petrology mineral chemistry and geochemistry of late triassic ni cu ore bearing mafic ultramafic intrusions hongqiling northeastern china petrogenesis and tectonic implications the hongqiling magmatic ni cu sulfide deposit situated on the southern margin of the eastern central asian orogenic belt caob is composed of over 30 mafic ultramafic intrusions these ore beari

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

lithological and geochemical constraints on the magma conduit systems of the huangshan ni cu sulfide deposit nw china magmatic ni cu sulfide deposits in northern xinjiang china are associated with small mafic ultramafic complexes with the sulfide ores generally occurring in ultramafic rocks the huangshan deposit up to 65 mt of ore at 0 49 ni and 0 31 cu one of the largest magmatic ni cu deposits in northern xinjiang is composed of a layered sequence of lower websterite lower lherzolite websterite norite gabbro gabbro diorite and gabbronorite with sulfide mineralization mainly found in the lower lherzolite lower websterite and websterite systematic variations of the major oxides and trace elements suggest that the rocks of the huangshan deposit are fractionated from the same parental magma with the sharp contact and discontinuous trends of major oxide contents between different lithologies implying intrusion of four distinct stages of magma from a single deep seated staging chamber the reversals in olivine fo contents and major oxides in the lower lherzolite were the result of inhomogeneity in olivine within the lower chamber the se s ratios 63 1 150 10 6 and the negative correlation between se s and 34s 0 63 2 42 of the sulfide ores suggest that a large contribution of crustal s caused the sulfide segregation the sulfides in the lower lherzolite have lower cu contents 1386 2200 ppm and cu pd ratios 2 31 105 1 36 106 relative to those in the mineralized lower websterite cu 2300 to 18 700 ppm and cu pd 6 65 105 to 2 73 106 a positive correlation between pd ir and ni ir for the vein textured sulfides in the lower websterite likely reflects fractionated sulfides picked up by a new pulse of magma in contrast the restricted range of pd ir ratios indicates that the pge contents of the disseminated sulfides in the lower lherzolite resulted from reaction between the sulfides and new pulses of s undersaturated magma

genesis of the huangshannan high ni tenor magmatic sulfide deposit in the eastern tianshan northwest china constraints from pge geochemistry and os s isotopes abstract the huangshannan magmatic ni cu sulfide deposit is one of a group of permian magmatic ni cu deposits located in the southern central asian orogenic belt in the eastern tianshan northwest china it is characterized by elevated ni tenor concentrations in recalculated 100 sulfide in sulfide within ultramafic rocks 9 19 wt with values much higher than other deposits in the region sulfides of the huangshannan deposit are composed of pentlandite chalcopyrite and pyrrhotite and the host rock is relatively fresh indicating that the high ni tenor is a primary magmatic feature rather than formed by alteration processes it is shown that sulfides with high ni tenor can be generated by sulfide olivine equilibrium at an oxygen fugacity of qfm 0 5 for magmas containing 450 ppm ni and 20 olivine ores with 10 wt sulfur have relatively low pge and ni tenors compared to other ores r factor mass ratio of silicate to sulfide liquid modeling of ni indicates that they formed at moderate r values 150 600 based on this constraint on r values ores with 4 5 wt as sulfide rich samples are also depleted in cu and as interstitial sulfides in those samples are physically interconnected at a scale of several cms the low pt and pd anomalies are attributed to solid pt and pd phases crystallization and retention with the monosulfide solid solution mss and cu rich sulfide liquid percolation during mss fractionation this finding indicates that pt anomalies in sulfide rich rocks from magmatic ni cu deposits in the eastern tianshan are the result of sulfide fractionation rather than a hydrothermal effect 187 os 188 os 278ma values of the lherzolite samples vary from 0 27 to 0 37 and os 278ma values vary from 110 to 189 indicating significant magma interaction with crustal sulfides rich in radiogenic os well constrained os values and 34 s values 0 4 to 0 8 indicate that crustal contamination occurred at depth before the arrival of the magma in the huangshannan chamber regionally deposits with high ni tenor have not been reported other than the huangshannan deposit however many intrusions with high ni contents in olivine are present in nw china such as the erhongwa poyi and poshi intrusions those intrusions are capable of forming high ni tenor sulfides due to olivine sulfide silicate equilibrium and relative high ni content in parent magma making them attractive exploration targets

petrogenesis of syn orogenic rare metal pegmatites in the chinese altai evidences from geology mineralogy zircon u pb age and hf isotope abstract recently an increasing number of anatetic pegmatites have been confirmed in contrast to the granitic pegmatite the anatetic pegmatite has no relation to granite it is therefore necessary to reacquaint the origin and classification of pegmatitic rocks as one of the largest pegmatite provinces the chinese altai provides a natural laboratory for pegmatite study to date the type age source and tectonic setting of the syn orogenic pegmatites in the chinese altai remain unclear in this work the cms chemical composition mineral assemblage structural geology classification is primarily applied on the pegmatitic rocks in the chinese altai five types pegmatitic rocks including metapegmatite pegmatoid pegmatite pseudopegmatite and granite pegmatite are identified by their cms features in addition the geology mineralogy zircon u pb ages and hf isotopes of six pegmatites are presented in this work the pegmatites numbered jmhb02 qbl02 tlt01 aljk01 amlg01 and tmlt01 are dated at 394 8 4 0 ma 402 6 5 5 ma 385 9 3 5 ma 368 0 4 0 ma 358 3 4 6 ma and 333 0 6 0 ma respectively indicating that they were formed during the syn orogenic stage of the altai orogenic process they are exposed in the qiongkuer domain in the southern chinese altai juxtaposed with the late and or post orogenic pegmatites in the same pegmatite field no parental granite can be confirmed for all these pegmatites comparatively the synorogenic pegmatites are scarce and have lower mineralization grades than the late and postorogenic pegmatites zircon hf isotopic compositions of the syn orogenic pegmatites have positive hf t values of 2 06 8 28 and old t dm2 ages of 1 234 860 ma and are consistent with those of most of the syn orogenic i and s granites which indicates that the pegmatites and granites have a common immature crustal source from the early paleozoic metasedimentary rocks compared to the post orogenic pegmatites in the central altai domain the syn orogenic pegmatites in this work have larger positive hf t values and younger t dm2 ages indicating that more juvenile components were involved in their magma sources combining this study with previous works we suggest that the anatexis of metasediments induced by decompression and injection of heat energy and mantle derived materials under a forearc extensional setting led to the formation of the syn orogenic pegmatites in the chinese altai

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

seafloor geomorphology and glacimarine sedimentation associated with fast flowing ice sheet outlet glaciers in disko bay west greenland fast flowing outlet glaciers currently drain the greenland ice sheet gis delivering ice meltwater and debris to the fjords around greenland although such glaciers strongly affect the ice sheet s mass balance their glacimarine processes and associated products are still poorly understood this study provides a detailed analysis of lithological and geophysical data from disko bay and the vaigat strait in central west greenland disko bay is strongly influenced by jakobshavn isbrae greenland s fastest flowing glacier which currently drains 7 of the ice sheet streamlined glacial landforms record the former flow of an expanded jakobshavn isbrae and adjacent gis outlets through disko bay and the vaigat strait towards the continental shelf thirteen vibrocores contain a complex set of lithofacies including diamict stratified mud interbedded mud and sand and bioturbated mud deposited by 1 suspension settling from meltwater plumes and the water column 2 sediment gravity flows and 3 iceberg rafting and ploughing the importance of meltwater related processes to glacimarine sedimentation in west greenland fjords and bays is emphasised by the abundance of mud preserved in the cores radiocarbon dates constrain the position of the ice margin during deglaciation and suggest that jakobshavn isbrae had retreated into central disko bay before 10 6 cal ka bp and to beyond isfjeldsbanken by 7 6 7 1 cal ka bp sediment accumulation rates were up to 1 7 cm a 1 for ice proximal glacimarine mud and 0 007 0 05 cm a 1 for overlying distal sediments in addition to elucidating the deglacial retreat history of jakobshavn isbrae our findings show that the glacimarine sedimentary processes in west greenland are similar to those in east greenland and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime

delineating ore forming rock using a frequency domain controlled source electromagnetic method abstract several magmatic ni cu deposits associated with permian triassic mafic ultramafic intrusions have been discovered during the last three decades in the southern part of the central asian orogenic belt the northeastern margin of tarim and the margin of the north china craton the accurate delineations of the large resistive rock masses are crucial for locating potential ore bodies when they are located beneath rock masse the controlled source electromagnetic method csem is an important tool for investigating resistivity contrast in earth subsurface in this study we present a comprehensive example of using frequency domain csem survey to delineate the resistive rock masses that are related to the forming of orebody the horizontal electric field which is more sensitive to resistive target than the other components is used in our study we first built a geophysical model of the survey area based on prior confirmed geophysical and geological information then both forward and inverse modeling were performed in order to assess the detectability of the resistive ore forming rock masses in the model finally this study acquired field data in the kalatongke ni cu deposit which is located in the kalatongke district of the southern section of the central asian orogenic belt and is specifically part of china s southern altai orogenic belt the resistive ore forming rock masses were successfully identified during the survey process and further verified by the drilling results it was observed that both the synthetic and field examples indicated that the adopted frequency domain csem method successfully measured the electrical fields and could be utilized to explore deeply buried resistive targets in future prospecting activities

the kalatongke magmatic ni cu deposits in the central asian orogenic belt nw china product of slab window magmatism the permian kalatongke ni cu deposits in the central asian orogenic belt are among the most important ni cu deposits in northern xinjiang western china the deposits are hosted by three small mafic intrusions comprising mainly norite and diorite its tectonic context petrogenesis and ore genesis have been highly contested in this paper we present a new model involving slab window magmatism for the kalatongke intrusions the origin of the associated sulfide ores is explained in the context of this new model minor amounts of olivine in the intrusions have fo contents varying between 71 and 81 5 mol which are similar to the predicted values for olivine crystallizing from coeval basalts in the region analytic modeling based on major element concentrations suggests that the parental magma of the kalatongke intrusions and the coeval basalts represent fractionated liquids produced by 15 of olivine crystallization from a primary magma itself produced by 7 8 partial melting of depleted mantle peridotite positive end values 4 to 10 and significant negative nb anomalies for both intrusive and extrusive rocks can be explained by the mixing of magma derived from depleted mantle with 6 18 of a partial melt derived from the lower part of a juvenile arc crust with a composition similar to coeval a type granites in the region plus up to 10 contamination with the upper continental crust our model suggests that a slab window was created due to slab break off during a transition from oceanic subduction to arc arc or arc continent collision in the region in the early permian decompression melting in the upwelling oceanic asthenosphere produced the primary magma when this magma ascended to pond in the lower parts of a juvenile arc crust it underwent olivine crystallization and at the same time triggered partial melting of the arc crust mixing between these two magmas followed by contamination with the upper crust after the magma ascended to higher crustal levels formed the parental magma of the kalatongke intrusions the parental magma of the kalatongke intrusions was saturated with sulfide upon arrival primarily due to olivine fractional crystallization and selective assimilation of crustal sulfur sulfide mineralization in the kalatongke intrusions can be explained by accumulation of immiscible sulfide droplets by flow differentiation gravitational settling and downward percolation which operated in different parts of the intrusions platinum group element pge depletion in the bulk sulfide ores of the kalatongke deposits was due to depletion in the parental magma which in turn was likely due to depletion in the primary magma pge depletion in the primary magma can be explained by a relatively low degree of partial melting of the mantle and retention of coexisting sulfide liquid in the mantle

a review of the cu ni sulphide deposits in the chinese tianshan and altay orogens xinjiang autonomous region nw china principal characteristics and ore forming processes abstract several cu ni sulphide deposits and occurrences have recently been discovered along parallel deep faults in the chinese tianshan and altay orogenic belts xinjiang province nw china the kalatongke and several other cu ni mineralized intrusions are located along the irtysh fault which separates the altay orogenic belt from the junggar basin the huangshan huangshandong xiangshan tudun erhongwa tula ergen and hongling deposits occur along the kanggurtag suture which separates the jueluotage orogenic belt from the turpan hami tuha basin the baishiquan tianyu and tianxiang deposits are located along the arqikekuduke fault which separates the jueluotage orogenic belt from the central tianshan precambrian terrane the poyi poshi and luodong deposits are located along the baidiwa fault which separates the central tianshan precambrian terrane from the beishan paleozoic rift re os dating of cu ni sulphide ores reveals that these cu ni ore belts formed in a narrow age range of 298 282 ma this age range is about the same as those of associated intrusions and dykes dated by the shrimp zircon u pb method tectonic and geochronological constraints suggest that the amalgamation of continental blocks mainly occurred during the late carboniferous in the central asian orogenic belt large scale hydrothermal and magmatic metallogenesis in the region occurred during post collisional stages of latest carboniferous to early permian age the cu ni sulphide deposits are part of this metallogenic event the cu ni orthomagmatic sulphide deposits in northern xinjiang are represented by 1 net textured type deposits by segregation of a cu ni metal sulphide melt and 2 magma conduit type some mafic ultramafic suites exhibit lithological zoning caused by strong differentiation stratiform orebodies are hosted by ultramafic rocks at the base of the magma chamber good examples are the kalatongke huangshandong and poshi deposits others such as the xiangshan baishiquan tianyu and tula ergen deposits are hosted by magma conduits consisting of peridotite troctolite and pyroxenite these ultramafic rocks either occur within faults or are surrounded by gabbroic and dioritic intrusions these two types of orthomagmatic cu ni sulphide deposits are also distributed along the same ore belts for instance the differentiated sill related huangshandong deposit co exists with the magma conduit type tula ergen deposit in the jueluotage orogenic belt orthomagmatic cu ni sulphide deposits in northern xinjiang formed during post collisional extension and are possibly related to a late carboniferous early permian mantle plume event the mafic ultramafic suites and associated cu ni deposits are commonly accompanied by dyke swarms and are characterized by elongated outcrops occurring along parallel e w trending regional faults these mafic ultramafic suites and accompanying dyke swarms are generally fractionated implying that they were feeders of presently eroded flood basalts

the erbutu ni cu deposit in the central asian orogenic belt a permian magmatic sulfide deposit related to boninitic magmatism in an arc setting the erbutu ni cu sulfide deposit is hosted in a small ultramafic intrusion located at the southern margin of the central asian orogenic belt inner mongolia this deposit is the first case of a magmatic sulfide deposit related to boninitic magmatism in an arc setting the host intrusion is composed of orthopyroxenite and olivine orthopyroxenite more than three quarters of the intrusion contains economic disseminated sulfide mineralization shrimp u pb dating of zircons from the intrusion gives a crystallization age of 294 2 2 7 ma similar to the age of the permian tarim plume in northwest china olivine orthopyroxenite is characterized by olivine crystals with relatively high fo contents 85 88 mol and extremely low ca contents 250 ppm coexisting orthopyroxene crystals have clinoenstatite composition with enstatite from 86 to 88 mol whole rock data show characteristic enrichments of light ree relative to heavy ree pronounced negative nb ta anomalies and moderately positive hf anomaly the 34s values of sulfide separates are 4 to 5 significantly higher than the typical mantle value 0 2 the hf values of zircons are from 4 to 9 these data indicate that the parental magma was a boninite crustal contamination was involved during magma evolution and ore formation

the dwyka group in the northern part of kwazulu natal south africa sedimentation during late palaeozoic deglaciation abstract multiple sedimentary sequences up to and over 300 m thick and comprising the late palaeozoic dwyka group in the southeastern part of the african subcontinent were deposited during deglaciation of the gondwana ice sheet attention is focused on the northern part of kwazulu natal in south africa where the dwyka group represented by glaciogenic deposits rests on an uneven surface of archaean basement rocks these deposits occur on the northwestern flank of an elongate pre dwyka crustal downwarp which had a significant influence on the mode of sedimentation as it progressively subsided stratigraphic sections from selected localities in northern kwazulu natal display the thickness variations and marked vertical and lateral lithofacies changes that characterise the dwyka group of this region diamictite consistently occurs at the base of the dwyka sequences but is also interstratified with mainly arenaceous and conglomeratic lithotypes which predominate in the upper 60 160 m these heterolithic sequences reflect sedimentation from a retreating marine ice sheet during a rise in relative sea level which commenced towards the close of the carboniferous period in southwestern gondwana as the margin of the ice sheet receded towards an archaean upland region in the northwest this ice mass was locally grounded and stabilised on bathymetric highs of the irregular basement topography release of glacial debris produced diachronous sedimentary sequences as the ice sheet was temporarily pinned on successive basement highs during its episodic retreat matrix and clast supported conglomerates and associated sandstones testify to a plexus of sediment gravity flow and subaqueous outwash processes that occurred near the grounding line thick homogeneous blanket like diamictite facies in the southeastern and southern part of the region suggest an unimpeded retreat of the sediment laden marine sheet in the deeper parts of the basin rapid dissipation of the ice in the closing stages of deglaciation was followed by accumulation of postglacial muds which mantled the glaciogenic sediments in the northernmost part of the study area proximal products of deglaciation represented by conglomeratic deposits and associated sandstones are preserved in deep partly exhumed glaciated valleys and depressions along the southern periphery of the archaean upland the distinctive character of the dwyka group in northern kwazulu natal is partly attributable to the complex tectonic setting in which it occurs and reflects an interplay of various factors that controlled the styles of sedimentation during deglaciation

late pleistocene glacimarine record in saanich inlet british columbia canada abstract late pleistocene deposits were cored at two sites in saanich inlet and provide a record of the sedimentary environment during deglaciation of this fjord at site 1033 at the southern end of the fjord 59 3 m of late pleistocene sediment was obtained in a hole drilled to 105 1 mbsf at site 1034 4 8 km to the north a hole was drilled to 118 2 mbsf recovering 49 8 m of late pleistocene sediment sediments were deposited in this deep 200 m fjord basin as a lobe of the cordilleran ice sheet retreated at the end of fraser glaciation this is the first recovery of basin fill sediments from the pleistocene retreat of the cordilleran ice sheet lithofacies analysis particle size measurements and 17 ams 14 c dates on marine shells or wood fragments are used to reconstruct the glacimarine sedimentary environment sediments are dense gray to olive gray terrigenous silty clay with thick graded sand beds and interlaminated fine sand and silt with mud scattered dropstones clusters of pebbles and pods of sand and granules are common bioturbation indicated by disruption of laminae and horizontal burrows or black mottles is minimal to moderate and decreases downcore a calving tidewater glacier retreated northward through saanich inlet however the ice contact sediments are beneath the depth cored at both sites the glacier retreated rapidly and the basin was open to marine exchange through satellite channel prior to 13 270 60 14 c yr bp the oldest date from the cores deposition of lithofacies association i occurred in an iceberg zone depositional environment dominated by turbid meltwater plumes and intense iceberg rafting within approximately 10 km of the glacier terminus after the glacier grounded at the head of cowichan bay lithofacies association ii was deposited in the ice distal depositional environment by turbidity currents that by passed the sill and turbid meltwater plumes lithofacies association iii was deposited under post glacial conditions at the end of the pleistocene

late wisconsinan glaciomarine deposition and isostatic rebound northern puget lowland washington the distribution and age of glaciomarine and marine sediment in the northern puget lowland washington demonstrate that rapidretreatofcontinentalice theeverson marineincursion andhighratesofisostatic reboundoccurredbetweenabout13 600and 11 300 14 c yr b p 11 3 ka glaciomarine and marine deposits are thickest in zones where retreating ice lobes grounded in the northeast puget lowland and near large drainages glaciomarine sediment was depositedmainlyfrom 1 submarineoutwash in ice proximal zones 2 turbid underflows dispersed melt water icebergs and resedimentation in transitional zones and 3 dispersedmeltwaterandcurrentsinicedistal zones marine estuarine and emergence intertidalandbeach faciesaccumulated in areas more than 10 km from ice margins particularly near major rivers molluscan and foraminiferal assemblages intheglaciomarineandmarinedepositsindicate that turbid cool brackish water covered much of the puget lowland during the everson interval water was generally shallower 30 m in the southern part of the area and deeper 15 60 m to the north mineralogy and geochemical properties such as boron or sodium content of the gravel free fraction do not clearly distinguish glaciomarine and marine deposits from terrestrial deposits isostatic rebound rapidly lifted the glaciomarine and marine deposits through sea level between about 13 5 and 11 3 ka the presentaltitudesofradiocarbon datedshell and the marine limit show that initial rates of isostatic rebound exceeded 10 cm yr 21 in thenorthernpugetlowland butdroppedto 2cmyr 21 before 11 ka the uplift gradient is about 0 6 m km 21 to the north and steepens locally to at least 1 3 m km 21 the pattern of emergence in the northern puget lowland is anomalous locally perhaps as a result of complex isostatic effects near the glacier margin rapid rise of sea level or tectonic deformation

origin of pge depleted ni cu sulfide mineralization in the triassic hongqiling no 7 orthopyroxenite intrusion central asian orogenic belt northeastern china the 216 ma hongqiling no 7 intrusion is located in the southern margin of the central asian orogenic belt northeastern china it was the second largest ni producer after jinchuan in china the intrusion crops out in an area of 0 013 km2 on the surface it intruded gneisses and marbles of the paleozoic hulan formation the intrusion is mainly composed of orthopyroxenite 95 vol with minor harzburgite and norite over 90 vol of the intrusion contains disseminated net textured or massive sulfides the bulk sulfide ores recalculated to 100 sulfide have low average pge concentrations 5 6 ppb os 3 1 ppb ir 4 7 ppb ru 2 2 ppb rh 31 ppb pt and 11 ppb pd and high cu pd ratios 3 105 3 107 consistent with the compositions of sulfide liquids segregated from pge depleted magma olivine composition fo 86 mol indicates a fractionated parental magma back calculation shows that the parental magma was possibly derived by olivine fractionation from a primary magma containing 16 wt mgo numerical modeling indicates that pge depletion in the parental magma of the hongqiling no 7 intrusion was due to previous sulfide segregation in the staging chamber whole rock data show light rare earth element ree enrichments negative nb ta anomalies and positive nd t 216 ma values from 3 to 5 which can be explained by mixing of a mantle derived magma with a granitic melt formed by magma underplating in the crust the os t 216 ma values of sulfide ores vary from 50 to 187 the highly variable os t values coupled with similar nd t values indicate preferential assimilation of crustal sulfides during magma rock interaction based on the observations we propose that the parental magma of the hongqiling no 7 intrusion formed by contamination of mantle derived s undersaturated magma by crustally derived granitic melt together with olivine crystallization in a staging chamber the contaminated magma became pge depleted due to sulfide segregation in response to crustal contamination the pge depleted magma became s undersaturated again during ascent due to the negative effect of pressure on the maximum solubility of sulfur in magma upon arrival near the present level of the hongqiling no 7 intrusion a second event of sulfide segregation took place due to addition of crustal sulfides from immediate country rocks the immiscible sulfide liquids and orthopyroxene crystallizing from the magma were retained in a dynamic conduit to form the ore bearing intrusion while much of the magma left the conduit to form some of the nearby sulfide poor intrusions we suggest future exploration in the region to focus on olivine bearing and orthopyroxene dominant intrusions with ages similar to that of the hongqiling no 7 intrusion

volcanosedimentary paleoenvironments of ediacaran fossils in newfoundland a new perspective on paleoenvironments of ediacaran fossils of the upper conception group newfoundland comes from geochemical and sedimentological study of volcanic tuffs and sedimentary rocks tuffs in the conception group have major and trace element compositions and u pb ages comparable with those of source volcanics on the nearby burin and bonavista peninsulas and the islands of st pierre and miquelon loss of silica and alkalies in some ashes indicates weathering on land not marine diagenesis volcanic crystal and lapilli tuffs fail to show grading and have lapilli and highly vesicular scoria scattered in a fine grained matrix and so they were deposited on land not in water these as well as block and ash flows volcanic spindle bombs and degassing features are evidence of eruptions from nearby subaerial volcanic edifices the fossiliferous conception group accumulated within a forearc basin formed on continental crust inboard of the holyrood horst and uplifted as part of an ancient subduction complex or accreted terrane like analogous forearc basins in oregon washington southern chile and japan the conception group includes not only marine bay turbidites but also a variety of intertidal and terrestrial tsunamites seismites tempestites and paleosols traditional marine turbidite models explain deposition of the mall bay lower drook and lower briscal formations of the conception group but the gaskiers upper drook upper briscal and mistaken point formations were deposited in coastal plains and intertidal zones paleoenvironments of vendobiont fossils preserved in life position in newfoundland were terrestrial to marginal marine not deep sea

u pb zircon geochronology and geochemistry of paleoproterozoic magmatic suite from east sarmatian orogen tectonic implications on columbia supercontinent abstract extensive paleoproterozoic magmatism occurred in the east sarmatian orogen eso located at the junction of the sarmatian and volga ural segments of the east european craton generating numerous felsic to mafic ultramafic complexes here we report geochemical and zircon u pb age data from a suite of ultramafic mafic and diorite granodiorite intrusive rocks from this orogen shrimp u pb dating of zircons yielded the following concordant ages for the magmatic suites 1 2085 17 to 2093 20 ma sub volcanic high mg intrusions of shmb like melanorite melaquartz diorite melagranodiorites and quartz diorite tonalite granodiorites 2 2072 4 8 2073 8 3 and 2068 13 ma ultramafic mafic diorite layered intrusions 3 2053 14 to 2058 22 ma magnesian ferroan quartz diorite tonalite granodiorite intrusions and 4 2035 18 ma ferroan norite diorite intrusions the trace and rare earth element geochemistry indicate arc related features the enrichment in lree and lile in the mafic ultramafic and diorite granodiorite suites is correlated with melting of metasomatised lithosphere mantle along with involvement of crustal components in their petrogenesis the third magmatic event conforms to the age of the post collision s and a granitoids of the region our data indicate two major magmatic events in the post collisional setting the former immediately after metamorphism with the formation of schistosity in the host rocks and the latter two during the culmination of the orogenic cycle in the voronezh crystalline massif the duration of the paleoproterozoic orogeny during the collision of the sarmatian and volga ural segments of the east european craton is estimated to be approximately 100 million years from 2140 to 2035 ma we propose that the layered orogenic plutons were derived from relatively deeper mantle source whereas the sub volcanic rock series are derivatives of the slightly shallow mantle source the paleoproterozoic collision in the region broadly coincides with timing of amalgamation of the global supercontinent columbia

the permian huangshanxi cu ni deposit in western china intrusive extrusive association ore genesis and exploration implications the permian huangshanxi cu ni deposit is the second largest magmatic sulfide deposit discovered to date in a major ni cu province related to protracted basaltic magmatism in eastern xinjiang china it is hosted by a small mafic ultramafic intrusion comprised predominantly of lherzolites olivine websterites gabbronorites and gabbros the huangshanxi intrusion is coeval with permian basalts of tholeiitic and alkaline affinities in the tuha and tarim basins respectively to evaluate a possible genetic relationship between the huangshanxi intrusion and a specific type of coeval basalt in the region as well as ore genesis in the intrusion we have carried out an integrated mineralogical petrological and geochemical study our data reveal that the huangshanxi intrusive rocks are characterized by relatively flat chondrite normalized ree patterns depletion in nb and ta and elevated end values varying between 6 and 10 these features are similar to those of coeval tholeiitic basalts in the nearby tuha basin but are significantly different from those of coeval alkaline basalts in the relatively remote tarim basin the geochemical similarities and differences suggest that the huangshanxi intrusion is genetically related to the tholeiitic basalts in the tuha basin not to the alkaline basalts in the tarim basin as suggested previously by some researchers this implies that regional exploration for the huangshanxi type cu ni deposits should be centered in the tuha basin instead of the tarim basin more specifically the uplifted areas around the tuha basin where similar intrusions may have been brought close to the surface should be carefully examined for mineralization potential intrusive relations and mass balance constraints from incompatible trace elements and sulfide abundances suggest that the huangshanxi intrusion represents a dynamic magma conduit through which multiple pulses of magma ascended to higher levels or to the surface numerical simulation of magma evolution and mixing calculations using sr nd isotopes indicate that selective assimilation of s bearing crustal materials is important for sulfide saturation during the early stages of magma evolution when lherzolites formed fractional crystallization may have also played a role in the attainment of sulfide saturation during the later stages of magma evolution when olivine websterites and gabbronorites formed in both cases immiscible sulfide droplets were retained in the conduit to form disseminated sulfide lenses while the fractionated silicate liquids and buoyant phases such as plagioclase continued to ascend extremely low pge tenors in the sulfide ores of the huangshanxi deposit suggest that the parental magma was highly depleted in chalcophile elements possibly due to previous sulfide segregation at depth

research on snow and ice this review unlike its predecessor martinelli et al 1979 is an intentionally selective survey of recent advances in selected areas of snow and ice research i have chosen to concentrate on studies relating to large scale aspects of the cryosphere and to consider their wider significance for other disciplines results obtained by new measurement techniques and the application of remote sensing methods are also stressed at the same time the broad lines of advance in glaciological research as represented in books conference themes and major field or laboratory programs are noted and a detailed bibliography is appended

os and s isotope studies of ultramafic rocks in the duke island complex alaska variable degrees of crustal contamination of magmas in an arc setting and implications for ni cu pge sulfide mineralization the duke island complex is one of the several ural alaskan intrusions of cretaceous age that occur along the coast of se alaska significant quantities of magmatic ni cu pge sulfide mineralization are locally found in the complex primarily within olivine clinopyroxenites sulfide mineralization is ni poor consistent with petrologic evidence which indicates that sulfide saturation was reached after extensive olivine crystallization olivine clinopyroxenites were intruded by magmas that produced sulfide poor adcumulate dunites as part of a study to investigate the potential for ni rich sulfide mineralization in association with the dunites a re os and s isotope study of the dunites as well as sulfide mineralization in the olivine clinopyroxenites was initiated importantly recent drilling in the complex identified the presence of sulfidic and carbonaceous country rocks that may have been involved in the contamination of magmas and generation of sulfide mineralization os 110 ma values of two sulfidic country rocks are 1022 and 2011 34s values of the country rocks range from 2 6 to 16 1 187os 188os ratios of sulfide minerals in the mineralization hosted by olivine clinopyroxenites are variable and high with os 110 ma values between 151 and 2059 extensive interaction with re rich sedimentary country rocks is indicated in contrast os 110 ma values of the dunites are significantly lower ranging between 2 and 16 187os 188os ratios increase with decreasing os concentration this inverse relation is similar to that shown by ultramafic rocks from several arc settings as well as altered abyssal dunites and peridotites the relation may be indicative of magma derivation from a sub arc mantle that had experienced metasomatism via slab derived fluids alternatively the relation may be indicative of minor contamination of magma by crustal rocks with low os concentrations but high 187os 188os ratios a third alternative is that the low os concentrations and elevated 187os 188os ratios denote subsolidus interaction with seawater or meteoric water 34s values of the dunites range between 6 4 and 6 6 and are consistent with the addition of s during fluid rock interaction and serpentinization the sharp contrast between the os isotope ratios of the dunites and those of the sulfide mineralization illustrate that magmas that were spatially part of the same intrusive system may have experienced very different histories of interaction with country rocks an important corollary is that because of the concentrations of os and s elevated os isotope ratios a function of high re concentrations and variable sulfur isotope ratios of sulfidic and carbonaceous country rocks both s and os isotope data from the olivine clinopyroxenite hosted sulfide mineralization are consistent with less than 2 of bulk rock contamination even lower fractional abundance values may be indicated if the contaminant was a s c os rich fluid or partial melt derived from the sulfidic carbonaceous metasedimentary country rocks despite the low degrees of contamination the amounts of os and s in the sulfide mineralization that may have been derived from country rocks often exceed 50

crustal contamination and sulfide immiscibility history of the permian huangshannan magmatic ni cu sulfide deposit east tianshan nw china abstract the huangshannan mafic ultramafic intrusion is a permian ni cu sulfide bearing intrusion in the southern margin of the central asian orogenic belt the intrusion consists of an ultramafic unit which is composed of lherzolite and olivine websterite and a mafic unit which is composed of olivine gabbronorite gabbronorite and leuco gabbronorite this intrusion was formed by two separate pulses of magma a more primitive magma for the early ultramafic unit and a more evolved magma for the late mafic unit u pb isotope geochronology of zircon from the mafic unit yields an age of 278 2 ma according to its olivine and cr rich spinel compositions the estimated parental magma of lherzolite for the huangshannan intrusion has 12 4 wt mgo indicating picritic affinity fractional crystallization modeling results and the presence of rounded sulfide inclusions in an olivine crystal fo 86 7 indicate that sulfide immiscibility was achieved at the beginning of olivine fractionation co magmatic zircon crystals from gabbronorite have a 18o value close to 6 5 which is 1 2 higher than the typical mantle value and suggests significant crustal contamination 20 the positive ehf t values of co magmatic zircon which vary from 9 2 to 15 3 and positive whole rock end t values which vary from 4 7 to 7 8 also indicate that the parental magma was derived from a depleted mantle source and contaminated by 5 20 juvenile arc crust and then by 5 upper crustal materials however modeling results of sulfur content at sulfide saturation reveal that such a large amount of crustal contamination is not sufficient to trigger sulfide saturation in the parental magma which strongly suggests that external sulfur addition probably during contamination has played a critical role in causing sulfide immiscibility furthermore the arc magmatism geochemical signatures of the huangshannan intrusion such as significant nb and ta depletion relative to la and low ca contents in olivine are interpreted as the result of slab derived fluid modification during previous subduction we speculate that the contamination of juvenile arc crust may have occurred in the lower crust because of picritic magma underplating and that partial melting in the mantle was triggered by the impingement of a mantle plume or lithosphere delamination in a post subduction environment

ichnological signatures of shallow freshwater lakes in the glacial itarare group mafra formation upper carboniferous lower permian of parana basin s brazil abstract the upper carboniferous lower permian glacigenic deposits of the itarare group parana basin are widely known and cover an extensive area in the southern brazil these deposits consist of different arrangements of massive shales diamictites rhythmites and fine to medium grained sandstones with trough cross stratification five genetically distinct thickening locally coarsening upward successions of regular rhythmites can be distinguished in the mafra rio negro region santa catarina and parana states southern brazil representing the landward portion of an incised valley filled during deglaciation a low diversity invertebrate ichnofauna composed of a freshwater shallow burrow dominated suite and trackway dominated suite occurs in these rhythmites the freshwater shallow burrow dominated suite is composed of cochlichnus anguineus cruziana cf problematica gordia arcuata gordia marina hormosiroidea meandrica rusophycus cf carbonarius and treptichnus pollardi as well as undichnia consulca and intermittent rusophiciform traces it represents a mermia ichnocoenosis and occurs in the rhythmites of the upper sets commonly overlapped by d gouldi and d biformis in palimpsest preservation d gouldi and d biformis compose the trackway dominated suite which occur in all ichnofossiliferous paired mudstone siltstone of the basal sets of the rhythmite succession and in almost all of the upper sets it represents an atypical scoyenia ichnocoenosis and is generally preserved over microbially induced wrinkle structures the rhythmic deposition suggests distal underwater gravity flow deposits filling shallow lakes or ponds in depressed areas the siltstones deposited by melting currents and the mudstones by sediment fall out after the flux ceased the abundant wrinkle structures suggest quiet waters the overlying deposits bearing a brackish water ichnofauna and marine fossils suggest a coastal setting connected with the sea although atypical the occurrence of a scoyenia ichnocoenosis in almost all ichnofossiliferous rhythmite couplets preserved over wrinkle structures or overlapping mermia ichnocoenosis suggests that these shallow lakes were episodically dried up at least partially the present data allow interpreting the regular ichnofossiliferous rhythmites of the mafra formation as deposited in shallow lakes or ponds developed in outwash plains at the landward side of a fjord embayment during deglaciation

timing and depositional environments of a middle pleistocene glaciation of northeast england new evidence from warren house gill county durham at various times during the quaternary north eastern england was a zone of confluence between dynamic ice lobes sourced from the pennines northern scotland the cheviots and scandinavia the region thus has some of the most complex exposures of middle to late pleistocene sediments in britain with both interglacial and glacial sediments deposited in terrestrial and marine settings we investigated sedimentary sequences exposed on the coastline of county durham at warren house gill and present a new model of british and fennoscandian ice sheet interaction in the north sea basin during the middle pleistocene the stratigraphy at warren house gill consists of a lower diamicton and upper estuarine sediments both part of the warren house formation they are separated from the overlying weichselian blackhall and horden tills by a substantial unconformity the lower diamicton of the warren house formation is re interpreted here as an mis 8 to 12 glaciomarine deposit containing ice rafted lithics from north eastern scotland and the northeast north sea and is renamed the ash gill member it is dated by lithological comparison to the easington raised beach middle pleistocene amino acid racemisation values and indirectly by optically stimulated luminescence the overlying shallow subaqueous sediments were deposited in an estuarine environment by suspension settling and bottom current activity they are named the whitesides member and form the uppermost member of the warren house formation during glaciation ice rafted material was deposited in a marine embayment there is no evidence of a grounded onshore scandinavian ice sheet in county durham during mis 6 which has long been held as the accepted stratigraphy this has major implications for the currently accepted british quaternary stratigraphy combined with recent work on the middle pleistocene north sea drift from norfolk which is now suggested to have been deposited by a scottish ice sheet the presence of a scandinavian ice sheet in eastern england at any time during the quaternary is becoming increasingly doubtful

palaeoproterozoic glaciomarine sedimentation in an extensional tectonic setting the honkala formation finland abstract the honkala formation of the honkajarvi group in the kainuu schist belt of northern finland central fennoscandian shield provides evidence of palaeoproterozoic glaciation on the fractured surface of the craton the diamictites and associated rocks of the honkala formation are some 190 m thick in the studied area they consist of a remnant of the glacigenic sequence deposited during an incipient stage of crustal extension the rocks rest unconformably on the late archaean basement and conformably on rift related volcanics the volcanics were erupted during a period of general fragmentation and rifting of the late archaean basement 2 4 2 3 ga ago at this time shallow intracratonic basins and depressions started to form on a continental scale subsequently many of these basins subsided below sea level the lower part of the honkala formation consists of turbiditic non glacial mudstones and sandstones up to 70 m thick glacial advance is indicated by ice rafted deposits forming a succession of some 10 to 50 m deposition took place in a glaciomarine rift basin extending towards the interior of the archaean craton waning glacial influence is indicated by some 70 m of sandstones the uppermost sandstones were influenced by intermittent chemical weathering indicating that these deposits were subjected to subaerial conditions and warmer climate correlation on a global scale is possible during the early palaeoproterozoic the fennoscandian and north american cratons were probably situated close together at a high latitude and both were affected by a major continental glaciation the fennoscandian craton then shifted to lower latitudes whereas the north american cratonic margin recorded further glaciations at high latitudes

re os geochronology on sulfides from the tudun cu ni sulfide deposit eastern tianshan and its geological significance the tudun deposit is a medium sized cu ni sulfide deposit located at the westernmost edge of the huangshan jing erquan belt in the northern part of eastern tianshan nw china sulfide separates including pentlandite pyrrhotite and chalcopyrite from the tudun deposit contain re common os and 187os ranging from 40 46 to 201 2 0 8048 to 6 246 and 0 1709 to 0 9977 ppb respectively they have very low 187os 188os ratios of 1 224 2 352 the sulfides yield a re os isochron age of 270 0 7 5 ma mswd 1 3 consistent within uncertainty with the shrimp zircon u pb age for the tudun mafic intrusion gabbro of 280 0 3 0 ma the calculated initial 187os 188os ratio is 0 533 0 022 and os values range from 283 to 307 with a mean of 297 indicating significant crustal contamination of the parent melt prior to sulfide saturation the tudun deposit shares the same age and re os isotopic compositions with other orthomagmatic cu ni sulfide deposits in huangshan jing erquan belt suggesting that they have formed in early permian

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

a modified genetic model for the huangshandong magmatic sulfide deposit in the central asian orogenic belt xinjiang western china the huangshandong ni cu deposit is the largest magmatic sulfide deposit discovered to date in the central asian orogenic belt in northern xinjiang western china the host intrusion is a 274 ma composite mafic ultramafic intrusion consisting of four separate intrusive units a large layered gabbroic sequence phase i a sheet like ultramafic body phase ii a dyke like gabbronorite body phase iii and an irregular ultramafic unit phase iv important sulfide mineralization is present in the last three intrusive units predominantly as disseminated and net textured sulfides pyrrhotite pentlandite and chalcopyrite the huangshandong mafic ultramafic intrusive rocks are characterized by arc like geochemical signatures such as low ca content in olivine and negative nb ta anomalies in whole rocks this together with a post subduction setting for the east tianshan in the permian suggests that the source mantle was modified previously by slab derived fluids in the carboniferous the mantle derived magma was ponded in a staging chamber in the lower part of the newly formed arc crust the first batch of magma to arrive at huangshandong was most fractionated and depleted in ni crystallizing fe rich and ni depleted olivine fo67 300 ppm ni the second batch of magma was more primitive crystallizing more primitive olivine fo81 84 the third batch of magma was also highly fractionated and depleted in ni crystallizing fe rich and ni depleted olivine fo72 600 ppm ni the final batch of magma became more primitive again crystallizing the most primitive olivine fo81 86 the occurrence of rounded sulfide inclusions in olivine primocrysts in the huangshandong ultramafic rocks indicates that immiscible sulfide liquid droplets were present during olivine crystallization the ni tenors of disseminated sulfide ores in the gabbronorite dyke vary mainly between 5 and 8 wt which are too high to have been produced by the parental magma of the dyke the ni cu and platinum group elements pge tenors of disseminated sulfide ores in the dyke phase iii and the ultramafic sheet phase ii are remarkably similar these observations together with the sequence of magma emplacement suggest that the sulfide liquids entrapped in the magma of the dyke formed at depth by a previous pulse of more primitive magma the estimated parental magma for the most primitive lherzolites in the huangshandong intrusion contains 10 wt mgo modeling shows that sulfide saturation in the parental magma of the huangshandong lherzolites could have resulted from fractional crystallization significant pge depletions relative to ni and cu in the disseminated sulfide ores of the huangshandong deposit may be due to sulfide retention in the source mantle

preparation and analysis techniques for studies of laminated sediments laminated sediments commonly represent the highest resolution continuous records available of marine and lacustrine variability to exploit this information effectively careful sampling and preparation procedures must be followed thus the method of analysis chosen must have sufficient resolution to recover the data the scanning electron microscope because of its good spatial resolution is an ideal tool for analyzing laminated sediment fabric backscattered electron imagery produces preserved flux data on intra annual time scales which enables high resolution fabric studies palaeoenvironmental reconstructions and compilation of data for time series analysis this contribution summarizes the techniques used for laminated sediment fabric investigation and discusses the use of the scanning electron microscope including the best preparation method for thin sections and the procedure for backscattered electron imagery analysis

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

holocene glacial history and sea level changes on james ross island antarctic peninsula a reconstruction of deglaciation and associated sea level changes on northern james ross island antarctic peninsula based on lithostratigraphical and geomorphological studies shows that the initial deglaciation of presently ice free areas occurred slightly before 7400 14 c yr bp sea level in connection with the deglaciation was around 30 m a s l a glacier readvance in brandy bay of at least 7 km with the initial 3 km over land reached a position off the present coast at ca 4600 yr bp the culmination of the advance was of short duration and by 4300 yr bp the coastal lowlands again were ice free a distinct marine level at 16 18 m a s l was contemporaneous with or slightly post dates the brandy bay advance thus indicating the relative sea level around 4600 4500 yr bp our results from james ross island confirm that over large areas in this part of antarctica the last deglaciation occurred late 1997 by john wiley sons ltd

ice proximal glaciomarine sedimentation and sea level change in the inverness area scotland a review of the deglaciation of a major ice stream of the british late devensian ice sheet abstract evidence of both rising and falling relative sea levels and glacitectonic movements is preserved in two formations of raised glaciomarine deposits that were laid down in front of an oscillating grounded tidewater glacier in the inverness firth these changes occurred during the latter stages of the disintegration of the moray firth ice stream one of the major ice streams that drained the british main late devensian ice sheet most of the glaciomarine deposits antedate a sequence of glacio isostatically tilted late devensian marine shorelines and associated littoral and estuarine deposits the shorelines began forming at about 13 000 bp and record a progressive fall in relative sea level a new model for the deglaciation of the moray firth region is proposed after a critical appraisal of published accounts of both onshore and offshore quaternary sequences the disintegration of the moray firth ice stream involved several rapid phases of retreat to pinning points caused by iceberg calving and triggered by rising global sea level each retreat was followed by minor readvances or stillstands possibly caused by short lived accelerated periods of glacio isostatic rebound and concomitant temporary falls in relative sea level two such events occurred in the inverness firth the ardersier oscillation and the alturlie stillstand substantial differences lower relative sea levels later deglaciation are apparent between the pattern of ice retreat in the moray firth region and published accounts of the deglaciation of the irish sea basin these differences require a reassessment of some current hypotheses concerning the disintegration of major ice streams associated with high relative sea levels furthermore geological and geomorphological evidence suggesting both rising and falling sea levels in the inverness area prior to ca 13 500 bp is not fully compatible with recently published computer simulations of the dissolution of the british main late devensian ice sheet

biogenic facies in the antarctic glacimarine environment basis for a polar glacimarine summary abstract the association of glacial deposits diamicts or tillites with biogenic and or chemically derived sedimentary rocks in the ancient record is one which continues to challenge interpretation an analogous association can be found on portions of the east antarctic continental shelf where relict glacial and glacimarine diamictons are overlain by a varied and complex suite of modern biogenic deposits carbonate bioclastic material can be found in two distinct zones and its deposition may have been contemporaneous with partial glacial expansion onto the shelf a nearshore carbonate facies consists of in situ and partially reworked barnacles bryozoans ostracods pelycepods gastropods planktonic and benthonic foraminifera a siliceous biogenic component is intermixed within the shallow water 500 m siliceous facies of pelagic hemipelagic and sediment gravity flow origin is found within inner shelf depressions and consists predominantly of diatom frustules and radiolaria these accumulations of siliceous ooze and mud clearly post date glacial recession from the shelf and contain laminated cross laminated and massive interbeds which are accumulating at rates of 0 3 cm yr the extreme polar climate inhibits meltwater production and terrigenous influx into marine basins this allows for the accumulation of biogenic rich material which is also favored by the high seasonal productivity inherent in the south polar oceans ancient analogs to these modern deposits exist and their association with glacimarine strata could be used to infer polar climatic settings and glacial retreat that is related to eustatic sea level rather than regional warming

petrogenesis and ore genesis of the permian huangshanxi sulfide ore bearing mafic ultramafic intrusion in the central asian orogenic belt western china abstract the permian huangshanxi mafic ultramafic intrusion hosts one of the two largest magmatic sulfide deposits in the eastern tianshan which is situated in the southern margin of the central asian orogenic belt in this paper we use mineral compositions and whole rock geochemical data to decipher the genetic relationship between magma evolution and sulfide mineralization the huangshanxi intrusion consists of three separate intrusive units important sulfide mineralization occurs in the base of the last intrusive unit an elongated layered ultramafic body composed of lherzolite at the bottom olivine websterite in the middle and websterite at the top based on olivine liquid equilibria and mass balance the mgo and feo contents in the parental magma for a lherzolite sample are estimated to be 8 71 and 8 36 wt respectively the huangshanxi mafic ultramafic intrusive rocks and the estimated trapped liquids for several olivine orthopyroxene cumulate rocks all show light rare earth element enrichments relative to heavy rare earth elements and significant nb depletions relative to th and la which are similar to the characteristics of coeval basalts in the region the arc like geochemical features are attributed to pre permian mantle metasomatism by slab derived fluids partial melting of the previously modified mantle is thought to have resulted from heating by upwelling asthenosphere associated with post subduction lithosphere delamination or by mantle plume activity the relationship between the fo and ni contents of olivine crystals from the huangshanxi sulfide poor ultramafic rocks in situ differentiation stage during which the sulfide droplets and olivine crystals settled to form the sulfide olivine cumulate zones at the base of the huangshanxi magmatic system

geochronological and geochemical constraints on sulfide mineralization in the qingmingshan mafic intrusion in the western part of the proterozoic jiangnan orogenic belt along the southern margin of the yangtze craton abstract the qingmingshan magmatic fe ni cu sulfide deposit is located in the southern margin of the yangtze craton in the western part of the proterozoic jiangnan orogenic belt sulfide mineralization occurs as disseminated zones in a dike like mafic body intruding early neoproterozoic meta sedimentary rocks the host intrusion can be further divided into an upper gabbronorite unit a middle dolerite unit and a lower gabbronorite unit each unit contains at least one disseminated sulfide zone sulfide mineral assemblages are composed of pyrrhotite pentlandite and chalcopyrite zircon u pb dating yields a crystallization age of 847 8 3 8 ma 2 for the intrusion the host rocks are characterized by enrichment in light rare earth elements ree relative to heavy ree and show pronounced negative nb ta anomalies similar to the characteristics of arc mafic igneous rocks worldwide mixing calculations indicate that the variations of th yb n and th nb n in the intrusion are consistent with between 10 and 20 wt crustal contamination of the parental magma the sulfide separates are characterized by elevated 34s values from 1 5 to 3 5 with a peak at 2 6 and by os values from 2 to 89 indicating addition of crustal sulfur and os to the parental magma the trace element data and s os isotopes support the premise that sulfide saturation in the qingmingshan magma was triggered by crustal contamination variations of pge tenors in different sulfide zones can be explained by variable r factors from 300 to 1000 during sulfide segregation from the magma mass balance calculations indicate that the parental magma was severely depleted in pge which could be a primary signature of arc basaltic magma formed by low degrees of partial melting or due to previous sulfide segregation at depth the lithological and mineralization zonation across the dike like qingmingshan mafic intrusion indicates that at least three separate pulses of sulfide charged magma were involved in the formation of the qingmingshan magmatic sulfide deposit the qingmingshan mafic intrusion is interpreted to be a part of a sub arc magma plumbing system coeval ultramafic intrusions formed from more primitive magma in the region are good exploration targets for magmatic sulfide deposits with higher ni cu ratios than the qingmingshan deposit

subduction of diverging plates and the principles of slab window formation consumption of an ocean basin by subduction commonly brings a sea floor spreading ridge toward a deep sea trench if plate divergence and convergence continue after the ridge intersects the subduction zone a slab window forms between the subducted parts of the diverging oceanic plates producing anomalous thermal physical and chemical effects in the surrounding asthenospheric mantle in turn these conditions alter the tectonic and magmatic evolution of the overriding plate usually disturbing ordinary fore arc and arc regimes differential lithospheric stresses on opposite sides of the triple junction contribute to disturbances in the overriding plate anomalous magmatism from fore arc to back arc may be accompanied by fore arc metamorphism strike slip faulting uplift extension and in extreme cases rifting the shape and size of the window are controlled mainly by the pre subduction ridge transform trench configuration slab dip angles and vectors of plate convergence subducted ridge segments expand into windows whose margins approximately parallel the motion vectors between the triple junction and the subducting plates subducted transform faults continue to be active usually as oblique slip faults until the plates separate as transform faults subduct they become longer on the plate which occupies the acute angle between ridge and trench and shorter on the other plate trains of isolated windows produced by subduction of a segmented ridge transform system progressively expand during descent commonly merging together to form a composite slab window oblique subduction of a highly segmented ridge is likely to produce two or more fraternal slab windows one at each site of ridge trench intersection above a slab window arc volcanism diminishes and may be replaced by volcanism of mid ocean ridge or rift affinity the change in chemical character reflects various processes including elevated heat flow decreasing hydration of the upper mantle juxtaposition of supra and sub slab mantle reservoris asthenospheric upwelling and melting of the trailing plate edges if the slab window migrates the anomalous magmatic regime may be replaced by renewed arc volcanism identifying the effects of slab windows in ancient convergent margin assemblages requires an understanding of slab window principles and implications

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

coeval brittle and ductile deformation beneath the late wisconsinan puget lobe washington state usa late wisconsinan glacial sediments exposed on whidbey island and camano island puget sound washington state usa were deposited in a proglacial shallow marine outwash environment during northward retreat of the puget lobe of the cordilleran ice sheet sediments mainly comprise massive and cross bedded sand and gravels and rhythmically bedded clay and silt fine sand couplets interbedded with diamictons that were deposited by a range of mass flows of different viscosities although sediment stratigraphy and ice advance retreat patterns are well established for the puget lobe brittle and ductile deformation structures within and separating these sediment units are less well understood these structures record the nature of ice bed interactions taking place in subglacial and proglacial environments this study examines evidence for these processes and environments key deformation structures identified include open to overturned folds normal and reverse faults clastic dikes and hydrofractures and passive loading structures evidence for coeval development of ductile and brittle deformation structures shows the close relationship between porewater changes sediment rheology and sediment system responses to changes in strain caused by ice bed interactions

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

zircon dating hf sr nd os isotopes and pge geochemistry of the tianyu sulfide bearing mafic ultramafic intrusion in the central asian orogenic belt nw china abstract the tianyu mafic ultramafic intrusion is one of many important sulfide bearing mafic ultramafic intrusions in the eastern tianshan terrane located in the southern margin of the central asian orogenic belt in north xinjiang nw china the origin of sulfide mineralization in these intrusions their relationship with permian basalts and a type granites and the geodynamic setting of the bimodal magmatism in the region are controversial in this paper we use zircon u pb age hf sr nd os isotope and lithophile chalcophile trace element constraints from the tianyu mafic ultramafic intrusion to address these important issues the u pb age of zircon from the tianyu intrusion determined by sims is 280 2 ma this confirms that the tianyu intrusion is coeval with most sulfide bearing mafic ultramafic intrusions and some basalts and a type granites in the tianshan region similar to coeval basalts in the nearby tuha basin the tianyu intrusive rocks are characterized by negative nb anomaly and elevated end values varying between 1 and 4 6 the negative nb anomaly in the tianyu intrusion is not as pronounced as in the coeval a type granites but the end values for these bimodal rocks are similar the ehf values of zircon from the tianyu intrusion are positive varying between 3 and 8 these values suggest that the parental magma of the tianyu intrusion was dominated by melt derived from a depleted source mantle the os values of pyrrhotite from the tianyu intrusion are high ranging from 725 to 995 which can be modeled by selective assimilation of sulfide from the lower and upper crusts negative pt anomaly is present in relatively sulfide rich samples such as semi massive and massive sulfide ores but not in sulfide poor samples which is more consistent with the effect of post magmatic hydrothermal alteration than the original signature of the parental magma the results of modeling using the compositions of selected disseminated sulfide samples suggest that the parental magma of the tianyu intrusion was depleted in all pge which is consistent with previous sulfide segregation at depth our data and modeling results support the model of decompression melting of upwelling asthenosphere due to slab break off during a transition from oceanic subduction to arc arc or arc continent collision in the permian decompression melting of the upwelling asthenosphere in the region produced mafic magma partial melting in the lower parts of a juvenile arc crust due to mafic magma underplating produced granitic melts mixing of the mafic magma with a small amount of granitic melts at depth followed by contamination with the upper crust at a higher level formed the parental magma of the tianyu intrusion pge depletion in the parental magma of the tianyu intrusion can be attributed to sulfide segregation associated to the first stage of crustal contamination at depth we suggest that the formation of sulfide ores in the intrusion was related to the second stage of crustal contamination in the upper crust

textural relationship of sulfide ores pge and sr nd os isotope compositions of the triassic piaohechuan ni cu sulfide deposit in ne china the 216 ma piaohechuan no 4 intrusion in northeastern china situated in the easternmost part of the central asian orogenic belt is composed of hornblende olivine gabbro overlain by hornblende gabbro the intrusion is about 630 m long 40 to 250 m wide and 50 to 150 m thick nickel sulfide mineralization is restricted to the lower part of the intrusion and contains 10 000 metric tons t of ni with average pge concentrations of 40 ppb os 30 ppb ir 36 ppb ru 26 ppb rh 255 ppb pt and 161 ppb pd in 100 sulfide

ostracod faunas in a large late pleistocene ice dammed lake southern ontario canada abstract in the lake ontario basin of mid continent north america near toronto canada a low diversity micro crustacean ostracod community dominated by candona caudata and candona subtriangulata occurs in several poorly sorted pebbly mud diamicts units sunnybrook seminary and meadowcliffe tills the diamicts were deposited in an ancestral ice dammed lake ontario with a level at least 90 m above the modern lake during the early and middle phases of the wisconsin glaciation 25 000 75 000 yr b p poorly sorted sediments accumulated by ice rafting and mud deposition from meltwater plumes and are separated by shallower water deltaic facies comparison of the modern habitat ranges of ostracods specifically their water depth temperature and dissolved oxygen preferences provides important palaeolimnological data regarding late pleistocene ice dammed lakes

recent glacier variations and volcanic eruptions the injection of volcanic dust and gases into the atmosphere during major eruptions has been advanced to explain short term variations of climate1 4 a calculated global cooling of 1k during episodes of intense volcanic activity3 could lead to a snowline depression sufficient to cause glacier advances equivalent to those of the last several centuries the hypothesis would therefore be strengthened if a close relationship could be demonstrated between global volcanicity and the pattern of recent glacier variations glacier activity in the northern hemisphere during much of the past 100 yr shows a lack of synchrony with that in the southern hemisphere but in each hemisphere the sequence of glacier variations matches the acidity record in polar ice cores and the frequency of volcanic eruptions in successive latitude belts this suggests that glaciers fluctuate in response to atmospheric build up of volcanic aerosols produced during large eruptions and that explosive volcanism may therefore be a major factor in modulating climate on the decadal scale

glaciomarine facies from the western sector of the last british ice sheet malin beg county donegal ireland the coastal margins and mountainous core of county donegal republic of ireland have been areally scoured and deeply eroded along structural lineaments by major late devensian ice streams which moved generally westwards onto the continental shelf a raised glaciomarine sequence is selectively preserved along a gully at malin beg and comprises mud muddy diamict sand and diamict 1 the mud which was deposited from suspended sediment plumes passes upwards into muddy diamict which reflects an increase in ice rafting the muds contain a redeposited foraminiferal assemblage of ice proximal origin pumped into the water column by jets reworking previously deposited outwash the presence of middle devensian shells have been identified from the mud by amino acid analysis this suggests a late devensian age for the succession 2 the overlying sand indicates an increase in traction current activity at the site 3 there is a sharp planar contact between the sands and the overlying tabular diamict unit 4 a surficial sheet of coarse grained breccia is attributed to intense periglacial weathering along the slopes of leahan mountain this sequence and those at other sites in western ireland e g belderg co mayo provide a record of deep isostatic depression and sedimentation in a peripheral trough at the north western margin of the last british ice sheet directional indicators including drumlin fields and major troughs indicate that the north western sector of the ice sheet was drained by major ice streams these ended in calving bays ice marginal response to ice wastage depended largely on catchment factors such as the magnitude of the ice reservoirs and the length of flow lines ultimately calving led to accelerated ice flow and areal down draw and collapse of the north western sector of the ice sheet

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

compositional variations of several early permian magmatic sulfide deposits in the kalatongke district southern altai western china with genetic and exploration implications abstract a permian magmatic ni cu sulfide deposit cluster occurs in the kalatongke district in the southern chinese altai orogenic belt western china these deposits are associated with the mafic units of the y1 y2 y3 y9 and g21 mafic intermediate complexes in this paper we report the first zircon u pb ages for the y3 and g21 intrusions which are 283 3 1 3 ma and 281 1 1 5 ma respectively our new age data confirm that the sulfide bearing mafic units of the y1 y2 connected with y1 at depth y3 y9 and g21 intrusions all formed in early permian between 281 and 287 ma new and existing petrological geochemical data show some important regular variations between these deposits the host lithologies change from olivine bearing rocks for the y1 y2 y9 deposits to olivine free rocks such as norite for the y3 deposit and leucogabbro for the g21 deposit the olivine fo contents of the y1 deposit are up to 82 mol which are slightly higher than those of the y2 deposit up to 81 mol and the y9 deposit up to 79 mol the average plagioclase an contents of the olivine bearing y1 y2 y9 deposits are higher than those of the olivine free y3 g21 deposits among the three deposits y1 y2 and y3 that occur closely along the same structural lineament the ni cu ratios of bulk sulfides decrease from the olivine bearing deposits y1 and y2 to the olivine free deposit y3 the pge tenors of these deposits y1 y2 and y3 and the nearby coeval deposits y9 and g21 are extremely low indicating that their parental magmas are severely depleted in pges the variations of pge tenors within a single deposit as well as among the different deposits are mainly due to variable r factors the host rocks of these deposits are all characterized by elevated initial 87sr 86sr ratios from 0 7045 to 0 7047 positive end values from 4 95 to 6 86 positive ehf values of zircon from 9 to 16 and elevated 18o values of zircon from 6 15 to 6 7 the isotope data indicate that the parental magmas for these deposits experienced up to 15 wt crustal contamination the 34s values of the sulfide minerals from these deposits are from 3 1 to 0 4 with a peak at 2 2 indicating the involvement of crustal sulfur the isotope data and mineral chemistry together indicate that both olivine fractional crystallization and addition of crustal sulfur played a role in triggering sulfide saturation in the parental magmas for these deposits based on higher ni cu ratios of sulfide mineralization in the olivine bearing intrusions y1 y2 y9 than in the coeval olivine free intrusions y3 g21 we recommend that ni exploration in the region focus on the olivine bearing intrusions that were emplaced in the early permian

geochemistry of the permian kalatongke mafic intrusions northern xinjiang northwest china implications for the genesis of magmatic ni cu sulfide deposits the kalatongke cu ni sulfide deposit in northern xinjiang northwest china is located on the southern side of the regional irtysh fault zone which is the boundary between the early paleozoic altai orogenic belt to the north and the late paleozoic junggar terrane to the south in the kalatongke region there are 11 mafic intrusions which were emplaced in lower carboniferous strata economic ni cu sulfide ores are found within three of these intrusions which are well differentiated and compositionally zoned four rock types are recognized which from top to base of the three mineralized intrusions include biotite diorite biotite hornblende norite biotite hornblende olivine norite and biotite hornblende dolerite the biotite hornblende olivine norites and biotite hornblende norites are the most favorable host rocks for ni cu mineralization the initial 87sr 86sr t t 280 ma ratios of the intrusions vary from 0 70375 to 0 70504 and end t from 6 3 to 8 2 implying that the magmas originated from depleted asthenospheric mantle however the strong enrichment of lithophile elements such as k rb th u and lree the negative nb and ta anomalies and the high 18o values of whole rocks 5 4 10 6 suggest significant crustal contamination these patterns are present in almost all samples from the intrusions indicating that the contamination took place before the magma was emplaced at its present level in the crust crustal contamination is interpreted to have driven the magma to s saturation and brought orthopyroxene onto the liquidus convection or perhaps flow differentiation of the crystal bearing magma during ascent caused the dense sulfide melt with entrained olivine and orthopyroxene crystals to become concentrated in the center of the intrusions whereas the fractionated magmas formed other less mafic intrusions which intrude the nearby strata

neoarchean convergent margin ni cu mineralization axis lake and nickel king ni cu deposits in the south rae craton of the canadian shield abstract the southern portion of the rae craton in the canadian shield is host to multiple ca 2 63 ga ni cu rich metamorphosed mafic intrusions with noritic noritic anorthositic and pyroxenitic compositions including those hosting the undeveloped axis lake and nickel king deposits found in northern saskatchewan and southeast northwest territories in order to understand the setting of these intrusions and their concomitant mineralization we investigated their geochemical and isotopic characteristics mineralized intrusions at axis lake and nickel king are metamorphosed up to granulite facies with local partial melting the intrusions preserve whole rock major element geochemistry consistent with a sub alkaline basaltic composition e g sio2 46 54 wt tio2 the nd isotope values of the axis lake intrusion ndt2630 0 3 to 2 1 are more juvenile and closer to the depleted mantle value relative to those of the nickel king deposit ndt2630 2 4 to 0 4 this agrees with their also distinctive th yb and nb yb distributions suggesting oceanic and continental arc like settings respectively the axis lake and nickel king nd isotope compositions are indistinguishable from other arc like 2 61 to 2 58 ga mafic to felsic intrusions and volcanic rocks recognized in the rae craton and the neighboring chesterfield block the age spatial distribution and geochemistry of the studied intrusions coincide with the initial stages of a recently defined 2 63 2 60 ga continental arc the roots of which are found in the south rae craton our data indicate that neoarchean intrusions with an arc like geochemistry may be a significant exploration target in the rae craton this broadens possible host suites beyond the established paleoproterozoic rift related rocks most commonly considered as the prime target for ni cu pge mineralization

rhythmically bedded glaciomarine sediments on whidbey island washington abstract several facies of late pleistocene glaciomarine sediments on whidbey island washington are rhythmically bedded the first consists of stratified silty sand which fines upward transitionally into pebbly mud several successions each approximately 0 6 m thick comprise a proximal meltwater facies thought to have been deposited in a shallow 10 m submarine fan environment both the positive lobe shape morphology of the exposure and the inferred depositional processes support this view underflow currents either high concentration turbidity currents or grain flows are thought to have deposited the silty sand while flocculation settling from turbid overflow and or interflow plumes and ice rafting were responsible for pebbly mud deposition such inferences are based on text ral analysis and observations of sedimentary structures the rhythmic interbedding is explained by invoking seasonal fluctuations of meltwater discharge this caused a variation of depositional process in areas proximal to meltwater input into the basin rhythmic interbedding is also observed within a channelized sequence of gravel sand and mud which comprise a fining upwards succession that includes turbidites laminations of sand and silt found in the upper portion of this section closely resemble the type of varved bedding commonly reported from glaciolacustrine sequences

up down or sideways emplacement of magmatic fe ni cu pge sulfide melts in large igneous provinces the preferential localization of fe ni cu pge sulfides within the horizontal components of dike sill lava flow complexes in large igneous provinces lips indicates that they were fluid dynamic tra

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

sedimentology of an ice contact glaciomarine fan complex nastapoka hills eastern hudson bay northern quebec abstract emerged holocene coalescing glaciomarine fans are exposed along the nastapoka hills eastern hudson bay the fans form part of a regional stratified drift belt associated with terrestrial and submarine frontal moraines and other grounding lines deposits these thick extensive and in many cases coalescent sediment bodies were deposited during a stillstand of the quebec labrador sector qls of the laurentide ice sheet lis that pinned on the hills during eastward retreat from hudson bay the fans are composed of basal interbedded and interlaminated sand silt and silty clay facies association i fa i deposited by suspension settling from overflow plumes sediment gravity flows and ice rafting towards the ice contact zone fa i interfingers with diamict layers fa ii deposited by gravity flows and ice rafting these two sedimentary units are overlain by interbedded sand and gravel fa iii formed by reworking during subsequent emergence parts of fa i and fa ii were remobilized by submarine gravity flows which prevailed long after ice retreat the sedimentology of the nastapoka hills provides information on the processes operating near the grounding line of a temperate ice sheet reaching tidewater

geochemistry of the kalatongke ni cu pge sulfide deposit nw china implications for the formation of magmatic sulfide mineralization in a postcollisional environment the kalatongke also spelt as karatungk ni cu platinum group element pge sulfide deposit containing 33 mt sulfide ore with a grade of 0 8 wt ni and 1 3 wt cu is located in the eastern junggar terrane northern xinjiang nw china the largest sulfide ore body which occupies more than 50 vol of the intrusion y1 is dominantly comprised of disseminated sulfide with a massive sulfide inner zone economic disseminated sulfides also occur at the base of the intrusions y2 and y3 the main host rock types are norite in the lower part and diorite in the upper part of each intrusion enrichment in large ion lithophile elements and depletion in heavy rare earth elements relative to mid ocean ridge basalt indicate that the mafic intrusions were produced from magmas derived from a metasomatized garnet lherzolite mantle the average grades of the disseminated ores are 0 6 wt ni and 1 1 wt cu whereas those of the massive ores are 2 wt ni and 8 wt cu the pge contents of the disseminated ores 14 69 ppb pt and 78 162 ppb pd are lower than those of the massive ores 120 505 ppb pt and 30 827 ppb pd however on the basis of 100 sulfide pge contents of the massive sulfides are lower than those of the disseminated sulfides very high cu pd ratios 4 5 104 indicate that the kalatongke sulfides segregated from pge depleted magma produced by prior sulfide saturation and separation a negative correlation between the cu pd ratio and the pd content in 100 sulfide indicates that the pge content of the sulfide is controlled by both the pge concentrations in the parental silicate magma and the ratio of the amount of silicate to sulfide magma the negative correlations between ir and pd indicate that the massive sulfides experienced fractionation

permian bimodal dyke of tarim basin nw china geochemical characteristics and tectonic implications abstract this study reports for the first time the occurrence of bimodal dyke in the shuigongtuan area of bachu county tarim basin nw china here quartz syenite porphyry and diabase dykes occur in direct contact showing bimodal feature the quartz syenitic porphyry is metaluminous enriched in k2o na2o 10 11 wt and total rare earth elements ree with low mg mg fe ratios high lree hree and negative eu anomalies the chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with a type granites the diabase dyke shows 45 52 wt sio2 and mg mg fe ratio in the range of with high total ree high lree hree ratios and lack of eu anomalies broadly corresponding to tholeiitic composition based on low y nb as low as 0 4 and less than 1 2 enrichment in lile and hfse and uniform nb enrichment patterns in spider diagram for the quartz syenitic porphyry together with the geochemical patterns of the diabases this biomodal association is interpreted to be derived from a mantle source and formed under typical within plate environment the quartz syenitic porphyry and diabase have daly gap of 46 wt 67 wt in sio2 which is explained through formation under bimodal rifting the quartz syenitic dyke probably formed during early permian 277 ma and has geochemical affinity with the xiaohaizi syenitic body we propose that magmas sourced from the mantle intruded into middle upper crust and were emplaced as dykes which indicate large scale extension during the permian in tarim basin the bimodal dyke has genetic affinity with the huge volume of permian basalts and igneous rocks 248 292 ma that occur in the tarim basin the magmatism manifests the culmination of the major thermal event in the tarim basin

late paleozoic volcanic record of the eastern junggar terrane xinjiang northwestern china major and trace element characteristics sr nd isotopic systematics and implications for tectonic evolution article i nfo the eastern junggar terrane of the central asian orogenic belt includes a late paleozoic assemblage of volcanic rocks of mixed oceanic and arc affinity located in a structurally complex belt between the siberian plate the kazakhstan block and the tianshan range the early history of these rocks is not well constrained but the junggar terrane was part of a cordilleran style accreted arc assemblage by the late carboniferous late paleozoic volcanic rocks of the northern part of the east junggar terrane are divided from base to top into the early devonian tuoranggekuduke formation fm middle devonian beitashan fm middle devonian yundukala fm late devonian jiangzierkuduke fm early carboniferous nanmingshui fm and late carboniferous batamayineishan fm we present major element trace element and sr nd isotopic analyses of 64 ultra mafic to intermediate volcanic rock samples of these formations all devonian volcanic rocks exhibit remarkably negative nb ta and ti anomalies on the primitive mantle normalized trace element diagrams and are enriched in more highly incompatible elements relative to moderately incompatible ones furthermore they have subchondritic nb ta ratios and their zr nb and sm nd ratios resemble those of morbs characteristics of arc related volcanic rocks the early devonian tuoranggekuduke fm middle devonian beitashan fm and middle devonian yundukala fm are characterized by tholeiitic and calc alkaline affinities in contrast the late devonian jiangzierkuduke fm contains a large amount of tuff and sandstone and its volcanic rocks have dominantly calc alkaline affinities we therefore propose that the jiangzierkuduke fm formed in a mature island arc setting and other devonian fms formed in an immature island arc setting the basalts from the nanmingshui fm have geochemical signatures between n morb and island arcs indicating that they formed in a back arc setting in contrast the volcanic rocks from the batamayineishan fm display geochemical characteristics of continental intraplate volcanic rocks formed in an extensional setting after collision thus we propose a model that involves a volcanic arc formed by northward subduction of the ancient junggar ocean and amalgamation of different terranes during the late paleozoic to interpret the formation of the late paleozoic volcanic rocks in the eastern junggar terrane and the altai and junggar terranes fully amalgamated into a cordilleran type orogen during the end of early carboniferous to the middle late carboniferous

delta slope processes and turbidity currents in prodeltaic submarine channels queen inlet glacier bay alaska large submarine channels lead away from the coarse grained fjord head delta in queen inlet glacier bay alaska coarse sediment loads from carroll glacier are transported down the delta foreslope and through the submarine channels and finer material is dispersed throughout the fjord from overflow plumes slides and slumps occur intermittently on the delta foreslope a recording current meter positioned in a submarine channel 1 m above the bottom and 2 7 km seaward from the delta brink indicated during july 1989 predominantly quasi continuous downfjord currents although several small surges were also observed flows occurred throughout the daily tidal cycle in both neap and spring periods for intervals of up to several hours often beginning and ending rapidly current velocities ranged from 0 to 120 cm s 1 averaging 12 cm s 1 over one 56 h period and 16 cm s 1 over a 13 h period suspended sediment concentrations 1 m above bottom commonly exceeded 2 g l 1 and attained 8 2 g l 1 the density added to

sedimentation in an ice contact subaqueous setting the mid pleistocene north sea drifts of norfolk u k in east anglia the mid pleistocene north sea drifts extend over some 1500 km2 of the coastal zone of north norfolk they are the oldest pleistocene glacial sequences exposed in britain deposited during the anglian glaciation ca 450 ka bp laminated and stratified pebbly mud diamict facies of the north sea drifts are widely regarded as the product of subglacial deposition below a terrestrial ice margin in this paper these facies are identified as the product of subaqueous deposition in front of the margin of an ice sheet terminating in a large water body laminated stratified and massive diamict facies were deposited by the rain out of fine grained sediment from suspension and coarse debris from floating ice combined with downslope sediment gravity flow intraformational folds are the product of episodic downslope slumping and identify a regional paleoslope to the east away from a major ice marginal moraine ridge the cromer ridge exposures at cromer show bulldozed ice contact subaqueous sediments and ice thrust chalk rafts a fall in water level emplaced shelly shoreface sands and beach gravels which are loaded into the underlying diamicts as large pan shaped sag basins with diapiric structures at their margins comparable sedimentary sequences are exposed elsewhere around the southern north sea basin a glaciomarine setting in response to glacio isostatic depression around the anglian ice sheet is suggested

mantle wedge control on back arc crustal accretion at mid ocean ridges plate separation leads to upward advection and pressure release partial melting of fertile mantle material the melt is then extracted to the spreading centre and the residual depleted mantle flows horizontally away in back arc basins the subducting slab is an important control on the pattern of mantle advection and melt extraction as well as on compositional and fluid gradients modelling studies predict significant mantle wedge effects on back arc spreading processes here we show that various spreading centres in the lau back arc basin exhibit enhanced diminished or normal magma supply which correlates with distance from the arc volcanic front but not with spreading rate to explain this correlation we propose that depleted upper mantle material generated by melt extraction in the mantle wedge is overturned and re introduced beneath the back arc basin by subduction induced corner flow the spreading centres experience enhanced melt delivery near the volcanic front diminished melting within the overturned depleted mantle farther from the corner and normal melting conditions in undepleted mantle farther away our model explains fundamental differences in crustal accretion variables between back arc and mid ocean settings

the association of mafic ultramafic intrusions and a type magmatism in the tian shan and altay orogens nw china implications for geodynamic evolution and potential for the discovery of new ore deposits abstract the nw china region is characterised by tectonic and lithostratigraphic domains such as the tian shan and altay orogens the tarim junggar and turpan basins the tian shan and altay orogens are part of the central asian orogenic belt the nw china region was affected by a series of thermal events that occurred between the silurian and the triassic which resulted in the emplacement of numerous granitic plutons and mafic ultramafic intrusions a number of these granitic plutons are of a type affiliation which on the basis of the positive end values are likely to have been derived from mantle sources in addition at least two large igneous provinces lips can be recognised in nw china namely the 345 325 ma tian shan lip and the ca 270 280 ma tarim lip age and field data suggest a spatial and temporal relationship between the mafic ultramafic intrusions and a type granites within the lips in this paper we discuss mafic ultramafic intrusions that host magmatic ni cu sulphide deposits kalatongke in the altay huangshan and poyi poshi in the eastern tian shan these intrusions are typically zoned characterised by an envelope of early gabbroic rocks that enclose later ultramafic units these zoned mafic ultramafic intrusions have some features that are comparable with alaskan type complexes taking into consideration the spatial temporal relationship of the mafic mafic ultramafic rocks and a type granites we suggest that these magmatic events occurred during an extensional regime possibly related to a mantle superplume event that affected much of central asia during the permian of which the siberian traps and the emeishan continental flood basalts of sw china are part if the a type felsic magmatism took place during a superplume event we also suggest that these rocks may be conducive to host iron oxide copper gold iocg style mineralisation we conclude with a model that attempts to explain the relationship between the zoned mafic ultramafic intrusions and mantle plume activity in nw china during the permian

subglacial meltwater discharge in the open marine tidewater glacier environment observations from nordaustlandet svalbard archipelago the ice proximal environment of the nordaustlandet tidewater ice cap svalbard archipelago is one of the best analogues for understanding glacial geologic processes of northern continental shelves during initial pleistocene deglaciation investigations of the proglacial region in 1980 1983 showed that the sedimentary environment is dominated by numerous meltwater outflows which discharge sediment laden water from subglacial meltwater streams during the summer two large stable meltwater outflows were observed in embayments along the southern part of the ice front landsat images show that both outflows have been in approximately the same position since at least 1976 they are located at the intersection of glacial drainage basins and centered over depressions in the underlying bedrock an outflow valley extending away from the ice front was observed in front of the western meltwater outflow sidescan sonar profiling along the glacier front showed a 200 m wide gap in acoustic reflection at the base of the western meltwater outflow probably caused by meltwater effluence enhanced sediment accumulations in this region observed as a 3 ms sediment drape in front of the outflow and large arcuate ridges in the outflow valley testify to the transport efficiency of the subglacial meltwater stream several mounds up to about 25 m high and 200 m wide are observed on sidescan and 3 5 khz profiles directly in front of the outflow although samples from these structures are absent they are most likely composed of sediment and are similar to beaded eskers observed in pleistocene glacimarine sequences indicating locally very high sedimentation rates fine grained components of the subglacial discharge incorporated in the buoyant meltwater plume are usually entrained in a westerly coastal current elevated suspended particulate material concentrations are observed within the coastal waters in a region extending about 15 km perpendicular to the glacier front and at least 60 km along the ice front extending into the northwestern barents sea

what were the primary forcing mechanisms of high frequency holocene climate and glacier variations a compilation of holocene glacial advances throughout the world is compared with summer solar insolation integrated over the northern hemisphere and the magnitudes of global acid fallout from volcanic eruptions north of 20 s estimated from the acidity signal of annual ice layers in the crete and camp century ice cores in greenland correlation analysis between glacial advances versus volcanic eruptions yielded a correlation coefficient of r 0 71 a climatic forcing curve solar insolation and volcanic eruptions weighted 1 1 versus glacial advances increased the correlation coefficient to r 0 90 this suggests that the combined effect of volcanic aerosols and orbital related northern hemisphere summer insolation may have been the primary forcing mechanism of worldwide climate and glacier fluctuations throughout the holocene

criteria to distinguish between subglacial glaciotectonic and glaciomarine sedimentation i deformation styles and sedimentology abstract this paper compares and contrasts the sedimentology and structural geology of a quaternary glaciomarine site melabakkar asbakkar iceland and a quaternary subglacial glaciotectonic site west runton uk research suggests that the glaciomarine environment is dominated by sedimentary processes related to sediment supply water content and distance from the glacier margin glaciotectonic deformation however is dominated by deformational processes related to effective pressure shear strain nature of the subglacial material and distance from the glacier margin from this study a series of criteria are suggested to distinguish both quaternary and contemporary glaciotectonic and glaciomarine environments in addition the paper also discusses the subsequent effects of glaciotectonic deformation on a primary glaciomarine site due to a glacial readvance

compositional variations of olivine and sulfur isotopes in the noril sk and talnakh intrusions siberia implications for ore forming processes in dynamic magma conduits olivine from the noril sk i main and northwestern talnakh ore bearing intrusions in the noril sk region occurs as inclusions discrete grains and poikilitic crystals the original compositions of olivine inclusions have been well preserved by their host oikocrysts from reaction with interstitial silicate and sulfide liquids in contrast the compositions of discrete and poikilitic olivine crystals have been variably modified by reequilibration with trapped silicate and sulfide liquids there are abrupt changes in the contents of nickel in olivine inclusions 500 1 500 ppm between different rock units in all three intrusions which indicates that the different rock units in these intrusions are not related to each other via in situ differentiation of a common parental magma but rather are consistent with separate pulses of magma with variable degrees of differentiation possibly involving olivine crystallization and assimilation of siliceous crustal material in a staging chamber the 34s values of the samples with high sulfur contents 800 ppm sulfur from all three ore bearing intrusions vary between 8 and 14 per mil two sulfur poor samples 600 ppm sulfur from the northwestern talnakh intrusion yield 34s values of 1 5 and 3 6 per mil these values are similar to the values of the sulfur poor rocks from the ore barren intrusions in the region and illustrate the fact that high sulfur contents couple with increasing 34s values such a relationship is consistent with the addition of crustally derived 34s enriched sulfur to the magma of the ore bearing intrusions in contrast to other models of sulfide segregation in closed systems we propose that sulfide segregation occurred in an open system and the magma involved was undersaturated in sulfur and undepleted in chalcophile elements we envision that the 34s enriched sulfur was introduced via circulating fluids that transported sulfur from evaporite in the underlying sedimentary sequence to the magma in a dynamic magma conduit the immiscible sulfide liquids that segregated during sulfur contamination settled down in the wider parts of the conduit as the magma continued to travel successive pulses of new magma entered the conduit reacted with the early sulfide and displaced much of the early magma in the conduit the ore bearing intrusions are thought to have crystallized within the wider parts of the conduits and their voluminous sulfide poor peripheral sills represent some if not all of the magma that flowed out of the conduits

magma mixing in the genesis of the kalatongke dioritic intrusion implications for the tectonic switch from subduction to post collision chinese altay nw china abstract the kalatongke complex located in south chinese altay of the central asian orogenic belt caob consists of the 308 ma dioritic suite intruded by the 287 ma noritic suite the noritic suite is composed of olivine norite and hornblende norite and hosts sulfide mineralization the dioritic suite is composed of ferrodiorite diorite and quartz diorite ferrodiorites have 43 6 to 51 8 wt sio 2 8 2 to 12 1 wt fe 2 o 3 t 2 87 to 4 86 wt mgo with mg ranging from 42 to 53 they have highly variable al 2 o 3 17 4 20 7 wt na 2 o 2 78 4 50 k 2 o 0 58 3 70 sr 280 1300 ppm and ba 219 3100 ppm diorites and quartz diorites have 15 2 19 6 wt al 2 o 3 239 890 ppm sr and170 1100 ppm ba 11 2 25 5 ppm y and1 2 2 2 ppm yb all rocks have lree enriched ree patterns and do not display eu anomalies they have primitive mantle normalized trace element patterns enriched in large ion lithosphile elements lile e g ba and sr and depleted in ti nb and ta both ferrodiorites and diorites have relatively constant initial 87 sr 86 sr ratios of 0 7037 to 0 7040 but highly variable e nd t values of 4 5 to 11 6 whereas quartz diorites have higher initial 87 sr 86 sr ratios 0 7056 and lower e nd t values 0 5 plagioclase from ferrodiorites diorites and quartz diorites has similar initial 87 sr 86 sr ratios of 0 7015 to 0 7055 the dioritic suite formed from a mixed magma of an evolved mantle derived basaltic magma by partial melting of subduction modified mantle source in response to slab breakoff and a crustal derived granitic magma at 308 ma before mixing with granitic magmas basaltic magmas underwent fractional crystallization of olivine to form ferrodiorite the mixed magma also formed diorite and quartz diorite combining fractionation clinopyroxene amphibole and plagioclase the noritic suite formed from a mantle derived high mg magma in a post collisional environment both the dioritic and noritic suites in kalatongke suggest the switch from subduction to extension and the final collision between the junggar block and chinese altay at 308 ma

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime