terrigenous sediment supply in the scotia sea southern ocean response to late quaternary ice dynamics in patagonia and on the antarctic peninsula geochemical and mineralogical compositions of modern and late quaternary marine sediments from the scotia sea trace sources and transport paths of terrigenous sediment we discuss downcore variations of compositional data of two sediment cores from the northern and southern scotia sea that correlate with fluctuations in magnetic susceptibility sediments were derived from very different sources at both localities as revealed by contrasting clay mineral assemblages however a common feature is the input of more basic and undifferentiated crustal material with the potential of high magnetic susceptibility during glacial periods indicated by variable quartz feldspar ratios and major trace and rare earth elements terrigenous sediments mainly originate from nearby terrestrial sources or are introduced through interbasinal sediment transfer from adjacent seas the observed temporal compositional variations have to be attributed to changes in the relative detrital contributions from the diverse source areas ice mass extensions in southern patagonia on the antarctic peninsula and adjacent islands likely control the supply of glaciogenic detritus to the open ocean during times of glacial expansion diluting the sediment input of interbasinal origin current transport is mainly responsible for sediment dispersal to the pelagic scotia sea and may amplify the glaciological source signals during glacial climate periods because of a stronger wind forcing of the antarctic circumpolar current

a mid cretaceous age for the palmer land event antarctic peninsula implications for terrane accretion timing and gondwana palaeolatitudes new structural and age data suggest that west gondwana may have been at lower palaeolatitudes than previously interpreted from albian sequences in gondwana marginal suspect terranes the palmer land event which juxtaposed mesozoic terranes on the gondwana margin deformed granitoids in the southern antarctic peninsula u pb shrimp dating of zircons from a microgranite dyke yields a crystallization age of 106 9 1 1 ma this result and re interpretation of the structural position of another granite pluton date the palmer land event and probable terrane collision as late early cretaceous and not latest jurassic as formerly interpreted

interpretation of new aeromagnetic anomaly data from the central antarctic peninsula new high resolution aeromagnetic anomaly data from the central antarctic peninsula reveal a magnetic signature typical of a magmatic arc system analysis of the new aeromagnetic map together with susceptibility data and 2 5 dimensional modelling support the interpretation of the pacific margin anomaly as reflecting a mid crustal batholithic province consisting of magnetite rich plutons examination and analysis of the magnetic anomaly map shows variations in magnetic character along the antarctic peninsula these variations in conjunction with geological and other geophysical data sets are interpreted as indicating distinct segments of continental crust of particular importance is the identification of three distinct areas of basement on the eastern side of the antarctic peninsula of which the central area 66 s to 68 appears to be gneissic basement at a relatively high crustal level to the north of 66 s the basement is formed of late palaeozoic triassic accretionary material and to the south of 68 s the basement is unknown segmentation is a common feature of arcs worldwide and previous studies of the antarctic peninsula have linked the continental segmentation to the arrival of a series of ridge crests at the subducting pacific margin this study indicates that the major segmentation of the continental crust is linked to the pre cretaceous crustal structure of the peninsula which was subsequently modified by extension during the cenozoic it is suggested that this cenozoic extension was caused by a reduction in plate convergence rates at two distinct times rather than the arrival of ridge segments at the trench as previously proposed

circum pacific mid cretaceous deformation and uplift a superplume related event evidence of short lived episodes of mid cretaceous deformation metamorphism uplift and hiatus in sedimentation is widespread in the lower cretaceous rocks that bordered the cretaceous pacific basin i present a model in which these coeval but widely spaced events are linked to increased ridge push force at subduction zones triggered by large scale upwelling of mantle associated with the mid cretaceous superplume this model can account for mid cretaceous terrane accretion and ophiolite obduction events and can explain brief compressional phases in predominantly extensional orogenies as recognized in alaska british columbia california western south america and west antarctica

a plate tectonic mechanism for methane hydrate release along subduction zones negative carbon isotope excursions from a new record of terrestrial organic carbon d 13 corg 2 3x and from marine carbonate d 13 ccarb 0 8x were used to calculate a methane hydrate release of 1137 gt of carbon over 1 myr during the early aptian early cretaceous we show how the coincident and sudden near cessation of subduction along the northern boundaries of the farallon plate resulted in uplift along the continental margin by up to 4 0 km which may have triggered the release we conservatively estimated the amount of methane hydrate carbon likely to have been destabilized during the uplift and found it to be within 20 of the amount of carbon implied by the isotopic records within the same 1 myr time frame linking subduction triggered destabilization with isotopic evidence for methane release reveals a plate tectonic mechanism for the incorporation of methane hydrate release into long term carbon cycling d 2005 elsevier b v all rights reserved

chemistry and microstructures of clay particles in smectite rich shelf sediments south shetland islands antarctica the clay mineralogy of a holocene sediment core from the shelf of livingston island south shetland islands antarctica has been investigated by x ray diffraction xrd lattice imaging bulk chemical analysis of fine clay fractions and analytical transmission electron microscopy atem the clay minerals identified by xrd of 2 m fraction are smectite 63 chlorite 25 and illite 12 with little downcore variation lattice imaging of clay particles has confirmed the presence of interstratified illite smectite and interstratified chlorite smectite atem of ca saturated samples showed that the smectitic clay particles are rich in k fe and mg k in the smectitic particles is mostly present as a fixed cation in the interlayer confirming the presence of interstratified illite a comparison of the mineralogy of the bedrock soils in the probable source area and the core sediment strongly supports the view that the clay minerals must have originated by glacial erosion physical weathering and reworking of hydrothermally altered volcanic bedrock and tephra of the south shetland islands

significance of clay mineral assemblages in the antarctic ocean abstract typical examples from different morphological and geological settings in the antarctic ocean are reviewed in order to discuss the value of clay mineral assemblages for reconstructing the glacial history of antarctica the paleoceanographic history of the antarctic ocean and the sedimentary processes at the antarctic continental margin the significance of clay minerals for paleoenvironmental reconstructions strongly varies with both the position of the sites under investigation and the age of the sediments in late mesozoic to paleogene sediments clay mineral assemblages are sensitive tools for reconstructing climatic conditions for example the shift from smectite dominated assemblages to illite and chlorite dominated assemblages in the earliest oligocene clearly documents the transition from chemical weathering conditions under a warm and humid climate to physical weathering under cooler conditions submarine elevations such as maud rise and kerguelen plateau give the best record for direct paleoclimatic and paleoceanographic studies at the proximal sites of the continental slope and shelf as well as in the deep sea the paleoclimatic information normally is masked by a variety of processes resulting in sediment redistribution at those sites in contrast the clay mineral assemblages bear a wealth of information on different sedimentary processes after the establishment of a continental east antarctic ice sheet physical weathering prevailed variations in the clay mineral records predominantly reflect the influence of different sediment sources resulting from different glacial hydrographic or gravitational transport processes because these sedimentation processes are generally linked to climatic variations the clay mineral assemblages in most of the neogene and quaternary sediments provide indirect paleoclimatic information the processes are best documented in the clay mineral composition in those areas where changes in source regions with distinct petrographic differences are expected and where distances from the source region are low

ophiolite obduction pulses as a proxy indicator of superplume events abstract a major new synthesis of ophiolite geochronology and map of global phanerozoic distribution indicates that previously noted pulses of ophiolite obduction can be linked to superplume related tectonism a marked cyclicity is evident in obduction ages obtained from minerals in ophiolite metamorphic soles and obduction related minor intrusions this episodicity is in phase with periods of predominantly uniform polarity of the geomagnetic field formation of massive carbon rich deposits sea level highstands and formation of large flood basalt provinces all generally considered to be superplume proxy indicators a key to interpreting ophiolite obduction as a further proxy is the mid cretaceous superplume associated ocean margin compressional deformation during this event thermal rejuvenation and increased buoyancy of ocean lithosphere caused arc terrane collision marginal basin shoaling back arc basin closure and ophiolite obduction convergent margins were placed in compression with increased coupling between subducting and overriding plates resulting in major ocean margin deformation being directly datable and tectonically and petrologically distinctive makes ophiolite assemblages of considerable use for identifying superplume events

evidence for a two phase palmer land event from crosscutting structural relationships and emplacement timing of the lassiter coast intrusive suite antarctic peninsula implications for mid cretaceous southern ocean plate configuration 1 new analysis of the relationships between geological structural data and radiometric ages for the lassiter coast intrusive suite indicate that the collisional mid cretaceous palmer land event orogeny in the antarctic peninsula has had two kinematic phases forming an intersection orocline one of which can be related to cretaceous southern ocean plate motions both are compressional phases along the eastern palmer land shear zone phase 1 occurred at 107 ma with a principal paleostrain axis of 341 and is best expressed in southern palmer land although evident elsewhere on the antarctic peninsula phase 2 occurred at 103 ma with a principal paleostrain axis of 259 5 but is confined to between 68 s and 74 s a peak in lassiter coast intrusive suite magma emplacement rate was coeval with phase 1 whereas phase 2 may have coincided with a lull during phase 1 the allochthonous central and western domain terranes may have been transported to the gondwana margin represented by the para autochthonous eastern domain on board the phoenix plate or on board the south american plate the variable provenance indicators from the central and western terranes can be cited to support either or a combination of these scenarios the convergence direction evident from phase 2 structures cannot easily be reproduced in regional plate kinematic models this and the localized evidence for superposition of phase 2 structures on phase 1 structures suggests that phase 2 is unlikely to have occurred solely in response to changes in the kinematics of the large plates considered

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

autochthonous v accreted terrane development of continental margins a revised in situ tectonic history of the antarctic peninsula the allochthonous terrane accretion model previously proposed for the geological development of the antarctic peninsula continental margin arc is reviewed in light of recent data and the geology is reinterpreted as having evolved as an in situ continental arc this is based upon the following factors 1 the presence of early palaeozoic basement and stratigraphic correlation of sequences between the autochthonous and previously proposed allochthonous terranes 2 isotopic evidence for similar deep crustal structure across the different terranes 3 ocean island basalt magmas and deep marine sedimentary rocks formed during continental margin extension within the previously proposed accretionary wedge sequence i e not formed against an active oceanic arc 4 the distribution of magnetic susceptibility measurements and aeromagnetic data locating the palaeo subduction zone along the west of the peninsula 5 a lack of clear palaeomagnetic distinction between the terranes the following alternative tectonic history is proposed 1 amalgamation and persistence of gondwana 2 subsequent silicic large igneous province magmatism and extension 3 development and history of andean subduction until its cessation in the cenozoic a number of features in the antarctic peninsula correlate with those of other circum pacific margins supporting a global evaluation of allochthonous v autochthonous margin development to aid our understanding of crustal growth mechanisms

zircon isotope evidence for recycling of subducted continental crust in post collisional granitoids from the dabie terrane in china 1 recycling of subducted continental crust in continental collision belts is examined by a combined study of zircon u pb dating and o isotope analysis of mineral separates from post collisional granitoids in the dabie terrane east central china although zircon u pb dating give concordant ages of 121 to 131 ma for magma crystallization the occurrence of inherited cores is identified by cl imaging and shrimp dating in some zircon grains that yield older ages of 742 to 815 ma and 222 ma respectively in agreement with neoproterozoic protolith ages of uhp metaigneous rocks and triassic tectono metamorphic event in the dabie sulu orogen all the samples have zircon 18o values of 4 14 to 6 11 most of which differ from the 18o value of 5 3 0 3 for the normal mantle zircon this indicates the remelting of continental crust containing both 18o depleted and enriched components with significant isotope homogenization relative to the uhp metaigneous rocks these observations indicate the involvement of the subducted yangtze plate in the cretaceous granitoids and thus provide evidence for geochemical recycling of the continental crust that was thickened by the triassic collision

episodicity of mesozoic terrane accretion along the pacific margin of gondwana implications for superplume plate interactions a review of evidence for deformation and terrane accretion on the late triassic early jurassic margins of pangea and the mid cretaceous margins of the palaeo pacific ocean shows that deformation was global and synchronous with probable superplume events late triassic early jurassic deformation appears to be concentrated in the period 202 197 ma and was coeval with eruption of the central atlantic magmatic province onset of pangaea break up a period of extended normal magnetic polarity and a major mass extinction event all possible expressions of a superplume event mid cretaceous deformation occurred in two brief periods the first from approximately 116 to 110 ma in the west palaeo pacific and the second from roughly 105 to 99 ma in the east palaeo pacific with both events possibly represented in northeast siberia this deformation was coeval with eruption of major oceanic plateaus core complex formation and rifting of new zealand from gondwana the cretaceous normal polarity epoch and a major radiation of flowering plants and several animal groups all linked with the mid cretaceous superplume event a simple unifying mechanism is presented suggesting that large continental or oceanic plates when impacted by a superplume tend to break up reorganize associated with gravitational spreading away from a broad thermally generated topographic high and with a resulting short lived pulse of plate marginal deformation and terrane accretion

the origin of clay minerals in soils of king george island south shetland islands west antarctica and its implications for the clay mineral compositions of marine sediments abstract clay minerals in the soils of king george island south shetland islands west antarctica were investigated to evaluate their influence upon the composition of marine sediments derived from them paleohydrothermal activity has developed phyllic argillic alteration zones in restricted areas of the volcanic bedrock illite and kaolinite show a highly localized distribution in the soils of the phyllic argillic zones whereas chlorite dominates in the soils of unaltered bedrock the localized distribution indicates that illite and kaolinite are residues from altered bedrock whereas chlorite originates from unaltered bedrock smectite in the soils is rather uniformly distributed with no relationship to the phyllic argillic zones it is mostly the alteration product of eolian pumice shards which are found scattered throughout the soils on a microscopic scale the eolian provenance of smectite associated with pumice shards is supported by a uniform distribution of smectite coexistence of fresh and altered pumice shards and rather short exposure after deglaciation smectites likely have been formed in a remote source around volcanic craters and reworked by repeated eruptions formation of clay minerals by chemical weathering as suggested in previous studies appears to be insignificant on king george island even though the climate is warmer and more humid than in other antarctic regions smectite and kaolinite in seafloor sediments around the south shetland islands do not indicate chemical weathering in the source area instead their occurrence suggests that volcanism igneous intrusion and related hydrothermal alterations were active in the south shetland islands during the cenozoic

coeval blueschist exhumation along thousands of kilometers implications for subduction channel processes we herein focus on understanding what controls the detachment and migration of oceanic crustal slices along subduction zones we provide evidence for the coeval middle to late cretaceous exhumation of oceanic blueschists in the same neotethyan subduction zone across more than 3000 km from depths around 30 40 km over a short time interval similar to 25 ma compared to the duration of subduction 100 ma we stress the importance of such a geodynamic process and suggest that this exhumation was promoted by a regional scale change in the long term interplate mechanical coupling on the basis of geological and geophysical evidence we propose that the upward migration of oceanic fragments in subduction zones is normally inhibited and only occurs discontinuously as the subduction channel opens up in response to a major change in plate geodynamics slab geometry and dynamics mantle wedge and slab hydration or a combination of these

the role of bitumen in strata bound copper deposit formation in the copiapo area northern chile in northern chile between 27 and 33 s there are numerous deposits where residual petroleum is associated with cu ag mineralisation the most famous being el soldado all of these deposits are hosted by lower cretaceous volcanic or volcanoclastic facies along the axis of a former backarc basin this close relationship suggests that the generation migration and emplacement of hydrocarbons in the cretaceous volcanic units is a regional process associated with the evolution of the cretaceous backarc basin and points to the importance of pyrobitumen as an exploration tool for similar cu ag deposits the present work analyses four small strata bound copper deposits located along a north south belt approximately 10 km east of copiapo in northern chile these deposits are typically hosted by pyrobitumen rich andesitic volcanic to volcanoclastic rocks intercalated with the marine carbonate pabellon formation the youngest formation within the chanarcillo group the strong genetic and spatial relationships between the pyrobitumen rich lavas and the mineral deposits allow us to define this volcanic belt as the ocoita pabellon metallotect two hydrothermal events can be distinguished based on the mineralogical textural fluid inclusion and isotope data of ore and gangue and on the optical properties of residual petroleum during the early event petroleum was mobilised from the source rocks into the primary and secondary porosity of the lavas by fe rich hydrothermal fluids which precipitated pyrite as an early sulphide phase the second event is characterised by cu rich hydrothermal fluids which induced three successive sub stages of cu sulphide precipitation the hydrothermal fluids chemically and thermally altered the first stage bitumen transforming it into pyrobitumen the present work documents similarities between the ocoita pabellon metallotect and the el soldado ore deposit and emphasises important differences in the el soldado host rocks a petroleum reservoir existed prior to the arrival of the mineralising hydrothermal fluids the framboidal pyrite was formed by assistance of bacteria the s of the cu sulphides was inherited from the pyrite and the fluid source was basin connate metamorphic brine in the ocoita pabellon metallotect the hydrocarbons were mobilised into the host rocks by hydrothermal fluids the pyrite is epigenetic the 34s values of pyrite and copper sulphides are very different with distinctive light 34s signature of cu sulphides 34s between 44 7 and 17 9 and the calculated 18o of hydrothermal fluids indicates the participation of meteoric water in the late phases of the hydrothermal system

the auriga nunataks shear zone mesozoic transfer faulting and arc deformation in northwest palmer land antarctica the auriga nunataks shear zone places new tectonic and temporal constraints on the mesozoic evolution of west antarctica the shear zone is a long lived arc orthogonal ductile transfer fault that preserves a history of regional mesozoic compressional basement deformation and extensional arc pluton emplacement in the antarctic peninsula magmatic arc it forms an east west trending positive flower structure 2 4 km wide exposed along 5 km of strike marble graphite bearing pyroxene granulite granodiorite diorite amphibolite and gabbro are deformed to mylonite and marble hosted tectonic breccia the mesozoic history of the shear zone is interpreted as follows emplacement of granodiorite diorite at circa 206 ma during early jurassic dextral transtension and metamorphism that peaked at circa 188 ma d1 brecciation of marble and mylonitization of gneiss by late jurassic to early cretaceous sinistral shear during the peninsula wide palmer land orogeny d2 early cretaceous dextral transtension with emplacement of gabbro and garnet leucogranite between 140 and 135 ma d3 and mid cretaceous ocean vergent thrusting and sinistral transpression between 125 ma and 80 ma with a peak at circa 110 ma that folded mylonitized and brecciated preexisting plutonic and metamorphic rocks d4 this is responsible for the current geometry of the shear zone the auriga nunataks shear zone transferred motion between arc parallel compressional and extensional structural elements and by hosting plutons appears to have acted like a leaky transform fault during episodes of regional extension

recent advances in the cretaceous stratigraphy of korea abstract a subrounded accidental zircon grain from a rhyolite sample of the oknyobong formation has shown an u pb chime isochron age 187 ma implying its derivation from a jurassic felsic igneous rock such a lower limit of the geologic age of the oknyobong formation combined with its pre kyongsang upper limit constrains that the oknyobong formation belongs to the jasong synthem late jurassic early early cretaceous typified in north korea the jaeryonggang movement terminated the deposition of the jasong synthem and caused a shift of the depocenter from north korea to the kyongsang basin southeast korea the cretaceous paleocene kyongsang supergroup of the kyongsang basin is the stratotype of the kyongsang synthem an unconformity bounded unit in the korean peninsula the unconformity at the base of the yuchon volcanic group is a local expression of the interregionally recognizable mid albian tectonism it subdivides the kyongsang synthem into the lower kyongsang subsynthem barremian early albian and the upper kyongsang subsynthem late albian paleocene the latter is unconformably overlain by eocene and younger strata the late permian to early jurassic radiolarian fossils from the chert pebbles of the kumidong and the kisadong conglomerates of the aptian early albian hayang group of the kyongsang basin are equivalent with those of the cherts that constitute the jurassic accretionary prisms in japan the provenance of the chert pebbles in the kyongsang basin bimodal volcanisms throughout the history of the kyongsang basin is exemplified by the felsic kusandong tuff erupted abruptly and briefly in the late aptian when semi coeval volcanisms were of intermediate and mafic compositions the mean paleomagnetic direction shown by the kusandong tuff is in good agreement with the early cretaceous directions known from north china south china and siberia blocks

tectonic setting of primitive magmas in volcanic arcs an example from the antarctic peninsula abstract primitive magmas representing mantle partial melts minimally affected by fractionation and assimilation are rare in the magmatic arc environment most examples are either associated with high rates of arc parallel extension or occur along faults and dykes perpendicular to the trend of the arc and related to arc compression in two cases the vanuatu and solomon islands arcs such arc compression is being caused by collision of seamounts in the antarctic peninsula primitive mafic dykes were emplaced perpendicular to the continental arc ar ar and k ar data suggest intrusion of the dykes at c 126 106 ma possibly during mid cretaceous regional compression of the arc the dykes form two compositional groups one group has low la n yb n ratios 0 31 0 49 lower nb yb and higher th nb than n morb age corrected nd values of 7 3 to 7 9 and are interpreted as melts of subduction modified sub arc asthenosphere the other has high la n yb n ratios 3 86 8 92 higher nb yb and th nb than n morb age corrected nd values of 2 8 to 3 4 and are interpreted as melts of sub arc lithosphere the absence of dykes compositionally between these groups suggests that the primitive magmas avoided storage and mixing in magma chambers

mid cretaceous oblique rifting of west antarctica emplacement and rapid cooling of the fosdick mountains migmatite cored gneiss dome abstract in marie byrd land west antarctica the fosdick mountains migmatite cored gneiss dome was exhumed from mid to lower middle crustal depths during the incipient stage of the west antarctic rift system in the mid cretaceous prior to and during exhumation major crustal melting and deformation included transfer and emplacement of voluminous granitic material and numerous intrusions of mantle derived diorite in dikes a succession of melt and magma related structures formed at temperatures in excess of 665 50 c based on ti in zircon thermometry these record a transition from wrench to oblique extensional deformation that culminated in the development of the oblique south fosdick detachment zone solid state fabrics within the detachment zone and overprinting brittle structures record translation of the detachment zone and dome to shallow levels to determine the duration of exhumation and cooling we sampled granite and gneisses at high spatial resolution for u pb zircon geochronology and 40 ar 39 ar hornblende and biotite thermochronology u pb zircon crystallization ages for the youngest granites are 102 ma three hornblende ages are 103 to 100 ma and 12 biotite ages are 101 to 99 ma all overlap within uncertainty the coincidence of zircon crystallization ages with 40 ar 39 ar cooling ages indicates cooling rates 100 c m y that when considered together with overprinting structures indicates rapid exhumation of granite and migmatite from deep to shallow crustal levels within a transcurrent setting orientations of structures and age constrained crosscutting relationships indicate counterclockwise rotation of stretching axes from oblique extension into nearly orthogonal extension with respect to the marie byrd land margin the rotation may be a result of localized extension arising from unroofing and arching of the fosdick dome extensional opening within a pull apart zone or changes in plate boundary configuration the rapid tectonic and temperature evolution of the fosdick mountains dome lends support to recently developed numerical models of crustal flow and cooling in orogenic crust undergoing extension transtension and accords with numerous studies of migmatite cored gneiss domes in transcurrent settings

metamorphosed palaeosols associated with cretaceous fossil forests alexander island antarctica fossil soils are present within mid cretaceous fluvial sediments of the fossil bluff group alexander island antarctica the palaeosols contain in situ fossil trees and rooted plants these palaeosols are typically composed of two dominant horizons an upper organic rich horizon with identifiable plant remains and a lower horizon with well developed blocky ped structures clay cutans and mottling these features are typical of modern soils in seasonally dry climates although evidence of flooding is apparent from interbedded fluvial sandstones and mudstones the palaeosols indicate that this high latitude mid cretaceous environment was predominantly seasonally dry the presence of the zeolites laumontite prehnite and pumpellyite indicates a later metamorphic overprint on the palaeosols resulting from burial diagenesis of this region at depths of about 3 8 5 2 km and temperatures of 150 170 c

characteristics structural styles and tectonic implications of mesozoic cenozoic faults in the eastern heilongjiang basins ne china abstract the eastern heilongjiang basins ehbs are the assemblage of a series of meso cenozoic residual basins located in the northeastern corner of china the deformation pattern of the ehbs has significant implications for the history of the pacific plate subduction beneath the eurasia since the late mesozoic in this paper research on the characteristics and structural styles of the meso cenzoic faults in the ehbs has been conducted on the basis of a comprehensive analysis of field geology drilling data and seismic reflection profiles as a result five different stages of the meso cenozoic faults in the ehbs have been recognized these are in accordance with the time and relevant characteristics of fault movements i e the early stage of the early cretaceous normal fault the early stage of the late cretaceous thrust fault the late stage of the late cretaceous thrust fault the cenozoic synsedimentary normal fault and the late stage cenozoic shear fault a regional geological section has been generated across the ehbs by linking four local seismic profiles together a step by step reconstruction has been made to help better understand the mesozoic cenozoic tectonic evolution of the ehbs two phases of extension rifting in the early cretaceous period and the paleogene respectively are demonstrated to be interfered with two phases of regional uplift compression and erosion in the late cretaceous period the complicated development of multiple fault systems within the ehbs has reflected the evolution of a complex tectonic subduction of the pacific plate beneath the eurasia since the cretaceous period

cretaceous arc volcanism of palmer land antarctic peninsula zircon u pb geochronology geochemistry distribution and field relationships abstract the cretaceous marks an episode of enhanced magmatism sedimentation and tectonic processes along the entire proto pacific convergent margin of west gondwana cretaceous magmatism across the antarctic peninsula is dominated by the intrusive lassiter coast intrusive suite which developed as episodic flare up events during the mid cretaceous at a time of increased convergence volcanic rocks of this age are poorly defined as a consequence of limited field observations and an absence of accurate geochronology recent field mapping combined with unpublished field observations has identified a region 10 000 km2 of dominantly subaerial rhyolitic pyroclastic and epiclastic successions from northern palmer land of the antarctic peninsula volcanic successions up to 1500 m in thickness consist of dominantly silicic ignimbrites lavas heterolithic breccias and lahar deposits fed by caldera forming eruptions the volcanic rocks of this region were widely considered to be early cretaceous in age based on field relationships and early geochronology new u pb zircon ages identify three distinct volcanic episodes during the late cretaceous early cenozoic at 108 ma 93 ma and 64 ma lu hf data indicate significant proportions of ancient crust in the petrogenesis of the volcanic rocks and the slightly negative ehf values are consistent with a mid position 120 km within the magmatic arc relative to more juvenile compositions close to the trench

mesozoic porphyry cu au mineralization and associated adakite like magmatism in the philippines insights from the giant atlas deposit the atlas porphyry cu au deposit is located in central cebu island in the philippines with a proven mineral reserve of 1420 mt at 0 45 cu 0 24 g t au 0 018 g t mo and 1 8 g t ag it is associated with the lutopan quartz diorite porphyry stock that was emplaced into the cretaceous volcano sedimentary sequences of the cansi formation two stages of hypogene alteration have been identified at atlas stage i quartz magnetite chalcopyrite pyrite veins associated with potassic and propylitic alteration and stage ii anhydrite pyrite chalcopyrite specularite veins associated with phyllic alteration supergene gypsum veins are also present mineralization is mainly associated with the stage i and stage ii veins the lutopan quartz diorite porphyry yielded a zircon u pb age of 108 5 1 6 ma and is characterized by high sr y 54 69 with the corresponding magma having high oxygen fugacity avg fmq 2 7 avg ce4 ce3 of zircon 439 and h2o concentrations presence of amphibole and biotite phenocrysts and low magmatic temperatures avg ti in zircon thermometry 706 c the relatively low la yb ratios 9 11 listric shaped normalized ree patterns with weak or absent eu anomalies together with zircon ehf t values of 3 4 to 10 0 whole rock isr values of 0 70373 0 70382 end t values of 2 4 3 4 and mg numbers of 49 53 suggest that the lutopan quartz diorite porphyry was likely derived from partial melting of young lower continental crust or interaction between asthenospheric melts and lower crust melts that evolved to adakite like trace element compositions through amphibole fractionation stage i veins yielded a pyrite re os isochron age of 110 2 5 6 ma making atlas the only mesozoic porphyry deposit discovered in the philippines

glaciomarine sedimentation and its paleoclimatic implications on the antarctic peninsula shelf over the last 15 000 years abstract analyses of sedimentological geochemical and micropaleontological parameters from radiocarbon dated sediment cores retrieved from the antarctic peninsula s western continental shelf reveal a detailed paleoclimatic and or paleoceanographic history over the last 15 000 radiocarbon years deglaciation of the outer shelf off anvers island commenced prior to at least 15 000 yr bp marked by the deposition of distal glaciomarine diamicton facies 2 beneath a floating ice shelf and lasted for 3800 years with increasing diatom abundance and total organic carbon toc over time a return to colder conditions occurred between 12 800 and 11 600 yr bp with a drop in toc content and diatom abundance which is coincident with the younger dryas event in the north atlantic region at this time an abrupt increase in percentage sea ice taxa as well as in the ratio of fragilariopsis curta fragilariopsis cylindrus thalassiosira antarctica suggests renewed ice shelf advance in contrast the inner shelf was deglaciated somewhat later about 11 000 yr bp that is 3000 years after the outer shelf prior to 11 000 yr bp deposition of proximal glaciomarine diamicton facies 1 close to the grounding line under a floating ice shelf and or persistent sea ice may have occurred on the inner shelf after this date deposition of distal glaciomarine diamicton facies 2 followed a climatic optimum is recognized between 6000 and 2500 yr bp coinciding with a mid holocene climatic optimum from several other antarctic sites e g the palmer deep during this time as the glacial system receded from the shelf greatly enhanced primary productivity occurred in open marine conditions resulting in the deposition of diatomaceous mud facies 3 and causing post depositional dissolution of calcareous benthic and planktonic foraminifers in sediment around 2500 yr bp the onset of the neoglacial diatomaceous sandy mud facies 4 characterized by a decrease in toc and diatom abundance reflects the formation of more extensive and seasonally persistent sea ice as evidenced by an increase in percentage of sea ice taxa and in the ratio of f curta f cylindrus t antarctica our results provide evidence of climatic change on the antarctic peninsula s western shelf that helps to refine the existence and timing of late pleistocene and holocene millennial scale climatic events in the southern hemisphere

episodicity within a mid cretaceous magmatic flare up in west antarctica u pb ages of the lassiter coast intrusive suite antarctic peninsula and correlations along the gondwana margin long lived continental margin arcs are characterized by episodes of large volume magmatism or flare ups that can persist for 30 m y before steady state arc conditions resume flare up events ar

cenozoic sedimentation and clay mineralogy in the northern part of the magellan trough central pacific basin abstract assemblages of clay sized minerals in twelve deep sea cores from the northern part of the magellan trough in the central pacific basin clearly show that authigenic smectite together with clinoptilolite formed subsea in situ and predominated throughout palaeogene time clastic clay minerals such as chlorite illite and kaolinite increased at the expense of smectite in sediments deposited since the pliocene most of the authigenic smectites are of the di octahedral iron rich type the most probable origin of the authigenic smectites is formation from precursors such as volcanic glass as part of this process biogenic silica evidently contributed to the formation of smectite and zeolites as clinoptilolite the presence of a tri octahedral saponite and the tem morphology of some smectites on the other hand suggests that not all of the smectite studied was formed subsea in situ but that some had an allogenic origin systematic vertical changes in the assemblage of clay sized minerals suggest that the authigenesis of submarine smectite and clinoptilolite prevailed in conditions of reduced aridity and weak wind activity throughout the palaeogene in the study area however allogenic clay minerals such as chlorite and illite increased since the olduvai event under conditions of severe aridity and strong wind activity caused by global climatic change the west northwest movement of the pacific plate must have partly played a role in deposition of the clastic clay sized minerals from the asian continent by westerlies in the study area the widespread occurrence of cenozoic hiatuses in the study area is attributed to the influence of antarctic bottom water aabw the latter must have influenced non deposition of the clay sized minerals at times during the cenozoic

sequence stratigraphy of the mesozoic domeyko basin northern chile the domeyko basin of northern chile records late triassic to early cretaceous mixed carbonate and siliciclastic marine deposition along the western margin of gondwana sequence stratigraphical analysis has identified five long term sequences of 11 17 ma duration comparison of the relative sea level fluctuations interpreted from the domeyko basin succession with those documented from other similar aged south american marginal basins and northern hemisphere basins allows the distinction of regional from global events relative sea level fall in the early pliensbachian early aalenian and early valanginian and rises in the early hettangian early and late toarcian early and late bajocian late bathonian and early oxfordian of the domeyko basin appear time equivalent to similar events in other southern and northern hemisphere basins and are thus interpreted to be products of global sea level cycles long term relative sea level falls in the early bathonian late oxfordian early valanginian and rise in the late kimmeridgian are interpreted to be tectonically driven continental scale changes in sediment accommodation space the domeyko basin succession thus appears to have been dominantly controlled by global sea level fluctuations during the early to mid jurassic and by continental scale but not global fluctuations during the mid jurassic to mid cretaceous interpreted to have been driven by the fragmentation of gondwana

geodynamic evolution of the antarctic peninsula during mesozoic times and its bearing on weddell sea history this review of the tectonic evolution of the antarctic peninsula during mesozoic times highlights four main events 1 late triassic late jurassic extension 2 late jurassic early cretaceous dextral transpression 3 early cretaceous extension and 4 mid cretaceous compression magmatism was virtually continuous during much of this period with the exception of possible breaks in the known record in early jurassic and late jurassic early cretaceous times the second of these breaks corresponded to the first compressional event there was no apparent hiatus in the magmatic record during the mid cretaceous compressional event although there was a significant change in the pattern of sedimentation in the larsen basin on the eastern margin of the weddell sea at about that time the tectonic evolution of the peninsula is compared to and puts some constraints on existing weddell sea models the late triassic late jurassic arc extension correlates with initial rifting in the weddell sea region during sinistral motion between east and west gondwana however there is no known record of large scale pre mid jurassic transcurrent deformation in the antarctic peninsula that would have been consistent with rotation of west antarctic crustal blocks in the initial rifting period the peninsula wide late jurassic early cretaceous compressional event may correlate with the major change in gondwana plate motions from e w to n s african reference frame separation of east and west gondwana this change probably resulted in formation of an ocean continent boundary along the northern margin of the weddell sea embayment and initial seafloor spreading geological data do not seem to support subduction of southwestern proto weddell sea oceanic lithosphere beneath the eastern margin of the peninsula at that time cretaceous arc extension was coeval with the initial seafloor spreading phase in the weddell sea mid cretaceous arc compression linked to a global increase in ocean floor spreading rates and a superplume event correlates with a change from ne sw to nw se spreading in the weddell sea

clay mineral distribution in surface sediments of the south atlantic sources transport and relation to oceanography abstract surface samples mostly from abyssal sediments of the south atlantic from parts of the equatorial atlantic and of the antarctic ocean were investigated for clay content and clay mineral composition maps of relative clay mineral content were compiled which improve previous maps by showing more details especially at high latitudes large scale relations regarding the origin and transport paths of detrital clay are revealed high smectite concentrations are observed in abyssal regions primarily derived from southernmost south america and from minor sources in southwest africa near submarine volcanoes of the antarctic ocean south sandwich bouvet island smectite contents exhibit distinct maxima which is ascribed to the weathering of altered basalts and volcanic glasses the illite distribution can be subdivided into five major zones including two maxima revealing both south african and antarctic sources a particularly high amount of mg and fe rich illites are observed close to east antarctica they are derived from biotite bearing crystalline rocks and transported to the west by the east antarctic coastal current chiorite and well crystallized dioctaedral illite are typical minerals enriched within the subantarctic and polarfrontal zone but of minor importance off east antarctica kaolinite dominates the clay mineral assemblage at low latitudes where the continental source rocks west africa brazil are mainly affected by intensive chemical weathering surprisingly a slight increase of kaolinite is observed in the enderby basin and near the filchner ronne ice shelf the investigated area can be subdivided into ten large scale clay facies zones with characteristic possible source regions and transport paths clay mineral assemblages of the largest part of the south atlantic especially of the western basins are dominated by chlorite and illite derived from the antarctic peninsula and southernmost south america and supported by advection within the circumantarctic deep water flow in contrast the east antarctic provinces are relatively small assemblages of the eastern basins north of 30 s are strongly influenced by african sources controlled by weathering regimes on land and by a complex interaction of wind river and deep ocean transport the strong gradient in clay mineral composition at the brazilian slope indicate a relatively low contribution of tropically derived assemblages to the western basins

distribution of clay minerals and proxies for productivity in surface sediments of the bellingshausen and amundsen seas west antarctica relation to modern environmental conditions surface sediments from the antarctic continental margin in the bellingshausen and amundsen seas pacific sector of the southern ocean were investigated in order to decipher their capability to record modern environmental conditions spatial distribution of terrigenous sand and mud reflect regional differences in current induced redeposition of glaciogenic debris clay mineral assemblages in the shelf sediments are controlled by the supply of terrigenous detritus from source rocks in the adjacent hinterland suggesting the occurrence of yet unknown sedimentary rocks in the hinterland of the amundsen sea clay mineral distribution on the continental rise in the bellingshausen sea points to the continuation of a bottom current from the antarctic peninsula rise to at least 94 w foraminifer bearing and opal poor deposits prevail on the continental margin in the western bellingshausen sea and the amundsen sea whereas diatom bearing and carbonate free sediments characterize the eastern bellingshausen sea different modes of biological production which were deduced from accumulation rates of biogenic barium during marine isotope stage 1 and recent productivity measurements obviously control the spatial pattern of opal and carbonate bearing sediments in the study area

mid cretaceous ductile deformation on the eastern palmer land shear zone antarctica and implications for timing of mesozoic terrane collision ar ar dating of high strain ductile mylonites of the eastern palmer land shear zone in the southern antarctic peninsula indicates that reverse movement on the shear zone occurred in late early cretaceous times albian and not latest jurassic times as previously supposed the eastern palmer land shear zone forms a major tectonic boundary separating suspect arc terranes from rocks of gondwana continental affinity the dated mylonites are developed in lower jurassic plutonic rocks at mount sullivan eastern palmer land and form part of a zone of ductile reverse deformation up to 25 km wide biotite from a fine grained mafic mylonite yields an ar ar cooling age of 102 8 3 3 ma movement of this age on the eastern palmer land shear zone is coeval with circum pacific deformation possibly related to a mantle superplume event and provides support for allochthonous terrane models for the antarctic peninsula with accretion in post early cretaceous times

paleoceanographic and paleoclimatic evolution in the weddell sea antarctica during the middle eocene late oligocene from a coarse sediment fraction and clay mineral data odp site 689 abstract paleoceanographic and paleoclimatic variations from the middle eocene to the late oligocene in the antarctic area atlantic sector have been deduced from a coarse fraction and clay mineral analysis of odp site 689 leg 113 sediments in the middle eocene smectite rich sediments were a consequence of warm climate with alternating wet and dry seasons on the antarctic margins productivity in the maud rise area of the southern ocean was low no opal was deposited preservation of carbonate is very good carbonate preservation shows cyclic changes clinoptilolite is a common mineral at the middle late eocene boundary 40 8 ma productivity suddenly increased enough to allow preservation of opal skeletons clinoptilolite disappeared where opal appeared illite appearance points to cooling of antarctic climates the presence of detrital kaolinite indicates a change in oceanic circulation in the late eocene cyclic changes in productivity cycle length 0 42 ma were associated with clay mineral compositional variations sediments from colder highly productive periods generally contain more illite and less smectite than warmer ones the early oligocene was a period of very high productivity highest opal accumulation rates correspond to strongest carbonate dissolution cyclic changes in productivity with a mean cycle duration of 0 4 0 5 myr were associated with cyclic changes in clay mineral composition highest productivity intervals are generally those with highest smectite content because of strong erosion of sediments of the antarctic margins sediments from less productive warmer periods most of the time contain more illite in the late oligocene the intensity of physical weathering on antarctica was stronger as documented by increasing fluxes of illite muscovite amphiboles and talc ice expanded on the east antarctic continent lower productivity than in the early oligocene is indicated by lower accumulation rates of opal and weaker carbonate dissolution cyclic variations in productivity correlate to cyclic variations in illite and smectite contents as in the early oligocene

radiolarian stratigraphy and origin of the mesozoic terranes of the continental framework of the northwestern pacific russia abstract tectonostratigraphic investigation shows that the mesozoic triassic neocomian allochthonous terranes of the anadyr koryak accretionary region from the northwestern continental framing of the pacific ocean form isolated tectonic nappes and slices dispersed all over the region rather than fragments undeformed paleostructures nappes and slices of different stratigraphic horizons derived from various geodynamic and paleolatitudinal environments have been tectonically amalgamated into the anadyr koryak region furthermore these tectonostratigraphic units are accompanied by slabs of paleozoic sequences which were also accumulated in various different paleoenvironments correlations of the tectonically separated mesozoic formations are based on the radiolarians and geochemical and lithologic methods the tectonostratigraphic units range from middle triassic to hauterivian and are tectonically arranged in various spatial patterns formations of several different geodynamic environments are recognized oceanic abyssal plain and mor island arcs and marginal basins the radiolarian assemblages suggest that the early mesozoic formations were deposited at different paleolatitudes tethyan anisian sinemurian north tethyan and boreal pliensbachian early bajocian and in a vast zone from the equator to south boreal late bajocian hauterivian early to late mesozoic tectonic paleoenvironments spanned a width greater than 3000 km this zone was later shortened to a width of 300 km the development of nappes and slices of the anadyr koryak region and the koryak west kamchatka orogenic belt on the whole was due to several collisions near the asian continental margin the main collision event occurred in the interval 125 105 ma

change of tectono stratigraphic regime in the australian plate during the 99 ma mid cretaceous and 43 ma mid eocene swerves of the pacific the clockwise bend at 99 ma mid cretaceous in linear volcanic chains in the tropical pacific coincides with a change from pre 99 ma head on chilean type subduction of the pacific plate beneath eastern gondwana to 99 43 ma sinistral oblique mariana type subduction and strike slip breakup by simple sea floor spreading between australia and antarctica and by backarc spreading in the southwest pacific the 99 ma breakup of australia from antarctica is documented by a mid cretaceous unconformity this tectono stratigraphic change founded modern australia with a mountain chain along an upper plate margin in the east and lowlands on the lower plate margin in the south the counterclockwise bend at 43 ma mid eocene the emperor hawaiian bend coincides with the onset of structure in the challenger rift of new zealand the eromanga cooper basin of central australia and the oil shale grabens of coastal queensland

the cretaceous iron belt of northern chile role of oceanic plates a superplume event and a major shear zone the cretaceous constitutes a turning point in the tectonic magmatic and metallogenic history of chile the geological evidence indicates that a major change occurred in late neocomian time when superplume emplacement mid pacific superplume and plate reorganization processes took place in the pacific the superplume event resulted in a major ridge push force resulting in increased coupling between the subducting and overriding plates this completely changed the tectonic setting of chile ending the early cretaceous extensional period aborted rifting in the back arc basin and increasing stress at a crustal scale as a consequence overpressurized dioritic magmas were pushed up mainly along the best possible structural path in northern chile i e the atacama fault zone eventually forming a 500 km long belt of kiruna type iron deposits with reserves of 2 000 mt 60 fe a unique case in chile s geological history

crustal scale fluid circulation and co seismic shallow comb veining along the longest normal fault of the central apennines italy the extensional val roveto fault which is the longest exhumed potentially seismogenic structure of central apennines italy is examined to constrain earthquake related fluid circulation and fluid sources within shallow carbonate hosted faults the study focuses on fault related comb and slip parallel veins that are calcite filled and cut through the principal surface of the val roveto fault we observe multiple crack and seal events characterized by several veining episodes probably related to different slip increments along the fault plane we show that vein calcite precipitated in late pleistocene time below the present day outcrop level at a maximum depth of similar to 350 m and temperatures between 32 and 64 degrees c from meteoric derived fluids modified by reactions with crustal rocks and with a mantle contribution up to similar to 39 the observed warm temperatures are not compatible with a shallow similar to 350 m precipitation depth which in this region is dominated by circulation of cold meteoric water and or shallow groundwater based on structural geochemical data we propose that deep seated crust mantle derived warm fluids were squeezed upward during earthquakes and were hence responsible for calcite precipitation at shallow depths in co seismic comb and slip parallel fractures as comb and slip parallel veins are rather common particularly along seismogenic extensional faults we suggest that further studies are necessary to test whether these veins are often of co seismic origin if so they may become a unique and irreplaceable tool to unravel the seismic history of hazardous active faults

stratigraphy and tectonosedimentary evolution of a late aptian albian carbonate margin the northeastern jebel akhdar sultanate of oman abstract upper aptian albian shallow water carbonates with rudists large foraminifera and calcareous algae are described from northern oman in the northeastern part of the parautochton of jebel akhdar the corresponding lithostratigraphic unit the al hassanat formation is partly a time equivalent of the nahr umr shales of albian p p age which have a wide extent on the arabian craton the al hassanat platform developed in two main phases first during the late aptian early albian the platform was fringing an emerged area central jebel akhdar with a limited extent basinward then during the middle albian the flooding of the central jebel akhdar resulted in an extensive development of the platform and a connection with the nahr umr shelf this sedimentary evolution and its palaeogeographic expressions were mainly controlled by structural patterns extensive uplift and block faulting to the edge of the antecedent early aptian platform with a significant differential subsidence then a sag of the arabian promontory this tectonosedimentary dynamics was related to the migration of the oceanic adjacent tethyan plate and took place during the global geodynamic albian revolution

episodic formation of neotethyan ophiolites tibetan plateau snapshots of abrupt global plate reorganizations during major episodes of supercontinent breakup abstract neotethyan ophiolites along the bangong nujiang and yarlung tsangpo sutures tibetan plateau consist of mantle peridotite cumulates isotropic gabbro diabase plagiogranite and basaltic lava they comprise morb iab oib and boninitic rocks and mostly belong to supra subduction zone ssz type compositionally different rocks crystallized synchronously over a distance of 2000 km along the bangong nujiang and yarlung tsangpo sutures during the short periods of 190 182 and 132 120 ma respectively resembling the izu bonin mariana ibm proto arc the early jurassic bangong nujiang ophiolites formed in forearc settings during subduction initiation while the middle jurassic early cretaceous bangong nujiang ophiolites and the early cretaceous yarlung tsangpo ophiolites formed in forearc settings at pre existing subduction zones crystallization of the neotethyan ssz ophiolites from the eastern mediterranean middle east tibetan plateau to southeast asia and formation of the associated metamorphic rocks temporally coincided with major supercontinent breakup events 1 initial breakup of pangea in central atlantic and westernmost tethys 190 ma 2 separation of west and east gondwana 170 160 ma and initial opening of piemont ligurian tethys 175 164 ma 3 initial breakups of east and west gondwana 135 125 ma and 4 final breakup of gondwana 104 96 ma far field forces associated with abrupt global plate reorganizations may have triggered subduction initiation or transient interplate coupling decoupling at pre existing subduction zones leading to episodic formation of the neotethyan ssz ophiolites and rapid exhumation of metamorphic rocks in subduction zones the formation events of neotethyan ssz ophiolites and associated metamorphic rocks represent snapshots of global plate reorganizations during the major episodes of supercontinent breakup

hydrothermal clay minerals found in sediment containing yellowish brown material from the japan basin abstract in a previous report we suggested that the fe p mineral discovered in the yellowish brown material from the deepsea bottom in the eastern part of the japan basin could have been formed in situ under hydrothermal conditions the present study of clay minerals in the muddy sediment containing the yellowish brown material confirms the possibility of a submarine hydrothermal origin of these clay minerals along with the fe p mineral fe smectites such as nontronite and ion rich saponite and fe mg chlorite indicated that fe types rather than mg type can be formed by slow alteration under submarine hydrothermal conditions at relatively lower temperatures

thrust emplacement of the hispaniola peridotite belt orogenic expression of the mid cretaceous caribbean arc polarity reversal articulo sobre el emplazamiento fallero en la zona de peridotitas de la hispaniola republica dominicana estudiando si es la expresion orogenica de la polaridad reversa en la zona del caribe en el cretacico medio