4o 7 bearing cais two hibonite fassaite microspherules and one anorthite spinel pyroxene inclusion were found cais from co3 meteorites exhibit all of the ree patterns commonly seen in inclusions from cv3 and cm2 chondrites most exhibit evidence of 26 ai and many have inferred 26 ai 27 ai o 5 10 5 the relative abundances of different types of cais in co3 chondrites differ from those in cv3 and cm2 chondrites cais in co3 chondrites have experienced considerable secondary alteration both before and after accretion signatures of nebular alteration include wark lovering rims and the high fe contents in spinels from all hibonite hercynite inclusions occasionally melilite and anorthite show evidence of nebular alteration to feldspathoids and pyroxene the magnesium aluminum systematics of some melilite rich inclusions were apparently disturbed prior to final accretion of the parent body parent body alteration is indicated by correlations between cai characteristics and the petrologic type of the host meteorite spinel in melilite rich and coarse grained spinel pyroxene inclusions becomes more fe rich with the development of relatively homogeneous hercynitic spinel 50 60 mol in cais from metamorphic grades 3 4 perovskite has been converted to ilmenite in types 3 4 melilite rich inclusions are abundant in co3 0 3 3 meteorites rare in 3 4 meteorites and absent meteorites of types 3 5 3 7 melilite rich cais are probably replaced by inclusions rich in feldspathoids pyroxene and fe rich spinel isotopic disturbance of the magnesium aluminum systematics may be more severe in higher petrologic types hibonite seems to be unaffected by this level of metamorphism three isotopically unusual inclusions were found one single crystal hibonite isna sp16 has a ree pattern strongly depleted in ce and y 26 ai 27 ai o 2 4 0 3 10 5 and mass fractionated calcium f ca 12 2 amu but no resolvable nuclear anomalies in neutron rich calcium isotopes the ree pattern which is thought to reflect nebular conditions and mass fractionated calcium indicative of evaporation are similar to those of the fun inclusion hal and related hibonites indicating similar formation conditions the absence in isna sp16 of the nuclear anomalies observed in hal and the difference in 26 ai 27 ai o between hal and isna sp16 indicate that the processes that produced hal type hibonites operated on diverse materials two hibonite bearing microspherules colony sp1 and alh82101 sp15 exhibit nearly flat ree patterns with negative europium anomalies and slightly negative 26 mg alh82101 sp15 has resolved excesses of 48 ca and 50 ti these characteristics are similar to those of previously described microspherules from murchison and lance implying that the microspherules formed via a single process from related but not identical source materials

sulfur and sulfides in chondrules abstract the nature and distribution of sulfides within type i po pop and pp chondrules of the carbonaceous chondrite vigarano cv3 have been studied by secondary electron microscopy and electron microprobe they occur predominantly as spheroidal blebs composed entirely of low ni iron sulfide troilite fes or troilite magnetite but in less abundance in association with metallic fe ni beads in opaque assemblages troilites are mainly located within the low ca pyroxene outer zone and their amounts increase with the abundance of low ca pyroxene within chondrules suggesting co crystallization of troilite and low ca pyroxene during high temperature events we show that sulfur concentration and sulfide occurrence in chondrules obey high temperature sulfur solubility and saturation laws depending on the f s 2 and f o 2 of the surrounding gas and on the melt composition mainly the feo content sulfur dissolved in chondrule melts may eventually reach a concentration limit the sulfur content at sulfide saturation scss at which an immiscible iron sulfide liquid separates from the silicate melt the occurrence of both a silicate melt and an immiscible iron sulfide liquid is further supported by the non wetting behavior of sulfides on silicate phases in chondrules due to the high interfacial tension between their precursor iron sulfide liquid droplets and the surrounding silicate melt during the high temperature chondrule forming event the evolution of chondrule melts from po to pp towards more silicic compositions very likely due to high p sio g of the surrounding nebular gas induces saturation of fes at much lower s content in pp than in po chondrules leading to the co crystallization of iron sulfides and low ca pyroxenes conditions of co saturation of low ca pyroxene and fes are only achieved in non canonical environments characterized by high partial pressures of sulfur and sio and redox conditions more oxidizing than iw 3 fe and s mass balance calculations also suggest the occurrence of an external source of iron very likely gaseous during chondrule formation we therefore propose that enrichments in sulfur and other volatile and moderately volatile elements from po to pp type i bulk chondrule compositions towards chondritic values result from progressive reaction between partially depleted olivine bearing precursors and a volatile rich gas phase

quaternary environmental changes in the drylands of china a critical review abstract this paper reviews our current understanding of quaternary climate and landscape changes in the desert areas of northern china a key portion of the middle latitude drylands on earth combining earlier studies with our recent research and experience we offer a comprehensive picture of the state of chinese deserts during the quaternary and in the interest of enhancing future research identify knowledge gaps and areas of uncertainty lacustrine deposits found over an area ranging from china s western taklamakan desert to the eastern hunshandake sandy lands suggest that extensive lakes occurred in china s deserts during the pleistocene analysis of digital elevation models from srtm shuttle radar topography mission data supports this interpretation and shows the significant extent of these former lakes new estimates of mean annual evaporation of ca 1000 mm from lake surfaces and ca 100 mm from land surfaces confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone especially during intervals when the mean annual rainfall is more than 100 mm rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of china are very sensitive ephemeral systems and not long lasting as previously thought available chronologies suggest that there were large lakes in the western taklamakan desert and the chadamu basin during mis marine isotope stage 3 at 30 ka probably related to a period of strong influence of northern hemispheric westerly winds channels and elevation models revealed by srtm data and remains of lacustrine sediments also indicate that there was a large lake in the hunshandake sandy lands in the eastern portion of the desert belt during the quaternary there is significant evidence that during the middle holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern china lacustrine records from the badain jaran desert in western inner mongolia suggest that it was generally dry before 10 cal ka becoming wetter from 10 to 4 cal ka and dry again afterwards study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt suggests that there was a period of wet and warm climate in this region during the mid holocene optimum at a minimum between 6 ka and 4 ka but possibly lasting longer recent observations dealing with the generation and transport of dust from central asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed these results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in chinese deserts are somehow similar to that having occurred in the sahara desert of north africa deserts in northern china were also important focal regions for neolithic cultures during intervals when environmental conditions supported a denser vegetative cover there is evidence that some areas of woody vegetation to the west of badain jaran desert were deforested by humans by ca 4000 yr b p although it is still debatable whether humans have had a significant impact in other areas at that time opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long term field based investigations

precursor and metamorphic condition effects on raman spectra of poorly ordered carbonaceous matter in chondrites and coals abstract geothermometers based on raman spectrometry of carbonaceous matter and covering a wide range of temperatures 100 650 c have been developed over recent years while raman data have been largely interpreted in terms of temperature they are also the fingerprint of certain metamorphic conditions especially in the low temperature range relevant to poorly ordered carbonaceous matter this study investigates the raman spectra of two series of chondritic carbonaceous matter and coal samples formed from different precursors and under different metamorphic conditions the raman spectra of polyaromatic carbonaceous matter pcm from 42 chondrites and 27 coal samples measured with visible 514 nm and ultra violet 244 nm excitation wavelengths are analyzed the raman spectra of low rank coals and chondrites of petrologic types 1 and 2 which contain the more disordered pcm reflect the distinct carbon structures of their precursors the 514 nm raman spectra of high rank coals and chondrites of petrologic type 3 exhibit continuous and systematic spectral differences reflecting different carbon structures present during the metamorphism event they result from differences in the chemical structures of the precursors concerning for instance the reticulation of polyaromatic units or an abundance of ether functional groups or possibly from a lack of carbonization processes to efficiently expel oxygen heteroatoms due to weak lithostatic pressure and confinement these results suggest that the use of low temperature carbon thermometers should be restricted to a given geological context at the same time the sensitivity of raman spectra to precursors and certain metamorphic conditions could be used to obtain information other than temperature the analysis also provides evidence of the accretion of relatively homogeneous pcm precursors among ordinary co and cv carbonaceous chondrite parent bodies given that the 514 nm raman spectra of pcm efficiently trace the metamorphism grades looking closer however the 514 nm raman data are more scattered in chondrites than in coals and the maturity tracers are less sensitive and miscorrelate with the atomic h c ratio suggesting slight compositional and structural differences among the pcm precursors accreted

high temperature condensation of iron rich olivine in the solar nebula abstract olivine is the most abundant mineral in many chondritic meteorites it is also the first major mg silicate to condense from a solar gas upon cooling the composition of olivine provides important information concerning its origin results of calculations are presented for the fe mn and ni contents of olivine condensing from a gas with solar composition but variable oxygen fugacity a basic computational method is described that takes into account the depletion of the gas in mg and si during condensation the first olivine that condenses from a solar gas has less than 10 2 mol feo independent of the oxygen fugacity of the otherwise solar gas at lower temperatures when most of the mg is condensed more feo can be incorporated in forsterite by condensation if the oxygen fugacity is sufficiently high the feo mno ratio of the first condensing olivine is above 1000 decreasing with decreasing temperature and increasing oxygen fugacity to values of around 100 which are actually observed in fayalitic olivine rims in allende the ni content of condensed olivine is below 10 7 mol even at high oxygen fugacities indicating that condensation of nio in olivine is a very unlikely process any ni in olivine in the ppm range is therefore indicative of metal olivine equilibration under increasingly oxidizing conditions h 2 o h 2 ratios of 0 01 0 1 chromite is an early phase to condense forming before forsterite isolated olivine grains in allende and olivine on the outside of chondrules have feo rich rims texture composition and morphology of these rims indicate that they formed by condensation from a gas our calculations suggest that the gas was enriched by a factor of 100 in oxygen relative to solar composition gas and that mg was almost completely condensed when rim formation occurred the sharp boundary between forsteritic and fayalitic olivine suggests an increase in oxygen fugacity and rapid formation of fayalitic olivine by condensation cr enrichment at the rim interface with the underlying forsterite probably reflects stability of chromite under oxidizing conditions conventional models of feo bearing silicate formation require oxidation of metal silicate assemblages at temperatures as low as 400 k it is shown here that diffusion at this temperature is so slow that the time needed for formation of the observed feo bearing phases would exceed the lifetime of the solar nebula other oxygen fugacity indicators reflect similar conditions for example the hercynite component of spinel in fine grained al rich inclusions indicates equilibration with a gas of similar composition as that responsible for condensation of fayalitic olivine suggesting formation of feo rich spinel by gas solid reactions mechanisms for producing oxidizing conditions in the solar nebula are briefly discussed

search for extinct 36cl vigarano cais the pink angel from allende and a ningqiang chondrule abstract we have searched for excesses of 36 s derived from the decay of extinct 36 cl in sodalite a secondary cl rich mineral in ca al rich inclusions cais from the vigarano and allende cv3 chondrites and in a chondrule from the ningqiang carbonaceous chondrite the presence of sodalite in two cais from vigarano and its absence from surrounding cai fragments suggests sodalite formation after cai fragmentation as for sodalite in the allende pink angel cai oxygen isotopic compositions have been interpreted as indicative of high temperature interactions thus suggesting formation prior to accretion to the parent body probably in a nebular setting sodalite in the ningqiang chondrule is considered to have formed via alkali ca exchange which is believed to have occurred before accretion to the parent body sodalites in the vigarano cais and in the ningqiang chondrule show no clear evidence for the presence of radiogenic 36 s the inferred 2 upper limits for 36 cl 35 cl at the time of sodalite formation are 1 6 10 6 vigarano cais and 3 3 10 6 ningqiang chondrule respectively in the pink angel cai sodalite exhibits small 36 s excesses which weakly correlate with 35 cl 34 s ratios the inferred 36 cl 35 cl ratio of 1 8 2 2 10 6 2 error is lower than that found by hsu et al hsu w guan y leshin l a ushikubo t and wasserburg g j 2006 a late episode of irradiation in the early solar system evidence from extinct 36 cl and 26 al in meteorites astrophys j 640 525 529 thus indicative of heterogeneous distribution of 36 cl in this cai spallation reactions induced by energetic particles from the young sun are suggested for the origin of 36 cl similar to the case of 10 be while 10 be appears to be present in roughly equal abundance in all studied cais our study indicates the level of 36 cl abundances to be variable so that there seems to be no simple relationship between 10 be and 36 cl this would be expected if trapped cosmic rays rather than early solar system spallation were the dominant source of 10 be in the early solar system since their contribution to 36 cl would have been tiny if the variability of 36 cl abundances is caused by temporal differences in the alteration that formed sodalite sodalite in the vigarano cais and in the ningqiang chondrule may have formed 0 5 and 0 2 ma after formation of the sodalite in the ningqiang cai analyzed by lin et al lin y guan y leshin l a ouyang z and wang d 2005 short lived chlorine 36 in a ca and al rich inclusion from the ningqiang carbonaceous chondrite proc natl acad sci usa 102 1306 1311 the pink angel sodalite that we analyzed may have formed 0 3 ma after formation of the sodalite in the pink angel analyzed by hsu et al hsu w guan y leshin l a ushikubo t and wasserburg g j 2006 a late episode of irradiation in the early solar system evidence from extinct 36 cl and 26 al in meteorites astrophys j 640 525 529 the estimated temporal differences suggest that alteration extended over at least 0 5 ma if previous works showing very low initial 36 cl 35 cl in the allende cais and a h3 chondrite cai are also considered then alteration processes may have been more than 1 7 ma

historical settlement abandonment in the middle hexi corridor linked to human induced desertification abstract understanding past human environment interactions over a long time scale offers an analogue to predict adapt and mitigate the environmental issues caused by global change and human activities in the future the transient existence of historical cities from arid northern china can provide a valuable reference for this issue in this study we investigated a set of sand dunes which accumulated alongside the city wall of south heishuiguo ancient city shc from the middle hexi corridor in arid northern china dating these dune sands can provide the timing of both desertification and city abandonment a series of sand samples a total of 20 were collected and their ages were determined by luminescence dating of k feldspar fraction the results suggest an abrupt sand dune accumulation between 0 40 0 03 ka and 0 25 0 02 ka corresponding to 1590 1790 ce this study confirms a phase of desertification between the late 16th century and the late 18th century in the hexi corridor and the abandonment of the shc at the 17th century in order to assess the anthropogenic influences on desertification we also reconstructed the population history of the hexi corridor over the last 2000 years based on historical literature as a quantitative index of human activity intensity by comparison of the timing of onset of desertification around the shc with robust paleoclimate and historical population reconstructions we conclude that 1 the desertification of 1590 1790 ce was likely the result of considerably enhanced human activities between the late ming and the early qing dynasties as this period was dominated by a relatively moist climate and could restrain the sand deflation and 2 the desertification in turn caused abandonment of shc as the impact of environmental changes on people

relationships between organics water and early stages of aqueous alteration in the pristine cr3 0 chondrite met 00426 abstract in order to investigate the nature of organics at the time of their accretion into chondrite parent bodies as well as their subsequent evolution with aqueous alteration we have conducted a study of the morphologies spatial distribution and relationships between organic particles and the surrounding matrix phases in one of the most pristine carbonaceous chondrites currently known met 00426 cr which is therefore likely to contain the best preserved record of pre accretion features focused ion beam sections were extracted for transmission electron microscope observations from its matrix organic matter om shows a heterogeneous population of grains most of them smaller than 1 m diverse morphologies are observed such as compact rounded aggregates individual and aggregated nanoglobules and micron to nanometer sized veins a common feature is the systematic presence of cracks connected to the grains and filled with om the surrounding matrix groundmass consists of amorphous iron rich silicate particles intimately mixed with phyllosilicates sulfides and occasional tochilinite with sizes ranging from several hundreds of nanometers to below 10 nm a close spatial relationship is commonly observed between some of the organic matter particles and alteration phases such as tochilinite and phyllosilicates phyllosilicates sometimes occur intimately intercalated with organic matter at a scale below 10 nm we used tem eds techniques to quantify the water concentration in the matrix amorphous silicate material and the phyllosilicates the water contents of both materials are identical at 10 6 wt h 2 o and demonstrate that the amorphous silicate material in this meteorite is hydrated therefore even though these cr3 0 chondrites are the least altered objects from a mineralogical point of view their matrices contain significant amounts of water in the amorphous silicate this coupled in situ study of organics and aqueous alteration suggests that a significant population of the om accreted as a mixture of soluble and insoluble molecules together with water ice grains and that the om was mobile at the micrometer scale the spatial distribution of the om grains can therefore in part be attributed to parent body processes we suggest that as accreted ice melted hydration of the amorphous silicates and formation of tochilinite and phyllosilicates occurred in the immediate vicinity of the composite water ice organic matter grains the water soluble component of the organics was likely transported and redistributed in the surrounding porosity cracks grain boundaries as water circulated the textural settings suggest that some of the om material could have been polymerized during aqueous alteration and transformed into insoluble molecules perhaps during the last stages of alteration as water was consumed by silicate hydration reactions

the onset of metamorphism in ordinary and carbonaceous chondrites ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by xray mapping techniques a variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe scanning electron microscopy sem transmission electron microscopy tem and cathodoluminescence cl methods the distribution of cr in feo rich olivine systematically changes as metamorphism increases between type 3 0 and type 3 2 igneous zoning patterns are replaced by complex ones and cr rich coatings develop on all grains cr distributions in olivine are controlled by the exsolution of a cr rich phase probably chromite cr in olivine may have been partly present as tetrahedrally coordinated cr3 separation of chromite is nearly complete by petrologic type 3 2 the abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type tem shows this to be the result of crystallization of albite residual glass compositions systematically change during metamorphism becoming increasingly rich in k glass in type i chondrules also gains alkalis during metamorphism both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules the matrix in the least metamorphosed chondrites is rich in s and na the s is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules alkalis initially leave the matrix and enter chondrules during early metamorphism feldspar subsequently nucleates in the matrix and na re enters from chondrules these metamorphic trends can be used to refine classification schemes for chondrites cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3 0 and 3 1 into types 3 00 through 3 15 on this basis the most primitive ordinary chondrite known is semarkona although even this meteorite has experienced a small amount of metamorphism allan hills alh a77307 is the least metamorphosed co chondrite and shares many properties with the ungrouped carbonaceous chondrite acfer 094 analytical problems are significant for glasses in type ii chondrules as na is easily lost during microprobe analysis as a result existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised

determination of the petrologic type of cv3 chondrites by raman spectroscopy of included organic matter abstract this paper reports the first reliable quantitative determination of the thermal metamorphism grade of a series of nine cv3 chondrites allende axtell bali mokoia grosnaja efremovka vigarano leoville and kaba the maturity of the organic matter in matrix determined by raman spectroscopy has been used as a powerful metamorphic tracer independent of the mineralogical context and extent of aqueous alteration this tracer has been used along with other metamorphic tracers such as fe zoning in type i chondrules of olivine phenocrysts presolar grain abundance and noble gas abundance bulk and p3 component the study shows that the petrologic types determined earlier by induced thermoluminescence were underestimated and suggests the following values pt allende axtell 3 6 pt bali mokoia grosnaja 3 6 pt efremovka leoville vigarano 3 1 3 4 pt kaba 3 1 the most commonly studied cv3 allende is also the most metamorphosed bali is a breccia containing clasts of different petrologic types the attribution suggested by this study is that of clasts of the highest petrologic types as pointed out by iom maturity and noble gas bulk abundance cv3 chondrites have complex asteroidal backgrounds with various degrees of aqueous alteration and or thermal metamorphism leading to complex mineralogical and petrologic patterns fe mg chemical zoning in olivine phenocrysts on the borders of type i chondrules of porphyritic olivine and pyroxene rich textural types has been found to correlate with the metamorphism grade this suggests that chemical zoning in some chondrules often interpreted as exchanges between chondrules and nebular gas may well have an asteroidal origin furthermore the compositional range of olivine matrix is controlled both by thermal metamorphism and aqueous alteration this does not support evidence of a nebular origin and does not necessarily mirror the metamorphism grade through fe mg equilibration on the other hand it may provide clues on the degree of aqueous alteration vs thermal metamorphism and on the timing of both processes in particular mokoia experienced significant aqueous alteration after the metamorphism peak whereas grosnaja which has similar metamorphism grade did not

indicators of aqueous alteration and thermal metamorphism on the cv parent body microtextures of a dark inclusion from allende abstract an unusual dark clast in the allende cv3 chondrite termed allende af which was previously interpreted as a primary aggregate formed in the solar nebula kurat et al 1989 palme et al 1989 was re examined our study reveals abundant evidence suggesting that it probably experienced extensive aqueous alteration and subsequent thermal metamorphism on the meteorite parent body allende af contains numerous rounded to oval shaped inclusions embedded in a dark matrix the inclusions consisting predominantly of fine grains of fe rich olivine have internal textures suggesting that they are pseudomorphs after chondrules several inclusions appear to be replaced cais veins filled with fibrous olivine grains occur abundantly in both inclusions and matrix some veins up to 4 mm in length penetrate several inclusions providing strong evidence that aqueous alteration occurred after accretion the fibrous morphology of olivine in veins and inclusions suggests that the olivine was produced by dehydration and thermal transformation of phyllosilicate that had been formed by aqueous alteration olivine grains in the matrix contain numerous micro inclusions of fe ni sulfide which were probably incorporated during transformation from phyllosilicate allende af is probably related to the fine grained variety of dark inclusions reported from cv3 chondrites that has been described as the type containing abundant porous aggregates of fe rich olivine by johnson et al 1990 many dark inclusions previously described appear to be similar in texture and mineralogy to allende af and probably experienced similar secondary process on the meteorite parent body the wide variation in texture of dark inclusions can be explained by different degrees of aqueous alteration that preceded thermal metamorphism the size distribution of chondrule pseudomorphs and the abundance of cai pseudomorphs suggest that the precursor of allende af is a cv type chondrite probably allende itself oxygen isotopic and chemical compositions are consistent with this interpretation the cv parent body has been commonly thought to have escaped major secondary processing however allende af provides evidence that extensive aqueous alteration and thermal metamorphism have occurred locally on the cv parent body

matrices of type 3 ordinary chondrites primitive nebular records petrologic studies were made on the fine grained matrices of type 3 ordinary chondrites of the lowest petrologic subtype the matrix minerals in order of abundance are olivine fo99 to fo9 enstatite or bronzite augite or subcalcic augite albite fe ni metal troilite magnetite spinel mgal2o4 chromite and calcite fe and mg rich fluffy particles and albite like particles are also major constituents the chemical compositions of olivine and pyroxenes vary within and among the chondrites and are in gross disequilibrium showing that the matrix materials were hardly heated after their formation textural relationships indicate that magnesian olivine was formed after ca pyroxene followed by intermediate to iron rich olivine intermediate olivine was formed from enstatite and metallic iron under relatively oxidizing conditions the observations indicate that matrices of chondrites are neither the fragments of chondrules nor the precursors of chondrules they were mostly the products of condensation and reaction among solids and or between solids and the ambient gas mostly at low temperatures and thus they contain records of primitive processes in the nebula in order to explain the presence of olivines more iron rich than fo50 the presence of free sio2 or a high activity of sio2 in the gas is necessary which was not shown in previous thermochemical calculations mineral assemblages of matrix minerals of chondrites of different chemical groups differ systematically according to oxidation state of the parental meteorites indicating that they were formed at different oxygen fugacities the rims of chondrules and surrounding matrix materials must have accreted onto chondrules during turbulent movements of the nebula

historical desertification of the mu us desert northern china a multidisciplinary study abstract the problem of historical desertification of the mu us desert northern china has been paid considerable attention during the past several decades through the analysis of stratigraphic evidence historical records and archaeological discoveries this paper studied the problem using a multidisciplinary approach the results show that two phases of serious desertification occurred during the last two millennia one is during the mid to late tang dynasty about a d 800 and the other during the late ming dynasty about a d 1500 1600 further investigation of the cause of each phase of desertification demonstrates that the former phase of desertification is closely related to abrupt climate change occurring in the mid eighth century but the latter which started during the ming dynasty and stopped at late 1980s is not consistent with climatic causation therefore we suggest that human activities contributed to the development of the latter phase of desertification

fayalitic olivine in matrix of the krymka ll3 1 chondrite vapor solid growth in the solar nebula fayalitic olivine fa54 94 is a ubiquitous component in the matrix of krymka ll3 1 as well as in other highly unequilibrated chondrites ordinary and carbonaceous in krymka the fayalitic olivine has an unusual anisotropic platy morphology that occurs in at least five types of textural settings that can be characterized as 1 isolated platelets 2 clusters of platelets 3 euhedral to subhedral crystals 4 overgrowths of platelets on forsteritic olivine and 5 fluffy porous aggregates from transmission electron microscope tem investigation the direction of elongation of the platy olivine overgrowths on forsteritic olivine substrates is along the c axis and in most cases it corresponds with the c axis of the substrate olivine which suggests that the fayalitic olivine grew in this unusual morphology and is not a replacement product of preexisting material the fayalitic olivine in the matrix of krymka is compositionally similar to olivine with platy morphology in the matrix of some cv3 chondrites and both have similar fe mn ratios but important morphological differences indicate that their relationship needs to be explored further textural and compositional data indicate that the fayalitic olivine in the matrix of krymka as well as in some other unequilibrated ordinary chondrites formed prior to final lithification of the meteorite and probably prior to parent body accretion we find that formation of the fayalitic olivine by vapor solid growth provides the best explanation for our observations and data and is the only feasible mechanism for the formation of fayalitic olivine in the matrix of krymka we propose that the fayalitic olivine formed by vaporization and recondensation of olivine rich dust during a period of enhanced dust gas ratio in the nebula

late holocene dune mobilization in the horqin dunefield of northern china abstract the late holocene environmental change and its relationship with climate and human activities in the horqin dunefield of northern china are poorly understood in the current study we presented a new reconstruction of late holocene dune mobilization in the horqin dunefield based on 68 quartz osl ages from 25 dune sections and interpretations of historical documents these sections were selected from a variety of different geomorphological units across the studied region the results show that at least four phases of dune mobilization were distinguished during the last 2000 years in horqin dunefield corresponding to 400 700 ce 1200 ce 1800 ce and after 1900 ce respectively by comparison with other well dated paleoclimate records and analysis on human activity records we infer that the cold arid climate caused the dune mobilization around 400 700 ce dune mobilization around 1200 ce can be attributed to the combinative impacts of cold climate and extensive human activities increasing human activities play a dominate role in the latest two phases of dune mobilization at around 1800 ce and after 1900 ce even though the climate warming and drying in 20th century may also contribute to the last phase of dune mobilization

aqueous alteration in the kaba cv3 carbonaceous chondrite the kaba cv3 carbonaceous chondrite has undergone pervasive aqueous alteration that produced fe bearing saponite in chondrules and matrix saponite in chondrules is coarse grained and shows a crystallographic orientation relationship such that c of saponite parallels a of enstatite matrix saponite exhibits a variety of textures including coarse and fine grained clusters isolated packets and sparse lamellar replacements of fe rich olivine the coarse grained clusters were probably derived from altered chondrules that were fragmented during regolith gardening the fine grained clusters and isolated packets formed from material released during the partial dissolution of matrix silicates much saponite is associated with submicron fe ni sulfides suggesting that conditions were not oxidizing during aqueous alteration we believe that the alteration occurred after accretion and on the kaba parent body because saponite is present throughout the sample by analogy to terrestrial occurrences the saponite in kaba probably formed at low temperatures 100 c the distribution of saponite in kaba is determined by local bulk compositions enstatite in chondrules has been altered more extensively than the fine grained olivine in matrix the alteration products in kaba resemble those in other aqueously altered carbonaceous chondrites such as the mokoia cv3 chondrite and in certain ci chondrites there are however significant differences kaba lacks the abundant high al phyllosilicates in chondrules and in cais reported from mokoia also lacking in kaba is the serpentine and ferrihydrite found in orgueil alteration products in kaba matrix are dissimilar from those in co3 chondrites even though their prealteration mineralogies were similar an observation that probably reflects different temperatures during alteration

sodium metasomatism in chondrules in co3 chondrites relationship to parent body thermal metamorphism we have studied the mineralogy and petrology of mesostases of 783 type i chondrules in seven co3 chondrites that range in petrologic subtype from 3 0 to 3 7 chondrule mesostases in the co chondrite of subtype 3 0 consist mainly of primary glass and plagioclase while chondrule mesostases in the co chondrites of higher subtypes 3 2 3 7 contain various amounts of nepheline in addition to glass and plagioclase nepheline has replaced glass and plagioclase forming finegrained aggregates and thin parallel lamellar intergrowths with plagioclase the nephelinization has proceeded preferentially from the outer margins of chondrules toward the inside although the degree of nephelinization differs widely among chondrules in each of the metamorphosed chondrites our modal analyses and bulk chemical analyses of individual mesostases indicate that the amounts of nepheline in chondrules systematically increase with the increasing petrologic subtype of the host chondrites nepheline also has a tendency to increase in grain size with increasing petrologic subtype we conclude that nepheline in chondrules in the co3 chondrites has formed largely as a result of effects related to heating on the meteorite parent body we suggest that nepheline initially formed as hydrous nepheline under the presence of aqueous fluids and subsequently was dehydrated after exhaustion of aqueous fluids the degree of hydrothermal activity must have increased with increasing degree of heating and thus chondrules in more thermally metamorphosed chondrites produced larger amounts of nepheline the results imply that co3 chondrites have gone through lowgrade aqueous alteration and subsequent dehydration at the early stage of heating on the meteorite parent body

general characteristics of temperature variation in china during the last two millennia three alternate china wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores tree rings lake sediments and historical documents five periods of temperature variation can be identified a warm stage in ad 0 240 a cold interval between ad 240 and 800 a return to warm conditions from ad 800 1400 including the medieval warm period between ad 800 1100 the cool little ice age period between 1400 1920 and the present warm stage since 1920 regional temperature variation is found during ad 800 1100 when warm conditions occurred in eastern china and in the northeastern tibetan plateau and in ad 1150 1380 when the southern tibetan plateau experienced a warm interval in contrast evidence for cool conditions during the lia is more consistent among the proxy records the temperature reconstructions for china and the northern hemisphere show good agreement over the past millennium

millennial scale environmental changes in the asian monsoon margin during the holocene implicated by the lake evolution of huahai lake in the hexi corridor of northwest china the pattern of holocene environmental changes in the asian monsoon margin on a millennial timescale remains controversial based on lithological characteristics and sedimentological proxies we reconstructed holocene effective humidity changes and the lake evolution of huahai lake in the marginal area of the asian monsoon in the hexi corridor of nw china our results show that alluvial and aeolian deposition before 10 4 cal ka bp indicate an arid environment that lacustrine deposition from 10 4 to 8 8 cal ka bp indicates a transition from an arid to a humid environment and that lacustrine deposition from 8 8 to 5 5 cal ka bp occurred during the most humid conditions indicated by proxy records grain size carbonate toc and c n after 5 5 cal ka bp a depositional hiatus implicates an arid environment in the late holocene holocene environmental changes on millennial timescales in huahai lake imply that climate was arid to humid in the early holocene most humid in the mid holocene and arid in the late holocene these moisture changes were influenced by the asian monsoon particularly the transportation of water vapor by the indian monsoon in addition these moisture changes could have been affected by westerly winds that could have contributed to the water vapor supply to this region during the mid holocene the most humid conditions that occurred in the study area during the mid holocene may have been caused by strong westerlies and low levels of evaporation

significance of variations in the wind energy environment over the past 50 years with respect to dune activity and desertification in arid and semiarid northern china climate data from 339 meteorological stations collected from the 1950s to the early 2000s was employed to discuss aeolian activity in arid and semiarid northern china the results show that at decadal time scales erosivity varied greatly in this region most of arid and semiarid northern china was characterised by environments with moderate to low wind energy after the 1980s the erosivity was only 20 to 50 of that beforehand and this difference had a significant impact on the environmental changes observed during the two periods the dune mobility index was consistent with the observed dune activity after the 1980s dune activity decreased and in some deserts with vegetated dune systems during the 1970s most of the dune plinths were active until the 1980s after which only the crests were active some mobile dunes that had developed at the margins of mobile deserts were replaced by semi anchored or anchored dunes because most desert areas with vegetated dune systems in arid and semiarid northern china are used for farming or grazing the results of our monitoring show that the desertification trends were consistent with the trends in erosivity and dune activity in this region desertification was controlled much more by climatic changes than has previously been acknowledged and especially by fluctuations in wind energy

organic thermometry for chondritic parent bodies abstract a unique spectroscopic feature has been identified in a study of twenty five different samples of meteoritic insoluble organic matter iom spanning multiple chemical classes groups and petrologic types using carbon x ray absorption near edge structure xanes spectroscopy the intensity of this feature a 1s exciton appears to provide a precise measure of parent body metamorphism the intensity of this exciton is also shown to correlate well with a large negative paramagnetic shift observed through solid state 13c nmr experiments reveal that upon heating primitive iom is transformed into material that is indistinguishable from that in thermally processed chondrites including the development of the 1s exciton a thermo kinetic expression is derived from the experimental data that allows the intensity of the 1s exciton to be used to estimated the effective temperature integrated over time a good correlation is observed between the intensity of the 1s exciton and previously published microraman spectral data these data provide a self consistent organic derived temperature scale for the purpose of calibrating raman based thermometric expressions

widespread hydrothermal alteration minerals in the fine grained matrices of the tieschitz unequilibrated ordinary chondrite mineralogic textural and compositional studies of black and white matrices in the unequilibrated ordinary chondrite tieschitz h l 3 6 show for the first time in an ordinary chondrite the presence of widespread randomly distributed geode like voids and veins scanning electron microscope sem and transmission electron microscope tem studies show that these voids and veins are partially or completely filled by sodic calcic amphiboles winchite and barroisite the occurrence of amphiboles provides unequivocal evidence of the involvement of fluids in the metamorphic evolution of the parent body of tieschitz the presence of amphiboles as the main hydrous phases rather than phyllosilicates indicates that aqueous fluids were present at or close to the peak of thermal metamorphism rather than during the waning stages of the cooling history of the parent body in addition ferrous olivine crystals in association with the amphibole also establish an important link between thermal metamorphism and hydrous phases formed at high temperatures mineralogic and textural evidence suggests that the white matrix and amphibole formed contemporaneously from the same hydrous fluid prior to the formation of ferrous olivine crystals additionally a dark inclusion identified in the host chondrite has mineralogic petrologic and bulk chemical characteristics that are similar to the black matrix of host tieschitz suggesting that this dark inclusion was emplaced before or during parent body metamorphism

the formation of ca fe rich silicates in reduced and oxidized cv chondrites the roles of impact modified porosity and permeability and heterogeneous distribution of water ices cv vigarano type carbonaceous chondrites comprising allende like cvoxa and bali like cvoxb oxidized and reduced cvred subgroups experienced differing degrees of fluid assisted thermal and shock metamorphism the abundance and speciation of secondary minerals produced during asteroidal alteration differ among the subgroups 1 ferroan olivine and diopside hedenbergite solid solution pyroxenes are common in all cvs 2 nepheline and sodalite are abundant in cvoxa rare in cvred and absent in cvoxb 3 phyllosilicates and nearly pure fayalite are common in cvoxb rare in cvred and virtually absent in cvoxa 4 andradite magnetite and fe ni sulfides are common in oxidized cvs but rare in reduced cvs the latter contain kirschsteinite instead thus a previously unrecognized correlation exists between meteorite bulk permeabilities and porosities with the speciation of the ca fe rich silicates pyroxenes andradite kirschsteinite among the cvox and cvred meteorites the extent of secondary mineralization was controlled by the distribution of water ices permeability and porosity which in turn were controlled by impacts on the asteroidal parent body more intense shock metamorphism in the region where the reduced cvs originated decreased their porosity and permeability while simultaneously expelling intergranular ices and fluids the mineralogy petrography and bulk chemical compositions of both the reduced and oxidized cv chondrites indicate that mobile elements were redistributed between ca al rich inclusions dark inclusions chondrules and matrices only locally there is no evidence for large scale several cm fluid transport published 53mn 53cr ages of secondary fayalite in cv co and unequilibrated ordinary chondrites and carbonates in ci cm and cr chondrites are consistent with aqueous alteration initiated by heating of water ice bearing asteroids by decay of 26al not shock metamorphism

deciphering the nebular and asteroidal record of silicates and organic material in the matrix of the reduced cv3 chondrite vigarano we have conducted scanning electron microscope sem and transmission electron microscope tem studies of a variety of occurrences of matrix in the reduced cv3 chondrite breccia vigarano matrix which occurs as clastic interchondrule material and finer grained rims is dominated by morphologically variable olivines that host submicron hercynitic spinel and carbonaceous inclusions clastic matrix and fine grained rims show significant differences in their olivine morphologies abundance and composition of olivine inclusions and characteristics of the carbonaceous matter we suggest that these differences are the result of different degrees of alteration of clastic matrix and rims and are not due to variability in their precursor materials textural and compositional characteristics of olivine in the matrix are consistent with formation by growth possibly from an amorphous precursor material during asteroidal metamorphism in the presence of limited quantities of aqueous fluids spinel inclusions in olivine may be nebular condensates that acted as seeds for nucleation of olivine or may have formed during metamorphism and were subsequently overgrown by olivine carbonaceous material occurs as nanometer sized inclusions within olivine in both fine grained rims and clastic matrix but is most abundant as 100 200 nm grains interstitial to matrix olivines most carbonaceous material is amorphous but poorly graphitized carbon pgc also occurs as a minor component in both olivine inclusions and interstitial c the widespread occurrence of fine grained amorphous carbon grains in the interstitial regions between olivine grains may preserve the distribution and grain size of nebular organic material no clear textural relationships exist between carbonaceous grains and the other mineralogical components of vigarano matrix that could help constrain the origin of the organic grains i e evidence for fischer tropsch type reactions finally there are considerable differences between matrix olivines in vigarano in comparison with those in oxidized cv3 chondrites in particular the mineralogy and morphology of the matrix olivines and the nature composition and distribution of inclusions in the olivine grains are distinct based on these differences we conclude that matrix in the oxidized cv3 chondrites could not have formed by thermal processing of vigarano like material

evaporation of olivine low pressure phase relations of the olivine system and its implication for the origin of chondritic components in the solar nebula low pressure phase relations and vapor pressures of forsterite and fayalite were studied with the knudsen method in the temperature range of 1400 1860 c for forsterite and 1100 1160 c for fayalite the triple points are 5 2 10 5 bar 1890 c and 6 3 10 8 bar 1217 c for forsterite and fayalite respectively the enthalpy and entropy of evaporation of forsterite are hv 543 33 kj mol and sv 169 21 j mol k and those for fayalite are 502 9 kj mol and 199 6 j mol k respectively by assuming that gas and olivine are ideal solutions vaporous and solidus curves of the olivine solid solution system in the pressure range from 10 10 to 10 3 bar were calculated from the thermochemical data at pressures above the triple point of forsterite the phase diagram is the same as that at 1 bar because the vapor field is at higher temperatures than those of liquid bearing fields at pressures between the triple points of forsterite and fayalite liquid bearing stability fields appear below the gas solid stability field in the fe rich portion of the system the compositional range of liquid bearing fields expand with increasing pressure at 10 4 bar the liquid bearing fields cover most of the olivine system xmg 0 9 liquid is absent at pressures below the triple point of fayalite regardless of the composition large mgfe fractionation between gas and solid is more extensive compared to the solid and liquid relationship when heated in equilibrium olivine melts before evaporation in the pressure range of 10 7 10 3 bar in a solar nebula with total pressure of 10 3 bar olivine melts when the nebula is enriched in dust by more than an order of magnitude over the solar nebular value and when the mg si fe h ratio increased the origin of type ia and ii chondrules and matrix olivine in ordinary and carbonaceous chondrites can be explained in terms of the pressure of olivine gas type ia chondrules were formed in the gas solid phase field where volatiles feo na2o and others were lost during heating events responsible for chondrule formation the residual materials became enriched in refractory elements type ii chondrules were formed in the temperature range of the liquid solid phase field under these conditions the original compositions were retained after heating of chondrule formation provided that type ia and ii chondrules were formed at a similar temperature type ia chondrules were formed at an olivine pressure one order of magnitude lower than that of type ii chondrules in this model matrix olivine is a condensate from gas which formed by partial evaporation of chondritic material during type ia chondrule formation

distribution of aliphatic amines in co cv and ck carbonaceous chondrites and relation to mineralogy and processing history the analysis of water soluble organic compounds in meteorites provides valuable insights into the prebiotic synthesis of organic matter and the processes that occurred during the formation of the solar system we investigated the concentration of aliphatic monoamines present in the hot acid water extracts of the unaltered antarctic carbonaceous chondrites dom 08006 co3 and mil 05013 co3 and the thermally altered meteorites allende cv3 lap 02206 cv3 gra 06101 cv3 alh 85002 ck4 and eet 92002 ck5 we have also reviewed and assessed the petrologic characteristics of the meteorites studied here to evaluate the effects of asteroidal processing on the abundance and molecular distributions of monoamines the co3 cv3 ck4 and ck5 meteorites studied here contain total concentrations of amines ranging from 1 2 to 4 0 nmol g of meteorite these amounts are one to three orders of magnitude below those observed in carbonaceous chondrites from the ci cm and cr groups the low amine abundances for cv and ck chondrites may be related to their extensive degree of thermal metamorphism and or to their low original amine content although the co3 meteorites dom 08006 and mil 05013 do not show signs of thermal and aqueous alteration their monoamine contents are comparable to those observed in moderately extensively thermally altered cv3 ck4 and ck5 carbonaceous chondrites the low content of monoamines in pristine co carbonaceous chondrites suggests that the initial amounts and not asteroidal processes play a dominant role in the content of monoamines in carbonaceous chondrites the primary monoamines methylamine ethylamine and n propylamine constitute the most abundant amines in the co3 cv3 ck4 and ck5 meteorites studied here contrary to the predominance of n amino acid isomers in co3 and thermally altered meteorites there appears to be no preference for the larger n amines

the primitive matrix components of the unique carbonaceous chondrite acfer 094 a tem study the mineralogical and chemical characteristics of the fine grained matrix 53 m of the unique primitive carbonaceous chondrite acfer 094 have been investigated in detail by scanning electron microscopy sem and analytical transmission electron microscopy atem generally the fine grained matrix represents a highly unequilibrated assemblage of an amorphous material small forsteritic olivines 200 300 nm low ca pyroxenes 300 400 nm and fe ni sulfides 100 300 nm the matrix is basically unaffected by secondary processes only minor amounts of serpentine and ferrihydrite as products of hydrous alteration are present texturally the amorphous material acts as a groundmass to olivines pyroxenes and sulfides mostly exhibiting rounded or elongated morphologies only very few clastic mineral grains have been found the texture and chemical composition of the amorphous material are consistent with an origin by disequilibrium condensation in either the cooling solar nebula or a circumstellar environment as such the amorphous material may be considered as a possible precursor of matrix materials in other types of chondrites the non clastic matrix olivines fo98 99 and pyroxenes en97 100 are suggested to have formed either by condensation in the solar nebula under highly oxidizing conditions or by recrystallization from the amorphous material the formation of these grains by fragmentation of chondrule components is unlikely due to chemical and microstructural reasons rapid cooling caused the observed intergrowths of clino orthoenstatite in the mg rich matrix pyroxenes although some similarities exist comparing the fine grained matrix of acfer 094 with the matrices of the unequilibrated c03 chondrite alha77307 and the unique type 3 chondrite kakangari acfer 094 remains unique since it contains the highest measured concentrations of circumstellar sic and the second highest of diamond highest is orgueil it seems reasonable to suggested that at least parts of the amorphous material in the fine grained matrix may be of circumstellar origin

holocene moisture variations over the arid central asia revealed by a comprehensive sand dune record from the central tian shan nw china abstract arid central asia aca is one of the largest arid desert areas in the world and its climate is dominated by the westerlies in this study we examined sand dune evolution from the bayanbulak basin in the tian shan xinjiang nw china aiming to infer the holocene moisture history of the aca combined with stratigraphic observation and environmental proxies analysis grain size magnetic susceptibility and total organic content large numbers of luminescence ages from multiple sites eight sections 79 samples were applied to reconstruct the evolution of the sand dune accumulation in the study basin the overall results imply very dry conditions characterized by sand dune accumulation at 12 6 5 ka a wet interval between 6 5 and 0 8 ka when soil formation occurred and decreased moisture during the last 0 8 ka this moisture variation pattern is generally consistent with that inferred from many lacustrine records in the core zone of aca suggesting a widespread dry period in the early to middle holocene and relatively wet middle to late holocene thus the moisture history derived from the current sand dune system contrasts with that in asian monsoon areas which are characterized by a strong monsoon high precipitation in the early and mid holocene and a weak monsoon low precipitation and dry climate during the late holocene our results strongly suggest that the winter solar insolation and the external boundary conditions such as atmospheric co2 concentration ice sheets and meltwater fluxes have been major influential factors triggering the holocene moisture evolution in the core zone of aca

origin of iron rich olivine in the matrices of type 3 ordinary chondrites an experimental study in order to understand the origin of iron rich olivine in the matrices of type 3 ordinary chondrites the reaction of metallic iron and enstatite with and without forsterite and sio2 has been experimentally reproduced at temperatures between 1150 and 800 c and po2 between 10 11 and 10 16 atm between the iqf and mw buffers the olivine produced ranges from fo58 to fo34 and this composition does not change significantly with temperature and time of the runs the magnesian olivine which forms does become more magnesian with increasing forsterite enstatite ratio of the starting materials iron rich olivine fo 35 cannot be formed by the reaction of enstatite and metallic iron with or without forsterite as starting materials but it can be formed in the presence of free silica the composition of olivine becomes more iron rich with increasing silica enstatite ratio the compositional range of olivine formed from each mixture is 25 30 mole fo regardless of the temperature composition mineral assemblage and run duration from these experimental results two possibilities suggested for the origin of the iron rich olivine in the matrices of type 3 ordinary chondrites 1 free silica must have been present if the iron rich olivine was formed by solid state reactions under oxidizing condition in the solar nebula 2 reaction of silicon rich gas with metallic iron took place under oxidizing condition in the solar nebula though it is difficult to define which alternative was dominant the formation of free silica or silicon rich gas may be a result of fractional condensation this is possible if there is a reaction relation between forsterite and gas to produce enstatite the suggested fractional condensation is supported by the fact that the compositions of the fine grained matrices of type 3 ordinary chondrites are more silica rich than the bulk compositions of the chondrites though it is not known whether such conditions were established all over the nebula or locally in the nebula both fractionation and more oxidizing conditions than the average solar nebula are required for the formation of matrix olivine