emeishan basalts sw china reappraisal of the formation s type area stratigraphy and a discussion of its significance as a large igneous province the late permian emeishan basalt formation of sw china is one of earth s lips large igneous provinces yet its basic geology remains poorly documented recent work on sections close to the type area in sichuan province enable us in part to rectify this descriptions of the formation and associated units at two areas one on the lower flanks of mt emei and another from a series of outcrops in ebian county 50 70 km to the sw are presented the basalt pile is 180 270 m thick and in both areas comprises 12 flows that were erupted in relatively quick succession it rests conformably upon shallow marine limestones lignites suggesting emplacement close to sea level the upper half of the youngest basalt was intensively weathered but not eroded prior to it being conformably succeeded by complex body of rocks c 30 m thick that includes thin basalts pyroclastic rocks tuffs and organic rich terrestrial sediments this unit which has previously been described as a sedimentary package presumably because intense weathering has obscured the primary lithological fabric in key outcrops is considered to mark the volcanic waning phase uppermost permian and triassic terrestrial sediments conformably overlie the terminal volcanic rocks the sub regional stratigraphy is compared as best it can be with that described from two sections 400 km to the se one section matches reasonably well the other does not indicating that regional correlations need to be developed carefully the information is discussed in the context of lip generator models several key features of the emeishan basalt terrain are at odds with those commonly encountered in lip s the most important conclusion is that the unit marks a prematurely terminated system in which full bloodied rifting leading to the development of an ocean basin never started

surface subsidence caused by mantle plumes and volcanic loading in large igneous provinces abstract large igneous provinces form with massive flood basalts being erupted over a large region within a few million years a prevailing model for their formation is a mantle plume model in which a plume head originates from the core mantle boundary ascends through the mantle and produces topographic uplift and eventually massive melting at the surface however many geological observations indicate surface subsidence in the central region before or during flood basalt eruptions in this study we demonstrate that a plume head temporarily ponding below the 660 km phase change boundary causes significant subsidence at the earth s surface over an extended period before the eruption and that the loading from erupted basalts causes surface subsidence at the periphery of the eruption area that affects the environment for subsequent episodes of basalt eruptions our studies therefore demonstrate that the observed subsidence history in many flood basalt provinces is characteristic of the dynamics of mantle plumes and may be used as diagnostics for identifying plume induced flood basalt events

facies analysis and sea level change at the guadalupian lopingian global stratotype laibin south china and its bearing on the end guadalupian mass extinction abstract the guadalupian lopingian boundary stratotype at penglaitan and the nearby tieqiao section near laibin south china record a series of major environmental changes within the jiangnan basin during a mid permian biotic crisis the sequence stratigraphic petrographic and palaeontological record of these sections has been studied and the associated strontium isotopic fluctuations have been assayed mass extinction of fusulinid foraminifers is most clearly associated in time with onset of volcanism and a relative sea level fall that led to the establishment of mid ramp conditions laibin limestone in settings that were previously dominated by radiolarian mudstones the regression also coincides with a low point of 87 sr 86 sr ratios the lowstand deposits contain mafic scoriaceous grains that record pyroclastic volcanism probably centred in the emeishan flood basalt province 800 km to the west of laibin thus unusually violent eruptions associated with flood basalts in this province may have contributed to the environmental stresses responsible for the extinction event subsequent environmental changes included transgression spread of dysoxic waters indicated by populations of small pyrite framboids and a major negative c isotope excursion all these phenomena have been previously related to the end guadalupian extinction but they in fact post date the crisis because a post extinction fauna of foraminifers is encountered at this time

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

sedimentation and lithofacies paleogeography in southwestern china before and after the emeishan flood volcanism new insights into surface response to mantle plume activity abstract investigations into permian sedimentation and reconstruction of paleogeography in sw china are aimed at characterizing sedimentary responses to the emeishan mantle plume in addition to erosional features on the sediments underlying the uplifted emeishan basalts unusual depositions of permian age are also present in the emeishan large igneous province lip specifically carbonate gravity flows and submarine incised canyon fillings were developed in the western margin of the postulated uplifted area and rifting trenches were developed along the eastern margin alluvial fan deposits occur at the boundary between the inner and intermediate zones these depositions all rest on the maokou formation and are in turn covered by the emeishan basalts implying synchronism between crustal uplift and depositional events these deposits and the associated extension and normal faulting along the margin of and within the lip represent sedimentary features resulting from dynamic behavior of mantle plume com

sedimentary evidence for a rapid kilometer scale crustal doming prior to the eruption of the emeishan flood basalts biostratigraphic and sedimentologic investigations in 67 sections have been carried out for the middle permian maokou formation that immediately underlies the emeishan flood basalts in southwest china the results suggest a domal crustal thinning before the emplacement of the emeishan large igneous province variably thinned carbonates in the maokou formation are capped by a subaerial unconformity which is generally manifested by karst paleotopography paleoweathering zone or locally by relict gravels and basal conglomerates provenance analysis indicates that these gravels and conglomerates were mainly derived from the uppermost maokou formation therefore the stratigraphic thinning likely resulted from differential erosion due to regional uplift iso thickness contours of the maokou formation delineate a subcircular uplifted area in accordance with the crustal doming caused by a starting mantle plume as predicted by experimental and numerical modeling the duration of this uplift is estimated to be less than 3 myr and the magnitude of uplift is greater than 1000 m the sedimentary records therefore provide independent supporting evidence for the mantle plume initiation model for the generation of the emeishan flood basalts

pre eruptive uplift in the emeishan in their correspondence he and colleagues question our conclusion of little or no uplift preceding emeishan volcanism that we reported in our letter1 debate concerns the nature of the contact between the maokou limestone and emeishan volcanics the depositional environment and volumetric significance of mafic hydromagmatic deposits mhds and evidence for symmetrical domal thinning mhds in the daqiao section are separated from the maokou limestone by 100 m of subaerial basaltic lavas but elsewhere mhds previously interpreted as basal conglomerates2 3 directly overlie the maokou2 3 mhds thus feature strongly in basal sections of the emeishan lava succession as also recently shown4 elsewhere in the emeishan an irregular surface at the top of the maokou limestone has been interpreted as an erosional unconformity2 3 but clastic deposits presented as evidence of this erosion2 3 are mhds produced by explosive magma water interaction1 a clear demonstration that this irregular top surface is an erosional truncation of limestone reef facies slope rim flat lagoonal is currently lacking but is critical because reefs and carbonate platforms show considerable natural relief of tens of metres the persistent hot wet climate since the oligocene has produced well developed weathering profiles on exposed palaeozoic marine sedimentary sequences5 but weathering and karst relief of the uppermost maokou limestone underlying the flood basalts have not been properly documented nor shown to be of middle permian age and immediately preceding emplacement of the large igneous province

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

mafic volcaniclastic deposits in flood basalt provinces a review flood volcanic provinces are assumed generally to consist exclusively of thick lavas and shallow intrusive rocks mostly sills with any pyroclastic rocks limited to silicic compositions however mafic volcaniclastic deposits mvds exist in many provinces and the eruptions that formed such deposits are potentially meaningful in terms of potential atmospheric impacts and links with mass extinctions the province where mvds are the most voluminous the siberian traps is also the one temporally associated with the greatest phanerozoic mass extinction a lot remains to be learned about these deposits and eruptions before a convincing genetic link can be established but as a first step this contribution reviews in some detail the current knowledge on mvds for the provinces in which they are better known i e the north atlantic igneous province including greenland the faeroe islands the british isles and tephra layers in the north sea basin and vicinity the ontong java plateau the ferrar and the karoo we also provide a brief overview of what is known about mvds in other provinces such as the columbia river basalts the afro arabian province the deccan traps the siberian traps the emeishan and an archean example from australia the thickest accumulations of mvds occur in flood basalt provinces where they underlie the lava pile faeroes n1 km ferrar province z400 m siberian traps 700 m in the faeroes case the great thickness of mvds can be attributed to accumulation in a local sedimentary basin but in the ferrar and siberian provinces the deposits are widespread n310 5 km 2 for the latter on the ontong java plateau over 300 m of mvds occur in one drill hole without any overlying lavas where the volcaniclastic deposits are sandwiched between lavas their thickness is much less in most of the cases reviewed primary mvds are predominantly of phreatomagmatic origin as indicated by the clast assemblage generally consisting of basaltic clasts of variable vesicularity dominantly non to poorly vesicular mixed with abundant country rock debris the accidental lithic components often include loose quartz particles derived from poorly consolidated sandstones in underlying sedimentary basins east greenland ferrar karoo these underlying sediments or sedimentary rocks were not only a source for debris but also aquifers that supplied water to fuel phreatomagmatic activity in the

karst development and the distribution of karst drainage systems in dejiang guizhou province china abstract the nature of karstification of two contrasting areas on the north guizhou plateau south china is shown to be controlled by structure lithology geomorphic history and tectonics and causes significant differences to arise in the subsurface drainage systems of the areas the shaqi area lies in a syncline of permo triassic limestones underlain by an insoluble sandy shale which forms the local base level karst landforms are strongly influenced by the presence of four erosion levels corresponding to four periods of rejuvenation of the drainage systems drainage is concentrated along the syncline axis and one system naoshuiyan has been pirating another lengshuiyan by headward retreat cave passages are typically phreatic the dejiang town area lies in an anticline of cambrian dolomite and ordovician limestone three large subsurface drainage systems have developed along parallel faults and have typically vadose cross sections

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

field survey and analysis of hillslopes on tower karst in guilin southern china limestone dissolution in tropical and subtropical humid southern china created residual hills with steep slopes a landform that is referred to as tower karst two types of tower karst landform feature fenglin or peak forest isolated towers and fengcong or peak cluster linked base towers were identified in guilin previous studies proposed two hypotheses regarding their origin and evolution one is the sequential evolution model from peak cluster to peak forest the other is a parallel development model which postulates that both peak cluster and peak forest have developed simultaneously through detailed field survey and analysis of slope forms on tower karst in guilin it was found that the mean slope angle of the towers is very high 62 4 and ranges from 60 to 75 there is no significant difference in mean slope angle and slope angle distribution between towers in the peak cluster basin and peak forest floodplain areas mean slope angle increases with intensified fluvial dissection three levels of caves in the towers of the peak forest in guilin were identified in previous research the isolated towers of the peak forest as well as scattered residuals of peak cluster are generally distributed in the centre of the guilin syncline favourable circumstances of allogenic water concentration indicate that development of the peak forest resulted from the combined effects of subcutaneous and subterranean dissolution as well as subsequent collapse and recession by fluvial erosion after uplifting by contrast peak clusters generally occur on the limbs of the syncline or at the periphery of the guilin basin with relatively higher elevations the thick vadose zone and predominantly vertical flow suggests that peak clusters are mainly formed by the combination of intensive uplifting and the enhancement of original dolines the evidence of slope survey and slope analysis suggests that both isolated towers and linked base towers developed simultaneously but by different mechanisms of formation and different combinations of development processes copyright 2000 john wiley sons ltd

geology and geochemistry of three sedimentary rock hosted disseminated gold deposits in guizhou province people s republic of china abstract five sedimentary rock hosted disseminated gold deposits have been discovered since 1980 in southwestern guizhou province prc submicron sized gold is disseminated in silty carbonate and carbonaceous shale host rocks of permian and triassic age arsenic antimony mercury and thallium accompany the gold associated hydrothermal alteration resulted in decarbonatization of limestone silicification and argillization and depletion of base metals barium and many other elements organic material occurs in most host rocks and ores it was apparently devolatilized during a regional heating event that preceded hydrothermal activity and thus was not mobilized during mineralization and did not affect gold deposition the geologic setting of the guizhou deposits includes many features that are similar to those of sedimentary rock hosted deposits of the great basin western united states the heavy element suite that accompanies gold is the same but base metals are even scarcer in the guizhou deposits than they are in u s deposits the guizhou deposits discovered to date are smaller than most u s deposits and have no known spatially associated igneous rocks

emeishan basalts sw china and the end guadalupian crisis magnetobiostratigraphic constraints abstract a magnetostratigraphic investigation of the permian emeishan lip large igneous province was carried out on a composite section in ebian county close to the type area in sichuan sw china the main succession of twelve flows 175 m thick carries a normal polarity whilst the one reliable site from the overlying 30 m thick volcanic waning sequence is marked by a reverse polarity the data enable a correlation to be proposed with an emeishan basalt sequence in western guizhou c 400 km to the se from our knowledge of the geomagnetic field9s reversal behaviour during the permian it suggests that the main lava pile along the eastern half of the emeishan basalt outcrop belt was erupted within a half to one million years using magnetobiostratigraphic data from the adjacent south china platform the normal polarity magnetozone is correlated with the normal polarity chron associated with the upper part of the maokou limestones constrained by conodont data the main emei basalts appear to be at least two biozones older 1 1 5 ma than the mid late permian boundary it is possible however that the emei basalt waning zone sequence which represents an explosive volcanic phase might be coeval with the end guadalupian biotic crisis thus arguments implicating emei basalt volcanism as the causal mechanism behind this major global event have to accommodate the new relative age constraints

silicic lava dome growth in the 1934 1935 showa iwo jima eruption kikai caldera south of kyushu japan the 1934 1935 showa iwo jima eruption started with a silicic lava extrusion onto the floor of the submarine kikai caldera and ceased with the emergence of a lava dome the central part of the emergent dome consists of lower microcrystalline rhyolite grading upward into finely vesicular lava overlain by coarsely vesicular lava with pumice breccia at the top the lava surface is folded and folds become tighter toward the marginal part of the dome the dome margin is characterized by two zones a fracture zone and a breccia zone the fracture zone is composed of alternating layers of massive lava and welded oxidized breccia the breccia zone is the outermost part of the dome and consists of glassy breccia interpreted to be hyaloclastite the lava dome contains lava with two slightly different chemical compositions the marginal part being more dacitic and the central part more rhyolitic the fold geometry and chemical compositions indicate that the marginal dacite had a slightly higher temperature lower viscosity and lower yield stress than the central rhyolite the high temperature dacite lava began to effuse in the earlier stage from the central crater the front of the dome came in contact with seawater and formed hyaloclastite during the later stage low temperature rhyolite lava effused subaerially as lava was injected into the growing dome the fracture zone was produced by successive fracturing ramping and brecciation of the moving dome front in the marginal part hyaloclastite was ramped above the sea surface by progressive increments of the new lava the central part was folded forming pumice breccia and wrinkles subaerial emplacement of lava was the dominant process during the growth of the showa iwo jima dome

volcanism mass extinction and carbon isotope fluctuations in the middle permian of china the 260 million year old emeishan volcanic province of southwest china overlies and is interbedded with middle permian carbonates that contain a record of the guadalupian mass extinction sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations these show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae the temporal coincidence of these two phenomena supports the idea of a cause and effect relationship the crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean atmosphere carbon cycle

the transition from sedimentation to flood volcanism in the kangerlussuaq basin east greenland basaltic pyroclastic volcanism during initial palaeogene continental break up primary basaltic pyroclastic deposits compose volumetrically c 35 50 of the lower palaeogene vandfaldsdalen mikis and haengefjeldet formations within the lower volcanic series of the east greenland flood basalt province the eruption and emplacement mechanisms of these deposits can be used to evaluate the volcanotectonic evolution of continental break up and initiation of flood basalt volcanism we present a revised stratigraphy for the pre volcanic sedimentary rocks and synvolcanic pyroclastic and epiclastic deposits and lavas from the kangerlussuaq basin east greenland primary basaltic pyroclastic deposits range from airfall tuffs to bomb beds surge deposits and vent sites with cinder cones early volcanism was apparently restricted to localized basins and formed shield volcano structures 30 40 km in diameter that are characterized by a heterogeneous sequence of intercalated hyaloclastites sediments pyroclastic deposits and lavas the lateral variation of deposit morphology reflects distance from source and indicates a migrating locus of volcanism along the axis of rifting towards the ne paired with continued down dropping of inactive volcanic centres the complex stratigraphic architecture of the initial volcanic deposits reflects local tectonic and sedimentary processes interacting with regional flood basalt volcanism and continental rifting

understanding the offshore flood basalt sequence using onshore volcanic facies analogues an example from the faroe shetland basin flood basalts in associated volcanic rifted margins such as the north atlantic igneous province have a significant component of lavas which are preserved in the present day in an offshore setting a close inspection of the internal facies architecture of flood basalts onshore provides a framework to interpret the offshore sequences imaged by remote techniques such as reflection seismology a geological interpretation of the offshore lava sequences in the faroe shetland basin using constraints from onshore analogues such as the faroe islands allows for the identification of a series of lava sequences which have characteristic properties so that they can be grouped these are tabular simple flows compound braided flows and sub aqueously deposited hyaloclastite facies the succession of volcanic rocks calculated in this study has a maximum thickness in excess of 6800 m down to the top of the sub volcanic sediments the offshore volcanic succession has a thickness of about 2700 m where it can be clearly identified across much of the area with a further 2700 m or more of volcanic rock estimated from the combined gravity and seismic modelling to the north and west of the region a large palaeo waterbody is identified on the basis of a hyaloclastite front apron consisting of a series of clinoforms prograding towards the eastern part of the basin this body was 500 m deep must have been present at the onset of volcanism into this region and parts of the water body would have been present during the continued stages of volcanism as indicated by the distribution of the hyaloclastite apron

paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism abstract the 260 ma emeishan large igneous province elip in southwest china has previously been demonstrated to provide compelling evidence for pre volcanic crustal doming in support of the mantle plume hypothesis however this has been questioned by ukstins peate and bryan 2008 by showing hydrothermal magmatic activity at the daqiao section to solve this argument a detailed characterization of the contact between the emeishan basalts and the maokou formation was carried out the contact is shown to be an unconformity which is characterized by paleokarst on top of the maokou formation including paleokarst relief sinkholes caves tower karst and its corresponding rocks such as kaolinite bauxite and ferruginous duricrust and collapsed breccias etc this paleokarst unconformity was in turn covered or infilled by the emeishan basalts and tuffs suggesting that uplift and erosion occurred prior to the eruption of the elip the extent of erosion of the maokou formation indicates the elip can be divided into three roughly concentric zones the inner intermediate and outer zones the paleokarst features on the top of maokou formation vary across the elip in the inner zone a likely sinkhole and an incision valley with 450 m relief in height are found in the intermediate zone various paleokarst landforms such as karst relief sinkholes and tower karsts are well developed some sinkholes that developed in the qixia formation below the maokou formation imply that the paleorelief is more than 350 m in height in the outer zone the paleokarstic surface is a paleo weathering layer with minor karstification and development of caves at 10 50 m this spatial variation of the paleokarst reflects variation of uplift height across the elip the extent of minimal uplift is estimated to be at least 450 m in the inner zone 350 m in the intermediate zone whereas uplift is minor tens 50 m in the outer zone the magnitude and shape of the uplift is roughly consistent with that predicted by mantle plume models the paleokarst was formed after the deposition of the maokou formation and the eruption of the emeishan basalts at the end guadalupian and indicates a short duration of uplift thus this study lends further support to domal uplift prior to the emeishan flood volcanism but also to the mantle plume initiation model for the generation of the elip

comment on paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism a department of geoscience 121 trowbridge hall university of iowa iowa city ia 52242 usa b biogeoscience queensland university of technology brisbane queensland 4001 australia c department of earth and environment university of leeds leeds ls2 9jt uk d dougalearth ltd 12 nevilles cross villas durham dh1 4jr uk e department of earth sciences university of hong kong pokfulam road hong kong china

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

re evaluating plume induced uplift in the emeishan large igneous province numerical and fluid dynamic modelling predicts that mantle plumes should generate a broad domal uplift 1 000 km wide 500 to 1 000 m high preceding volcanism in large igneous provinces the emeishan large igneous province southwest china has been offered as the best example of plume induced uplift where kilometre scale pre and syn volcanic relief was interpreted to develop in response to the impingement of a plume head here we document voluminous mafic hydromagmatic deposits and submarine extrusions that formed during the initiation and early stages of the emeishan large igneous province these deposits were previously interpreted to be alluvial fan sediments shed from a pre volcanic domal high the abundance of such deposits consisting of variable proportions of marine limestone and basaltic fragments strongly suggests that the bulk of this province was emplaced at sea level evidence for dynamic pre volcanic uplift as predicted by plume models is lacking and such a lack may be the more general case any positive relief that developed was more likely the result of the formation of a volcanic edifice and rapid accumulation of the volcanic pile thick alluvial fan sediments from the core of the emeishan large igneous province have been considered as critical field evidence in support of plume induced pre volcanic doming and uplift these sediments are now reinterpreted as mafic hydromagmatic deposits emplaced at sea level precluding dynamic pre volcanic uplift as predicted by mantle plume models

nanograin formation and reaction induced fracturing due to decarbonation implications for the microstructures of fault mirrors abstract principal slip zones often contain highly reflective surfaces referred to as fault mirrors shown to consist of a nanogranular coating there is currently no consensus on how the nanograins form or why they survive weathering on a geological time scale to simplify the complex system of a natural fault zone where slip and heat generation are inherently coupled we investigated the effect of elevated temperatures on carbonate rock surfaces as well as their resistance to water exposure this allows us to isolate the role of the decarbonation process in the formation of nanograins we used cleaved crystals of iceland spar calcite manually polished dolomite protolith as well as natural dolomite fault mirror surfaces the samples were heated to 200 800 c in a 5 h heating cycle followed by slow cooling 12 h to room temperature subsequently we imaged the samples using scanning electron microscopy and atomic force microscopy nanograin formation on all sample surfaces was pervasive at and above 600 c the foiana fault mirror samples were initially coated with aligned naturally formed nanograins but display a non directional nanogranular coating after heating the nanograins that were formed by heating rapidly recrystallized to bladed hydroxides upon exposure to deionized water whereas the nanograins on unheated fault mirror samples remained unchanged in water this shows that the nanograins formed by heating alone are different from those formed in fault zones and calls for a better characterization of nanograins and their formation mechanisms furthermore we find a characteristic star shaped crack pattern associated with reacted regions of the carbonate surfaces the existence of this pattern implies that the mechanical stresses set up by the decarbonation reaction can be sufficiently large to drive fracturing in these systems we propose that this mechanism may contribute to grain size reduction in fault zones