tectonic control of erosion in the southern central andes abstract landscape evolution modeling and global compilations of exhumation data indicate that a wetter climate mainly through orographic rainfall can govern the spatial distribution of erosion rates and crustal strain across an orogenic wedge however detecting this link is not straightforward since these relationships can be modulated by tectonic forcing and or obscured by heavy tailed frequencies of catchment discharge this study combines new and published along strike average rates of catchment erosion constrained by 10be and river gauge data in the central andes between 28 s and 36 s these data reveal a nearly identical latitudinal pattern in erosion rates on both sides of the range reaching a maximum of 0 27 mm a near 34 s collectively data on topographic and fluvial relief variability of rainfall and discharge and crustal seismicity suggest that the along strike pattern of erosion rates in the southern central andes is largely independent of climate but closely relates to the n s distribution of shallow crustal seismicity and diachronous surface uplift the consistently high erosion rates on either side of the orogen near 34 s imply that climate plays a secondary role in the mass flux through an orogenic wedge where the perturbation to base level is similar on both sides

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

phanerozoic magmatic tempos of north china abstract detrital zircons from northeast china record cyclic magmatism along the northern and eastern margins of the north china block during late paleozoic time and mesozoic time respectively the late paleozoic zircons record three magmatic flare ups with a period of 60 m y that occurred within a magmatic arc constructed along the paleoasian northern margin of north china and are accompanied by negative e hf t excursions representing shortening and increased crustal melting over the duration of each flare up the intervening magmatic lulls are accompanied by rapid positive e hf t excursions signifying influxes of juvenile magma into the arc probably during extension and foundering of underlying melt residua the lack of similar isotopic patterns in zircons derived from contemporaneous intrusions into older continental settings inboard of the arc indicate that this process was restricted to the arc itself mesozoic magmatism in north china occurred along the paleo pacific margin following closure of the paleoasian ocean and exhibits a 50 m y periodicity that is out of phase with that of the paleozoic arc although the tectonic setting of north china during mesozoic time is complex and still controversial it is possible that this younger periodicity is governed by similar processes as those that dominated the paleozoic arc this is a testable hypothesis that warrants further attention crustal shortening was widespread in north china during mesozoic time and documented lithosphere removal events in eastern north china occurred during the mesozoic magmatic lulls lithospheric thickening foundering cyclicity well documented in cordilleran arc systems may be a common process in continental arcs through space and time

exhumation and preservation of porphyry cu au deposits at oyu tolgoi south gobi region mongolia field relationships and u pb data zircon are used to constrain the timing of tectonomagmatic events that occurred shortly after the formation of late devonian 372 ma porphyry cu au deposits at oyu tolgoi mongolia in the two northernmost of the several discrete porphyry centers hugo dummett deposits upper devonian rocks positioned stratigraphically above copper gold mineralization preserve a record of uplift exhumation and subsequent burial shortly after mineralization strongly altered and mineralized quartz monzodiorite and volcanic rocks at hugo dummett are overlain by an unmineralized dacite sequence 369 2 ma the basal breccia and conglomerate of the dacite sequence contain mineralized porphyry clasts derived from erosion of the porphyry deposits two zircon grains recovered from one of these mineralized porphyry clasts yielded chemical abrasion thermal ionization mass spectrometry ca tims 206 pb 238 u dates of 374 0 1 9 and 371 4 1 6 ma which are consistent with previously published ages for mineralized intrusions this implies that oyu tolgoi or other nearby porphyry deposits were exhumed shortly after the main mineralization event weakly mineralized granodiorite dikes intruded the postmineralization dacite sequence as well as devonian sedimentary and volcaniclastic rocks that structurally overlie the dacite a weighted mean 206 pb 238 u age of 370 6 0 5 ma for this rock is based on the three youngest grains analyzed by the ca tims technique mswd 1 14 burial of the cu au deposits at oyu tolgoi soon after their exhumation was critical to their preservation exhumation and subsequent burial occurred at 371 ma during a short time frame within the overlapping u pb zircon ages for the quartz monzodiorite mineralized porphyry clast unmineralized dacite sequence and granodiorite unit

endorheic exorheic transitions of the rio grande and east african rifts this research was supported by nsf ear 1516680 and spanish government project mite cgl2014 59516

latitudinal trends in modern fluvial erosional efficiency along the andes abstract latitude is a dominant control on climate influencing both temperature and precipitation leading to potential gradients in erosional efficiency previous work focused on the latitudinal control of glacial erosion on topography however the expected latitudinal trend in erosional efficiency in the absence of glacial processes is unknown we parameterize a suite of numerical models using uniform rock uplift and climate from the andes to explore how latitudinal patterns of rainfall could influence the efficiency of fluvial bedrock erosion we use the child landscape evolution model parameterized with storm duration intensity and frequency statistics from ncep ncar reanalysis data along the andes over 31 years to predict latitudinal trends in topography subject only to fluvial and hillslope erosion modeled elevations as a metric for erosional efficiency vary 2 30 fold depending on the erosional and hydrological model parameterization modeled elevation trends generated using stochastic storm generation vary significantly from those generated using mean annual precipitation map the variation suggests map may not capture the true erosional efficiency of the modern climate in some locations but may in others explaining the discrepancy of conclusions in previous studies erosional efficiency is greatest in the tropics 5 15 s where high intensity and frequent storms occur and mid latitudes 30 35 s where less frequent but intense storms occur erosional efficiency is lowest in the subtropics 20 to 25 s where low intensity and infrequent storms occur and upper mid latitudes 45 50 s where low intensity and somewhat frequent storms occur erosional efficiency varies across the width of the orogen because of across orogen effects the results provide further evidence supporting climate s control on erosion processes and topography highlighting the importance of stochastic storm distributions and suggesting that latitudinal controls on rainfall can explain some observed trends in topography the modern latitudinal trend in topography is frequently used as an argument for a glacial buzzsaw however our results suggest more information on the pre glacial distribution of topography is needed to justify such an argument since latitude dependent rainfall regimes may generate similar topographic trends

modeling the formation of advanced argillic lithocaps volcanic vapor condensation above porphyry intrusions hypogene advanced argillic alteration typically quartz alunite with halos of kaolinite dickite and roots of pyrophyllite diaspore forms in the epithermal environment from condensates of magmatic vapor that contain so2 and hcl which exsolved from an underlying intrusive source the most aggressive nearly isochemical leaching of the host rock by the most acidic condensate commonly ph 1 leaves residual silica that recrystallizes to quartz within the flow channel at a high condensate rock ratio forming the core of alteration the alteration characteristically flares upward along feeder structures and if a permeable lithologic unit is intersected the alteration zones mushroom to form a subhorizontal blanket due to lateral flow where subsequently mineralized the residual quartz commonly with a vuggy texture that reflects the texture of the original lithology has higher au and cu grades than the quartz alunite halo tonnage in these high sulfidation systems may develop within the subhorizontal lithocap although the highest grades are typically confined to the structurally controlled feeders we modeled a typical volcanic vapor condensate starting with the measured composition of 877 c fumaroles from satsuma iwojima rhyolite dome japan as it cooled and reacted with a host rhyolite the predicted hydrothermal mineralogy reproduces the alteration pattern observed in lithocaps that host high sulfidation deposits the modeling confirms that aluminum rich minerals pyrophyllite diaspore locally andalusite are stable at higher temperature at depth whereas at lower temperature and shallower depth na and k alunite become stable at the lowest temperature 10 1 and where so2 h2s in the original volcanic vapor this so2 dominant composition is typical of andesitic to rhyolitic volcanoes the reason for this mineral transition and the upward flare widening of the alteration zone along structures is related to the dissociation and increased reactivity of h2so4 and hcl as the temperature decreases below 200 c only quartz pyrite native s and anhydrite are stable hence the formation of the dominant quartz from the silica residue a further check on our modeling is the observation that the calculated composition of the condensate after reaction with fresh satsuma iwojima rhyolite and alteration minerals and cooling to 100 c is similar within a factor of two to that of acidic springs with ph 1 that discharge around satsuma iwojima and other active volcanoes the most extensive lithocap alteration residual quartz and or quartz alunite is commonly offset from the surface projection of the causative intrusion this observation can be explained by a combination of two factors hydrology and temperature due to hydraulic gradients at shallow depths in a volcanic edifice the acidic condensate tends to flow along permeable lithologic units away from the locus of the high temperature vapor plume which rises directly over the intrusion where lateral flow occurs the most intense leaching and widespread advanced argillic alteration which develops largely at temperatures of 200 to 250 c based on our modeling will form away from the near surface projection of the intrusion which is the area of highest surface temperature due to ascent of the vapor plume this potential for lithocap alteration to form on the shoulder of the underlying causative intrusion must be assessed when exploring for high sulfidation ore the highest ore grades are commonly related to structures that are proximal to the parent intrusion but they are unlikely to lie directly over the intrusion in addition identifying the most likely location of the source intrusion will help the explorer to efficiently assess any potential for deeper porphyry style mineralization

tidally driven pore water exchange within offshore intertidal sandbanks part ii numerical simulations field measurements presented by gibbes b robinson c li l lockington d a carey h 2008 tidally driven pore water exchange within offshore intertidal sandbanks part i field measurements estuarine coastal and shelf science 79 pp 121 132 revealed a tidally driven pore water flow system within an offshore intertidal sandbank in moreton bay australia the field data suggested that this flow system might be capable of delivering nutrients and in particular bio available iron across the sediment water interface bio available iron has been implicated as a key nutrient in the growth of the toxic marine cyanobacteria lyngbya majuscula and therefore this pore water exchange process is of interest at sites where l majuscula blooms have been observed in this study two dimensional numerical simulations were used in conjunction with hydraulic data from field measurements to further investigate the tidally induced pore water flow patterns simulation results generally showed good agreement with the field data and revealed a more complex residual pore water flow system in the sandbank than shown by the field data the flow system strongly influenced by the geometry of the sandbank was characterized by two circulation cells which resulted in pore water discharge at the bank edge and also to a permanently ponded area within the sandbank interior simulated discharge volumes in these two zones were in the order of 0 813 m 3 and 0 143 m 3 per meter width along shore of sandbank per tidal cycle at the bank edge and sandbank interior respectively transit times of pore water circulating through these cells were found to range from approximate to 17 days to 60 years with an average time of 780 days the results suggest that the tidally driven flow systems might provide a mechanism for transport of bio available iron across the sediment water interface this flow could constitute a previously unrecognized source of bio available iron for l majuscula blooms in the bay c 2008 elsevier ltd all rights reserved

geology and geochronology of the tiegelongnan porphyry epithermal cu au deposit tibet china formation exhumation and preservation history abstract the tiegelongnan rongna deposit is a giant porphyry epithermal cu au deposit within the duolong porphyry district in the south qiangtang terrane central western tibet china the deposit is centered on multiphase granodiorite porphyry gp intrusions intruded in jurassic sandstone phase 1 and 2 gp are associated with biotite and sericite alteration whereas gp3 and 4 occur in middle and shallow parts of the deposit affected by sericite and advanced argillic alteration alunite kaolinite dickite pyrophyllite sericite alteration is pervasive in the deep part of the deposit replacing biotite alteration and hosting porphyry stage chalcopyrite bornite pyrite molybdenite mineralization advanced argillic alterationis associated with epithermal stage high sulfidation tennantite enargite bornite and digenite mineralization overprints the sericite and biotite alteration from the shallow part of the deposit the top of the tiegelongnan hydrothermal system was weathered with a layer of supergene oxidation and enrichment zone exhumated and covered by andesite and gravel muscovite sampled from deep sericite alteration yields a 40ar 39ar age of 120 9 0 8 ma which is consistent with previously reported hydrothermal biotite 40ar 39ar age of 121 1 0 6 ma molybdenite re os ages of 121 2 0 6 and 119 0 1 4 ma and gp 1 and 2 zircon u pb ages of 121 5 1 5 120 2 1 0 ma la icp ms results and 118 7 0 9 ma sims result phase 3 gp 3 yields a ca id tims zircon u pb age of 119 9 0 2 ma which constrains the age of porphyry magmatic hydrothermal events the porphyry system was then unroofed weathered and superimposed by discrete stages of advanced argillic alteration and high sulfidation mineralization two pulses of alunite events yield 40ar 39ar ages of 116 3 0 8 ma and 111 7 1 0 ma which represent the principal epithermal alteration and mineralization ages at tiegelongnan the first alunite pulse age is consistent with younger porphyry gp4 age of 116 2 0 4 ma zircon la icp ms age weathering and exhumation of the porphyry epithermal deposit were continuing until the cover of andesite at 110 ma and by post andesite gravel the andesite was affected by a younger weak hydrothermal alteration at 108 7 0 7 ma constrained by a muscovite 40ar 39ar age another barren alunite yields a 40ar 39ar age of 100 6 2 0 ma which may represent the youngest hydrothermal event the long life span discrete hydrothermal activities from 120 to 100 ma in the tiegelongnan deposit is consistent with the long lasting tectonic magmatic events of the bangong nujiang suture zone the discrete epithermal mineralization events at tiegelongan are younger than the porphyry mineralization events which is analogous to several other epithermal deposits worldwide the 10 m y exhumation history at tiegelongan is slower than the typical and rapid erosion history of 1 2 m y porphyry deposits in low altitude tropical climates regions and during a specific abrupt uplift pulse in the andean region the slow exhumation at tiegelongnan is interpreted to be an integrated result of an arid climate environment relatively flat topography and a slow uplift condition during cretaceous in central western tibet

the ichnogenus rhizocorallium classification trace makers palaeoenvironments and evolution rhizocorallium is one of the oldest known trace fossils with wide distribution through the phanerozoic and all over the world originally introduced from the epicontinental triassic of central germany its high morphological lability gave reason for the subsequent erection of about twenty ichnospecies the study of newly collected material from the type area and many specimens from various collections permits the conclusion that rhizocorallium jenense and rhizocorallium commune are the only valid ichnospecies of rhizocorallium the type ichnospecies r jenense is a comparatively small inclined and heavily scratched firmground burrow with passive fill while r commune consists of extensive more or less horizontal burrows with occasionally scratched marginal tubes and an actively filled spreite between the tubes the faecal pellets coprulus oblongus are typically associated with r commune morphological variations of r commune are captured in ichnosubspecies and varieties of this ichnospecies and can aid a refined reconstruction of palaeoenvironments a review of more than 180 records from the literature reveals the common confusion of both ichnospecies which has consequences for the application of rhizocorallium in facies interpretations the end members of both ichnospecies may be linked by transitional forms which suggests the same kind of trace maker polychaetes are the most likely producers of marine rhizocorallium based on their long ranging occurrence morphological features appearance of faecal pellets associated soft body remains and modern analogues r commune occurs from early cambrian to holocene while r jenense just appears after the end permian mass extinction probably as a consequence of an adapted firmground burrowing lifestyle of its producer fluvial r jenense are probably produced by mayfly larvae in homology to marine polychaete burrows a consequent application of the newly established classification scheme allows for a more rigorous application of rhizocorallium in the reconstruction of palaeoenvironments thus palaeozoic and mesozoic r commune are restricted to the cruziana ichnofacies of shallow marine environments while in cenozoic time similar forms are also found in deep marine deposits r jenense on the other hand is a constituent of the widespread glossifungites ichnofacies and aside from continental environments occurs in peritidal to deep marine deposits several studies have demonstrated the value of rhizocorallium for interpreting sequence stratigraphical surfaces current directions and fluctuations in salinity and oxygen

earth s copper resources estimated from tectonic diffusion of porphyry copper deposits improved estimates of global mineral endowments are relevant to issues ranging from strategic planning to global geochemical cycling we have used a time space model for the tectonic migration of porphyry copper deposits vertically through the crust to calculate earth s endowment of copper in mineral deposits the model relies only on knowledge of numbers and ages of porphyry copper deposits earth s most widespread and important source of copper in order to estimate numbers of eroded and preserved deposits in the crust model results indicate that 125 895 porphyry copper deposits were formed during phanerozoic time that only 47 789 of these remain at various crustal depths and that these contain 1 7 1011 tonnes t of copper assuming that other types of copper deposits behave similarly in the crust and have abundances proportional to their current global production yields an estimate of 3 1011 t for total global copper resources at all levels in earth s crust thus 0 25 of the copper in the crust has been concentrated into deposits through phanerozoic time and about two thirds of this has been recycled by uplift and erosion the amount of copper in deposits above 3 3 km a likely limit of future mining could supply current world mine production for 5500 yr thus quantifying the highly unusual and nonrenewable nature of mineral deposits

the role of exhumation in the temporal distribution of ore deposits we show here that the temporal age frequency distribution of ore deposits is controlled largely by exhumation the combination of burial uplift and erosion that exposes subsurface rocks and ore deposits exhumation rates calculated from modal ages and emplacement depths for epithermal porphyry copper and orogenic gold deposits of phanerozoic age are 167 158 and 63 m m y respectively these rates agree with rates estimated for continent scale terranes by numerous independent methods thus the scarcity of precambrian epithermal and porphyry copper deposits is probably due to their removal by exhumation archean and pale oproterozoic orogenic gold deposits are more abundant than indicated by the exhumation record of their phanerozoic counterparts suggesting that the precambrian deposits formed in greater numbers recognition of the pivotal role of exhumation requires that the temporal distribution of ore deposits be corrected for this effect before it can be used as an indicator of large scale changes in earth history

implications for timing of andean uplift from thermal resetting of radiation damaged zircon in the cordillera huayhuash northern peru abstract the cordillera huayhuash is a north south oriented range along the drainage divide of the northern peruvian andes the range has high topography with peaks in excess of 5500 m and the second highest peak in peru nevados yerupaja 6617 m bedrock is dominated by folded mesozoic miogeoclinal rocks unconformably overlain by mid tertiary volcanics intruded by late tertiary granitic rocks and silicic dikes zircon fission track zft and u th he zhe dating of zircons along a west east transect elucidates the thermal evolution of exhumed and uplifted rocks the stability of fission tracks in zircons is a function of single grain radiation damage in samples with grain to grain variability in radiation damage resetting results in variable resetting and multiple age populations low retentive zircons lrzs which have a partly disordered crystalline structure have significant radiation damage and a low temperature of annealing ca 180 200 c high retentive zircons hrzs which are nearly cry

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

tectonism and exhumation in convergent margin orogens insights from ore deposits abstract three widespread and abundant types of ore deposits epithermal silver gold ag au porphyry copper cu and orogenic gold au form by hydrothermal activity during tectonic convergence along continental margins and their preservation provides new insights into rates of those processes that form and destroy ore deposits as well as overlying rock ages for each of the three deposit types define lognormal age frequency distributions that are nearly identical in form but differ in their modal ages epithermal ag au porphyry cu and orogenic au deposits exhibit age modes at 3 11 and 199 ma respectively these ore types form at depths of 0 5 1 9 and 10 km respectively such that modal age increases with depth of ore emplacement qualitatively the dearth of deposits younger than their modal age reflects the fact that ore deposits form at depth within the crust and time is required for exhumation to expose them continued erosion serves to destroy ore bodies giving rise to fewer deposits

dominance of tectonics over climate in himalayan denudation landscape denudation in actively deforming mountain ranges is controlled by a combination of rock uplift and surface runoff induced by precipitation whereas the relative contribution of these factors is important to our understanding of the evolution of orogenic topography no consensus currently exists concerning their respective infl uences to address this question denudation rates at centennial to millennial time scales were deduced from 10be concentrations in detrital sediments derived from 30 small basins 10 600 km2 in an 200 km wide region in central nepal along a northward strike perpendicular transect average denudation rates sharply increase from 0 5 mm yr in the lesser himalayas to 1 mm yr when crossing the physiographic transition and then accelerate to 2 3 mm yr on the southern flank of the high peaks in the greater himalayas despite a more than five fold increase in denudation rate between the southern and northern parts of this transect the corresponding areas display similar precipitation rates the primary parameter that presents a signifi cant co variation with denudation is the long term rockuplift rate that is interpreted to result from the ramp fl at transition along the main himalayan thrust we propose that in this rapidly uplifting mountain range landscapes adjust quickly to changing climatic conditions such that denudation is mainly limited by the rate at which material is pushed upward by tectonic processes and made available for removal by surface processes in this particular context variations in precipitation appear to have only a second order role in modulating the denudation signal that is primarily set by the background rock uplift rate 2014 geological society of america

differential exhumation histories between qulong and xiongcun porphyry copper deposits in the gangdese copper metallogenic belt insights from low temperature thermochronology abstract the qulong and xiongcun porphyry deposits in the gangdese copper molybdenum metallogenic belt gcmb are both giant porphyry deposits they were located in the eastern and the central gcmb about 400 km apart and were generated in the miocene and the jurassic respectively in order to reveal why the two asynchronous deposits could occur in the same metallogenic belt the in situ zircon u pb zircon and apatite fission track zft and aft and apatite u th he ahe dating were conducted their associated exhumation amounts and histories were compared and finally the prospecting significance was evaluated ahe ages of the qulong deposit indicate it underwent an amount of at least 1 3 2 8 km exhumation since 13 8 13 1 ma however aft data and modeling results reveal that the xiongcun deposit experienced two stages of rapid cooling at 20 13 ma and 13 8 ma respectively the temperature decreases from 160 c to 40 c after 20 ma and the corresponding exhumation amount is about 4 6 km integrated the regional thermochronological data exhumation amounts of 4 6 km and

from crucible to graben in 2 3 ma a high resolution geochronological study of porphyry life cycles boyongan bayugo copper gold deposits philippines the boyongan and bayugo porphyry copper gold deposits are part of a belt of gold rich copper deposits in the surigao district of northeast mindanao philippines the detailed age relationships described in this study provide insight into the geologically short life cycles that characterize porphyry formation in dynamic arc environments since their late pliocene emplacement 2 3 2 1 ma shrimp sensitive highresolution ion microprobe u pb zircon dating at depths of 1 2 2 0 km these deposits were exhumed deeply weathered and buried weathering of these deposits led to the development of the world s deepest known porphyry oxidation profile 600 m thick at boyongan and a modest 30 70 m oxidation profile at adjacent bayugo this earlymiddle pleistocene supergene event followed a period of rapid uplift and exhumation in northeast mindanao 2 5 km ma u th he apatite age elevation spectrum subsequent rapid subsidence 0 34 km ma radiocarbon age elevation spectrum and burial of these deposits are attributed to a mid pleistocene shift from transpressional tectonics to the present day transtensional setting in northeast mindanao during this period debris flows volcanic material and fluviolacustrine sediments accumulating in the actively extending mainit graben covered the weathered deposits preserving the supergene profiles beneath 50 500 m of cover this detailed geochronological study documents the geologically short 2 3 ma time scales over which these major intrusion centered mineral deposits evolved from emplacement exhumation deep oxidation and burial highlighting the dynamism of tectonic processes in environments such as the philippine mobile belt 2012 geological society of america

the geology of the darien panama and the late miocene pliocene collision of the panama arc with northwestern south america the geology of the darien province of eastern panama is presented through a new geologic map and detailed biostratigraphic and paleobathymetric analysis of its upper cretaceous to upper miocene sediments the sequence of events inferred from the stratigraphic record includes the collision of the panama arc the southwestern margin of the caribbean plate and south american continent three tectonostratigraphic units underlie the darien region 1 precollisional upper cretaceous eocene crystalline basement rocks of the san blas complex form a series of structurally complex topographic massifs along the northeastern and southwestern margins of the darien province these rocks formed part of a 20 m y submarine volcanic arc developed in a pacific setting distant from the continental margin of northwestern south america the northerly basement rocks are quartz diorites granodiorites and basaltic andesites through dacites to rhyolites indicating the presence of a magmatic arc the southerly basement rocks are an accreted suite of diabase pillow basalt and radiolarian chert deposited at abyssal depths precollisional arc related rocks of eocene to lower miocene age consist of 4000 m of pillow basalts and volcaniclastics and biogenic calcareous and siliceous deep water sediments they consist of the eocene oligocene darien formation the oligocene porcona formation and the lower middle miocene clarita formation postcollisional deposits are mostly coarse to fine grained siliciclastic sedimentary rocks and turbiditic sandstone of upper middle to latest miocene age this 3000 m thick sedimentary sequence is deformed as part of a complexly folded and faulted synclinorium that forms the central chucunaque tuira basin of the darien the sedimentary package reveals general shallowing of the basin from bathyal to inner neritic depths during the 12 8 7 1 ma collision of the panama arc with south america the sediments are divided into the upper middle miocene tapaliza formation the lower upper miocene tuira and membrillo formations the middle upper miocene yaviza formation and the middle to upper miocene chucunaque formation the precollisional open marine units of late cretaceous middle miocene age are separated from the overlying postcollisional sequence of middle to late miocene age by a regional unconformity at 14 8 12 8 ma this unconformity marks the disappearance of radiolarians the changeover of predominantly silica deposition from the atlantic to the pacific the initiation of the uplift of the isthmus of panama and the onset of shallowing upward coarser clastic deposition this pattern is also recorded from the southern limon basin of caribbean costa rica to the atrato basin of northwestern colombia by the middle late miocene neritic depths were widespread throughout the darien region and a regional unconformity suggests completion of the central american arc collision with south america by 7 1 ma no pliocene deposits are recorded from either the darien or the panama canal basin and no sediments younger than 4 8 ma have been identified in the atrato basin of colombia suggesting rapid uplift and extensive emergence of the central american isthmus in the latest miocene northward movement of the eastern segment of the panama arc along a now quiescent panama canal zone fault during eocene oligocene time may have dislocated the pre collision arc since collision the portion west of this fault chorotega block has remained stable without rotation to the east in the darien region compression has been accommodated through formation of a panama microplate with convergent boundaries to the north north panama deformed belt and south south panama deformed belt and suturing with south america along the atrato valley deformation within the microplate has been accommodated in the darien province by several major left lateral strike slip faults that were active until the early pliocene since when the plate has behaved rigidly

quantifying exhumation at the giant pulang porphyry cu au deposit using u pb he dating the triassic pulang porphyry cu au deposit located in the south yidun terrane is the oldest and one of the largest porphyry deposits in the southeastern tibetan plateau the mineralization occurs mostly in the potassic alteration zone of the pulang intrusive complex u pb he triple dating namely apatite u th he zircon u pb and zircon u th he dating together with inverse thermal modeling reveals that the pulang complex was emplaced at a paleodepth of 5 0 to 6 5 km at 215 2 ma the deep level emplacement of the complex coupled with the episodic replenishment of the magma chamber gave rise to the establishment of a prolonged magmatic hydrothermal system at pulang although a range of single grain zircon and apatite u th he ages were obtained on each sample the weighted mean zircon and apatite u th he ages vary systematically with elevation defining a multistage cooling denudation history at pulang specifically three phases of cooling were recognized from inverse thermal modeling including rapid cooling 80 120 c m y in the late triassic moderate cooling 3 5 c m y from the late triassic to early cretaceous and a protracted slow cooling period 50 m y of extremely slow cooling and erosion at pulang could be related to the formation and preservation of a peneplain on the southeastern tibetan plateau since the late cretaceous a relict peneplain thus signifies a favorable tectonic environment for the preservation of ancient porphyry systems worldwide

long term stability of global erosion rates and weathering during late cenozoic cooling reports that the geological record of erosion indicates a fourfold increase in global sedimentation rates during the past 5 million years merited a global explanation explanations offered include an increased rate of mountain formation and global cooling now jane willenbring and friedhelm von blanckenburg reanalyse original data sets and use ocean records of beryllium isotope ratios to obtain an indirect measure of past erosion rates and rock weathering they find no clear evidence either for an increase in global erosion or for a pulse of weathered material in the oceans during the past 12 million years they suggest that cenozoic global cooling must have some other cause and the mountain building that did occur had little effect on erosion or weathering flux globally accelerated uplift and global cooling have been suggested as possible causes for a fourfold increase in global sedimentation rates and by inference in erosion rates or weathering fluxes during the past 5 million years here proxy evidence is provided that indicates stable weathering fluxes in the late cenozoic era it is proposed that processes different from an increase in denudation caused cenozoic global cooling over geologic timescales co2 is emitted from the earth s interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial this balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions1 changes in this balance have been attributed to changes in topographic relief where varying rates of continental rock weathering and erosion1 2 are superimposed on fluctuations in organic carbon burial3 geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation1 2 4 widespread observations of a recent 0 5 myr fourfold increase in global sedimentation rates require a global mechanism to explain them4 5 6 accelerated uplift and global cooling have been given as possible causes2 4 6 7 but because of the links between rates of erosion and the correlated rate of weathering8 9 an increase in the drawdown of co2 that is predicted to follow may be the cause of global climate change instead2 however globally rates of uplift cannot increase everywhere in the way that apparent sedimentation rates do4 10 moreover proxy records of past atmospheric co2 provide no evidence for this large reduction in recent co2 concentrations11 12 here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record13 as evidence we recast the ocean dissolved 10be 9be isotope system as a weathering proxy spanning the past 12 myr ref 14 this proxy indicates stable weathering fluxes during the late cenozoic era the sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean we conclude that processes different from an increase in denudation caused cenozoic global cooling and that global cooling had no profound effect on spatially and temporally averaged weathering rates

constraints on the paleogeographic evolution of the north china craton during the late triassic jurassic abstract this paper reports u pb hf isotopes of detrital zircons from late triassic jurassic sediments in the ordos ningwu and jiyuan basins in the western central north china craton ncc with the aim of constraining the paleogeographic evolution of the ncc during the late triassic jurassic the early late triassic samples have three groups of detrital zircons 238 363 ma 1 5 2 1 ga and 2 2 2 6 ga while the latest late triassic and jurassic samples contain four groups of detrital zircons 154 397 ma 414 511 ma 1 6 2 0 ga and 2 2 2 6 ga the precambrian zircons in the late triassic jurassic samples were sourced from the basement rocks and pre late triassic sediments in the ncc but the initial source for the 238 363 ma zircons in the early late triassic samples is the yinshan yanshan orogenic belt yyob consistent with their negative zircon e hf t values 24 to 2 for the latest late triassic and jurassic samples the initial source for the 414 511 ma zircons with e hf t values of 18 to 9 is the northern qinling orogen nqo and that for the 154 397 ma zircons with e hf t values of 25 to 12 is the yyob and the southeastern central asian orogenic belt caob in combination with previous data of late paleozoic early triassic sediments in the western central ncc and permian jurassic sediments in the eastern ncc this study reveals two shifts in detrital source from the late paleozoic to jurassic in the late permian early triassic the western central ncc received detritus from the yyob southeastern caob and nqo however in the early late triassic detritus from the caob and nqo were sparse in basins located in the western central ncc especially in the yan an area of the ordos basin we interpret such a shift of detrital source as result of the uplift of the eastern ncc in the late triassic in the latest late triassic jurassic the southeastern caob and the nqo restarted to be source regions for basins in the western central ncc as well as for basins in the eastern ncc the second shift in detrital source suggests elevation of the orogens surrounding the ncc and subsidence of the eastern ncc in the jurassic arguing against the presence of a paleo plateau in the eastern ncc at that time it would be subsidence rather than elevation of the eastern ncc in the jurassic due to roll back of the subducted paleo pacific plate and consequent upwelling of asthenospheric mantle

crustal tilting and differential exhumation of gangdese batholith in southern tibet revealed by bedrock pressures abstract the exhumation history of the gangdese batholith southern tibet bears on how magmatism and tectonism interact with surface processes in a long lived magmatic orogen in this study we applied al in hornblende barometry across the eastern gangdese batholith to obtain pluton emplacement pressures our results together with existing bedrock pressure data reveal the regional paleo depth pattern across the gangdese batholith the western part of the batholith near lhasa exposes plutons emplaced at 1 2 kbar whereas the eastern part near nyingchi exposes crust recording pressures typically of 6 12 kbar we coupled pressure data with new and published u pb zircon ages to constrain the exhumation history of the gangdese batholith the results show that since 100 ma the upper crust experienced limited exhumation except a pronounced oligocene miocene pulse in contrast the middle lower crust experienced a complex exhumation and burial history reflecting major tectonic events including the development of continental arc and continent continent collision since ca 10 ma the eastern nyingchi sector experienced fast exhumation total exhumation 40 km which was likely related to the exhumation of the eastern himalayan syntaxis the lhasa sector experienced comparatively limited exhumation total exhumation

lithologic effects on landscape response to base level changes a modeling study in the context of the eastern jura mountains switzerland landscape evolution is a product of the forces that drive geomorphic processes e g tectonics and climate and the resistance to those processes the underlying lithology and structural setting in many landscapes set the resistance to erosion this study uses a modified version of the channel hillslope integrated landscape development child landscape evolution model to determine the effect of a spatially and temporally changing erodibility in a terrain with a complex base level history specifically our focus is to quantify how the effects of variable lithology influence transient base level signals we set up a series of numerical landscape evolution models with increasing levels of complexity based on the lithologic variability and base level history of the jura mountains of northern switzerland the models are consistent with lithology and therewith erodibility playing an important role in the transient evolution of the landscape the results show that the erosion rate history at a location depends on the rock uplift and base level history the range of erodibilities of the different lithologies and the history of the surface geology downstream from the analyzed location near the model boundary the history of erosion is dominated by the base level history the transient wave of incision however is quite variable in the different model runs and depends on the geometric structure of lithology used it is thus important to constrain the spatiotemporal erodibility patterns downstream of any given point of interest to understand the evolution of a landscape subject to variable base level in a quantitative framework

a signature of transience in bedrock river incision rates over timescales of 10 4 10 7 years measured rates of river incision into bedrock are commonly interpreted as proxies for rates of rock uplift see refs 1 and 2 for example and indices of the strength of climatic forcing of erosion over time see refs 3 and 4 for example this approach implicitly assumes that river incision rates are in equilibrium with external forcings over a wide range of timescales here we directly test this assumption by examining the temporal scaling of bedrock river incision from 155 independent measurements of river incision compiled from 14 sites of these sites 11 exhibit a negative power law dependence of bedrock river incision rate on measurement interval a relationship that is apparent over timescales of 10 4 10 7 years and is independent of tectonic and geomorphic setting thus like rates of sediment accumulation rates of river incision into bedrock exhibit non steady state behaviour even over very long measurement intervals non steady state behaviour can be explained by episodic hiatuses in river incision triggered by alluvial deposition if such hiatuses have a heavy tailed length distribution regardless of its cause the dependence of incision rate on measurement interval complicates efforts to infer tectonic or climatic forcing from changes in rates of river incision over time or from comparison of rates computed over different timescales

spatiotemporal trends in erosion rates across a pronounced rainfall gradient examples from the southern central andes abstract the tectonic and climatic boundary conditions of the broken foreland and the orogen interior of the southern central andes of northwestern argentina cause strong contrasts in elevation rainfall and surface process regimes the climatic gradient in this region ranges from the wet windward eastern flanks 2 m yr rainfall to progressively drier western basins and ranges 0 1 m yr bordering the arid altiplano puna plateau in this study we analyze the impact of spatiotemporal climatic gradients on surface erosion first we present 41 new catchment mean erosion rates derived from cosmogenic nuclide inventories to document spatial erosion patterns second we re evaluate paleoclimatic records from the calchaquies basin 66 w 26 s a large intermontane basin bordered by high 4 5 km mountain ranges to demonstrate temporal variations in erosion rates associated with changing climatic boundary conditions during the late pleistocene and holocene three key observations in this region emphasize the importance of climatic parameters on the efficiency of surface processes in space and time 1 first order spatial patterns of erosion rates can be explained by a simple specific stream power ssp approach we explicitly account for discharge by routing high resolution satellite derived rainfall this is important as the steep climatic gradient results in a highly nonlinear relation between drainage area and discharge this relation indicates that erosion rates er scale with er ssp1 4 on cosmogenic nuclide time scales 2 we identify an intrinsic channel slope behavior in different climatic compartments channel slopes in dry areas 0 75 m yr with equal drainage areas thus compensating lower amounts of discharge with steeper slopes 3 erosion rates can vary by an order of magnitude between presently dry 0 05 mm yr and well defined late pleistocene humid 0 5 mm yr conditions within an intermontane basin overall we document a strong climatic impact on erosion rates and channel slopes we suggest that rainfall reaching areas with steeper channel slopes in the orogen interior during wetter climate periods results in intensified sediment mass transport which is primarily responsible for maintaining the balance between surface uplift erosion sediment routing and transient storage in the orogen

mega arrowhead interference patterns in the central part of the yanshan orogenic belt north china abstract the chengde pingquan region is located in the central part of the yanshan orogenic belt yob at daheishan and pingquan in the central yob thrusts and folds of variable trends are displayed in 2 km scale fold interference patterns detailed field mapping was conducted to decipher the geometry of these two superimposed structures map view geometry and stereonet plots for outcrop scale folds indicate that the superimposed structures form arrowhead interference pattern where nw se trending f 1 folds are refolded by later ene wsw f 2 folding after remove the effects of later faulting restored map views of the superimposed structures show that when the f 1 folds have inclined axial surfaces but with no an overturned limb an arrowhead interference pattern here called modified type 2 pattern can form our field data and reinterpretation of the findings of previous studies suggest that five major shortening phases have occurred in the chengde pingquan region the first two phases which formed the superimposed folds occurred earlier than the late triassic d1 and during the late triassic to early jurassic d2 these two phases were followed by three deformation phases that are mainly characterized by thrusting and strike slip faulting which strongly modified the large scale fold interference patterns

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

precisely dating paleozoic kimberlites in the north china craton and hf isotopic constraints on the evolution of the subcontinental lithospheric mantle abstract kimberlite a deep sourced ultramafic potassic rock carries not only diamond but also invaluable mantle xenoliths and or xenocrysts which are important for tracking the evolution of subcontinental lithospheric mantle sclm however it is challenging to accurately determine the emplacement age of kimberlite and its compositions of primary magma because of modifications by crustal and or mantle contamination and post emplacement alteration this paper reports emplacement ages of diamondiferous kimberlites in mengyin and fuxian of the north china craton ncc using three different dating methods for mengyin kimberlite single grain phlogopite rb sr dating yields an isochron age of 485 4 ma u th pb analyses on perovskite give a 238u 206pb age of 480 6 2 9 ma and a 232th 208pb age of 478 9 3 9 ma and baddeleyite yields a 207pb 206pb age of 480 4 3 9 ma for fuxian kimberlite baddeleyite gives a 207pb 206pb age of 479 6 3 9 ma indicating that the paleozoic kimberlites in the ncc were emplaced at 480 ma numerous lines of evidence indicate that the studied baddeleyites are xenocrysts from the sclm and can be used to constrain hf isotope compositions ehf t 6 of the sclm when kimberlite erupted combined with data from mesozoic cenozoic mantle derived rocks and xenoliths the hf isotope evolution trend of the sclm beneath ncc before craton destruction was tentatively constructed which suggested that the archean slcm was enriched by metasomatism at 1 3 ga further hf isotope investigations on additional sclm derived materials could be used to compare with the constructed hf isotope evolution trend before craton destruction to determine when lithospheric thinning occurred

impacts of cenozoic global cooling surface uplift and an inland seaway on south american paleoclimate and precipitation δ18o stable isotope records of precipitation 18 o 18 o prec have been used as paleoclimate and paleoelevation archives of orogens however interpretation of these records is limited by knowledge of how 18 o prec responds to changes in global and regional climate during mountain building events in this study the influence of atmospheric co 2 levels the extent of the antarctic ice sheet changes in andean surface elevation and the presence of the south american inland seaway on climate and 18 o prec in south america are quantified using the genesis v3 atmospheric general circulation model with isotope tracking capabilities results are presented in the context of cenozoic south american climate and 18 o prec changes more specifically we find 1 precipitation rates in the andes are sensitive to andean surface elevation the seaway and to a lesser extent co 2 levels increasing andean elevations and the presence of a seaway both cause large increases in precipitation but in different parts of the andes the growth of the antarctic ice sheet is found to have a small influence on south american precipitation 2 the stable isotopic composition of precipitation is sensitive to all of the parameters investigated an increase in 18 o prec of up to 8 is found in simulations with higher atmospheric co 2 in agreement with previous studies 18 o prec decreases with increasing andean elevation by an amount greater than that predicted by the modern adiabatic lapse rate furthermore the presence of an inland seaway causes a decrease in 18 o prec of 1 8 in the northern and central andes the amount of depletion is dependent on the isotopic composition of the seaway simulations without the antarctic ice sheet result in 18 o prec that is 0 3 lower than the modern finally time specific simulations for the miocene and eocene show that 18 o prec has decreased during the cenozoic and that local geographical gradients of 18 o prec have increased particularly in regions of high modern elevation we demonstrate that in addition to andean uplift and associated climate change co 2 levels and an inland seaway are likely to have influenced 18 o carb records from south america consideration of these global and paleogeographic changes is necessary when interpreting paleoclimate or paleoelevation from stable isotope records of 18 o prec

hydrothermal fluid evolution at the tiegelongnan porphyry epithermal cu au deposit tibet china constraints from h and o stable isotope and in situ s isotope abstract the tiegelongnan porphyry epithermal cu au deposit is located in the duolong porphyry district north of the bangong nujiang suture zone tibet china mineralization is hosted by jurassic sedimentary sandstone and several phases of diorite and granodiorite porphyry dikes intruded between 123 and 116 ma the hydrothermal alteration is characterized by alunite kaolinite dickite overprinting quartz muscovite pyrite and biotite alteration zones porphyry chalcopyrite pyrite molybdenite stage 1 mineralization is associated with biotite alteration porphyry chalcopyrite bornite stage 2 and covellite stage 3 mineralization is associated with quartz muscovite pyrite alteration formed at 121 ma epithermal mineralization consisting of pyrite alunite stage 4 chalcopyrite bornite digenite stage 5 and tennantite enargite stage 6 is hosted by two pulses of alunite kaolinite breccia and veins at 116 ma and 112 ma the fluid composition related to muscovite with average 18o of 8 9 and d of 56 indicates a magmatic water origin fluid 18o composition in equilibrium with quartz veins decreases from 6 7 to 2 3 which are likely the results of the water rock isotopic exchange quartz fluid inclusions d values between 50 to 84 are partly lower than that obtained from muscovite alteration fluids which may result from h fractionation during fluid inclusions decrepitation epithermal stage fluid composition equilibrium with alunite yield 18o from 1 2 to 2 7 and d from 71 to 51 n 11 which is comparable to the fluid composition equilibrium with type kaolinite hosting ores with 18o between 2 5 and 2 9 and d between 72 and 51 it suggests that alunite and type kaolinite formed with mixing between magmatic and high altitude cretaceous meteoric water late types and iii kaolinite filling alunite and quartz veins fluid 18o and d values plot along a mixing line between magmatic and low altitude cretaceous meteoric water probably following the erosion and plateau subsidence porphyry mineralization sulfide stage 1 chalcopyrite and pyrite yield 34s values between 5 8 and 0 9 with an average fluid 34sh2s 2 5 n 10 whereas stage 2 chalcopyrite returns 34s values from 8 7 to 3 with an average 34sh2s 5 6 n 5 the lower fluid 34sh2s values during sulfides stage 2 compared to that of stage 1 suggest that the chalcopyrite bornite mineralization formed under higher oxidation conditions than that of the chalcopyrite pyrite mineralization alunite yields 34s values from 11 to 18 3 n 8 and the associated sulfide stage 4 pyrite have varying 34s values from 32 2 to 5 4 disequilibrium s isotope in alunite pyrite pairs was likely because of rapid cooling and retrograde s isotope exchange during later sulfides emplacement epithermal mineralization sulfide stage 4 s equilibrated pyrite 14 9 to 9 5 stage 5 chalcopyrite 11 6 to 8 2 and stage 6 enargite 5 4 to 2 6 display increasing 34s values suggesting epithermal fluid compositions evolve towards more reducing conditions

a climate signal in exhumation patterns revealed by porphyry copper deposits porphyry copper deposits are emplaced at a fixed crustal depth in convergent tectonic settings the age and distribution of deposits exposed at the surface suggest that mountain exhumation is influenced by precipitation rates

oligocene miocene age of aridity in the atacama desert revealed by exposure dating of erosion sensitive landforms the age of onset of hyperaridity in the atacama desert chile which is needed to validate geological and climatological concepts has been heretofore uncertain measurement of cosmogenic 21 ne in clasts from erosion sensitive sediment surfaces in northern chile shows that these surfaces have been barely affected by erosion since 25 ma surface exposure ages of sediment clasts give replicate values at 25 20 and 14 ma and individual values at 37 and 9 ma predominantly hyperarid conditions are required to preserve these oldest continuously exposed surfaces on earth our findings are compatible with the hypothesis that the onset of aridity in the atacama desert could be the reason for rather than the consequence of uplift of the high andes

geomorphology rain revs the crustal conveyor it is intuitive but evidence that high levels of precipitation increase erosion rates has been elusive the ages of exposed porphyry copper deposits reveal that rocks emplaced at depth travel to the surface faster where precipitation rates are high

oblique closure of the northeastern paleo tethys in central china a branch of the paleo tethys ocean once separated the north china plate from the south china plate however the mode of closure of the northeastern paleo tethys ocean during the late paleozoic to early mesozoic has been debated one reason for this debate is that the collisional suture zone was later buried by large scale thrust faults in the southern qinling dabieshan orogen which made it difficult to reconstruct the amalgamation of the supercontinent in central china new regional geologic mapping provides stratigraphic and structural constraints on the mechanism of this ocean closure our results indicate that dextral transpressional suturing in the southern qinling dabieshan foreland fold thrust belt resulted in the formation of the northern yangtze foreland basin where the stratigraphy precisely shows the time transgressive closure of the ocean and the orogenic sediments shed over 1000 km westward from eastern china to the closing paleo tethys therefore we propose an oblique subduction model to describe the closure of the paleo tethys ocean our findings suggest that prolonged slab pull during the oblique subduction of the oceanic plate continued to drive deep continental subduction thereby forming high and ultrahigh pressure metamorphic rocks and leading to sustained ocean closure

climatic control of bedrock river incision bedrock river incision drives the development of much of earth s surface topography and thereby shapes the structure of mountain belts and modulates earth s habitability through its effects on soil erosion nutrient fluxes and global climate although it has long been expected that river incision rates should depend strongly on precipitation rates quantifying the effects of precipitation rates on bedrock river incision rates has proved difficult partly because river incision rates are difficult to measure and partly because non climatic factors can obscure climatic effects at sites where river incision rates have been measured here we present measurements of river incision rates across one of earth s steepest rainfall gradients which show that precipitation rates do indeed influence long term bedrock river incision rates we apply a widely used empirical law for bedrock river incision to a series of rivers on the hawaiian island of kaua i where mean annual precipitation ranges from 0 5 metres to 9 5 metres ref 12 over 70 per cent of the global range and river incision rates averaged over millions of years can be inferred from the depth of river canyons and the age of the volcanic bedrock both a time averaged analysis and numerical modelling of transient river incision reveal that the long term efficiency of bedrock river incision across kaua i is positively correlated with upstream averaged mean annual precipitation rates we provide theoretical context for this result by demonstrating that our measurements are consistent with a linear dependence of river incision rates on stream power the rate of energy expenditure by the flow on the riverbed these observations provide rare empirical evidence for the long proposed coupling between climate and river incision suggesting that previously proposed feedbacks among topography climate and tectonics may occur