on the antarctic peninsula batholith the plutonic rocks of the antarctic peninsula magmatic arc form one of the major batholiths of the circum pacific rim the antarctic peninsula batholith is a 1350 km long by 210 km wide structure which was emplaced over the period 240 to 10 ma with a cretaceous peak of activity that started at 142 ma and waned during the late cretaceous early jurassic and late jurassic early cretaceous gaps in intrusive activity probably correspond to episodes of arc compression in a northern zone of the antarctic peninsula the batholith intrudes palaeozoic mesozoic low grade meta sedimentary rocks and in a central zone it intrudes schists and ortho and paragneisses which have late proterozoic nd model ages and were deformed during triassic to early jurassic compression in a southern zone the oldest exposed rocks are permian sedimentary rocks and deformed jurassic volcanic and sedimentary rocks all these pre batholith rocks formed a belt of relatively immature crust along the gondwana margin with few exceptions jurassic plutons crop out only within the central zone many are peraluminous having s like mineralogies and relatively high 87sr 86sri they are considered to consist largely of partial melts of upper crust schists and gneisses and components of mafic magmas that caused the partial fusion by contrast early cretaceous plutons crop out along the length of the batholith few magma compositions appear to have been affected by upper crust the bulk being compositionally independent of the type of country rock they intrude they are dominated by metaluminous calcic si oversaturated 1 type granitoid rocks with relatively low 87sr 86sri intermediate silicic compositions 5 mgo we interpret these to represent partial melts of basic to intermediate igneous locally garnet bearing lower crust contemporaneous mafic magmas e g syn plutonic dykes form a more alkaline si saturated series having higher 143nd 144nd at the same87sr 86sr than the intermediate silicic series to which they are not petrogenetically related the change from limited partial fusion of upper crust in jurassic times to widespread partial fusion of lower crust in early cretaceous times is considered to be a result of an increasing volume of basaltic intrusion into the crust with time

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

provenance of triassic cretaceous sandstones in the antarctic peninsula implications for terrane models during gondwana breakup abstract the antarctic peninsula is the largest of twelve micro continental fragments between southern south america east antarctica and new zealand their original positions and movement history following gondwana breakup are poorly constrained recent work on the antarctic peninsula fore arc arc back arc suggests it consists of two suspect terranes that originated elsewhere and collided with the pacific margin of gondwana in the cretaceous this study reviews provenance models for three laterally extensive kilometers thick sedimentary units in the antarctic peninsula using previous studies and new sandstone detrital modes and chemistry 1 the trinity peninsula group accretionary complex triassic was possibly derived from a glaciated continental margin and may consist of several accreted tracts the deformed quartzose view point and legoupil formations were eroded from a deeply eroded stable continental margin containing an old arc and mature quartzose sandstones with provenance ages suggesting sources in north patagonia and local antarctic peninsula basement the weakly deformed and more feldspathic hope bay formation was derived from an eroded arc possibly the early permian arc of the north patagonian massif 2 the lemay group accretionary complex middle triassic middle cretaceous is dominated by arkoses derived from an eroded continental margin of carboniferous and permian age possibly in the marie byrd land sector with several belts of volcanilithic sandstones representing episodes of arc magmatism the youngest part of the lemay group contains abundant metamorphic detritus derived from basement uplifted during mid cretaceous terrane docking 3 the latady formation in the southern antarctic peninsula has a completely different petrology comprising mature sublitharenites 190 ma of gondwanan provenance deposited in restricted rift basins younger volcanic litharenites 180 ma are dominated by ree enriched low eu eu rhyolitic material eroded from silicic calderas associated with gondwana breakup abundant dacitic to andesitic detritus in the youngest lf 160 145 ma was derived from a contemporaneous arc possibly on the thurston island block as the latady evolved into a back arc basin

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

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

metamorphic evolution of a subduction complex south shetland islands antarctica a subduction complex composed of ocean floor material mixed with arc derived metasediments crops out in the elephant island group and at smith island south shetland islands antarctica with metamorphic ages of 120 80 ma and 58 47 ma respectively seven metamorphic zones i vii mapped on elephant island delineate a gradual increase in metamorphic grade from the pumpellyite actinolite facies through the crossite epidote blueschist facies to the lower amphibolite facies geothermometry in garnet amphibole and garnet biotite pairs yields temperatures of about 350 c in zone iii to about 525 c in zone vii pressures were estimated on the basis of si content in white mica al2o3 content in alkali amphibole nam4 aliv in sodic calcic and calcic amphibole alvi si in calcic amphibole and jadeite content in clinopyroxene mean values vary from about 6 7 5 kbar in zone ii to about 5 kbar in zone vii results from the other islands of the elephant island group are comparable to those from the main island smith island yielded slightly higher pressures up to 8 kbar with temperatures estimated between 300 and 350 c zoned minerals and other textural indications locally enable inference of p t t trajectories all with a clockwise evolution a reconstruction in space and time of these p t t paths allows an estimate of the thermal structure in the upper crust during the two ductile deformation phases d1 d2 that affected the area this thermal structure is in good agreement with the one expected for a subduction zone the arrival and collision of thickened oceanic crust may have caused the accretion and preservation of the subduction complex in this model d1 represents the subduction movements expressed by the first vector of the clockwise p t t path d2 reflects the collision corresponding to the second vector with increasing temperature and decreasing pressure and d3 corresponds to isostatic uplift accompanied by erosion under circumstances of decreasing temperature and pressure

marine to continental transition in himalayan foreland mapping sedimentological studies and sequence stratigraphic analysis in parts of the himalayan peripheral foreland basin of northwest india suggest that deposition of basinal turbidites derived from both the orogenic and ramp sides took place due to progressive uplift of the basin margin causing forced regression the forced regressive wedge of shoreface white sandstone thus deposited throughout the foreland basin across the regressive surface of marine erosion cannot be included in the alluvial sediments of dagshai formation contrary to earlier inferences the unconformity between the subathu and dagshai formations is found to occur at the top of the white sandstone marked by caliche development or erosion by dagshai channel sand interpreted as a type 1 sequence boundary the reworked fossils in calciturbidite units suggest that the upper limit of the subathu formation must be significantly younger than ca 44 ma and the proposition of a synchronous orogen scale unconformity of 10 m y duration and early exhumation of himalayan rocks should be reassessed the duration of unconformity between subathu and dagshai formations is interpreted to be 3 m y the sea level fall and shoaling of subathu sea that was already set in by forced regression received tectonic enhancement only at the beginning of the dagshai formation which resulted a total turnaround from a marine to a continental alluvial system

spatial variation of groundwater arsenic distribution in the chianan plain sw taiwan role of local hydrogeological factors and geothermal sources summary we present here major ion trace element stable and radioisotope data based on forty six groundwater samples collected from various locations along few selected profiles across the chianan plain southwestern taiwan including the area affected by well known blackfoot disease manifested by peripheral vascular gangrene the objective of the study was to understand the role of local hydrogeology in terms of spatial variation of arsenic concentration in groundwater wells of the entire chianan plain and the foothill belt of the central mountain range an attempt has also been made to assess the contribution of nearby geothermal sources to the arsenic budget in groundwater of the chianan plain our study shows a gradual increase in all major and trace ion concentrations including total arsenic from foothill belt arsenic median 4 g l range 0 667 6 g l sample number n 16 to coastal zones arsenic median 42 74 g l range 0 14 348 6 g l n 15 of the plain inverse geochemical modeling shows that ca may be exchanged on clays and that the degree of the exchange increases from the foothill to the coastal zones inverse geochemical modeling further suggests that the oxidation of organic matter ch2o required in various east west profiles across the plain to balance the total bicarbonate concentration and co2 input from organic matters significantly increases from the foothill to the coastal zones with transfer coefficients ranging from 1 55 10 2 to 1 69 10 5 mol l high concentrations of tritium mean 1 33 0 11 tu n 4 in foothill groundwater and low concentration of tritium in groundwater of central zone suggest gradually increasing water rock interaction from the foothill to the coastal part few elevated arsenic median 171 8 g l maximum 667 60 g l minimum 24 g l n 6 hotspots are identified in the foothill belt available lithologs and aquifer test data suggest that the presence of impermeable clay around those pockets possibly inhibits vertical and lateral flushing of the aquifer and aids strong water rock interactions subsequently leading to release of arsenic into groundwater using oxygen isotope and chloride mass balance method we estimated that geothermal sources can recharge a maximum of 4 of groundwater in proximal aquifers and contribute

mesozoic radiolarian faunas from the antarctic peninsula age tectonic and palaeoceanographic significance new assemblages of radiolaria including some of the few occurrences of high southern latitude jurassic and cretaceous radiolarian faunas show that several localities in the lemay group of alexander island range in age from latest jurassic earliest cretaceous to at least albian by demonstrating that sedimentation and deformation in the lemay group was diachronous younging oceanwards to the northwest these new age assessments support the model of the lemay group as an accretionary complex the polarity of subduction beneath alexander island was not affected by arc collisions from at least the lower jurassic to the oligocene and such a long period of continuous accretion appears to be unusual deposition of the lemay group spans the kimmeridgian to albian sedimentation in the fossil bluff group fore arc basin thus making the earlier concept of the lemay group as pre jurassic basement untenable allochthonous latest jurassic earliest cretaceous radiolarian assemblages with some supposed tethyan affinities are present in the lemay group in contrast an in situ latest jurassic assemblage from the nordenskjold formation of the back arc basin and a further jurassic assemblage from a probable trench slope basin have characteristics believed diagnostic of high latitudes the biogeographic affinities of radiolarians from cherts in the lemay group accretionary complex suggest that both these cherts and associated basalts are far travelled slices of the phoenix plate rocks from the probable trench slope basin formerly assigned to the younger fossil bluff group fore arc basin sequence now appear to be part of a new previously unrecognized formation

rotational overthrusting of the northwestern himalaya further palaeomagnetic evidence from the riasi thrust sheet jammu foothills india abstract thermal demagnetization results 316 samples are presented for the tertiary succession of the riasi thrust sheet jammu foothills northwestern himalaya primary and secondary magnetization directions of murree group red beds miocene to upper eocene sampled northeast of jammu indicate for this part of the riasi thrust sheet a clockwise rotation over about 45 with respect to the indian shield since late eocene early miocene time this accords with clockwise rotations of similar magnitude observed in the panjal nappe and the krol belt and is interpreted as representative for the northwestern himalaya results from the western part of the kalakot inlier sampled northwest of jammu i e basal murree claystone middle eocene and carbonate from the subathu group lower middle to lower eocene indicate an aberrant 20 25 counterclockwise rotation which is of local importance only available observations on rotation of himalayan thrust sheets with respect to the indian shield indicate that the himalayan arc has formed through oroclinal bending this supports powell and conaghan s and veevers et al s model of greater india with large scale intracontinental underthrusting along the main central thrust beneath the tibetan plateau minimal magnitudes of underthrusting of 550 km in the krol belt and 650 km in the thakkhola region are concluded palaeolatitude observations herein and in 1 agree with absolute positioning of the indian plate based on india africa relative movement data fixed to a hotspot frame in the atlantic ocean and with palaeolatitude observations from dsdp cores on the indian plate collision related secondary magnetic components observed both to the north and to the south of the indus tsangpo suture zone show palaeolatitudes between the equator and 7 n comparison of both datasets indicates that initial contact between greater india and south central asia had been established in the hindu kush karakorum region by about 60 ma ago whereas eastwards progressive suturing had advanced to the lhasa block segment of the indus tsangpo suture zone before 50 ma ago

short paper the significance of mid palaeozoic basement in graham land antarctic peninsula a mid palaeozoic basement to the antarctic peninsula is confirmed by a geochronological study of the gneissose country rock of the mesozoic magmatic arc of eastern graham land rb sr whole rock ages of 410 15 and 426 12 ma from samples of orthogneiss indicate a previously unrecognized episode of granitic magmatism in the antarctic peninsula during the silurian sm nd data on garnet whole rock pairs indicate that subsequent amphibolite facies metamorphism occurred in late carboniferous times probably as a result of plutonism

studies on settling traction and entrainment of larger benthic foraminiferal tests implications for accumulation in shallow marine sediments settling and traction velocities were measured on optimally preserved tests of larger foraminifera using a settling tube and flume tank within larger foraminifera with porcelaneous tests the peneroplids peneroplis antillarum p planatus p pertusus and dendritina cf d zhengae are distinguished by low test densities ca 1 2 that do not change with growth buoyancy is high because of low reynolds numbers and increases in large individuals because of the allometric change of test shape the fusiform alveolinella quoyi with test densities ca 1 6 is characterized by high reynolds numbers inducing the weakest buoyancy within porcelaneous larger foraminifera the highest buoyancy was recorded for the three soritids parasorites orbitolitoides sorites orbiculus and amphisorus hemprichii because of their low test densities ca 1 25 and the extremely flat biconcave plate like shape flat tests however reduce traction and entrainment from smooth surfaces within hyaline larger foraminiferat the amphisteginids show thick lenticular amphistegina lobifera a radiata to thin lenticular tests a bicirculata a papillosa influencing buoyancy here high test densities ca 1 8 decrease with growth in a lobifera a lessonii and a bicirculata and remain constant in a radiata and a papillosa minimum velocities required for entrainment are lower for thick lenticular tests and higher for thin lenticular tests test densities remain constant with growth in the calcarinid baculogypsina sphaerulata 1 78 and decrease slightly in calcarina gaudichaudii and neorotalia calcar starting at 1 85 all living under extreme hydrodynamic conditions density decreases the most in baculogypsinoides spinosus starting at 1 8 resulting in higher buoyancy through low reynolds numbers traction is promoted in spherical tests of baculogypsina and baculogypsinoides within nummulitids the thick lenticular palaeonummulites venosus test density decreasing with size starting at 1 78 is less buoyant expressed in high reynolds numbers but easily entrained thick lenticular juveniles and extremely flat adults distinguish operculinella cumingii heterostegina depressa and the giant cycloclypeus carpenteri test densities increase during growth starting from ca 1 6 and attaining a maximum of 1 8 buoyancy is low in small tests and high in large tests while entrainment velocities are reduced as the tests flatten high buoyancy is also a characteristic of the entirely flat tests in operculina ammonoides from deeper regions and planostegina operculinoides which is expressed in the lowest reynolds numbers within larger foraminifera

metamorphic rocks in the antarctic peninsula region the distribution of metamorphic rocks in the antarctic peninsula region new quantitative peak pressure temperature data along the antarctic peninsula and a literature review on the current knowledge of metamorphic conditions in the antarctic peninsula region have been compiled into a single metamorphic map the pressure temperature data for the antarctic peninsula indicate 1 burial of supracrustal rocks to low to mid crustal depth along the eastern and western side of the antarctic peninsula and on some islands adjacent to the western side of the peninsula 2 uplift of lower to mid crustal metamorphic rocks along major shear and fault zones and 3 a reversed succession of metamorphic grades for the western domain of the antarctic peninsula region compared to the eastern domain along the eastern palmer land shear zone eplsz of the antarctic peninsula the metamorphic data are consistent with oblique convergence between alexander island the western domain palmer land central domain and the gondwana margin the eastern domain supporting a model of 1 exhumation and shearing of the higher pressure rocks from central western up to 9 4 kbar and from northeast 7 kbar to 9 kbar palmer land 2 the exhumation and shearing of low to medium pressure rocks in western palmer land and along the eastern palmer land shear zone and 3 shallow burial and subsequent exhumation of sediments of the gondwana margin along the eastern palmer land shear zone based on the high amphibolite grade rocks exposed in central western palmer land our data also support earlier suggestions that the eastern palmer land shear zone is the surface expression of a northwest to west dipping deep level high temperature crustal shear zone extending below the western part of the central domain of the antarctic peninsula

new aerogeophysical view of the antarctic peninsula more pieces less puzzle new airborne geophysical data reveal subglacial imprints of crustal growth of the antarctic peninsula by mesozoic arc magmatism and terrane accretion along the paleo pacific margin of gondwana potential field signatures indicate that the antarctic peninsula batholith is a composite magmatic arc terrane comprising two distinct arcs separated by a 1500 km long suture zone similar to the peninsular ranges batholith in southern and baja california aeromagnetic aerogravity and geological data suggest that a mafic early cretaceous western arc was juxtaposed against a more felsic eastern arc which in mid cretaceous times was intruded by highly magnetic tonalitic granodioritic plutons of island arc affinity suturing of the two arcs against the gondwana margin caused the mid cretaceous palmer land orogenic event convergence and suturing may have been driven by two subduction zones or alternatively by a decrease in slab dip leading to an inboard migration of the arc as in california

characterization on arsenic sorption and mobility of the sediments of chia nan plain where blackfoot disease occurred higher levels of arsenic in the aquifers of chia nan plain in southwestern taiwan were attributed to the cause of blackfoot disease in the area half a century ago although extensive studies were conducted on the occurrence speciation mobility and transport of arsenic in the region the relationship between arsenic adsorption by different aquifer materials and the concentration and speciation of arsenic in these aquifers was poorly delineated this study focused on characterization of sediments in the region as well as determination of relations between arsenic adsorption and other geochemical and clay mineralogical properties of the sediments the arsenic adsorption capacity was positively related to the clay minerals fe and mn contents in the sediments the higher arsenic adsorption capacity of the sediments served as a sink for the arsenic during its transport from the central mountains to the coast and as a source for its release under reduced environment and in the presence of humic substances

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

how deep was the early himalayan foredeep abstract the himalayan foredeep is a good archive of the events that occurred during different stages of the basin evolution the early part of this archive is used here to interpret depositional environments and paleobathymetry based on facies associations sedimentary structures and larger foraminifera three facies associations are recognized in the early himalayan foreland basin sequences facies association i containing chert breccia bauxite quartzose sandstone coal and black shale was deposited in short lived ephemeral streams swamps and inner parts of lagoons the limestones and shales of the facies association ii were deposited in a barrier lagoonal system where the former represent barrier and the latter represent lagoon deposits the limestone beds containing hummocks and wavy ripples were deposited under the influence of oscillatory storms and represent tempestites siltstone beds containing hummocky cross stratification and ripple cross laminae were deposited in the shoreface or foreshore zone where storm activities were dominant facies association iii comprises marl laminites and purple shale deposited in intertidal and supratidal zones of a tidal flat larger foraminifera such as nummulites and assilina flourished in the tropical climatic belt and accumulated in the coastal zone as a result of their transportation by waves and tides in general the sedimentation took place on a ramp similar to the present day persian gulf with a paleobathymetry of 55 m in strike continuity in pakistan the coeval sequences were deposited on shelves with a paleobathymetry

role of strike slip faulting in the tectonic evolution of the antarctic peninsula the antarctic peninsula mesozoic magmatic arc has had a long history of dextral strike slip deformation the deformation was initially associated with the development of a wide accretionary complex by the migration of fore arc slivers and the formation and inversion of a thick fore arc basin succession it also formed an important component within major shear zones in the arc and may have controlled the formation of sedimentary basins in the back arc region although some transcurrent motion within the fore arc region was related to a component of oblique subduction the main movement occurred during the breakup of gondwanaland and the formation of a major transtensional rift system a new reconstruction for this part of gondwanaland is presented taking this transcurrent motion into consideration

u pb ion microprobe zircon geochronology from the basement inliers of eastern graham land antarctic peninsula new geological mapping combined with u pb ion microprobe zircon geochronology on the isolated but locally extensive exposures of crystalline basement inliers of eastern graham land has greatly improved our understanding of the region s early crustal evolution and has allowed a more thorough evaluation of patagonia antarctic peninsula connections prior to gondwana break up at eden glacier diorite gneisses yield early ordovician protolith ages of 487 3 and 485 3 ma and represent the oldest in situ rocks recorded on the antarctic peninsula and indicate a significant spatial extension of famatinian age magmatism of patagonia zircon overgrowths in the early ordovician protoliths and granitic leucosomes developed within them record two phases of permian metamorphism at c 275 and c 257 ma coincident in part with diorite plutonism of the area at 272 2 ma at adie inlet granitic leucosomes from paragneiss have been dated at 276 3 ma and these are in turn cut by 257 3 ma xenolith rich diorite gneiss the diorite intruded during a second phase of deformation which folded the paragneiss leucosomes into tight folds this whole assembly is cut by intensely brecciated megacrystic granodiorite which yielded a 259 3 ma age south of cabinet inlet a very different sequence of events is evident with triassic magmatism at c 236 ma extensive along the joerg peninsula migmatitic leucosomes are dated at c 224 ma and magmatism and deformation events apparently continued to c 209 ma at cape casey our data indicate that the devonian and carboniferous magmatism at target hill considered to represent the classic basement complex of the antarctic peninsula is not representative regionally the target hill crustal block contains a major break along cabinet inlet to the north ordovician and permian protoliths were variably migmatized during two episodes of permian deformation and metamorphism whereas to the south triassic protoliths and triassic metamorphism are encountered supplementary material u pb isotopic data are available at http www geolsoc org uk sup18526

mixing properties and stability of jadeite acmite pyroxene in the presence of albite and quartz the stability of synthetic jadeite acmite pyroxene coexisting with albite and quartz has been determined at 600 700 and 900 c the end member reaction albite jadeite quartz has been determined to lie between 1 67 and 1 70 gpa at 600 c 1 88 and 1 90 gpa at 700 c and 2 44 and 2 48 gpa at 900 c jd78acm22 quartz is stable above 1 58 1 78 and 2 33 gpa at 600 700 and 900 c respectively jd61acm39 quartz is stable above 1 47 1 67 and 2 18 gpa at 600 700 and 900 c respectively addition of as much as 40 of acmite component in jadeite extends pyroxene stability by less than 300 mpa at 900 c unit cell parameters measured for synthetic jadeite acmite pyroxenes indicate linear volume composition relations the data are consistent with ideal mixing in jadeite acmite solutions

rb sr geochronology of graham land antarctica thirty five new rb sr whole rock and mineral isochrons are reported for igneous rocks from graham land magmatism was essentially continuous but peaks of activity occurred in early jurassic early cretaceous late cretaceous and eocene times the oldest dated granite is triassic 209 3 ma volcanic rocks were erupted throughout this history and some previously supposed upper jurassic volcanic rocks must be mid cretaceous or younger a change in magma type from uniformly acid to predominantly basic or intermediate combined with westward migration of the arc may be partly responsible for previously reported transverse geochemical variations there is a marked trend of decreasing initial 87 sr 86 sr ratio of the plutonic rocks with time from c 0 707 to 0 704 although volcanic rocks tend to have higher values this trend is ascribed to the waning influence of an as yet unidentified pre magmatic crustal basement due to increasing depth of magma generation close parallels to the observed age pattern imply continuity of the andean belt through southern south america into graham land back to early mesozoic times and are not compatible with reconstructions of gondwana in which the antarctic peninsula is located w of south america

aqueous and solid phase arsenic speciation in the sediments of a contaminated wetland and riverbed abstract mobility of as in the environment is controlled by its association with solid phases through adsorption and co precipitation to elucidate the mobilization potential of as deposited in wetland and riverbed sediments of the wells g h wetland in woburn ma as the result of decades of industrial activity as retention mechanisms were inferred from aqueous and solid phase geochemical measurements of sediment cores testing included a sequential extraction method designed for and standard tested with as phases and pe ph equilibrium modeling the uppermost sediments in the wells g h wetland contain elevated concentrations of both dissolved and solid phase as up to 2 000 g l and 15 000 g g respectively and a maximum concentration between 30 and 40 cm depth measurements obtained in this study suggested that as in the wetland sediments was predominantly adsorbed likely onto amorphous fe hydr oxide phases and mixed valence fe phases in the riverbed sediments however a relatively greater proportion of the solid as was associated with more reduced and crystalline phases and adsorbed as was more likely associated with al oxide or secondary reduced fe phases ph pe modeling of the fe as s system was consistent with observations the association of as with more oxidized phases in the wetland compared with the riverbed sediments may result from a combination of plant activities including evapotranspiration driven water table depression and or root oxygenation

predicting natural arsenic contamination of bedrock groundwater for a local region in korea and its application a logistic regression model for the probability of arsenic exceeding the drinking water guidelines 10 g l in bedrock groundwater was developed for a selected county in korea where arsenic occurrence and release reactions have been investigated arsenic was enriched naturally by the oxidation of sulfide minerals in metasedimentary rocks and mineralized zones and due to high mobility in alkaline ph conditions concentrations were high in groundwater of the county when considering these reactions of arsenic release and water quality characteristics several geological and geochemical factors were selected as influencing variables in the model in the final logistic regression model geological units of limestone and metasedimentary rocks the concentrations of nitrate and sulfate and distances to closed mines and adjacent granite were retained as statistically significant variables predicted areas of high probability agreed well with known spatial contamination patterns in the county the model was also applied to an adjacent county where the groundwater has not previously been tested for the presence of arsenic and a probability map for arsenic contamination was then produced through the analysis of arsenic concentrations at the wells of high probability it was determined that the applied model accurately indicated the arsenic contamination of groundwater the logistic regression approach of this study can be applied to predict arsenic contamination in areas of similar geological and geochemical conditions to the county used in this model

granitoid pluton formation by spreading of continental crust the wiley glacier complex northwest palmer land antarctica abstract the emplacement mechanism geometry and isotope geochemistry of plutons of the wiley glacier complex suggest that new continental crust grew by multiple injection of tonalitic dykes during dextral transtension in the antarctic peninsula magmatic arc in early cretaceous times the suggested mechanism is analogous to basalt dyke injection during sea floor spreading during normal dextral shear the burns bluff pluton a sheeted moderately east dipping syn magmatically sheared tonalite granodiorite intruded syn magmatically sheared quartz diorite of the creswick gap pluton and 140 5 ma hornblende gabbro u pb dating of zircon and ar ar dating of hornblende and biotite suggest that both granite s l plutons were emplaced between 145 and 140 ma but that extensional shearing was active from the time of emplacement until ca 127 ma the burns bluff pluton is chilled at its margin and grades through mylonitised porphyritic tonalite granodiorite sheets and tonalite granodiorite sheets with minor chilling to a kilometre scale body of coarse grained hypidiomorphic tonalite granodiorite co magmatic microdiorite forms dykes and abundant synplutonic mafic enclaves these dykes opened as echelon veins during episodic dextral shear and were deformed to trains of enclaves during continued normal dextral shear pluton marginal porphyritic and hypidiomorphic tonalite granodiorite forms large fault hosted sheets emplaced progressively under extension with minor dextral shear kinematic indicators from pluton marginal granite s l dykes suggest that early in pluton accretion intrusive sheets cooled rapidly with simple shear prior to full crystallisation changing to ductile simple shear during cooling kinematic indicators towards the pluton core suggest that as the pluton grew and cooled more slowly emplacement switched from sheeting to in situ inflation with simple shear distributed across a broad zone prior to full crystallisation of magma cross cutting relationships with the coeval syn extensional creswick gap pluton suggest that the burns bluff pluton was emplaced in a steeper second generation shear structure like those in normal fault systems this suggests that the wiley glacier complex was emplaced above the base of the brittle ductile transition zone 15 18 km depth the burns bluff pluton has nd and sr isotope values that range from mantle dominated nd141 3 8 87 sr 86 sr 141 0 70468 to more crustally influenced nd141 1 7 87 sr 86 sr 141 0 70652 this range probably represents different degrees of mixing between mantle derived magma and lower crustal partial melts generated in the garnet stability zone 40 km depth addition of new crustal material by mafic underplating at the base of the crust and by redistribution of granitic s l and mafic modified underplated magma to mid crustal levels along extensional shear zones as the arc spread were the primary mechanisms of crustal growth

a complete arc trench system recognized in gondwana sequences of the antarctic peninsula region prior to late triassic early jurassic times the geological history of the antarctic peninsula region was dominated almost entirely by gondwana sequences that together comprised a major arc trench system subduction complex trench slope break and fore arc basin sedimentation can all be recognized and deposition was at least partly on early palaeozoic or older continental crust the only evidence for a contemporaneous magmatic arc situated in the antarctic peninsula at this time consists of patchy occurrences of metavolcanic rocks possibly representing the frontal edge of the arc and the major outcrop area of these rocks is believed to lie under the broad shallow continental shelf e of the antarctic peninsula this is contrary to most current hypotheses in which a marginal basin presumably floored by oceanic crust is thought to crop out close to the e coast of the antarctic peninsula however the complete absence of substantial outcrops of pre jurassic volcanic rocks anywhere in eastern antarctica and south africa which are the closest and most likely places in which these should exist supports the new proposal moreover the identification of back arc elements of the arc trench system foreland fold thrust belt and retro arc foreland basin in eastern antarctica and south africa greatly strengthens the likelihood of the arc cropping out in the area suggested towards the end of the triassic and during the early jurassic periods an intense diastrophic event or culmination of events of orogenic magnitude occurred gondwanian orogeny causing substantial redistribution of the pre existing elements of the arc trench system in particular all the fore arc sequences were strongly deformed some possibly for the first time e g in the fore arc basin and became firmly accreted to the continental margin moreover the magmatic foci migrated trenchwards to intrude the deformed rocks in the antarctic peninsula because many of the plutons were emplaced synkinematically they often closely resemble basement gneisses the distinction between these rocks remains a serious problem in the antarctic peninsula and it can be solved only partially by radiometric dating

basement chronology of the antarctic peninsula recurrent magmatism and anatexis in the palaeozoic gondwana margin abstract a revised pre jurassic chronology is presented for the antarctic peninsula on the basis of new u pb zircon dating using both conventional 11 samples and shrimp microprobe data 10 samples the age range for plutonism and high grade metamorphism is from 435 8 ma silurian to c 206 ma approximately the triassic jurassic boundary with peaks of activity in devonian carboniferous permian and mid triassic times although some are represented by rocks with limited outcrops the new data confirm the importance of mid and latest triassic magmatic events previously identified using rb sr geochronology the adie inlet gneiss previously thought to be neoproterozoic is recognized as a permian migmatite derived from paragneiss with a provenance dominated by cambrian granitoids granite gneiss from nw palmer land previously dated as cambrian is shown to be triassic detrital zircons in metasedimentary rocks and inherited zircons in granitoids are dominated by mesoproterozoic to cambrian components with sparse palaeoproterozoic to archaean grains suggesting sources within gondwana at times these sources were nearby as shown by an archaean cobble sized granite clast from a permo triassic conglomerate another clast in the same conglomerate previously thought to be devonian in age has an ordovician crystallization age

magmatic belts in accretionary margins a key for tectonic evolution the tonalite belt of north victoria land east antarctica occurring in the early palaeozoic palaeomargin of the east antarctica craton the tonalite belt of north victoria land is a narrow linear magmatic belt up to 200 km long made up of strongly foliated tonalitic and granodioritic intrusions they were synkinematically emplaced into the lanterman murchison shear zone a major tectonic structure across which different tectono metamorphic terranes were accreted during the late cambrian ross orogeny the deformational and kinematic features of the intrusions indicate that strain and displacement during terrane accretion were partitioned into oblique thrust high angle thrust and strike slip shear zones from this it is deduced that a transpressional regime prevailed during early palaeozoic deformation and terrane accretion this and other magmatic belts which exploited major tectonic structures in collisional margins such as the coast plutonic complex of nw america are basic keys for understanding deformational processes and kinematic regimes during terrane accretion moreover the occurrence of such types of magmatic belts might be regarded as a reliable indication of large scale strike slip motion between accreting terranes in an oblique convergent setting

evolution of the himalayan paleogene foreland basin influence of its litho packet on the formation of thrust related domes and windows in the eastern himalayas a review abstract eocene oligocene foreland basin was formed in response to the india asia collision and ensuing himalayan orogenesis the initial collision during late paleocene to early eocene was broadly contemporaneous laterally the paleogene sediments although discontinuously exposed are remarkably similar in their character and organization in the eastern himalayas it is virtually concealed tectonically but is exposed close to and beneath the main boundary thrust mbt as narrow but laterally extensive thrust slivers of fossiliferous eocene sediments lateral continuity and similar marine fauna in them establish the presence of thicker eocene sediments beneath mbt further north several domes and windows in the eastern himalayan frontal belt have evolved with similar geometry the largest siang window exposes duplex antiform of paleogene sediments and volcanics at the core which have arched up the mbt roof thrust the latter underlies passively domed up late plaeozoic and proterozoic himalayan thrust packets the cores of other windows mainly expose low grade proterozoic rocks with or without the late paleozoic rocks a similar sequence of pre tertiary thrust packet is exposed to the south in the frontal belt which override the neogene sediments across mbt a buried basement indenture of the indian continent continues beneath the siang window located at the eastern himalayan syntaxis the cores of other windows are possibly arched up by the duplexes of pre tertiary and tertiary sediments during the process of southward movement of the crystalline and foreland sheets

reverse fault step at engel peaks antarctic peninsula abstract a steep reverse fault at engel peaks antarctic peninsula cuts granophyre and overlying volcanic rocks and incorporates a lower angle zone or fault step the reverse fault step differs from the more familiar thrust ramp in that it cuts down section in the footwall in the direction of tectonic transport accommodation of the fault zone to this step and its associated sidewall are discussed with reference to kinematic models for pull apart zones and for the movement of thrust sheets over non planar surfaces during movement on the main fault the step acted as a fault jog and pull apart zone preserving cataclasite breccia and other structures demonstrating a brittle to ductile deformation history ultra fine grained rock in the step zone is the result of dynamic recrystallization of ultracataclasite during episodes of brittle slip the fault step acted as a dilational fault jog between the main steep reverse fault segments rotation of mylonite into the reverse fault step and its sidewall involved flexural flow parallel to foliation movement of material through the step zone resulted in shear parallel to the base of the step enhancement of breccia layering mixing of lithologies and cleavage formation it also involved extension at a high angle to the main movement direction to accommodate the extra length of the fault zone late steep reverse fault zones propagating from the main fault folded the breccias in the step and crenulated the earlier cleavage the fault step was a zone of brittle dilation hydration diffusive mass transfer and mineralization

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

very low and low grade metamorphism in the trinity peninsula group permo triassic of northern graham land antarctic peninsula the permo triassic trinity peninsula group is a widespread regionally metamorphosed metasedimentary sequence in northern graham land antarctica which forms the local basement to the mainly jurassic cretaceous antarctic peninsula magmatic arc the metamorphic grade thermal evolution and pressure series of this major tectono stratigraphical unit are largely unknown determining the nature of the metamorphism has relied hitherto on conventional optical identifications of the major phases mainly in rare volcanic beds however diagnostic mineral parageneses are generally absent and the precise metamorphic grade is unknown or has to be inferred over large areas using white mica illite crystallinity of interbedded mudrocks the trinity peninsula group is now shown to have been pervasively altered mainly at anchizonal and epizonal grades conditions ranged from upper anchizonal in the northeast to thoroughly epizonal in the southwest outwith thermal aureoles near plutonic intrusions the alteration temperatures ranged mainly from 250 to 325 c exceeding 300 c in the highest grade epizone greenschist facies parts of the sequence the facies series k white mica b cell dimension measurements and mineral phases present are characteristic of an intermediate pressure series altered under moderate geothermal gradients 35 c km corresponding to burial depths of c 7 10 km unroofing and substantial erosion of the trinity peninsula group took place during polyphasal vertical tectonic movements linked to the development of the magmatic arc in northern graham land the geological setting of the trinity peninsula group is ambiguous and could have been a foreland or back arc basin or the mid to upper levels of an accretionary prism

factors responsible for high arsenic concentrations in two groundwater catchments in taiwan abstract high as contents in groundwater were found in two neighboring catchments the chianan plain and the southern choushui river alluvial fan in taiwan the groundwater quality the redox potential and the as distribution of the chianan plain were characterized using factor analysis redox zoning and a geochemical program the results were compared with those of the southern choushui river alluvial fan possible as release mechanisms are also elucidated factors 1 and 2 of the groundwater in the chianan plain the salinization factor and the as enrichment factor are similar to those in the southern choushui river alluvial fan however the spatial distribution of reductive tendency in the chianan plain is different to that in the choushui river alluvial fan and yields spatially distinct hydrogeochemical environments in these two neighboring areas the reduction potential in the chianan plain is stronger than that in the choushui river alluvial fan the difference between the reduction potentials in these two vicinal areas influences the concentrations of as in groundwater the reductive dissolution of as rich fe oxyhydroxide is suggested to be the major mechanism for release of as to the groundwater in the chianan plain and the choushui river alluvial fan of taiwan

crustal growth of the antarctic peninsula by accretion magmatism and extension a subduction accretion model incorporating new geophysical data is presented to explain the geology of the antarctic peninsula from late palaeozoic to cenozoic time according to the model the peninsula consists of overlapping accretionary magmatic and extensional regimes that were diachronous across the peninsula and have built the crust to its present form the crust which contains a small proportion of sialic basement was mainly formed by accretionary and magmatic processes and modified to its present shape by extension the gondwanide orogeny for the antarctic peninsula is interpreted in terms of the accretionary processes

paleogeographic and paleotectonic evolution of the himalayan range as reflected by detrital modes of tertiary sandstones and modern sands indus transect india and pakistan detrital modes of sandstones derived from the himalayan suture belt record the history of the mountain range since initial collision between india and asia which began in latest paleocene time tertiary clastic wedges deposited in fore arc foreland and remnant ocean basins and exposed along the indus transect from northernmost india to the arabian sea represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision quartzose continental block and feldspatholithic magmatic arc sandstones were deposited respectively on the passive indian tethys himalayan succession and active asian indus group continental margins during late cretaceous paleocene time closure of the neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the indian plate during deposition of sediments dated at foraminiferal zones p6 pakistan to p8 india starting in early eocene time deposition of chulung la formation and murree supergroup volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding piggy back and foreland basins homogeneous petrographic composition within the eocene lower miocene murree supergroup with only slight progressive increase of detrital feldspars suggests erosion of largely supracrustal rocks involved in thrusting in the north in middle miocene time marked enrichment in medium to high grade metamorphic detritus in foreland sandstones siwalik group reflects rapid uplift of a warm wedge of indian crust which was carried southward along the main central thrust this major paleogeographic change was recorded also by quartzolithic remnant ocean turbidites which were fed great distances along transverse fracture zones and later accreted in the coastal makran subduction complex panjgur association and makran group recycled orogen detritus derived from the elevated himalayan chain is still accumulating today in the indus fan enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid crustal rocks along the core of the growing orogen

the eastern palmer land shear zone a new terrane accretion model for the mesozoic development of the antarctic peninsula a major ductile fault zone the eastern palmer land shear zone has been identified east of the spine of the southern antarctic peninsula this shear zone separates newly identified geological domains and indicates that during late jurassic terrane accretion and collision two and possibly three separate terranes collided resulting in the palmer land orogeny the orogeny is best developed in eastern palmer land and eastern ellsworth land there shallow marine sedimentary rocks of the latady formation and a metamorphic and igneous basement complex of possible lower palaeozoic to pre early jurassic age are thrust and folded this forms an arcuate east directed foreland fold and thrust belt up to 100 km wide and 750 km long parallel to the axis of the antarctic peninsula the newly identified antarctic peninsula domains include 1 a parautochthonous eastern domain that represents part of the margin of the gondwana continent comparable to the western province of new zealand the ross province superterrane of marie byrd land the eastern series of south central chile the pampa de agnia and tepuel rocks of north patagonia and the cordillera darwin rocks of tierra del fuego 2 a suspect central domain that represents an allochthonous microcontinental magmatic arc terrane comparable to the median tectonic zone of new zealand the amundsen province superterrane of marie byrd land and coastal cordillera of north chile and 3 a suspect western domain with strong similarities to the eastern province of new zealand western series of south central chile and chonos metamorphic complex of north patagonia that represents either a subduction accretion complex to the central domain or another separate crustal fragment although an allochthonous terrane hypothesis for the antarctic peninsula remains to be fully tested this has much in common with models for the new zealand and south american parts of the pacific margin of gondwana the identification of a potential allochthonous terrane continent collision zone allows us to define the edge of the gondwana continent in the antarctic peninsula sector of the supercontinent margin which has implications for mesozoic reconstructions of gondwana

late palaeozoic early mesozoic fore arc basin sedimentary rocks at the pacific margin in western antarctica we infer that the trinity peninsula group of the antarctic peninsula was deposited in a fore arc basin s of composite type located between the gondwanian arc massif consisting of plutonic and older gneissose basement rocks and a subduction complex now represented by greenschists blueschists and albite epidote hornblende bearing rocks of the pre jurassic metamorphic complex

an estimate of albian sea level amplitudes and its implication for the duration of stratigraphic hiatuses abstract carbonate platform tops are reliable but incomplete recorders of past sea level fluctuations as they are riddled with hiatuses of various durations basinal sections represent a more complete record but fail to register regressive transgressive events with small to moderate amplitudes we seek to avoid these problems by combining information on past sea level fluctuations from coeval platform top slope and basinal sections the outcome of this study is a semiquantitative albian sea level curve from the southern tethyan margin in oman in subaerial exposure surfaces the northern oman margin recorded 4 high amplitude 50 m 6 intermediate amplitude 30 m and 26 low amplitude 10 m regressive transgressive cycles hiatuses that cap the platform top depositional sequences might account for between 30 to 70 of the cycle duration the resulting platform top depositional sequences have frequencies in the order of 230 20 kyr i e they are in the time range of orbital eccentricity cycles it appears that at least some of these albian regressive transgressive cycles were rapid and punctuated as opposed to sinus shaped milankovitchian sea level oscillations

magnetic susceptibilities of rocks of the antarctic peninsula implications for the redox state of the batholith and the extent of metamorphic zones a combination of 1555 magnetic susceptibility measurements from the antarctic peninsula between 65 s to 72 s for which the raw data are made available and petrological structural and metamorphic data has been used to improve understanding of 1 magma sources for the antarctic peninsula batholith 2 genetic relationships between granitoids and metamorphic rocks and 3 to provide a semi quantitative measure of the extent and grade of metamorphic zones the redox state of jurassic plutonic rocks indicates that these had continental magma sources in the tectonostratigraphic terranes of the central and eastern domains triassic and cretaceous plutons on the other hand had subduction related sources in the central domain of the western antarctic peninsula and continental sources in the gondwana margin eastern domain circum pacific comparisons of magnetite ilmenite belt geometries identify the antarctic peninsula belt as a natural continuation of comparable south american belts susceptibility trends are generally retained by orthogneisses suggesting that they formed by deformation of plutonic rocks mostly at or below upper amphibolite facies conditions metasedimentary rocks are weakly magnetic across the peninsula and are spatially associated with continentally derived or crustally contaminated plutons ilmenite series orthogneisses and metabasites from strongly magnetic plutonic environments show areas of very low magnetic susceptibilities that may be linked to fluid enhanced tectonometamorphism induced reduction of magnetic susceptibility the distribution of reduced magnetic susceptibility areas follows the surface traces of major shear and fault zones in palmer land our results are consistent with tectonic interpretations of oblique compression and uplift of an arc block on the pacific margin of gondwana during the palmer land event

petrological evolution of the paleogene coal deposits of jammu jammu and kashmir india abstract a detailed macro and micro petrological investigation of 8 coal seam profiles of eocene age from the sub himalayan zone of jammu was undertaken in order to characterize them petrographically and to focus on their evolution the quantitative data suggest that these coals are vitrinite rich with low concentrations of inertinite and rare occurrences of liptinite according to microlithotype concentration these coals may be characterized as vitrinite rich with minor amounts of clarite vitrinertite and trimacerite the dominant minerals are clays siderite and pyrite occurring mostly as disseminations cavity filling and in framboidal state these coals are vitric in type low volatile bituminous in rank and ashy in grade the petrographic character and the presence of teleutospores suggest that similar to other tertiary coal deposits in the world the angiosperm flora contributed chiefly to the development of coal facies in the area the maceral and microlithotype composition shows that these coals originated from the low forest and undisturbed in situ peat in foreland basins under limno telmatic depositional conditions the water was brackish with regular influxes of fresh water