genesis of autochthonous and allochthonous apulian karst bauxites southern italy climate constraints abstract the apulian carbonate platform acp in southern italy has experienced several episodes of subaerial exposure which were in some cases associated with the formation of karst bauxite deposits the acp contains both autochthonous canyon like bauxite and allochthonous salento type bauxite with the latter having been derived from a weathered and eroded pristine bauxite deposit the remnants of this pristine bauxite are preserved as transported pebbles embedded in a clayey matrix the autochthonous bauxite and the pebbles of the allochthonous bauxite have the same texture of sub spheroidal components ooids dispersed in a fine grained matrix the fractal dimension of ooids from both deposits is very similar and corresponds to the growth of aggregates under a diffusion controlled process the ooids of the autochthonous bauxite have a different composition to those in the pebbles of the allochthonous bauxite because they formed under different climatic conditions during the turonian autochthonous bauxite ooids formed in alternating wet tropical conditions promoting al hematite formation and drier conditions favouring boehmite stability in the allochthonous pebbles ooids formed mainly in a dry climate promoting the formation of large boehmite cores the ooids matrix ratio and the geometrical features of the ooids reflect these climate differences the differences in composition and age post turonian of the salento type bauxite bedrock suggest that the pristine bauxite that produced the salento type pebbles was different in composition to and younger in age than the canyon like bauxite the latter probably formed during a middle campanian emersion event evidenced by large karstic cavities which is correlated with the subaerial exposure of karst recorded on the adriatic island of brac

red soils with white net like veins and their climate significance in south china abstract the microstructure particle size distribution mineral and chemical compositions of both the white net like veins and the red matrix of the xuancheng laterite soil section in anhui south china in the middle to lower reaches of the yangtze river were investigated using x ray diffraction xrd x ray fluorescence spectrometry xrf polarized light microscopy observation and particle size distribution analysis there was more quartz while less clay minerals in the white veins relative to the red matrix in particle size distribution patterns the more abundant 5 20 m particle size component of the white veins resulted from their higher quartz content discrepancy in degree of weathering between the white veins and the red matrix was derived from the depletion of fe2o3 total and mno2 and the relative accumulation of sio2 in the white veins white veins across the lithological layers and inclusions of relict red matrix material in the white veins indicated that the net like soils originated from an initial uniform red soil the white spots or veins were derived from the long term modification of the pre existing soil or concurrent weathering soils hydrodynamic conditions of the groundwater exerted influence on the formation of white veins the formation process of the white net like veins was different from that of the red matrix suggesting that the white vein materials reflected a hydrological imprint upon the result of these conditions the net like soils in south china were compatible to the mottled soils in africa australia india and brazil however much more intense depletion of fe oxide and much better developed white veins in the net like soils of south china suggest probably even warmer and more humid palaeoclimatic conditions relative to those in africa australia india and brazil during the period

rapid exhumation at 8 ma on the liupan shan thrust fault from apatite fission track thermochronology implications for growth of the northeastern tibetan plateau margin abstract the liupan shan mountain is one of the outermost ranges in northeastern tibetan plateau the onset of its uplift provides insight on whether the plateau grew sequentially outward or broad areas of the plateau deformed simultaneously the apatite fission track method can be used to date rapid cooling as the result of unroofing of rocks in response to tectonically induced vertical motion fission track data from apatite in early cretaceous sedimentary strata exposed on the hanging wall of liupan shan thrust fault in northeastern tibet suggest that a late cenozoic rapid cooling events occurred at 7 3 8 2 ma or 8 ma this age apparently dates fault activity of the liupan shan thrust in response to northeastward growth of the tibetan plateau uplift and lateral growth which continues today numerous studies of the tibetan plateau suggest that the onset of deformation in eastern and northern margin of tibetan plateau occurred in the latest miocene

geomorphic constraints on surface uplift exhumation and plateau growth in the red river region yunnan province china field observations digital elevation model dem data and longitudinal profi le analysis reveal a perched low relief upland landscape in the red river region yunnan province china which correlates to an uplifted regional low relief landscape preserved over the eastern margin of the tibetan plateau as with other major rivers of the plateau margin the red river has deeply incised the lowrelief upland landscape which we interpret to be the remnants of a pre uplift or relict landscape we examine longitudinal river profi les for 97 tributaries of the red river most profi les consist of three segments separated by sharp knickpoints an upper lowgradient channel segment a steeper middle channel segment and a very steep lower channel segment upper channel segments correspond to the relict landscape and have not yet experienced river incision steeper middle and lower segments indicate onset of rapid two phase river incision on the basis of which changes in external forcings such as climate or uplift can be inferred in terms of two end member scenarios two phase incision could be the result of pulsed plateau growth in which relatively slow uplift during the fi rst phase is followed by rapid uplift during the second phase or it could refl ect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth reconstruction of the paleo red river indicates 1400 m river incision 1400 1500 m surface uplift and a maximum of 750 m vertical displacement across the northern red river fault elevating the northern ailao shan range above the surrounding relict landscape on the basis of stratigraphic constraints incision along the red river likely began in pliocene time

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

karst bauxite deposits in the zagros mountain belt iran more than 190 occurrences of bauxitic lateritic deposits were investigated in seven areas within the zagros simply folded mountain belt in southwestern of iran the bauxitic horizons are situated in eroded major nw se trending anticlines and occur in karst cavities near or at the boundary between the sarvak and ilam formations uplift in the cenomanian turanian period had exposed the sarvak limestone to karst weathering and during a period of unconformity layers of ferruginous argillaceous limestone debris developed and accumulated on its surface the ferruginous argillaceous debris was partly converted to bauxite folding and faulting in oligocene miocene time with ensuing erosion exposed the bauxitic horizons on the limbs and cores of anticlines the karst bauxite deposits are probably of authigenic origin as evidenced by their lithologic associations textural and mineralogy

two phase growth of high topography in eastern tibet during the cenozoic high topography in eastern tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the indo asian collision implying that crustal flow alone could not have created the high topography

terrestrial deposition processes of quaternary gibbsite nodules in the yongjiang basin southeastern margin of tibet and implication for the genesis of ancient karst bauxite abstract the terrestrial deposition process for karst bauxite is difficult to constrain due to its allochthonous origin multiple controls and the difficulty in geodynamic reconstruction this ambiguity has been clarified from investigation of the provenance and geologic geographic conditions for the formation of quaternary gibbsite nodules in the yongjiang basin this karst basin located at the southeastern propagation front of the tibet plateau was affected by the se asia monsoon climate developed since the late oligocene and a later quaternary glaciation a thick blanket of quaternary laterite is located on paleozoic carbonate bedrock and covers an area about 1000 km2 along the east flowing river systems in the basin the laterite profiles are well layered with a layer of iron rich gibbsite nodules overlying on a basal clay zone and irregularly covered by a thin clayey topsoil gibbsite nodules from most localities yield detrital zircons with age peaks at ca 1000 ma 450 ma and 250 ma corresponding to those of the mesozoic clastic and magmatic rocks exposed on the western and southern surrounding highlands nevertheless those from the pingtianshan area produce an exclusive spike at ca 100 ma consistent with the emplacement age of nearby granites apatite fission track modeling for the mesozoic clastic rocks and darongshan granites shows a rapid cooling since the early miocene and that for the pingtianshan cretaceous granite reveals fast exhumation since the late miocene these data indicate differential erosion reshaped the topography and consequently a low relief karst basin was developed allowing a diverse material supply from the surrounding and local highlands via sheet flow and east flowing rivers under a monsoon influenced subtropical climate aluminum and iron oxides hydroxides were accumulated as nodules or concretions which were cemented by and coated with fe oxides due to variations in redox potential and alternating consolidation and swelling while silica was leached at greater depth groundwater solutions preferentially removed and brought upward fe under a reducing environment during the wet seasons while an underlying clay layer occurred due to the reduced solubility of silica later this bauxitization process was probably hindered by the quaternary glaciation which could have promoted the formation of the top clay layer this terrestrial deposition process of quaternary gibbsite nodules serves as one analogue for ancient karst bauxite in which the following submergence would improve the quality via further precipitation of alumina hydroxide and leaching of extra fe

the genesis of allochthonous karst type bauxite deposits of southern europe some mediterranean bauxite deposits in karst considered to be allochthonous originating from neighboring silicate rocks reveal the following common features of fluvial transport and sedimentation 1 the sio2 content increases in the direction of the transport 2 the trace elements indicate the area of origin 3 the bauxite was deposited in depressions of a slightly karstified coastal plain in a lagoonal or estuarine environment 4 the karst relief became accentuated after the bauxite was covered by sediments and 5 the depth of the karstic depressions was controlled by the former groundwater level therefore the thickness of the orebodies increases with the distance from the former shoreline these factors have an implication on the strategy of exploration the following examples are taken from central greece and montenegro and comparisons are made with the bauxite districts of france italy and jamaica

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

controls on the erosion of cenozoic asia and the flux of clastic sediment to the ocean rates of continental erosion may be reconstructed from variations in the rate of accumulation of clastic sediment most of which lies offshore global rates of marine sedimentation are usually considered to have reached a maximum after 3 4 ma driven by enhanced erosion in a variable glacial interglacial climate however a new compilation of seismic data from the marginal seas of asia now shows that only the red river reached its historic peak after 4 ma sediment flux from asia first peaked in the early middle miocene 24 11 ma well before the initiation of a glacial climate indicating that rock uplift and especially precipitation are the key controls on erosion at least over long periods of geologic time reconstructions of weathering in east asia show that faster erosion correlates with more humid warm climates in the early middle miocene changing to less erosive drier climates after 14 ma when antarctic glaciation begins average rates of sedimentation on most east asian continental margins since 1 8 ma are 5 6 times less than the modern fluvial flux implying that the flux to the oceans varies sharply on short timescales and is not always buffered over timescales of 10 4 yr by storage in flood plains

neogene weathering and supergene manganese enrichment in subtropical south china an 40ar 39ar approach and paleoclimatic significance deep weathering profiles and associated supergene mn oxides deposits are widely distributed in south china however data on their ages are not available until most recently ar 40 ar 39 laser incremental heating analysis of potassium bearing supergene mn oxides collected from four weathering profiles in the qinzhou fangcheng mn belt guangxi province south china provides for the first time numerical constraints on timing of weathering and supergene mn enrichment thirty eight of 42 cryptomelane grains yield well defined plateau 36 grains or pseudo plateau 2 grains ages ranging from 17 6 0 5 ma to 4 71 0 08 ma 2 sigma the results when combined with data from mn oxides deposits from the adjacent guangdong and hunan provinces document a protracted history of weathering and supergene mn enrichment spanning from the earliest miocene to the latest pliocene in south china this indicates that warm and humid climatic conditions conducive to intense weathering and secondary mineralization prevailed across south china during the whole neogene the climatic conditions inferred from weathering geochronology are consistent with sedimentary records and fossil floral and fauna associations from cenozoic inland and marginal sea basins of south china the weathering geochronology data also provide temporal constraints on the initiation and intensification of the east asian monsoon that has been the cause for the south china s humid climate c 2007 elsevier b v all rights reserved

tropical laterites life on land and the history of atmospheric oxygen in the paleoproterozoic the ca 2 2 ga hekpoort paleosol of the transvaal supergroup in southern africa has been considered a type example and the youngest iron depleted paleosol formed under a reducing atmosphere in the early precambrian however the mineralogical and geochemical data on recently acquired deep drill core intersections indicate that the hekpoort paleosol represents part of an ancient lateritic weathering profile with an iron depleted pallid lower zone and an iron enriched lateritic upper zone previous studies of the paleosol took place in areas where only the lower pallid zone was preserved from erosion prior to deposition of cover beds the laterite profile is comparable to that of modern tropical laterites formed under an oxic atmosphere in the presence of abundant terrestrial biomass revised stratigraphic correlation indicates that the hekpoort laterite profile is a correlative to highly ferruginous laterite profiles of wolhaarkop in griqualand west this information indicates that the oxygen evolution curve based on loss or retention of iron in paleosols should be reexamined

differential mobility of elements in burial diagenesis of siliciclastic rocks abstract mass balance calculations involving smectite rich siliciclastic mudstones sampled from boreholes show that significant k2o addition and cao loss correlate strongly with the progress of illitization of smectite and with the dissolution of calcite the calculations are based on the immobility of al2o3 and require a chemically homogeneous sediment at deposition such that the shallower samples represent protolith compositions of deeper samples constancy of ratios of tio2 al2o3 are used to 1 establish that both tio2 and al2o3 have similarly low differential mobilities and 2 identify stratigraphic sections available in the literature that are sufficiently homogeneous to allow the calcu ations our calculations show that most major oxide components are immobile at the 5 limit of resolution of the calculations exceptions are k2o which is almost universally added to mudstones and cao which is commonly removed from mudstones during diagenesis the addition of up to 50 k2o correlates with percent illite in mixed layer illite smectite indicating that illitization of smectite involves fixation of k2o from diagenetic fluids removal of 40 cao from some sections correlates with decreasing calcite mode and is attributed to dissolution of calcite together these reactions lead to a 10 15 loss of mineral volume a volume loss that must be added to porosity loss when modeling compaction illitization and carbonate dissolution may be linked because k fixation during illitization decreases the ph of the local fluid a reverse weathering reaction which enhances carbonate dissolution addition of up to 20 na2o in some rocks may be caused by albitization of plagioclase but na2o addition is not pervasive the apparent lack of mass transfer associated with dissolution of kaolinite and feldspars or precipitation of chlorite implies that these reactions are balanced by other reactions such that their oxide components in mudstones are conserved limited data from sandstone mudstone pairs are consistent with transfer of k2o from sandstones to mudstone via rising diagenetic fluids except for cao and the alkalis diagenesis of siliciclastic mudstones appears isochemical 5 relative for most major oxide components the much larger changes recorded in some reservoir sandstones are clearly exceptions and may not reflect changes occurring at the scale of kilometers

petrogenesis of the nanling mountains granites from south china constraints from systematic apatite geochemistry and whole rock geochemical and sr nd isotope compositions abstract the widespread mesozoic granitoids in south china 135 300 km2 were emplaced in three main periods triassic 16 of the total surface area of mesozoic granitoids jurassic 47 and cretaceous 37 though much study has been conducted on the most abundant jurassic nanling mountains nlm granites their rock affinities relative to the triassic darongshan drs and cretaceous fuzhou zhangzhou complex fzc granites which are typical s and i type respectively and the issue of their petrogenetic evolution is still the subject of much debate in this study we discuss the petrogenesis of nlm granites using apatite geochemistry combined with whole rock geochemical and sr nd isotope compositions sixteen apatite samples from six granite batholiths one gabbro and three syenite bodies in the nlm area were analyzed for their major and trace element abundances and compared with those collected from drs n 7 and fzc n 6 granites the apatite geochemistry reveals that na si s mn sr u th concentrations and ree distribution patterns for apatites from drs and fzc granites basically are similar to the s and i granite types of the lachlan fold belt australia whereas those from nlm granites have intermediate properties and cannot be correlated directly with these granite types according to some indications set by the apatite geochemistry e g lower u and higher eu abundances nlm apatites appear to have formed under oxidizing conditions in addition we further found that their ree distribution patterns are closely related to aluminum saturation index asi and nd isotope composition rather than sio2 content or degree of differentiation of the host rock the majority of apatites from nlm granites asi 0 97 1 08 and end t 8 8 to 11 6 display slightly right inclined apatite ree patterns distinguishable from the typical s and i type however those from few granites with asi 1 1 and end t 6 6 and gabbro and syenite are similar to fzc apatites strongly right inclined in light of sr and nd isotope compositions magmas of nlm intrusives except gabbro and syenite and few granites with end t 8 generally do not involve a mantle component instead they fit with a melt derived largely from in situ melting or anatexis of the pre mesozoic mainly caledonian granitic crust with subordinate pre yanshanian mainly indosinian granitic crust we suggest that an application using combined whole rock asi and end t values is as useful as the apatite geochemistry for recognizing possible sources for the nlm granites

how old is the asian monsoon system palaeobotanical records from china the recent discovery of monsoon records in early miocene raised a question of the time when the east asian monsoon system initiated a distinguishing feature of the modern monsoon system is its geographic distribution which disturbs the zonal pattern indigenous to the planetary climate system and the appearance of the monsoonal climate pattern in the geological records should signify the onset of the monsoon system here we present the results of a compilation of palaeobotanical and lithological data from 125 sites over china that has revealed two completely different patterns of climate zones the palaeogene pattern with a broad belt of aridity stretched across china from west to east and the neogene pattern with the arid zone restricted to northwest of china which has persisted until today the reorganization of the climate system around the oligocene miocene boundary provides evidence for the establishment of the modern east asian monsoon since then the neogene has witnessed significant variations of the monsoon system including enhancement of aridity and monsoon intensity at about 15 13 my around 8 my and 3 my the new data do not support the onset of the asian monsoon system around 8 my rather the new data led to a hypothesis that the transition to the monsoon climate system in east asia occurred in the latest oligocene

constructing the longmen shan eastern tibetan plateau margin insights from low temperature thermochronology 1 contrasting models of upper crustal shortening versus lower crustal flow have been proposed to explain the formation of thickened crust in the longmen shan lms eastern tibetan plateau tp margin these models require different structural kinematics along the lms whose structural geometry is defined by three parallel nw dipping fault zones from foreland southeast to hinterland northwest they are the guanxian anxian fault yingxiu beichuan fault ybf and wenchuan maowen fault wmf newly derived and previously published low temperature thermochronology data from the lms were synthesized to constrain the spatial exhumation and test previous models the results show that 1 exhumation increases abruptly across the range bounding ybf suggesting the fault being the main thrust boundary between the lms and the sichuan basin to the east 2 younger late cenozoic cooling ages are found on the hinterland wmf where a dichotomy of ages on the hanging wall versus footwall suggests late cenozoic thrust activity and 3 toward the hinterland to the west exhumation rates decrease twofold over a distance of 30 40 km this exhumation pattern indicates a westward decrease of tectonic uplift providing the regional topography approached a steady state whereby exhumation is in balance with tectonic uplift the observed exhumation estimates support an upper crustal configuration where thrusts in the lms merge gradually into a gentle detachment seated at a depth of 20 30 km results of this study support a revised upper crustal thrusting model

quantitative mineralogical characterization of karst bauxite deposits in the southern apennines italy the southern italian karst bauxite deposits occur at a late cretaceous hiatus on a bahamian type carbonate platform succession cropping out in the southern apennines and are mainly located in the abruzzi mountains in apulia gargano peninsula and murge area and in campania the bauxites of southern italy are presently uneconomic but can be considered as a model analogue for economic karst bauxite ores the texture of the bauxite deposits is mainly oolitic to pisolitic but can also be arenitic conglomeratic suggesting reworking of evolved lateritic soils the minerals boehmite and hematite are more abundant in the ooids whereas kaolinite is found at high levels in the groundmass and titanium oxides are also present furthermore small amounts of rare earth elements have been detected in most of the bauxite occurrences scanning electron microscopy with energy dispersive spectrometry sem eds and geochemical analyses on several of the deposits confirmed the diagenetic texture of the bauxite and provided an estimate of the mineralogy of the different components and their chemical composition the mineralogical and petrographic characteristics of bauxite are crucial for the bayer process and can influence its economic evaluation both the particle size distribution in the ore and the presence of reactive silica phases associated with ti and fe oxides can reduce the efficiency of processing quantitative analyses combining different methods x ray diffraction xrd rietveld quantitative phase analysis qpa and qemscan have been carried out on a limited number of samples from two of the bauxite districts of the campania region the matese mountains and the caserta province qemscan analysis allowed a more rapid quantification of mineralogy including trace detrital phases and assessment of the individual textural characteristics of the bauxite lithotypes showing a detailed image of the distribution of economic and noneconomic minerals and their intergrowths this methodology can augment or replace other time consuming quantitative phase analyses for mineralogical studies of bauxites provided that the species identification protocol sip database has been carefully validated by preliminary use of xrd and sem eds both xrd qpa and qemscan analytical techniques can be complementary for bauxite ore evaluation and a very powerful tool for exploitation and mineral processing

differential exhumation at eastern margin of the tibetan plateau from apatite fission track thermochronology abstract new apatite fission track aft ages from mesozoic sediments in the sichuan basin combined with previous fission track data demonstrate differential uplift and exhumation across the basin particularly significant change in exhumation at least 2000 m was found across the huaying mts modeled temperature time histories and the boomerang plot of aft dataset across the basin suggest rapid cooling and exhumation events during 120 80 ma and at 20 10 ma they reflect the start of the basin scale differential uplift and exhumation which effected the eastern growth of tibetan plateau in particular nested old age center separated by huaying mts was found in the center to northwest part of the sichuan basin a simplified one dimensional steady state solution model was developed to calculate the mean exhumation rate which is 0 05 0 2 mm yr in most parts of the basin it suggests a slow exhumation across much of the basin the regional pattern of aft age length and erosion rate supports a progressive change from the nested old age center towards the southwest this pattern supports the idea of a prolonged steady state uplift and exhumation process across the basin controlled by cratonic basin structure the eastern growth of the tibetan plateau has exerted a significant effect on the rapid exhumation of the southwestern part of the sichuan basin but not on all of the basin during the late cenozoic

development of the east asian summer monsoon evidence from the sediment record in the south china sea since 8 5 ma 128 samples from ocean drilling program odp site 1143 in the southern south china sea were analyzed for grain size clay minerals biogenic opal content and quartz in order to reconstruct changes in east asian monsoon climate since 8 5 ma an abrupt change of terrigenous mass accumulation rate mar clay mineral assemblage median grain size and biogenic opal mar about 5 2 ma suggests that between 8 5 5 2 ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern vietnam a simple model of east asian summer monsoon evolution was based on the clay feldspar ratio kaolinite chlorite ratio and biogenic opal mar the summer monsoon has two periods of maximum strength at 8 5 7 6 ma and 7 1 6 2 ma subsequently there was a relatively stable period at 6 2 3 5 ma continued intensification about 3 5 2 5 ma and gradually weakening after 2 5 ma since i ma the monsoon has intensified with remarkable high frequency and amplitude variability simultaneous increase in sedimentation rates at odp sites 1143 1146 and 1148 as well as in mar of terrigenous materials quartz feldspar and clay minerals at odp site 1143 at 3 5 2 5 ma may be the erosional response to both global climatic deterioration and the strengthening of the east asian summer monsoon after about 3 4 ma c 2006 elsevier b v all rights reserved

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

millennial scale iceberg surges after intensification of northern hemisphere glaciation iceberg discharges from continental ice sheets are widely believed to have exerted a great influence on global climate but an iceberg discharge regime in early glacial periods after intensification of northern hemisphere glaciation nhg remains largely unclear here we present high resolution rock magnetic records during the period from 2 1 to 2 75 ma after intensification of nhg reconstructed from the subpolar north atlantic although the establishment of the middle pliocene chronology of north atlantic sediments is often a serious problem we overcame it based on findings concerning the properties of magnetic susceptibility and natural gamma radiation reconstructed rock magnetic records indicate that millennial scale iceberg surges were dominant features in the early glacial periods additionally the millennial scale iceberg surges occurred within glacial stages during intervals when ratios of global oxygen isotope stack from benthic foraminifera lr04 18o stack surpassed approximately 3 5 these are comparable to the climatic and environmental changes in pleistocene glacial periods as represented by last glacial dansgaard oeschger cycles suggesting that continental ice sheets have oscillated and calved icebergs in a similar manner since intensification of nhg

drylines in southern africa rediscovering the congo air boundary abstractprojected rainfall decline in southern africa is likely to be highly sensitive to subtleties in the local atmospheric circulation in an effort to understand the regional circulation comple

geochemistry of the apulian karst bauxites southern italy chemical fractionation and parental affinities article i nfo this study focuses on a late cretaceous karst bauxite deposit in the murge area of the apulia district southern italy the first analysis of the vertical distributions of a wide range of elements including rees and selected trace elements throughout the deposit was shown in order to identify the processes determining element frac tionation during the evolution of the bauxite the studied karst bauxite deposit exhibits an ooidal texture is mineralogically homogeneous and contains higher abundances of boehmite than of hematite kaolinite and anatase the major element composition of the bauxite is dominated by elevated concentrations of sio2 t io2 a l2o3 a nd fe2o3 and analyses of element mo bility within the bauxite indicate that all elements except for nb and ni and to a lesser extent cr are depleted relative to the immobile element ti r mode factor analysis revealed a number of key findings i some low solubility elements e g zr th ti v ga were concentrated in detrital zircon and monazite zr th in anatase ti v and possibly in boehmite and hematite ga during the later stages of bauxitisation ii fe and cr were concentrated during wet conditions whereas al and co accumulated during dry conditions iii distributions of the light rees lrees and the heavy rees hrees are controlled by the same processes suggesting that little lree hree fractionation occurred during bauxite formation and iv the behaviour of cerium is different from that of the other rees and highly variable cerium anomalies are observed across the deposit with three characteristic ce ce maxima with values ofn2 parisite was the only authigenic cerium mineral detected during this study thus we propose a three step model to explain the distribution of ce cerianite is dissolved by cerium reduction is transported by downward moving meteoric water per descensum and finally parisite is precipi tated this cycle was repeated several times in the apulian karst bauxite in response to eh decreases under alka line conditions promoted by fluctuations in the groundwater level finally we used the value of the eu anomaly todiscuss theparental affinity or protolith of thebauxite the value of the eu anomaly min eu eu 0 76 max eu eu 0 89 indicates that the bauxite was not derived from carbonates but rather that the majority of the bauxite was influenced by intermediate to mafic magmatic sources eu eu vs sm nd diagram suggests that the parental material for the bauxite was derived from a combination of a distant magmatic source and clastic material derived from a continental margin northern africa to the south

mineralogy and geochemistry of claystones from the guadalupian lopingian boundary at penglaitan south china insights into the pre lopingian geological events abstract the guadalupian lopingian g l boundary at a stratigraphically well documented outcrop in penglaitan guangxi autonomous region south china has been approved as the global stratotype section and point gssp several volcanic ashes or tuffs occur at this boundary but their mineralogy and geochemistry are not available yet and no reliable age for this boundary has been obtained a combined study of mineralogy geochemistry and geochronology has been carried out in this study on six layers of claystones collected below group 1 and above group 2 the g l boundary at the penglaitan section both group 1 and group 2 claystones are likely clastic in origin rather than volcanic ashes as previously thought thus the penglaitan claystones are not suitable for age determination of the g l boundary they are significantly different in terms of mineralogy and geochemistry specifically group 1 claystones are likely derived from a mafic source which is genetically related to the emeishan large igneous province therefore providing additional evidence for the synchroneity between the g l boundary mass extinction and the emeishan volcanism group 2 samples were derived from a felsic source of which zircons yield an age spectrum peaked at 262 3 ma undistinguishable within the uncertainty from the currently accepted g l boundary age 260 4 0 4 ma nevertheless group 2 samples are not related to emeishan volcanism because their negative zircon ehf t values differ significantly from those of emeishan magmas and trace element compositions of zircons are indicative of an arc source rather than a within plate source in consideration of paleogeographic reconstruction we propose that the group 2 claystones may have been derived from continental arcs during the palaeo tethys evolution this is the first sedimentary evidence for permian continental arc in the northern margin of palaeo tethys

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

constraints on the early uplift history of the tibetan plateau the surface uplift history of the tibetan plateau and himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during cenozoic time its influence on monsoon intensity and its reflection of the dynamics of continental plateaus models of plateau growth vary in time from pre india asia collision e g 100 ma ago to gradual uplift after the india asia collision e g 55 ma ago and to more recent abrupt uplift 7 ma ago and vary in space from northward stepwise growth of topography to simultaneous surface uplift across the plateau here we improve that understanding by presenting geologic and geophysical data from north central tibet including magnetostratigraphy sedimentology paleocurrent measurements and 40ar 39ar and fission track studies to show that the central plateau was elevated by 40 ma ago regions south and north of the central plateau gained elevation significantly later during eocene time the northern boundary of the protoplateau was in the region of the tanggula shan elevation gain started in pre eocene time in the lhasa and qiangtang terranes and expanded throughout the neogene toward its present southern and northern margins in the himalaya and qilian shan

mineralogical characteristics of the superlarge quaternary bauxite deposits in jingxi and debao counties western guangxi china abstract in recent decades more than 0 5 billion tons of ores scattered in the quaternary laterite in western guangxi china have been explored the ores were derived from a bauxite horizon in permian via physical break up and re sediment process utilizing various test methods i e xrd dta tg dtg sem eds and epma the mineralogical characteristics of the quaternary bauxite ores in jingxi and debao counties were investigated xrd was used together with tg dtg to obtain relatively accurate ore mineral abundance diaspore is the major phase whereas hematite kaolinite anatase chamosite gibbsite goethite illite and rutile are minor diaspore is characterized by a small particle size low degrees of crystallinity and complex chemical composition both gibbsite and goethite have a varied particle size and goethite crystals contain high al substitution and si it is clarified that diaspore chamosite and anatase were formed in a mildly reduced and alkaline depositional environment in permian while gibbsite hematite goethite and part kaolinite were precipitated from al 3 si 4 and fe 3 enriched solutions within an quaternary oxidized environment the ions al 3 si 4 and fe 3 are mostly released from chamosite in its dissolution process the different physicochemical conditions between the permian depositional and the quaternary weathering periods resulted in a complex mineral assemblage in the quaternary bauxite

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

metasedimentary melting in the formation of charnockite petrological and zircon u pb hf o isotope evidence from the darongshan s type granitic complex in southern china abstract charnockites are opx bearing igneous rocks commonly found in high grade metamorphic terranes despite being volumetrically minor they show a wide range in both bulk geochemistry and intensive parameters they form a characteristic component of the amcg anorthosite mangerite charnockite granite suite but their association with typical s type granites is less well known the darongshan s type granitic complex dsgc in guangxi province southern china contains granites varying in mafic silicate mineral assemblages from bt crd darongshan suite to opx grt bt crd jiuzhou suite and opx crd bt taima suite corresponding to a geochemical transition from magnesian calc alkalic to ferroan calc alkalic however its genesis even the accurate age of intrusion remains highly contentious despite intensive research in order to understand the genesis of charnockite and its genetic relationship with s type granite here we first determined zircon u pb ages of each suite using a sims on the basis of a detailed petrological study zircon u pb ages show that all suites of the complex were emplaced contemporaneously at ca 249 ma monazite apparent u pb ages are indistinguishable from zircon u pb ages within analytical error further in situ zircon hf o isotope analyses reveal that the granitic complex was dominantly derived from reduced melting metasedimentary rocks 18ozircon ca 11 ehf t zircon ca 10 log fmq 0 mn in apatite oxybarometer with rare material input from the mantle the variation in 18o 7 8 12 9 is more likely a result of hybridization whereas that in ehf t 31 9 to 1 8 is a result of both hybridization and disequilibrium melting the variation in mineralogy and geochemistry may be interpreted as a result of entrainment of peritectic garnets from biotite dehydration melting nevertheless heat input from mantle through basaltic intrusion underplating is considered to play a major role in high temperature 850 c melting at mid crustal levels i e the cordierite stable field for generation of the granitic complex we interpret that the granites were intruded in a back arc setting and basaltic magmatism was directly associated with slab roll back and tearing during the latest permian and early triassic times

cenozoic deformation in western yunnan china myanmar border in the present paper we describe ductile and brittle deformation styles in western yunnan and ne myanmar using field data and landsat 7 imagery we show that this complex area located at the northern termination of sunda plate three rivers area was wedged during the tertiary between the left lateral ailao shan chong shan metamorphic belts to the east and the right lateral shan scarp gaoligong metamorphic belt in west this triangular region therefore underwent the effects of these continental size ductile strike slip faults separating major blocks with a dominant ew to ene compression since the late miocene date of the reversal of motion along the rrf the incipient eastward motion of the sunda block and the persisting right lateral motion along its western boundary sagaing fault created n s compression and e w to wnw extension underlined by left lateral transtension along the wanding nanting fault zones at the same time the diangcan shan situated along strike the ailao shan metamorphic belt was slightly impinged by the blocks extruded from the syntaxis and exhumed again from the early pliocene in accordance with this late and still active state of stress q 2004 elsevier ltd all rights reserved

the formation of representative lateritic weathering covers in south central guangxi southern china the mineralogy and geochemistry have been studied in three representative lateritic weathering covers close to the tropic of cancer guangxi south china with the purpose of studying formation and evolution processes of lateritic covers in this region the x ray diffraction and scanning electron microscope analysis results indicate that the contents particle sizes shapes and structures of secondary minerals such as iron and clay minerals are distinctly different in ferruginous nodular horizon and mottled clay layer of lateritic profiles the ferruginous nodules are characterized by high concentrations of iron and aluminum and low contents of silicon the energy analysis suggests that there are element exchanges between hematite crystal and clay minerals the mass balance calculation results show that there is exogenetic input of iron into lateritic covers especially within the ferruginous nodular horizon compared to the bottom layer of the profile the scanning electron microscope images also confirm that voids and fractures in ferruginous nodules were filled with ferruginous material derived from soil solution this could be a significant interpretation for the negative correlations between fe2o3 and al2o3 the iron and manganese oxides in ferruginous nodular horizon have an apparent effect on the adsorption and precipitation of cerium strontium compared to other alkali metal and alkali earth metal elements concentrates in mottled clay layer variation in the he gt ratio reflected by the o fe ratio in a small ferruginous concretion indicates that climate changes altered aqueous activity of the soil environment finally a model for the formation and evolution of typical lateritic weathering covers in south central guangxi supported by all the data was proposed

diatom inferred salinity changes from the yushe paleolake indicate an aridification during the pliocene pleistocene transition in north china abstract the global climate changed significantly during the pliocene pleistocene transition and a worldwide aridification occurred in order to investigate the influence of the aridification during the pliocene pleistocene transition in the east asian interior diatom assemblages from the upper zhangcun formation north china deposited during 2 7 2 5 ma bp were analyzed and the lake salinity was reconstructed using diatom environment transfer functions a total of 74 diatom taxa were found in the sediments belonging to 21 families and 32 genera four zones were established from the bottom to the top based on the changes in the diatom assemblages over the 15 7 m sediment sequence in zone 1 cyclotella iris dominated in assemblage while caloneis westii and staurosira construens were less presented among representative species in zone 2 c iris dominated which indicates carbonate rich water but in zone 3 benthic pennate taxa such as c westii and anomoeoneis sphaerophora became more abundant indicating a significant increase in water salinity from carbonate type to sulfate type caused by climatic change in zone 4 c iris became dominant again with abundant gomphonema intricatum and rare pinnularia rathsbergiana and martyana martyi species the salinity inferred by conductivity reconstruction increased from 1 9 ppt in zone 2 to 4 1 ppt in zone 3 the significant changes of anion ratio alk cl so42 indicate an abrupt change from carbonate rich to a sulfatic type water the increase of salinity reflects changes in the precipitation evaporation balance the change from carbonate to sulfatic water inferred from the diatom assemblages could indicate a significant aridification around ca 2 6 ma bp on the eastern edge of the loess plateau this is the most easterly record of aridification across the eastern asian interior and may be related with the global cooling and the development of the northern hemisphere glaciation

the western segment of the suture between the yangtze and cathaysia blocks constraints from inherited and co magmatic zircons from permian s type granitoids in guangxi south china the location of the suture between the yangtze craton and the cathaysia block is uncertain in the west three proposed locations for the western segment of the suture all go through guangxi but are up to 150 km apart inherited zircon crystals from the darongshan permian s type granitoid plutons which are derived from the lower crust and occur north of the southernmost location for the suture yield u pb ages with a major peak at 960 ma the ehf t values of the inherited zircons with ages around the major peak vary from 6 4 to 23 4 the age distribution and hf isotope variations of the inherited zircons are remarkably similar to those of precambrian detrital zircon crystals from the western cathaysia block but strikingly different from those of precambrian detrital zircon crystals from the yangtze craton these results indicate that the western part of the suture is situated to the north of the darongshan granitoid belt

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

lateritization and bauxitization events laterites and bauxites are produced in tropical soils by weathering which enriches iron of laterites and alu mina of bauxites as well as trace elements such as nickel gold phosphorus and niobium to ore grade la terites and bauxites can be redeposited into sedimentary sequences and remain as ores if not transported far and diluted with other materials the age of redeposited laterites and bauxites and of bauxitic and lateritic pa leosols can be established from the geologic age of overlying rocks an approach especially effective in pale osols within sequences of isotopically datable volcanic rocks lateritic profiles can also be dated by paleomag netic inclination in special cases in which land masses such as in australia and india drifted long distances northward during cenozoic time in addition cryptomelane and other k mn oxides can be dated by k ar and 40ar 39ar techniques to obtain multiple ages from different crystals in a single relict paleosol compilation of new and more accurate laterite and bauxite ages reveals unusually widespread and intense laterite and bauxite formation during events of less than 100 k y duration at 2 12 16 35 48 55 65 and 100 ma such events can also be inferred at times older than 100 ma from paleolatitudinal distribution of laterites and bauxites but these are poorly sampled laterite and bauxite peaks were coeval with times of global high warmth and pre cipitation elevated atmospheric carbon dioxide oceanic anoxia exceptional fossil preservation and mass ex tinction these co2 greenhouse events and attendant titration of carbonic acid with soils are interpreted as transient fluctuations in the atmosphere produced by meteorite impact flood basalt volcanism and methane outbursts concentration of bauxite and laterite resources in particular stratigraphic horizons formed during greenhouse crises suggests the usefulness of an event stratigraphic approach to exploration and exploitation of these and related ores

estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses cappa et al modelling pressure pulses in rock fractures estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses frederic cappa 1 yves guglielmi 2 jonny rutqvist 3 chin fu tsang 3 and alain thoraval 4 geosciences azur university of nice sophia antipolis sophia antipolis france geologie des systemes et des reservoirs carbonates university of provence aix marseille france earth sciences division lawrence berkeley national laboratory berkeley usa ineris ecole national superieure des mines de nancy parc de saurupt nancy france corresponding author fax 33 4 92 94 26 10 e mail address cappa geoazur unice fr f cappa