highly fractionated i type granites in ne china ii isotopic geochemistry and implications for crustal growth in the phanerozoic ne china is the easternmost part of the central asian orogenic belt caob the area is distinguished by widespread occurrence of phanerozoic granitic rocks in the companion paper part i we established the jurassic ages 184 137 ma for three granitic plutons xinhuatun lamashan and yiershi we also used geochemical data to argue that these rocks are highly fractionated i type granites in this paper we present sr nd o isotope data of the three plutons and 32 additional samples to delineate the nature of their source to determine the proportion of mantle to crustal components in the generation of the voluminous granitoids and to discuss crustal growth in the phanerozoic despite their difference in emplacement age sr nd isotopic analyses reveal that these jurassic granites have common isotopic characteristics they all have low initial 87 sr 86 sr ratios 0 7045f0 0015 positive end t values 1 3 to 2 8 and young sm nd model ages 720 840 ma these characteristics are indicative of juvenile nature for these granites other late paleozoic to mesozoic granites in this region also show the same features sr nd and oxygen isotopic data suggest that the magmatic evolution of the granites can be explained in terms of two stage processes 1 formation of parental magmas by melting of a relatively juvenile crust which is probably a mixed lithology formed by pre existing lower crust intruded or underplated by mantle derived basaltic magma and 2 extensive magmatic differentiation of the parental magmas in a slow cooling environment the widespread distribution of juvenile granitoids in ne china indicates a massive transfer of mantle material to the crust in a post orogenic tectonic setting several recent studies have documented that juvenile granitoids of paleozoic to mesozoic ages are ubiquitous in the central asian orogenic belt hence suggesting a significant growth of the continental crust in the phanerozoic d 2003 elsevier science b v all rights reserved

potential analogues for paleoclimatic variations in eastern interior alaska during the past 14 000 yr atmospheric circulation controls of regional temperature and moisture responses the paleoclimatic history of a region can be viewed as a series of surface temperature and moisture anomalies through time the effects of changes in large scale climatic controls e g insolation major circulation controls can be mediated by the influence of smaller scale controls e g topographic barriers coastlines this may result in heterogenous surface climatic responses at the regional and sub regional scale divergent paleoclimatic trajectories between regions may be explainable in terms of such meso scale patterns using modern analogues for paleoclimate we examine how the sequence of climatic variations in eastern interior alaska during the interval 12 000 0 14c yr bp could have been generated by specific atmospheric circulation patterns fossil pollen and lake level records document the long term trends in temperature and effective moisture for the region water balance modelling provides additional estimates of paleoprecipitation synoptic climatological patterns are described using the modern instrumental record of upper level and sea level pressure surface temperature and precipitation at 12 000 14c yr bp eastern interior alaska was cooler and drier than present a situation generated today by a southward displacement of the jet stream conditions warmer and drier than present at 9000 14c yr bp may have been generated by increased ridging north of alaska and a weakened westerly circulation warmer wetter conditions than present possibly prevailed in the late middle holocene these might reflect ridging over alaska and troughing further west cool wet conditions feature enhanced westerly flow into alaska through an eastward shift in the east asian trough and positive pressure anomalies in the north pacific they may be analogous to cold periods of the little ice age the analogues demonstrate how surface conditions in other parts of beringia may sometimes be similar to while at other times different from those in the eastern interior these broader spatial patterns provide hypotheses about past climates that can be tested with paleoclimatological data for example the widespread positive temperature anomalies associated with the warm dry 9000 14c yr bp analogue fit with the expansion northward of the eastern siberian treeline the anomalously cool conditions in northeast siberia associated with the warm wet analogue may explain the continued late middle holocene treeline advance in alaska while there was retreat in siberia

amphibole sponge in arc crust pressure temperature time paths followed by arc magmas ascending through the lithosphere dictate the phase assemblage that crystallizes and hence the compositions of liquid fractionates here we use la yb and dy yb versus sio 2 relationships from selected volcanoes to show that amphibole is an important mineral during differentiation of arc magma production of intermediate and silicic arc magmas occurs as magmas stall and cool in the mid lower crust where amphibole is stable because amphibole is rarely a phenocryst phase we term this cryptic amphibole fractionation if this process is as widespread as our investigation suggests then 1 amphibole cumulates may act as an effective filter for water dissolved in mantle derived magmas 2 amphibole cumulates may act as a fertile source of intracrustal melts and fluids and 3 recycling of amphibole cumulates has the potential to return incompatible trace elements and water to the mantle

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

geodynamic significance of s type granites in circum pacific orogens in phanerozoic circum pacific orogenic belts most post collisional s type granites and associated high temperature low pressure metamorphic complexes formed during early arc extension the granites are part of a tripartite association consisting of 1 inboard s type granite 2 outboard oceanic arc and 3 intervening turbidite filled backarc basin s type granites herald the formation of new outboard oceanic arc and extensional backarc systems but thickening of a preexisting sediment dominated back arc basin is a prerequisite for their generation in these environments s type plutonism is triggered by renewal of arc magmatism following thickening when hot basaltic magmas are intruded into the thickened backarc crust once slab retreat is reestablished with ongoing extension during retreat the crust becomes progressively thinned the sedimentary contribution is diminished and the granites lose their s type character such tripartite associations involving s type granite are probably diagnostic of repeated slab retreat episodes and the jurassic u s cordillera might be an example

radar investigation of mars mercury and titan radar astronomy is the study of the surfaces and near surfaces of solar system objects using active transmission of modulated radio waves and the detection of the reflected energy the scientific goals of such experiments are surprisingly broad and include the study of surface slopes fault lines craters mountain ranges and other morphological structures electrical reflectivities contain information about surface densities and to some extent the chemical composition of the surface layers radar probes the subsurface layers to depths of the order of 10 wavelengths providing geological mapping and determinations of the object s spin state radar also allows one to study an object s atmosphere and ionic layers as well as those of the interplanetary medium precise measurements of the time delay to surface elements provide topographic maps and powerful information on planetary motions and tests of gravitational theories such as general relativity in this paper we limit our discussion to surface and near surface probing of mercury mars and titan and review the work of the past decade which includes fundamentally new techniques for earth based imaging the most primitive experiments involve just the measurement of the total echo power from the object the most sophisticated experiments would produce spatially resolved maps of the reflected power in all four stokes parameters historically the first experiments produced echoes from the moon during the period shortly after world war ii see e g evans 1962 but the subject did not really develop until the early 1960s when the radio equipment was sufficiently sensitive to detect echoes from venus and obtain the first doppler strip maps of that planet the first successful planetary radar systems were the continuous wave cw radar at the goldstone facility of the caltech s jet propulsion laboratory and the pulse radar at the mit lincoln laboratory all of the terrestrial planets were successfully studied during the following decade yielding the spin states of venus and mercury a precise value of the astronomical unit and a host of totally new discoveries concerning the surfaces of the terrestrial planets and the moon this work opened up at least a similar number of new questions although the early work was done at resolution scales on the order of the planetary radii very rapid increases in system sensitivities improved the resolution to the order of 100 km but always with map ambiguities recently unambiguous resolution of 100 m over nearly the entire surface of venus has been achieved from the magellan spacecraft using a side looking synthetic aperture radar reviews of the work up to the magellan era can be found in evans 1962 muhleman et al 1965 evans hagfors 1968 see chapters written by g pettengill t hagfors and j evans and ostro 1993 the radar study of venus from the magellan spacecraft was a tour de force and is well described in special issues of science volume 252 april 12 1991 and in the journal of geophysical research volume 97 august 25 and october 25 1992 venus will not be considered in this paper even though important polarization work on that planet continues at arecibo goldstone and the very large array vla in this paper we review the most recent work in earth based radar astronomy using new techniques of earth rotation super synthesis at the vla in new mexico operated by the national radio astronomy observatory and the recently developed long code techniques at the arecibo observatory in puerto rico operated by cornell university note it was recently brought to our attention that the vla software doubles the flux density of their primary calibrators consequently it is necessary to half the radar power and reflectivity numerical values in all of our published radar results from the vla goldstone radar the symbiotic relationship in these new developments for recent advances in our understanding of mercury and mars is remarkable vla imaging provides for the first time unambiguous images of an entire hemisphere of a planet and the long code technique makes it possible to map mars and mercury using the traditional range gated doppler strip mapping procedure which was apparently developed theoretically at the lincoln laboratory by paul green based on a citation in evans 1962 richard goldstein was the first to obtain range gated planetary maps of venus as reported in carpenter goldstein 1963 such a system was developed earlier for the moon as reported by pettengill 1960 and pettengill henry 1962 we first discuss the synthesis mapping technique

reconstruction of annual temperature 1590 1979 for longmire washington derived from tree rings abstract annual growth records from trees at timberline in the cascade range of washington are correlated with variations in temperature and snow depth and used to reconstruct climatic variation in the past response surfaces indicate that growth of mountain hemlock tsuga mertensiana and subalpine larch larix lyallii is positively correlated with summer july to september temperature and negatively correlated with spring march snow depth when snow depth is at or below average during years of above average snow depth temperature has little effect on mountain hemlock but has a negative effect on growth in subalpine larch these interactions make it difficult to reconstruct these climatic variables separately using standard methods mean annual temperature values which combine information on both summer temperature and spring snow depth were estimated from a regression model that reconstructs past temperature at longmire washington as a function of larch and hemlock tree ring chronologies the reconstruction of mean annual temperature shows temperatures between 1590 and 1900 to be approximately 1 c lower than those of the 20th century only during a short period from 1650 to 1690 did temperatures approach 20th century values

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

petrogenetic constraints for the genesis of archaean sanukitoid suites geochemistry and isotopic evidence from karelia baltic shield new sm nd isotope data are presented for late archaean sanukitoid suites of the karelian granite greenstone terrane of the baltic shield within the terrane there are regional variations in the nd isotope compositions of the sanukitoids sanukitoids in the youngest central karelian domain have nd isotope characteristics similar to depleted mantle whereas those from the older west karelian and vodlozero domains have lower initial end values the isotopic heterogeneity of the sanukitoids is interpreted to result from variations in the time interval between mantle source enrichment and the partial melting that produced the sanukitoid magmas we therefore suggest a two stage model of the generation of sanukitoid magmas during first stage the mantle was metasomatised by fluids and or melts generated during subduction or tectonic underplating later between 2 74 and 2 70 ga a tectonothermal anomaly generated the sanukitoid magmas by melting of the previously metasomatised mantle most of the sanukitoid intrusions are cut by calc alkaline lamprophyre dykes that have the similar geochemical signatures to their sanukitoid wall rocks new sm nd isotope data for these lamprophyres suggest a genetic kinship between the sanukitoids and the lamprophyres comparison between chemical signatures of sanukitoids and modern subduction related magmas shows that archaean sanukitoids actually have no modern analogues sanukitoid melts can be modelled as partial melts of mantle that had been metasomatised a short time previously the melts could have been in equilibrium with residues containing ol cpx plus minor phl and grt at a pressure of about 2 5 gpa and a temperature of 1150 1230 8c the small percentage of residual phlogopite would retain rb in the mantle and explain the peculiar signature of low rb and high ba and sr characteristic of the sanukitoids we envisage a temporal evolution of the composition of the mantle in this region this pattern of evolution controlled production of the sanukitoid melts and explains why the sanukitoids have such a restricted range of ages sanukitoid magma production must have followed from a major global mantle enrichment event these magmas could not have been produced earlier because the archaean mantle had not become sufficiently enriched before 2 7 ga we suggest that their scarcity after the major period of sanukitoid magmatism may be due to the increased thickness of overlying crust which can inhibit mantle enrichment

surface modification of venus as inferred from magellan observations of plains in sedna planitia clear stratigraphic relations can be discerned among volcanic flow units young flows exhibit sar specific cross section values similar to fresh terrestrial basalt flows whereas older flows exhibit backscatter signatures similar to degraded terrestrial basalt flows total degradation of 1 m depth over 0 6 b y is inferred for the sedna area from radar signatures impact crater abundances and ejecta superposition relations with respect to volcanic flow units analyses of parabolic ejecta deposits associated with the crater stuart imply that the material is typically centimeters in thickness a relatively small fraction 10 of venusian impact craters exhibit prominent parabolic ejecta deposits these craters are interpreted to be relatively young and parabolic deposits are interpreted to be dispersed by aeolian activity over at least tens of millions of years the inferred dispersal rate 10 3 m yr is too low to produce the degradation of flows at sedna planitia and it is concluded that the dominant flow modification process is in situ weathering in addition elevation dependent weathering is inferred in western ovda regio where plains above 6054 km radius have enhanced reflection coefficients as compared to adjacent plains at lower elevations the inferred rate of generation of high reflection coefficient materials is no more than 10 2 m yr based on the inability of aeolian activity to cover high reflectivity surfaces with normal reflection coefficient materials and the ubiquitous nature of high reflectivity surfaces at high elevations surface modification rates on venus are orders of magnitude lower than on earth venusian rates are also much lower than the inferred rate of aeolian dispersal of friable materials on mars but are comparable to the estimated rate of weathering and erosion of martian bedrock low surface modification rates imply that it will be possible to determine regional scale age variations on venus based on the degree of preservation of volcanic landforms and microwave signatures

melting of continental crust during subduction initiation a case study from the chaidanuo peraluminous granite in the north qilian suture zone the chaidanuo granite batholith is a similar to 500 km 2 homogeneous high level intrusion in the north qilian oceanic suture zone three types of enclaves have been recognized including 1 supracrustal xenoliths 2 biotite gneiss that represents restite of the upper crustal melting and 3 coeval mantle derived mafic magmatic enclave mme the batholith consists dominantly of peraluminous biotite monzogranite with sio2 69 73 wt and a cnk 1 05 1 28 and shows geochemical affinity with the upper continental crust e g enrichment of large ion lithophile elements liles k rb u th pb depletion of high field strength elements hfses nb ta ti p eu and sr and enriched sr sr 87 sr 86 i 0 731 to 0 744 nd epsilon nd t 6 0 to 7 1 isotopes zircon u pb dating indicates that this batholith formed at 516 505 ma coeval with the mmes 510 ma which represent the early stage of seafloor subduction in the north qilian suture zone the hf isotopic composition of the mme epsilon hf t 6 0 to 2 1 is more depleted than that of the host granite epsilon hf t 14 8 to 4 7 suggesting mixing of mantle and crust derived melts the inherited zircon cores in the host granite yield an age peak at similar to 750 ma with a few detritals of 591 1683 ma zircons from a biotite gneiss enclave yield a protolith age of 744 ma and a metamorphic melting event at 503 ma sr nd isotopic modeling reveals that the batholith was generated by melting of neoproterozoic granitic rocks with the addition of 10 18 mantle derived magma therefore peraluminous granite can be produced by melting of crustal materials heated by mantle derived magmas during the early stage of subduction initiation at the site of a prior passive continental margin c 2014 elsevier ltd all rights reserved

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

reconstructed summer degree days in central alaska and northwestern canada since 1524 abstract three time series based on precisely dated annual tree ring widths have been used to reconstruct june plus july degree days for the central alaska and northwestern canada region the time series are the longest recently developed chronologies for the area and represent 57 core samples from 27 trees the degree day reconstruction extending back to a d 1524 exhibits much year to year variation and extended warming and cooling trends including a general warming trend from about 1840 to 1960 the reconstruction is in agreement with some subaretic glacial information and with data of percentage melting from arctic ice cores this and similar reconstructions can provide quantitative information to compare with general circulation and energy budget models for longer time periods than are available in recorded meteorological data

a cold early palaeozoic subduction zone in the north qilian mountains nw china petrological and u pb geochronological constraints the north qilian high pressure hp low temperature lt metamorphic belt is composed mainly of blueschists eclogites and greenschist facies rocks it formed within an early palaeozoic accretionary wedge associated with the subduction of the oceanic crust and is considered to be one of the best preserved hp lt metamorphic belts in china here we report new lawsonite bearing eclogites and eclogitic rocks enclosed within epidote blueschists in the north qilian mountains five samples contain unaltered lawsonite coexisting with omphacite and phengite as inclusions in garnet indicating eclogite facies garnet growth and lawsonite pseudomorphs were observed in garnet from an additional 11 eclogites and eclogitic rocks peak pressure conditions estimated from lawsonite omphacite phengite garnet assemblages were 2 1 2 4 gpa at temperatures of 420 510 c in or near the stability field of lawsonite eclogite and implying formation under an apparent geothermal gradient of 6 8 c km 1 consistent with metamorphism in a cold subduction zone shrimp u pb dating of zircon from two lawsonite bearing eclogitic metabasites yields ages of 489 7 ma and 477 16 ma respectively cl images and mineral inclusions in zircon grains indicate that these ages reflect an eclogite facies metamorphism an age of 502 16 ma is recorded in igneous cores of zircon grains from one lawsonite pseudomorph bearing eclogite which is in agreement with the formation age of early ordovician for some ophiolite sequences in the north qilian mountains and may be associated with a period of oceanic crust formation the petrological and chronological data demonstrate the existence of a cold early palaeozoic subduction zone in the north qilian mountains

transitional morphology in west deuteronilus mensae mars implications for modification of the lowland upland boundary abstract west deuteronilus mensae which lies along the lowland upland boundary of mars at 45 latitude 345 longitude exhibits both gradational l a rossbacher 1985 in models in geomorphology woldenberg ed pp 343 372 allen unwin boston and fretted terrain r p sharp 1973 j geophys res 78 4073 4083 boundary types to the west the boundary is gradational and to the east it is defined by fretted terrain the two types of boundaries do not merge with one another within the west deuteronilus mensae region however the gradational boundary materials appear to overlap the fretted terrain by about 500 km contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap the fretted terrain can be identified as much as 300 km north of the gradational boundary in this region lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion changes in the fretted terrain across the gradational boundary from uplands to lowlands include a reduction of canyon wall slopes and depths such that the fretted terrain north of the gradational boundary appears mantled but not obscured there are at least two major classes of processes which might explain the lateral overlap 1 erosion of stratified upland terrain and 2 deposition of plains materials onto the sloping upland margin and fretted terrain erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places of the possible plains emplacement mechanisms eolian deposition would not produce the sharp apparently topographically conformal gradational unit contacts volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain sediment deposition in either a liquid or ice covered sea could produce the draped appearance of the fretted terrain outflow channels along the lowland upland boundary particularly those of the circum chryse and west elysium regions may have flooded the northern lowlands to depths of tens to hundreds of meters the gradational unit contacts may represent the shorelines of such a sea the scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine style wave erosion and redistribution of material along the contacts our limited understanding of the martian paleoclimate and h 2 o inventories allows the possibility of clement periods in the past and other geological evidence e g small valley networks and outflow channels strongly suggests an extensive role of liquid water

multipolarization radar images for geologic mapping and vegetation discrimination the nasa jpl airborne synthetic aperture radar system produces radar image data simultaneously in four linear polarizations hh vv vh hv at 24 6 cm wavelength l band with 10 m resolution across a swath width of approximately 10 km the signal data are recorded optically and digitally and annotated in each of the channels to facilitate a completely automated digital correlation both standard amplitude and also phase difference images are produced in the correlation process individual polarization and range dependent gain functions improve the effective dynamic range but as yet do not permit absolute quantitative measurements of the scattering coefficients however comparison of the relative intensities of the different polarizations in individual black and white and color composite images provides discriminatory mapping information in the death valley california area rough surfaces of young alluvial deposits produce strong responses at all polarizations smoother surfaces of older alluvial deposits show significantly lower responses evaporite deposits of different types and moisture contents have distinct polarization signatures in the wind river basin wyoming sedimentary rock units show polarization responses that relate to differences in weathering local intensity variations in like polarization images result from topographic effects strong cross polarization responses denote the effects of vegetation cover and in some cases possible scattering from the subsurface in the savannah river plant south carolina forest cover characteristics are discriminated by polarization responses that reflect the density and structure of the canopy and the presence or absence of standing water beneath the canopy

topography of small martian valleys abstract small valleys are common in the ancient highlands of mars valley widths are typically a few kilometers and are independent of length for valleys longer than about 50 km topographic profiles across several representative small valleys produced using one dimensional photoclinometry have smoothly curved shapes and valley side slopes of 10 20 profiles of unusual valleys from maumee valles the flanks of alba patera and softened terrain also have slopes of 10 20 but the profiles of maumee valles are more v shaped than those of the typical small valleys while the profiles of the softened valley have proportionately longer upslope convexities depths from 15 to 800 m are measured for the small martian valleys and most valleys have depths between 20 and 250 m the mean depth to width ratio from 135 measurements of 45 different valleys is 0 08 standard deviation 0 04 when valley profiles with uneven rims are excluded the mean depth to width ratio is 0 07 standard deviation 0 03 applying the lower ratio to the widths of a larger sample of small valleys yields depths that are almost all between 40 and 300 m the majority of the small valleys we have studied are probably the result of groundwater sapping and in this context the measured valley depths imply that liquid water was often less than a few hundred meters below the surface in the vicinity of these valleys at the time early in martian history when the valleys formed

melting of a subducting slab and production of high mg andesite magmas unusual magmatism in sw japan at 13 15 ma characteristic high mg andesite magmas were produced in the sw japan arc at 13 15 ma that was synchronous with the commencement of subduction of a very young 11 m y lithosphere of the shikoku basin numerical simulation suggests that temperature at the surface of such a young subducting plate is high enough for partial melting both of the subducting sediments and oceanic crust at the beginning of the subduction high mg andesite magmas were likely to be produced by interaction between silicic slab melts and the overlying mantle wedge hma magmas may be commonly produced in the archean subduction zones under relatively high mantle temperature conditions contributing to making continental crusts

mars mapping with delay doppler radar mars radar imaging results from arecibo 12 6 cm observations are presented the images were derived from delay doppler mapping using a coded long pulse technique to mitigate the effects of echo overspreading images of the depolarized echo are used to identify regions of high decimeter scale roughness some of the strongest echo features are located on the major shield volcanoes or on relatively young off shield flows such as the olympus and pavonis lava aprons the shields themselves have highly irregular radar signatures suggesting complex volcanic histories some mars radar features have twice the depolarized brightness of the roughest terrestrial lava flows apparently due to higher levels of multiple scattering from surfaces of spectacular roughness or from volume scattering low brightness smooth areas are associated with older surfaces such as fractured and highland terra as well as with terrain interpreted to be debris lobes ash flows and aureoles in particular a close connection was found between the 12 6 cm counterpart of the stealth feature and the medusae fossae formation postulated to be deep ignimbrite deposits marte valus is anomalous in being the only outflow channel showing strongly enhanced echoes which supports the idea that this channel and the elysium basin that it drained are filled with lava flows a weak radar feature was found for the south polar residual ice cap comparisons with goldstone 3 5 cm data show that the south polar enhancement is much weaker at 12 6 cm than at 3 5 cm indicating that the southern ice cap becomes optically thin at the longer wavelength a north polar enhancement has also been found which is comparable in strength to the 12 6 cm south polar feature

petrogenesis of the early paleozoic low mg and high mg adakitic rocks in the north qilian orogenic belt nw china implications for transition from crustal thickening to extension thinning abstract the petrogenesis and geodynamic implications of the early paleozoic adakitic rocks in the north qilian orogenic belt remain topics of debate in this study petrology zircon u pb age and lu hf isotopic composition whole rock geochemistry and sr nd isotopes were carried on both low mg and high mg adakitic rocks from the north qilian orogenic belt these results will provide significant constraints on the evolution of the north qilian orogenic belt in general the low mg adakitic granites mainly consist of plagioclase 50 55 alkali feldspar 20 25 quartz 20 25 and biotite 5 in contrast the high mg adakitic granodiorites are generally composed of alkali feldspar 30 35 plagioclase 30 45 quartz 20 25 and amphibole 10 the low mg adakitic granitoids 446 457 ma are characterized by high sio2 69 72 wt low mg 39 42 and low cr and ni contents however the high mg adakitic granitoids 430 431 ma have relatively lower sio2 65 66 wt higher mg 50 59 and higher cr and ni contents the low mg adakitic rocks have high initial 87sr 86sr ratios 0 7068 0 7080 negative end t 2 3 to 3 3 and ehf t values 6 8 to 1 9 with old zircon hf model ages 1 2 1 6 ga however the high mg adakitic rocks show lower initial 87sr 86sr ratios 0 7044 0 7066 higher end t 1 8 to 3 0 and positive ehf t values 2 3 7 7 with younger zircon hf model ages 0 9 1 1 ga these results suggest that the low mg rocks were generated by partial melting of thickened crust whereas the high mg rocks were derived from anatexis of delaminated lower crust which subsequently interacted with mantle magma upon ascent the data obtained in this study provide significant information about the geological and tectonic processes after the closure of the qilian ocean the continent continent collision and thickening probably occurred during 440 467 ma with formation of low mg adakitic rocks and the transition of the tectonic regime from compression to extension probably occurred at 430 ma with formation of high mg adakitic rocks

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

neoarchean crustal recycling and mantle metasomatism hf nd pb o isotope evidence from sanukitoids of the fennoscandian shield abstract the growing knowledge of the geological record reveals evidence of crustal recycling in the archean eon in order to assess the role of recycling of crust into the mantle we have analyzed radiogenic hf in zircon as well as whole rock nd and pb isotope compositions of mantle derived granitoids of the sanukitoid series in the neoarchean karelian province fennoscandian shield homogeneous initial hf and nd values suggest that sanukitoids are derived from well mixed source s limited scatter in the initial pb isotope data within intrusions as well as in other radiogenic isotopes point to effective mixing processes in the mantle o isotope data for zircon from karelian sanukitoids indicate a dominant mantle source 18 o 5 5 6 1 with minor contributions from sources with elevated 18 o 7 0 to 8 5 such as sediments and altered upper oceanic crust our results suggest that the parental melts of sanukitoids are mixtures of depleted mantle and recycled crustal components a slab breakoff at the end stage of subduction is a plausible trigger mechanism for sanukitoid magmatism and it explains variable contributions from different 18 o sources

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

paleozoic magmatism and porphyry cu mineralization in an evolving tectonic setting in the north qilian orogenic belt nw china abstract the nww striking north qilian orogenic belt records the paleozoic accretion collision processes in nw china and hosts paleozoic cu pb zn mineralization that was temporally and spatially related to the closure of the paleo qilian qinling ocean the wangdian cu deposit is located in the eastern part of the north qilian orogenic belt nw china copper mineralization is spatially associated with an altered early paleozoic porphyritic granodiorite which intruded tonalites and volcaniclastic rocks alteration zones surrounding the mineralization progress outward from a potassic to a feldspar destructive phyllic assemblage mineralization consists mainly of quartz sulfide stockworks and disseminated sulfides with ore minerals chalcopyrite pyrite molybdenite and minor galena and sphalerite gangue minerals include quartz orthoclase biotite sericite and k feldspar zircon la icpms u pb dating of the ore bearing porphyritic granodiorite yielded a mean 206pb 238u age of 444 6 7 8 ma with a group of inherited zircons yielding a mean u pb age of 485 12 ma consistent with the emplacement age 485 3 6 2 ma of the barren precursor tonalite rhenium and osmium analyses of molybdenite grains returned model ages of 442 9 6 8 ma and 443 3 6 2 ma indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite rhenium concentrations in molybdenite 208 9 213 2 ppm suggest a mantle re source the tonalities are medium k calc alkaline they are characterized by enrichment of light rare earth elements lrees and large ion lithophile elements liles depletion of heavy rare earth elements hrees and high field strength elements hfses and minor negative eu anomalies they have ehf t values in the range of 3 6 to 11 1 with two stage hf model ages of 0 67 1 13 ga suggesting that the ca 485 ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and the lithosphere in contrast the 40 m y younger ore bearing porphyritic granodiorite is sub alkaline and peraluminous they are enriched in lrees and liles depleted in hfses and show weak negative eu anomalies they display ehf t values of captured or inherited zircons in the range of 8 5 to 10 0 and younger two stage hf model ages of 0 78 ga and 0 86 ga similar to those of ca 485 ma tonalite the ca 445 ma zircons have ehf t values of 2 1 to 9 9 with two stage hf model ages of 0 75 1 27 ga moreover they have relatively high oxygen fugacity than that of the precursor barren tonalite the ca 445 ma magmas at wangdian thus formed in a subduction setting and incorporated melts from the subduction modified lithosphere that had previously been enriched by additions of chalcophile and siderophile element rich materials by the earlier magmatism and metasomatism during the paleo qilian qinling ocean subduction event

magmatic relationships and ages between adakites magnesian andesites and nb enriched basalt andesites from hispaniola record of a major change in the caribbean island arc magma sources abstract located in the cordillera central of the dominican republic the late cretaceous tireo fm tf records a major change of the magma sources in the caribbean island arc it comprises a 3 km thick sequence of arc related volcanic and volcano sedimentary rocks with variable geochemical characteristics combined detailed mapping stratigraphy geochemistry and u pb ar ar geochronology show that the volcanic rocks of the tireo fm include two main volcanic sequences the lower volcanic sequence is dominated by monotonous submarine vitric lithic tuffs and volcanic breccias of andesite to basaltic andesite with minor interbedded flows of basalts and andesites fossil and u pb and 40ar 39ar geochronological data show that arc magmatism in the lower sequence began to accumulate before 90 ma from the aptian to turonian these rocks constitute an island arc tholeiitic suite derived from melting by fluxing of a mantle wedge with subduction related hydrous fluids the upper volcanic sequence is characterized by a spatial and temporal association of adakites high mg andesites and nb enriched basalts which collectivelly define a shift in the composition of the subduction related erupted lavas a dacitic to rhyolitic explosive volcanism with subaerial and episodic aerial eruptions and sub volcanic emplacements of domes characterize mainly this stratigraphic interval the onset of this volcanism took place at turonian coniacian boundary and continued in the santonian to lower campanian with minor events in the late campanian adakites represent melts of the subducting slab magnesian andesites the product of hybridization of adakite liquids with mantle peridotite and nb enriched basalts melts of the residue from hybridization we propose a model of oblique ridge subduction at 90 ma and possibly subsequent slab window formation as principal cause of magmatic variations recorded in the caribbean island arc above a southwestern dipping subduction zone

dendroecological evidence of lake level changes during the last three centuries in subarctic quebec abstract dendroecological analysis of black spruces picea mariana mill bsp near the shore of clearwater lake in the eastern canadian subarctic yielded information on water level over the past three centuries tree positions growth froms layering tree ring patterns and ice scars provide direct evidence of a major rise in lake level from the 17th century to the present trees on the lake shore were progressively submerged by the increasing water level which reached a maximum in this century higher levels began around the mid 18th century when shoreline spruce trees started to lean because extensive wave erosion caused landward shore displacement high mortality of leaning spruce and abundant ice scar formation occurred during this century the rise in water level in inferred to have been caused by snowier winters occurring parallel to climatic warming

petrogenesis and tectonic setting of early paleozoic granites and high mg diorites in the northern qilian orogen china abstract the northern qilian orogenic belt n qob was formed by oceanic subduction and collision between the alashan and central qilian belt in the early paleozoic new zircon u pb ages hf isotopic and whole rock elemental data of the intrusive rocks in the central n qob have been conducted to constrain the tectonic evolution of n qob zircon dating results revealed that the ladonggou suyougou granitic plutons and xichagou dioritic pluton were emplaced at 505 3 ma 471 3 m and 425 3 ma respectively the ladonggou monzogranite displays depletion of nb ta ti p and negative ehf t values 6 5 to 0 3 and old hf crustal model ages 1 5 1 9 ga suggesting generation from melting of ancient crust above subducted north qilian oceanic slab the suyougou granite possesses geochemistry of i type granite the relative enrichment of liles depletion of hfses and negative eu anomalies as well as prominent hf isotope heterogeneities and old hf crustal model ages 2 1 2 5 ga suggest a magma source of ancient crust mixed with minor mantle derived melts in a subduction related setting diorites from the xichagou plutonare characterized by high mg values enrichments in cr ni y yb and high sr y ratios and convincing subduction related features suggesting generation from partial melting of subducted sediments mixed with mantle components taking all these geochemistry and geochronology together with the regional geology we interpreted the ladonggou monzogranite suyougou granite and xichagou diorite were related to the long term northward subduction of north qilian oceanic lithosphere during ca 505 and 425 ma

origin of enclaves in s type granites of the lachlan fold belt abstract the more mafic s type granites of the lachlan fold belt contain a distinctive assemblage of lithic inclusions of deep crustal origin two types predominate the schistose enclaves and the microgranular enclaves there is also a small proportion of fragments of local country rock all the features of the schistose enclaves are consistent with an origin as lithic restite fragments from the source their ubiquity in the mafic s type granites and absence from both felsic s type granites and i type granites conform with such an origin the argument that these enclaves are not in chemical equilibrium with the host granite because they do not complement its composition is not valid since they represent less fertile parts of the source that had different compositions that as a result melted to a lesser extent models that derived these enclaves from regions of the crust above the zones of partial melting so that they are not restites are complex unnecessary do not conform with their ubiquity in the more mafic s type granites and are not consistent with their chemical compositions the origin of the microgranular enclaves is controversial in most s type granites these enclaves have been recrystallized to a similar mineral assemblage to the host granite with a higher proportion of biotite in a few places such material is seen to be forming by recrystallization of material in the core of the enclave which has the assemblage quartz calcic plagioclase orthopyroxene cordierite biotite with accessory ilmenite sulfide and apatite all of the microgranular enclave cores show pseudo doleritic texture in which calcic plagioclase crystals an60 and orthopyroxene crystals project into or are enclosed by quartz large plagioclase crystals are zoned with some core compositions as calcic as an94 the low na contents of the microgranular enclaves are not consistent with an igneous origin we consider that these enclaves were derived by metamorphism of calcareous mudstones or argillaceous limestones the pseudo igneous textures result from the presence of a partial melt during metamorphism an analysis of a calc silicate lens of upper amphibolite grade from the wilsons group of victoria land antarctica is remarkably similar in composition to the microgranular enclaves from lachlan fold belt s type granites we suggest that rocks equivalent to that group which is of appropriate age and general composition were the source rocks for the s type granites of the lachlan fold belt

regolith composition and structure in the lunar maria results of long wavelength radar studies radar measurements at 70 cm and 7 5 m wavelengths provide insight into the structure and composition of the upper 5 100 m of the lunar regolith and crust we combine high resolution 3 5 km 70 cm radar data for the nearside with earlier calibrated full disk observations at the same wavelength to provide a reasonable estimate of the lunar backscatter coefficient these data are tested against models for echoes from a buried substrate and mie scattering from surface and buried rocks these mechanisms are expected to dominate the 70 cm radar echo with their relative importance determined by the rock population regolith depth substrate roughness and the loss tangent of the soil results indicate that the 70 cm radar echo for the maria comes largely from mie scattering by rocks buried within the fine soil radar scattering from a buried substrate is not likely to greatly affect the observed return we also compared the 70 cm and 7 5 m radar images to infrared eclipse temperature maps crater population age estimates for the maria and to tio2 and feo abundances inferred from earth based telescopic and clementine multispectral observations these data imply that 1 the tio2 ilmenite content of the regolith controls variations in 70 cm depolarized echo strength among mare units with higher titanium abundance leading to lower echoes 2 changes in the average 70 cm return for a given tio2 abundance between maria of different ages do occur but uncertainties in the current radar data do not allow us to uniquely distinguish between variations in rock population with age and calibration effects 3 the 7 5 m radar echoes are controlled by the age of the mare basalt flows with older deposits having a greater degree of fracturing and higher backscatter future mapping at 12 6 cm and 70 cm wavelengths will help to resolve some of the issues raised here

radar images of mars full disk images of mars have been obtained with the use of the very large array vla to map the radar reflected flux density the transmitter system was the 70 m antenna of the deep space network at goldstone california the surface of mars was illuminated with continuous wave radiation at a wavelength of 3 5 cm the reflected energy was mapped in individual 12 minute snapshots with the vla in its largest configuration fringe spacings as small as 67 km were obtained the images reveal near surface features including a region in the tharsis volcano area over 2000 km in east west extent that displayed no echo to the very low level of the radar system noise the feature called stealth is interpreted as a deposit of dust or ash with a density less than about 0 5 gram per cubic centimeter and free of rocks larger than 1 cm across the deposit must be several meters thick and may be much deeper the strongest reflecting geological feature was the south polar ice cap which was reduced in size to the residual south polar ice cap at the season of observation the cap image is interpreted as arising from nearly pure co 2 or h 2o ice with a small amount of martian dust less than 2 percent by volume and a depth greater than 2 to 5 m only one anomalous reflecting feature was identified outside of the tharsis region although the elysium region was poorly sampled in this experiment and the north pole was not visible from earth

implications of paleozoic and mesozoic rocks in the soda mountains northeastern mojave desert california for late paleozoic and mesozoic cordilleran orogenesis study of the soda mountains in the northeastern mojave desert revealed new stratigraphic and structural features of this area a section of cambrian to jurassic rocks in the area displays various features of regional importance lower permian rocks have depositional characteristics indicative of mass flow deposition contrasting with underlying shelf strata and platformal rocks exposed in areas to the east these rocks are similar to deep water rocks exposed to the north in eastern california lower triassic rocks are named the silver lake formation and consist of shallow water siltstone and carbonate that contain conglomerate with volcanic and gneissic ciasts these latter rocks record the possible presence of permian triassic igneous and deformational activity in the area a complicated deformational history is also evident from this study we interpret several west dipping low angle faults active during intrusion of middle cretaceous granitoids to be normal faults rather than thrust faults as they were originally considered structures in the soda mountains probably correlate with similar ones in surrounding areas collectively the local structures imply a complicated stress regime during emplacement of the middle cretaceous plutonic rocks these new data imply that large thrusts faults placing paleozoic rocks over mesozoic rocks are not present in this area upper paleozoic and lower mesozoic rocks also tie this area to the western mojave desert indicating that strike slip faults with several hundred kilometers of displacement do not separate the two areas

causes and consequences of protracted melting of the mid crust exposed in the north himalayan antiform gneiss domes exposed by the north himalayan antiform in southern tibet provide evidence for protracted melting of the mid crust during convergent tectonics anatexis was initiated during underthrusting and recurred during the southwards extrusion of a low viscosity crustal sheet sr nd isotope systematics establish that the cores of the domes dominated by cambrian gneiss form a window of the high himalayan crystalline series hhcs indian plate combined trace element and isotopic analyses from 4 two mica granites that intrude both core and the metasedimentary mantle of the domes indicate an origin from melting of the high himalayan crystalline series by the incongruent breakdown of muscovite and to a lesser extent biotite at temperatures from 680 to 760 c u pb dating of accessory phases extends the known period of granite magmatism from the late oligocene to mid miocene a ca rich garnet bearing leucogranite of oligocene age 27 5 ma provides a rare insight into the pre miocene history of the underthrust indian plate reflecting prograde melting at greater depths during a period of crustal thickening the origin of the miocene granites 15 10 ma can be modeled from the exhumation of an extruding channel at a rate of ca 1 mm year constrained by ar isotope data melting over a protracted time scale along the leading edge of the indian plate less than 50 km from the suture accelerated horizontal shortening within the collision zone and provided a positive feedback mechanism between magmagenesis and deformation

petrology and geochronology of eclogites from the western segment of the altyn tagh northwestern china abstract the eclogites from the western segment of the altyn tagh occur as lens or boundins within quartzofeldspathic gneisses or pelitic gneisses characterized by amphibolite facies parageneses the petrographic features and reaction textures testify to three main metamorphic stages 1 the peak eclogite facies stage p 15 kbar t 665 880 c 2 the granulitic facies stage p 11 14 kbar t 670 800 c and 3 the amphibolite facies stage p 6 3 9 5 kbar t 619 738 c during decompression the trace element rare earth element and sm nd isotopic data suggest that most of the eclogites have protolith features resembling transitional type t type mid ocean ridge basalt morb the well preserved eclogite was selected for sm nd and u pb isotopic dating the sm nd isotopic data yield a whole rock garnet omphacite isochron of 500 10 ma age the u pb isotopic measurement of zircons from the same eclogite shows that the four grain populations are near concordant and are well plotted on concordia giving a weighted mean age of 503 9 5 3 ma the two different geochronological methods yield a similar age which is interpreted as the peak metamorphic age of eclogites and reflects the existence of a mountain root related to continental subduction during early paleozoic moreover based on the comparison with similar rocks in the northern margin of the qaidam basin a displacement of 350 400 km for the altyn tagh fault have been estimated

new constraints on the evolution of carolina bays from ground penetrating radar ground penetrating radar gpr data for the savannah river site srs in the upper coastal plain of south carolina combined with geological archaeological and ecological data place new constraints on the evolution of carolina bays extant srs bay morphology formed mainly during the holocene and did not involve migration of bays across the landscape multiple periods of bay rim accretion with intervening intervals of erosion may characterize the longer term evolution of the bays bay evolution however did not involve significant modification of the upland unit underlying the region during fluctuating but generally open water conditions breaking waves along bay shorelines eroded and transported sediment which was subsequently exposed for deflation during periods of low water deflation and transport of sand into standing vegetation along the margin of the bay depression created a rim in the form of a parabolic dune lacking obvious internal stratification simultaneously infilling occurred by shoreline erosion and transport from adjacent elevated surfaces this coupled with growth of emergent vegetation resulted in decreased hydroperiod wave energy shoreline modification and rim accretion transport of some rim sediments back into the bays via alluvial and colluvial activity created wedges of infilling sediment during waning stages of evolution the apparent contradiction of bay orientation with respect to prevailing winds might reflect seasonal changes in water level and wind direction southwesterly winds during spring high water causes nw se elongation of the bays whereas northwesterly winds during lower water in the fall and winter account for nearshore deflation and rim accretion along the east southeastern bay margins

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

a la icp ms u pb chronological study of zircons from meta acidic volcanics in baiyin orefield gansu province new evidence for metallogenic age of baiyin type massive sulfide deposits the baiyin orefield is located in the eastern part of north qilian mountains and its copper polymetallic ore bodies are controlled strictly by meta acid volcanic rocks however the long controversy on the problem of metallogenic epoch has hindered the further ore prospecting work in this paper cathodoluminescence image cl and la icp ms u pb isotope dating techniques were used to determine the metallogenic age it is found that zircons from meta acid volcanic rocks show features of magmatic zircon characterized by rhythmic crystallization and main th u ratio of 0 4 0 8 two main populations of zircons from meta quartz keratophyre were obtained giving average 206pb 238u ages of 467 3 2 9 ma and 414 2 2 7 ma respectively meanwhile three main populations of zircons from mylonitized quartz keratophyre were obtained giving average 206pb 238u ages of 467 1 2 2 ma 435 9 3 6 ma and 412 6 2 1 ma respectively it is considered that the age of 467 3 2 9 467 1 2 2 ma is the formation time of meta acid volcanic rocks and hence the metallo genic epoch should be middle ordovician 435 9 3 6 ma and 414 2 2 7 412 6 2 1 ma are probably the ages of two geological events i e mylonization related to ductile shearing and collision orogeny the findings are of great significance in further research on the tectonic evolution of the north qilian orogenic belt the formation environment of the baiyin type massive sulfide deposits and the ore prospecting directions

shuttle imaging radar physical controls on signal penetration and subsurface scattenng in the eastern sahara sir a signal penetration and subsurface backscatter within the upper meter or so of the sediment blanket in the eastern sahara of southern egypt and northern sudan are enhanced both by radar sensor parameters and by the physical and chemical characteristics of eolian and alluvial materials interpretation of sir a images by mccauley et al 1 2 dramatically changed previous concepts of the role that fluvial processes have played over the past 10000 to 30000000 years in shaping this now extremely flat featureless and hyperarid landscape in the present paper we summarize the near surface stratigraphy the electrical properties of materials and the types of radar interfaces found to be responsible for different classes of sir a tonal response the dominant factors related to efficient microwave signal penetration into the sediment blanket include a favorable distribution of particle sizes b extremely low moisture content and c reduced geometric scattering at the sir a frequency 1 3 ghz the depth of signal penetration that results in a recorded backscatter here called radar imaging depth was documented in the field to be a maximum of 1 5 m or 0 25 of the calculated skin depth for the sediment blanket radar imaging depth is estimated to be between 2 and 3 m for active sand dune materials diverse permittivity interfaces and volume scatterers within the shallow subsurface are responsible for most of the observed backscatter not directly attributable to grazing outcrops

crustal generation of the himalayan leucogranites abstract detailed studies of the himalayan two mica leucogranites such as the manaslu pluton indicate that they have very uniform mineralogical petrological and structural characteristics one can relate their occurrence to the thickest zones of the underlying tibetan slab in these zones migmatization attains its greatest development and vertical extension the granite is emplaced at first along the main disharmonic plane above the main central thrust mct at the top of the tibetan slab infrastructure ductile deformation of the granite is variable the granite being syn to late kinematic with regard to the functioning of the mct major elements are very homogeneous except for na and k implying that p t conditions of melting were relatively uniform the melted material was of a similar composition over a vast volume and the percentage of melting was small 10 15 trace elements are highly variable some are characteristic for very evolved material ta rb cs u or show the link with the tibetan slab ba sr whilst others are problematic th ree ree and th abundances being much less in the granite than in the tibetan slab imply that they have been extracted during one of the main stages of formation possibly by monazite radiogenic pb sr nd and stable o isotopes are consistent with the origin of the granite from the tibetan slab however the heterogeneous sr isotopic ratios make age dating difficult and imply poor mixing or little fluid interaction during its evolution h isotope data indicate that magmatic compositions of the main body of the manaslu granite have been preserved late or post magmatic alterations are extremely local in the main pluton to the north another belt of two mica granites occurs whose characteristics are very similar to the high himalaya belt they were probably generated in a similar way during this recent intracontinental evolution

subduction and accretionary tectonics of the east kunlun orogen western segment of the central china orogenic system abstract the kunlun orogen is generally divided into the east kunlun orogenic belt e kob and the west kunlun orogenic belt w kob by the altyn tagh fault the e kob forms part of the western segment of the central china orogenic system ccos and is considered to have formed by the collision between the qaidam block and qiangtang or bayanhar terrane as a consequence of the closure of the kunlun ocean branch of the paleo tethyan ocean based on a compilation recently published high quality data this contribution provides an overview of the composition nature and ages of the principal tectonic elements including ophiolitic melanges and related volcanic rocks intrusive plutons and sedimentary cover sequences in the e kob according to multiple lines of evidence from these tectonic elements we proposed herewith a paleozoic triassic subduction and accretionary tectonic model to interpret the spatiotemporal tectonic framework plate subduction polarity and tectonic processes from accretion to collision of the e kob three main ophiolitic melange zones are identified in the e kob from north to south they are the qimantagh xiangride ophiolitic melange zone qxm the aqikekulehu kunzhong ophiolitic melange zone akm and the muztagh buqingshan anemaqen ophiolitic melange zone mbam according to these ophiolitic melange zones the e kob is divided into four major tectonic units the north qimantagh belt the central kunlun belt the south kunlun belt and the bayanhar terrane based on several lines of evidence from geology geochemistry and geochronology the south kunlun belt is interpreted as a paleozoic to triassic fore arc and accretionary complex related to northward subduction of the kunlun ocean during the ordovician triassic time the akm mabm and the south kunlun belt constitute a wide accretionary complex along the kunlun suture zone that marks final closure of the major paleo tethyan ocean while the qxm represents the best expression of another suture that records final closure of the qimantagh back arc basin the central kunlun belt as a long lived island arc terrane from ordovician to triassic times rifted from the qaidam block due to the spreading of the qimantagh back arc basin during the period of ca 485 425 ma taken into all the geological geochemical and geochronological lines of evidence together a trench arc back arc basin tectonic system in the e kob was built up and evolved into a protracted and long lived northward subduction and accretion along the kunlun suture during paleozoic and triassic time

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

geochronology geochemistry and isotope compositions of piaochi s type granitic intrusion in the qinling orogen central china petrogenesis and tectonic significance abstract s type peraluminous granite can crop out in various tectonic settings the paleozoic piaochi granitic intrusion is a large s type peraluminous intrusion located in the north qinling orogen and has important implication for its tectonic evolution though intensively studied the age and tectonic setting of this intrusion are still controversial in this study we carried out an integrated study of zircon u pb age major and trace elements and sr nd hf o isotope compositions for the piaochi intrusion with aims to constrain its petrogenesis and tectonic significance sims and la icpms u pb zircon data obtained from magmatic zircons indicate that the piaochi intrusion was emplaced at 473 4 ma and contained ca 490 ma inherited zircons the granite samples from the piaochi intrusion show typical s type characteristics such as the relatively moderate aluminum saturation index 1 00 1 08 low zirconium saturation temperatures occurrences of muscovite and high zircon 18 o values 8 70 to 9 54 the relatively low sm nd 0 13 0 20 and feo t mgo ratios 2 21 3 9 suggest that the granites are unfractionated the geochemical compositions reveal that they were derived from partial melting of a clay poor but plagioclase and biotite rich psammitic source similar to metasedimentary rocks outcropping in the north qinling unit moreover the piaochi granites are moderately depleted in eu and heavy rare earth elements and have relatively high la yb n values 22 8 56 8 implying a high pressure plagioclase poor and garnet rich residual assemblage the piaochi granites have high and variable initial 87 sr 86 sr ratios 0 72167 0 72511 and low e nd t from 10 23 to 8 71 values with two stage nd model ages t dm2 of 1 91 2 03 ga which are comparable with those of supracrustal materials in the north qinling unit in addition our results show that the ca 470 ma magmatic zircons display a narrow e hf t array within those of the inherited cores these imply that the piaochi granites inherited their isotopic characteristics wholly from their sources and the hf isotopes might have been differently homogenized during the partial melting our new zircon u pb ages indicate that the piaochi granites were emplaced after the climax of the uhp metamorphism coeval with later retrograde metamorphism during exhumation therefore we suggest that the formation of the early paleozoic piaochi intrusion was triggered by the exhumation of the uhp rocks

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

floodplain dynamics of a wandering river dendrochronology of the morice river british columbia canada dendrochronological techniques are used to develop a history of flood occurrence and relative stage for the middle section of the morice river based on flood scars bank undercutting dates and tree establishment dates on fluvial features the morice river is the major tributary of the bulkley river skeena river system northwest british columbia canada reach 2 of the morice river drainage area 3499 km2 is forested and little disturbed by human activity it is presently a wandering multiple channel river and shows evidence of frequent channel changes which have reworked most of the floodplain several times in the last 180 years airphoto analysis and dendrochronology demonstrate that many channels show evidence of two or more periods of activity reoccupation and re excavation of pre existing channel segments is more frequent than development of new channels thirty one significant floods over the past 105 years were detected through dendrochronology of flood scarred trees on the morice river flood scars are predominantly caused by flood transported logs abundant log transport results in damage to channel margin trees during events only slightly above bankfull discharge the record of flood scars on channel margin trees and establishment dates of forest stands on abandoned channels and surfaces show that the morice river has maintained its present regimen for the past 115 years during the neoglacial the morice river was more active than in recent times and its channels occupied twice the present area tree establishment dates show that neoglacial surfaces and channels of the morice river were abandoned during the 1820 s the modern floodplain configuration was assumed by 1870

geochemistry of holocene volcanic rocks associated with ridge subduction in baja california mexico although the geochemistry of magmatism associated with the subduction of oceanic lithosphere is well understood1 6 the geochemical signature of lavas produced shortly after subduction of an oceanic spreading centre has not been characterized the baja california peninsula in mexico provides an ideal scenario to study the latter process geophysical models indicate that in response to oblique collision of the ancestral east pacific rise epr with the western seaboard of north america at 29 myr subduction of the farallon plate was succeeded by the progressive southwards development of a transform fault system7 9 at 12 5 myr a considerable length of the epr was simultaneously subducted beneath baja thus terminating subduction processes along this segment10 by 3 5 myr the locus of transcurrent faulting had switched from the west of baja to within the developing gulf of california coupling baja to the pacific plate11 13 we present here data for holocene volcanic rocks from baja california norte which show that post ridge subduction volcanism has a distinctive geochemistry these results have important consequences for the interpretation of ancient orogenic belts

origin of high magnesian andesites in the setouchi volcanic belt southwest japan i petrographical and chemical characteristics high magnesian andesites of middle miocene age occur in southwest japan forming an obvious volcanic belt these andesites have low feo mgo ratios 0 546 0 931 and are rich in ni 101 312 ppm co 30 0 45 1 ppm and cr 208 756 ppm they are relatively aphyric phenocrysts 10 vol and the phenocrysts of magnesian olivine fo88 are in equilibrium with the host high magnesian andesite magmas on the basis of the fe mg exchange partitioning these features suggest that the high magnesian andesites are not differentiated or accumulative they appear to represent primary andesites generated in the upper mantle these southwest japanese high magnesian andesites are rich in incompatible elements and show light rare earth enrichment relative to boninites suggesting that the former is derived from a less depleted mantle source than the latter

continuity of the north qilian and north qinling orogenic belts central orogenic system of china evidence from newly discovered paleozoic adakitic rocks abstract adakitic intrusive rocks of 430 450 ma were discovered in the north qilian orogenic belt the western section of the central orogenic system cos in china these adakitic rocks were lower crust melts rather than slab melts as indicated by their crustal ce pb nb u ti eu and nd sm ratios and radiogenically enriched 87sr 86sr i of 0 7053 0 7066 and end t of 0 9 to 1 7 while they are all characterized by low yb 65 and la yb n 13 7 ratios these adakitic rocks are classified into the low mgo ni cr and high mgo ni cr groups the low mgo samples were derived from partial melting of thickened lower crust whereas the high mgo samples were melts from delaminated lower crust which subsequently interacted with mantle peridotite upon ascent adakitic rocks from the adjacent north qinling orogenic belt also originated from thickened lower crust at 430 ma in addition the north qilian and north qinling orogenic belts both consist of lithological assemblages varying from subduction accretionary complexes at south to central arc assemblages which include adakitic rocks then to backarc phases at north such a sequence reflects northward subduction of the qilian and qinling oceans in these two orogenic belts the occurrence of adakitic rocks of common origin and ages together with the similarities in tectonic configurations and lithological assemblages are considered to be the evidence for the continuity between eastern qilian and western qinling forming a 1000 km early paleozoic orogenic belt in such a tectonic configuration the qilian and qinling oceans that subducted from south possibly represent parts of the large proto tethyan ocean this inference is supported by the coexistence of early paleozoic coral and trilobite specimens from asia america and australia in the north qilian orogenic belt post 400 ma volcanic rocks occur in the north qinling orogenic belt but are absent in the north qilian orogenic belt indicating that these two orogenic belts underwent distinct evolution history after the closure of the proto tethyan ocean 420 ma

collision leading to multiple stage large scale extrusion in the qinling orogen insights from the mianlue suture abstract the geologic framework of the phanerozoic qinling dabie orogen was built up through two major suturing events of three blocks from north to south these include the north china craton including the north qinling block the qinling dabie microblock and the south china craton including the bikou block separated by the shangdan and mianlue sutures the mianlue suture zone contains evidence for mesozoic extrusion tectonics in the form of major strike slip border faults surrounding basement blocks a late paleozoic ophiolite and a ca 240 200 ma thrust belt that reformed by 200 150 ma thrusts during a type intracontinental subduction the regional map pattern shows that the blocks are surrounded by complexly deformed devonian to early triassic metasandstones and metapelites forming a regional scale block in matrix melange fabric five distinct tectonic units have been recognized in the belt 1 basement blocks including two types of precambrian basement crystalline and transitional 2 continental margin slices including early paleozoic strata and late paleozoic fluviodeltaic sedimentary rocks proximal and distal fan clastics reflecting the development of a north facing rift margin on the edge of the south china plate 3 out of sequence oceanic crustal slices including strongly deformed postrift deep water sedimentary rocks sheeted dikes basalts and mafic ultramafic cumulates of a late paleozoic ophiolite suite developing independent of the rift margin in a separate basin 4 out of sequence island arc slices 5 accretionary wedge slices all the tectonic units were deformed during three geometrically distinct deformation episodes d 1 d 2 and d 3 during 240 200 ma units 2 4 involved southward thrusting and vertical then southward extrusion of about 20 km of horizontal displacement above the autochthonous basement during the d 1 episode thrust slices 20 km south of the mianlue suture are related to this vertical extrusion due to the same rock assemblages ages and kinematics the d 2 and d 3 episodes folded all the units in a thick skinned style about east west d 2 and west northwest d 3 axes in the mianlue suture zone an early foreland propagating sequence of accretion of late paleozoic rocks deposited above the yangtze craton is not involved in d 1 deformation but is temporally equivalent to the d 2 and d 3 deformation in the mianlue suture two stages of strike slip faulting mainly occurred at the end of d 2 and d 3 respectively during d 2 deformation the bikou block was obliquely indented to the ese into the mianlue suture rather than being thrust over the mianlue suture from the north as a part of the qinling dabie microblock during d 3 deformation however the bikou block was bounded by the south boundary fault of the mianlue suture and the yangpingguan fault on the south these faults are coeval strike slip faults but of opposite senses and accommodated minor southwestward extrusion of the bikou block into songpan ganze orogen the other basement blocks north of the mianlue suture were extruded eastward by about 20 km of lateral displacement based on the offset of the wudang dome during the d 3 episode due to the northeastward indentation of the hannan complex of the south china craton post d 3 emplacement of granite cutting across the strike slip faults such as the mianlue suture provides a minimum age of 200 ma for d 3 deformation therefore based on insights from the evolution of the mianlue suture the d 2 and d 3 episodes in the mianlue suture and its neighbors are not responsible for and associated with the two stage extrusion of the dabie uhp hp terranes from the foping dome to the present erosional surface more than 350 km

lava flow surface roughness and depolarized radar scattering surface roughness has a strong controlling influence on radar scattering and other types of remote sensing observations we compare field measurements of surface topography and dielectric constant for a range of lava flow textures to aircraft multipolarization radar observations at 5 7 24 and 68 cm c l and p band wavelengths the roughness is found to vary with scale in a self affine fractal manner for scale lengths between 25 cm the smallest horizontal step size and 3 5 m this result is used to demonstrate that a two component surface description consisting of the fractal dimension and rms height or slope at some reference scale can resolve some of the ambiguities in previous efforts to quantify roughness at all three radar wavelengths the hv backscatter cross section is found to vary in an approximately exponential fashion with the rms height or allan deviation at some reference scale up to a saturation point where the surface appears entirely diffusely scattering to the radar based on these observations we use a parameter defined as the ratio of rms height to the particular scale of measurement backscatter values at 24 cm wavelength and the topographic profile data were used to derive expressions which link the hv radar cross section to or to the analogous wavelength scale rms slope these equations provide a reasonable fit to 24 and 68 cm echoes and for rough surfaces at 5 7 cm but yield poor results for 5 7 cm echoes on smooth terrain we conclude that the roughness at the two larger scales is well described by a single fractal dimension and rms height but that texture at very small scales is characterized by different statistics this inference is supported by analysis of 5 cm horizontal spacing topographic profiles the relationships defined here allow determination of the surface rms height or slope at the scale of the radar wavelength given radar data at additional wavelengths a more complete view of the statistical properties of the surface can be developed such techniques may be useful in analyses of synthetic aperture radar images for terrestrial volcanic areas magellan data for venus and other planetary radar observations

reconstruction of past ice conditions in a hudson bay estuary using tree rings descriptions of ice conditions ranging from lake and sea ice to glacial advances and retreats form an important portion of the climatic record ice formation deterioration and changing areal extent are of increasing interest in climatology sea transportation petroleum exploration and the fishing industry with few exceptions quantitative information on ice conditions is generally brief with many records in the us and canada beginning only in the 1950s1 tree ring data from long lived trees can be used as quantitative proxy data for past climatically related parameters the record of first complete freezing of the churchill river estuary on hudson bay is reconstructed here for 298 yr 1680 1977 by means of tree ring analysis

protolith of eclogites in the north qaidam and altun uhp terrane nw china earlier oceanic crust an early paleozoic ultrahigh pressure metamorphic belt occurs in the north qaidam altun mountains and was offset about 400 km southwestward by the altyn tagh strike slip fault eclogites in the belt consist of major basaltic and minor picritic rock types and can be subdivided into three groups high tio2 2 5 wt medium tio2 1 2 wt and low tio2 1 wt geochemical evidence shows that the protoliths of the eclogite were basaltic rocks from different tectonic environments including mid ocean ridge basalt island arc basalt and ocean island basalt the nd isotopes of these rocks are similar to those of morb characterized by mainly positive and minor negative end 0 values providing further evidence that the eclogite protoliths were ocean floor basalts to which minor crustal components were added during subduction geochronological data indicate that the uhpm occurred about 500 440 ma ago and that there were two eclogite protoliths with ages of 800 750 and 1000 ma respectively geochemically and isotopically the eclogites are similar to basaltic rocks in luliangshan north qaidam mountains which have sr and nd ages of 768 39 and 780 22 ma the age and composition of these volcanic rocks suggest that they were one type of the protoliths for the eclogites a later series of calc alkaline island arc volcanic rocks was formed at about 500 ma ago essentially contemporaneous with the uhp metamorphism we propose the following tectonic model for the evolution of the north qaidam uhp belt at about 1000 ma ago a number of continents were amalgamated to form the rodinian continent in this general area which contained some oceanic volcanic rocks possibly as ophiolitic fragments this part of rodinia was then rifted at about 800 750 ma ago to form an oceanic basin with a variety of morb and ocean island basalts closure of this ocean basin produced the neoproterozoic ophiolites and granitic gneisses in the north qaidam mountains in the early paleozoic another qilian ocean basin formed and subduction of this oceanic lithosphere formed the island arc volcanic rocks at about 500 ma ago and the subduction related granites 470 450 ma once the oceanic lithosphere was consumed the subsequent continent continent collision led to deep subduction of continental crust which was tectonically mixed with the eclogites to cause the ultrahigh pressure metamorphism

dendroclimatic reconstruction of summer temperatures in northwestern canada since a d 1638 based on age dependent modeling abstract ring widths from five picea glauca stands at the alpine treeline in northwestern canada are used to investigate climate growth responses and to develop a long reconstruction of summer temperatures response function and linear regression analyses indicate that the radial growth response of these trees to climate varies with age and site at most sites the period of significant positive response to growing season temperatures declines with tree age age dependent and standard age independent models are then used to develop two reconstructions of june july temperatures for northwestern canada extending back to a d 1638 calibration statistics were similar for both models but the standard model performed poorly during verification the reconstruction produced using age dependent modeling suggests june july temperatures were cooler than present throughout most of the past 350 years with the exception of the late 18th century particularly cool periods occurred at 1700 and in the mid 19th century in constast the standard model suggests that temperatures were similar to or warmer than present during the last 350 years the age dependent reconstruction compares favorably with other proxy climate records from northern north america age dependent dendroclimatic modeling can provide a sensitive record of recent climatic change that allows the inclusion of previously rejected sites into dendroclimatic analyses

integrated analyses constraining the provenance of sandstones mudstones and conglomerates a case study the laojunshan conglomerate qilian orogen northwest china the qilian orogenic belt in the northern tibetan plateau connects the altaids to the north with the tethyan orogenic system to the south and occupies a key tectonic position in the evolution and assembly of asia the belt con tains a wide range of subduction accretion related petrotectonic units the early middle devonian laojunshan con glomerate deposited unconformably upon cambrian silurian strata along the northern margin of the north qilian terrane contains a record of the late paleozoic tectonism of the qilian orogen its provenance and tectonic setting are critical in understanding not only the tectonic evolution of tibetan plateau but paleozoic global reconstructions as well the composition of clastic conglomerates and heavy mineral assemblages of sandstones suggests that coeval mafic felsic metamorphic and sedimentary rocks were the main sources the geochemistry of volcanic clasts and paleocurrent and paleogeographic data suggest derivation from subduction accretion complexes in the north qilian terrane the geochemistry of siltstones and mudstones indicates that the laojunshan conglomerate was derived from an arc and accumulated in an active continental margin geochemical data of granitoid clasts suggest that they were de rived from ordovician silurian subduction related magmatic rocks mafic and ultramafic clasts chromite and magne tite decrease upwards in the stratigraphy whereas metamorphic sedimentary and granitoid clasts and garnet increase these data imply that mafic rocks were the predominant source during initial deposition regional studies suggest that the north china plate subducted southwards and produced subduction related arc magmatism along the southern margin of the north qilian terrane during the early middle devonian therefore we interpret the laojunshan conglomerate as a fore arc basin fill

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

magma sources and petrogenesis of the early middle paleozoic backarc granitoids from the central part of the qilian block nw china abstract the petrology geochemistry geochronology and sr nd hf isotopes of the backarc granitoids from the central part of the qilian block are studied in the present work both s and i type granitoids are present in petrographic classification they are granite alkali feldspar granite felsic granite diorite quartz diorite granodiorite and albite syenite the shrimp ages are 402 447 ma for the s type and 419 451 ma for the i type granitoids they are mostly high k calc alkaline granitoids the s type granitoids are weakly to strongly peraluminous and are characterized by negative eu anomalies eu eu 0 18 0 79 the i type granitoids are metaluminous to weakly peraluminous and are characterized mostly by small negative to small positive eu anomalies eu eu 0 71 1 16 the initial 87 sr 86 sr values are 0 708848 0 713651 for the s type and 0 704230 0 718108 for the i type granitoids the e nd 450 ma values are 8 9 4 1 and 9 7 1 9 for the s type and i type granitoids respectively the t dm values are 1 5 2 4 ga for the s type and 1 0 2 3 ga for the i type granitoids for the qilian block the backarc granitoid magmatism took place approximately 60 million years after the onset of the southward subduction of the north qilian oceanic lithosphere and lasted approximately 50 million years partial melting of the source rocks consisting of the neoproterozoic metasedimentary rocks of the huangyuan group and the intruding lower paleozoic basaltic rocks could produce the s type granitoid magmas partial melting of basaltic rocks mixed with lower continental crustal materials could produce the i type granitoid magmas major crustal growth occurred in the late archean and meso paleoproterozoic time for the qilian block the magma generation was primarily remelting of the crustal rocks with only little addition of the mantle materials after 1 0 ga for the qilian block

magmatic history of the northeastern tibetan plateau 1 the northeastern margin of the tibetan plateau is underlain by the qaidam and qilian terranes which consist primarily of mid proterozoic through lower paleozoic oceanic and arc type assemblages that have been accreted to the southern margin of the tarim sino korean craton most previous models suggest that these assemblages formed along a northeast dipping subduction system constructed along the margin of the tarim sino korean craton during early paleozoic time the main components are interpreted to have formed either as an archipelago of volcanic arcs and back arc basins or as a broad expanse of accretionary complexes our geochronologic data support a model suggested by sobel and arnaud 1999 in which the qaidam and qilian terranes are separated from the tarim sino korean craton by a mid paleozoic suture that closed along a southwest dipping subduction zone the basement to these terranes consists of oceanic assemblages that were amalgamated into a coherent crustal fragment prior to emplacement of 920 930 ma granitoids early paleozoic arc type magmatism occurred between 480 and 425 ma apparently sweeping southwestward across much of the qilian and qaidam terranes accretion related magmatism along the inboard margin of the qilian terrane occurred between 423 ma and 406 ma following silurian devonian accretion the region has experienced late paleozoic and mesozoic uplift and erosion and has been severely overprinted by tertiary thrusting uplift and strike slip motion along the altyn tagh fault correlation of geologic features and magmatic histories between the altun shan and the nan shan suggests that the eastern altyn tagh fault has a total left lateral offset of 375 km

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

early paleozoic to devonian multiple accretionary model for the qilian shan nw china abstract the qilian shan located in the northern tibetan plateau of nw china has an excellent record of early to middle paleozoic subduction accretion that resulted from convergence between the alax and qaidam blocks but there is no consensus about its detailed tectonic history this paper summarizes its tectonic divisions and discusses its tectonic evolution from the cambrian to devonian the belt has the following tectonic divisions in the far north the southern passive margin of the alax block is juxtaposed against an early cambrian to ordovician marianan type intra oceanic arc north qilian the north qilian arc is separated from a japanese type arc central qilian to the south by a high pressure metamorphic belt composed mostly of ophiolitic slices and oceanic crusts the central qilian is bounded to the south by a wide melange zone south qilian consisting of ophiolitic slices and continental margin sequences farther to the south lies the oulongbuluk microcontinent that is separated from the qaidam block and farther south by an ultrahigh pressure metamorphic belt tectonostratigraphic analysis together with geochemical geochronological and geophysical data indicates a complex evolution by subduction accretion processes from the cambrian to the devonian before final amalgamation and docking to the northern alax block this model solves the long lasting discussion on the polarity of subduction in paleozoic time this multiple subduction accretion history sheds light on the continuity of paleozoic sutures along the qilian shan and the nature of the altyn tagh fault and thus contributes to an improved understanding of the tectonic architecture of central asia

tracing magma mixing in granite genesis in situ u pb dating and hf isotope analysis of zircons in situ zircon u pb and hf isotopic data have been determined for mafic microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china in order to constrain the sources and petrogenesis of granites the zircon u pb age of the enclaves 120 1 ma is identical to that of the host monzogranite 120 1 ma establishing that the mafic and felsic magmas were coeval the hf isotopic composition of the enclaves ehf t 4 5 to 6 2 is distinct from the host monzogranite ehf t 15 1 to 25 4 indicating that both depleted mantle and crustal sources contributed to their origin the depleted mantle component was not previously revealed by geochemical and nd and sr isotopic studies showing that zircon hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information some wall rock contamination is indicated by inherited zircons with considerably older u pb ages and low initial hf isotopic compositions hafnium isotopic variations in early cretaceous zircons rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data

high mg diorites derived from sanukitic hma magmas kyushu island southwest japan arc evidence from clinopyroxene and whole rock compositions abstract high mg diorites that have similar whole rock composition to high mg andesites hmas should not be simply interpreted as rocks solidified from the hma magmas because the high mg diorites may be mafic cumulates derived from a different magma from the hmas the hmas contain unique clinopyroxenes with higher mg and si than those of other sub alkaline series igneous rocks the mg and si are controlled by the source magma composition rather than its crystallized conditions such as pressure and temperature the chemical composition of clinopyroxenes would present important information for the investigation of the source of high mg diorites we considered the source of early cretaceous high mg diorites on kyushu island southwest japan arc based on their clinopyroxene and whole rock compositions the clinopyroxenes have similar chemical characteristics to those in hmas rather than those in other sub alkaline rocks moreover the whole rock compositions are equivalent to the sanukitic hma and do not show features of mafic cumulates this indicates that the high mg diorites solidified from sanukitic hma magmas it is generally believed that the sanukitic hma magmas involve the subduction of a young and or hot oceanic slab was situated in their genesis therefore the occurrence of the high mg diorites suggests that kyushu was situated in the tectonic setting of young and or hot slab subduction in the early cretaceous

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

a 263 year record of summer temperature for northern quebec reconstructed from tree ring data and evidence of a major climatic shift in the early 1800 s abstract tree ring data are used to reconstruct 263 years of summer temperatures at a site located near the northern tree line in central western quebec a chronology comprising 20 ring density time series is used in conjunction with a chronology comprising 20 ring width time series in the regression analyses the increased precision of the temperature estimates obtained by using density data as an additional proxy time series places the reconstruction and its interpretation on a firmer basis than it is when only ring width data are used the results are considerably improved over the use of either tree ring parameter alone the temperature reconstruction reflects a major cooling event in the early nineteenth century comparisons with other temperature and proxy data series support the idea of a global cooling event with a persistence of the cool period of about three decades in high latitude north america and of much shorter duration in other regions of the world volcanic activity in the early 1800 s is suggested as partially responsible for the cooling event but is considered inadequate as cause for the extended period of low temperatures in the locale of this reconstruction

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

mars the regolith atmosphere cap system and climate change abstract a new model for predicting the behavior of the martian regolith atmosphere cap co 2 regime and describing its role in climate change is derived the model describes the time temperature histories of 90 regolith chunks on a latitude depth grid accounting for co 2 exchange by means of laboratory derived expressions relating temperature co 2 pressure p co 2 and adsorbed co 2 mass co 2 polar cap formation and sublimation is accounted for subject to the constraint of constant total co 2 in the atmosphere regolith cap system the influence of differences in regolith adsorption laws for basalt and clay and the influence of variations in regolith depth with latitude regolith thermal diffusivity and total exchangeable co 2 inventory on predicted variations in atmospheric pressure and cap mass are examined the following results are indicated 1 the atmosphere acts as a low capacity conduit through which flows between 10 and 100 times the current atmospheric mass of co 2 between two reservoirs a regolith ocean of adsorbed co 2 and a polar cap cryosphere 2 exchange between these reservoirs is driven by variations of obliquity with the polar cap the dominant co 2 sink at low and the regolith dominating at high atmospheric pressure ranges between 0 1 low and 15 mbar high pressures of up to 25 mbar could result from pre tharsis variations pressure up to 40 mbarare achieved only in models which also call for a huge quasi permanent present co 2 cap which is not apparent 3 at high the atmospheric pressure is buffered by the regolith and satisfies adsorption equilibrium for the 90 chunks as well as conservation of co 2 mass at low a potetially large co 2 cap appears and the atmospheric pressure is buffered by the cap not the regolith 4 the periodic reservoir flushing can account for the observation of simultaneous nonenrichment of 18 o and enrichment of 13 n 5 mars climate history may be divided into three parts a post tharsis formation history as described above b pre tharsis formation with qualitatively similar processes but larger oscillations between reservoirs and larger atmospheric pressure and cap mass variation and c the very early period of channel formation 6 the nature of the response of the three part regolith atmosphere polar cap martian climate system to surface insolation variations may be analogous to that of earth s ocean atmosphere cryosphere system

possible martian brines radar observations and models the 1971 and 1973 goldstone 12 6 cm radar observations of mars are separate data sets which include reflectivity as a function of latitude longitude and season it has been argued that secular reflectivity variations of mars surface are indicated by the data and that shallow subsurface melting is the causal mechanism most compatible with the observations however the melting hypothesis conflicts with accepted notions of the state and distribution of water on mars we examine the data to identify temporal and spatial domains within which statistically significant changes in measured reflectivity are clustered a few reflectivity changes may be genuine others may be due to ephemeris errors or binning during data reduction brines which might satisfy the best supported reflectivity variations are out of equilibrium with the chemical megaenvironment it is unclear whether such a brine if emplaced in the martian regolith at a depth shallow enough to affect the radar reflectivity could survive even a single freeze thaw cycle we suggest that some combination of unique scattering properties or some as yet unidentified process other than melting is responsible for any genuine reflectivity variations

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

the petrology and geochemistry of high magnesium andesites at the western tip of the setouchi volcanic belt sw japan k ar ages and petrographical and geochemical characteristics of high magnesium andesites and plagioclase phyric andesites from the ne kyushu region japan are presented k ar ages range from 10 7 0 3 to 14 4 0 4ma overlapping those reported for lavas of the setouchi volcanic belt in other regions 11 16ma this together with major and incompatible trace element and sr nd pb isotopic characteristics confirms that the setouchi volcanic belt which is characterized by the occurrence of high magnesium andesites extends for 600 km along the sw japan arc thus it may be suggested that the unusual tectonic setting required for high magnesium andesite magma generation was attained only for this limited region possibly in association with subduction of the young hence hot lithosphere of the shikoku basin two types of high magnesium andesite possessing identical bulk rock compositions are recognized one contains olivine phenocrysts with chromian spinel inclusions showing compositional characteristics consistent with their crystallization as liquidus phases whereas the other contains niand fe rich olivine and fe3 rich spinel one of the possible causes for such unusual mineral compositions could be effective elemental diffusion within and through olivine crystals associated with a long residence time in a crustal magma chamber and the slow rate of cooling of the host magma the compositions of liquidus chromite and olivine as well as whole rock major element compositions suggest that the ne kyushu highmagnesium andesite magmas were produced by higher degrees of partial melting than those in other regions of the setouchi volcanic belt

geothermal evidence from canada for a cold period before recent climatic warming three deep boreholes in a small area in quebec each having two high accuracy temperature logs separated by 22 years allow reliable determination of the ground surface temperature history during the past few centuries the temperature logs show that the recent climatic warming was preceded by a cold period near the end of the 19th century in this area the presence of such a cold period is also suggested by borehole temperature data from other areas in canada

ground penetrating radar as a tool for probing the shallow subsurface of mars 1 design and testing of an impulse ground penetrating radar gpr for possible rover deployment on mars in 2009 is well underway the gpr has mass power volume and data rate targets of 0 5 kg 3 w peak 3400 cm3 and 0 3 mb d and will possess easily modified bistatic high frequency e g 500 600 mhz and monostatic rat tail e g 100 mhz antennas the gpr should be capable of measuring in situ radar properties on mars to depths of up to 10 20 m thereby helping to constrain near surface geology and structure initial gpr tests at the site of the 2001 fido rover field trials near cronese lake california confirm the value of the instrument in defining local geologic setting and in providing context for data collected using other rover science payload elements a rover deployed gpr may enable three dimensional mapping of local stratigraphy which in turn can assist in evaluating the history of aqueous activity and the accessibility of near surface water