http://www.sciencedirect.com/science/article/pii/S1674987114000607

The Qinling Complex of central China is thought to be the oldest rock unit and the inner core of the North Qinling Orogenic Belt （NQOB）. Therefore, the Qinling Complex is the key to understanding the pre- Paleozoic evolution of the NQOB. The complex, which consists of metagraywackes and marbles, un- derwent regional amphibolite-facies metamorphism. In this study, we constrained the formation age of the Qinling Complex to the period between the late Mesoproterozoic and the early Neoproterozoic （ca. 1062-962 Ma）, rather than the Paleoproterozoic as previously thought. The LA-ICP-MS data show two major metamorphic ages （ca. 499 and ca. 420-400 Ma） for the Qinling Complex. The former age is consistent with the peak metamorphic age of the high- and ultra-high pressure （HP-UHP） rocks in the Qinling Complex, indicating that both the HP-UHP rocks and their country rocks experienced intensive regional metamorphism during the Ordovician. The latter age may constrain the time of partial melting in the NQOB between the late Silurian and early Devonian. The Qinling Complex is mostly affiliated with subduction-accretion processes along an active continental margin, and should contain detritus deposited in a forearc basin.     

http://www.sciencedirect.com/science/article/pii/S1674987113000054

Substantial part of the northern margin of Indian plate is subducted beneath the Eurasian plate during the Caenozoic Himalayan orogeny, obscuring older tectonic events in the Lesser Himalaya known to host Proterozoic sedimentary successions and granitic bodies. Tectonostratigraphic units of the Proterozoic Lesser Himalayan sequence (LHS) of Eastern Himalaya, namely the Daling Group in Sikkim and the Bomdila Group in Arunachal Pradesh, provide clues to the nature and extent of Proterozoic passive margin sedimentation, their involvement in pre-Himalayan orogeny and implications for supercontinent reconstruction. The Daling Group, consisting of flaggy quartzite, meta-greywacke and metapelite with minor mafic dyke and sill, and the overlying Buxa Formation with stromatolitic carbonate-quartzite-slate, represent shallow marine, passive margin platformal association. Similar lithostratigraphy and broad depositional framework, and available geochronological data from intrusive granites in Eastern Himalaya indicate strikewise continuity of a shallow marine Paleoproterozoic platformal sequence up to Arunachal Pradesh through Bhutan. Multiple fold sets and tectonic foliations in LHS formed during partial or complete closure of the sea/ocean along the northern margin of Paleoproterozoic India. Such deformation fabrics are absent in the upper Palaeozoic–Mesozoic Gondwana formations in the Lesser Himalaya of Darjeeling-Sikkim indicating influence of older orogeny. Kinematic analysis based on microstructure, and garnet composition suggest Paleoproterozoic deformation and metamorphism of LHS to be distinct from those associated with the foreland propagating thrust systems of the Caenozoic Himalayan collisional belt. Two possibilities are argued here: (1) the low greenschist facies domain in the LHS enveloped the amphibolite to granulite facies domains, which were later tectonically severed; (2) the older deformation and metamorphism relate to a Pacific type accretionary orogen which affected the northern margin of greater India. Better understanding of geodynamic evolution of the northern margin of India in the Paleoproterozoic has additional bearing on more refined model of reconstruction of Columbia.     

Were Late Cretaceous extinctions of gastropods selective by generic longevity?

Many gastropod taxa went extinct during the Late Cretaceous.The stratigraphic ranges of 268 genera permit to establish the longevity of extinction victims for each stage of this epoch."Young" taxa (originated within 3 epochs before the extinction) prevailed among victims of the extinctions in all stages.The proportion of "old" taxa(originated before the Cretaceous) that went extinct was the highest in the Cenomanian,and it was the lowest in the Coniacian and the Maastrichtian.It appears that the end-Cretaceous mass extinction affected chiefly "young" taxa.However,the comparison with the earlier time intervals suggests that this pattern of selectivity by generic longevity was not specific for the noted catastrophe,but,in contrast,it was typical for the entire Late Cretaceous.The latest Cenomanian environmental perturbation(OAE2) caused a stronger extinction of "old" taxa,and thus,this biotic crisis was less selective by generic longevity.This hypothesis,however,is not proven by the statistical test.     

http://www.sciencedirect.com/science/article/pii/S1674987114000929

Global sea-level has changed in a cyclic manner through geologic history, but the regularities of these changes are yet to be fully understood. Despite certain (and sometimes significant) differences, ...     

http://www.sciencedirect.com/science/article/pii/S1674987110000022

<正>The Early Cretaceous Hohhot metamorphic core complex(mcc) of the Daqing Shan(Mtns.) of central Inner Mongolia is among the best exposed and most spectacular of the spatially isolated mcc's that developed within the northern edge of the North China "craton".All of these mcc's were formed within the basement of a Late Paleozoic Andean-style arc and across older Mesozoic fold-and-thrust belts of variable age and tectonic vergence.The master Hohhot detachment fault roots southwards within the southern margin of the Daqing Shan for an along-strike distance of at least 120 km.Its geometry in the range to the north is complicated by interference patterns between(1) primary,large-scale NW-SE-trend-ing convex and concave fault corrugations and(2) secondary ENE-WSW-trending antiforms and synforms that folded the detachment in its late kinematic history.As in the Whipple Mtns.of California, the Hohhot master detachment is not of the Wernicke(1981) simple rooted type:instead,it was spawned from a mid-crustal shear zone,the top of which is preserved as a mylonitic front within Carboniferous metasedimentary rocks in its exhumed lower plate.~(40)Ar—~(39)Ar dating of siliceous volcanic rocks in basal sections of now isolated supradetachment basins suggest that crustal extension began at ca.127 Ma, although lower-plate mylonitic rocks were not exposed to erosion until after ca.119 Ma.Essentially synchronous cooling of hornblende,biotite.and muscovite in footwall mylonitic gneisses indicates very rapid exhumation and at ca.122—120 Ma.Contrary to several recent reports,the master detachment clearly cuts across and dismembers older,north-directed thrust sheets of the Daqing Shan foreland fold-and-thrust belt.Folded and thrust-faulted basalts within its foredeep strata are as young as 132.6±2.4 Ma,thus defining within 5—6 Ma the regional tectonic transition between crustal contraction and profound crustal extension.     

http://www.sciencedirect.com/science/article/pii/S167498711400108X

We present three 3D numerical models of deep subduction where buoyant material from an oceanic plateau and a plume interact with the overriding plate to assess the influence on subduction dynamics,trench geometry,and mechanisms for plateau accretion and continental growth.Transient instabilities of the convergent margin are produced,resulting in:contorted trench geometry;trench migration parallel with the plate margin;folding of the subducting slab and orocline development at the convergent margin;and transfer of the plateau to the overriding plate.The presence of plume material beneath the oceanic plateau causes flat subduction above the plume,resulting in a "bowed" shaped subducting slab.In plateau-only models,plateau accretion at the edge of the overriding plate results in trench migration around the edge of the plateau before subduction is re-established directly behind the trailing edge of the plateau.The plateau shortens and some plateau material subducts.The presence of buoyant plume material beneath the oceanic plateau has a profound influence on the behaviour of the convergent margin.In the plateau + plume model,plateau accretion causes rapid trench advance.Plate convergence is accommodated by shearing at the base of the plateau and shortening in the overriding plate.The trench migrates around the edge of the plateau and subduction is re-established well behind the trailing edge of the plateau,effectively embedding the plateau into the overriding plate.A slab window forms beneath the accreted plateau and plume material is transferred from the subducting plate to the overriding plate through the window.In all of the models,the subduction zone maintains a relatively stable configuration away from the buoyancy anomalies within the downgoing plate.The models provide a dynamic context for plateau and plume accretion in Phanerozoic accretionary orogenic systems such as the East China Orogen and the Central Asian Orogen(Altiads),which are characterised by accreted ophiolite complexes with diverse geochemical affinities,and a protracted evolution of accretion of exotic terranes including oceanic plateau and terranes with plume origins.     

http://www.sciencedirect.com/science/article/pii/S1674987111000867

By applying the ‘theory of synchronization’ from the science of complexity to studying the regional regularity of ore formation within the Nanling region of South China, a characteristic target-pattern regional ore zonality has been discovered. During the early and late Yanshanian epoch (corresponding respectively to the Jurassic and Cretaceous periods), two centers of ore formation emerged successively in the Nanling region; the former is mainly for rare metals (W, Sn, Mo, Bi, Nb) and one rareearth element (La) and was generated in the Jurassic period; whereas the latter is mainly for base metals (Cu, Pb, Zn, Sb, Hg), noble metals (Au, Ag), and one radioactive element (U) and was generated in the Cretaceous period. Centers of ore formation were brought about by interface dynamics respectively at the Qitianling and Jiuyishan districts in southern Hunan Province. The characteristic giant nonlinear targetpattern regional ore zonality was generated respectively from the two centers of ore formation by the spatio-temporal synchronization process of the Nanling complex metallogenic system. It induced the collective dynamics and cooperative behavior of the system and displayed the configuration of the regional ore zonality. Then dynamical clustering transformed the configuration into rudimentary ordered coherent structures. Phase dynamics eventually defined the spatio-temporal structures of the target-pattern regional ore zonality and determined their localization and distribution. The integral successive processes of synchronization-dynamical clustering-phase dynamics accomplished the regional ore zonality by way of “multiple field dynamics” of spatio-temporal superposition of multiple coupled pulsatory solitary wave trains of the zonal sequences of different ores. A new methodology for revealing regional ore zonality is developed, which will encourage further investigation of the formation of deep-seated ore resources and the onset of large-scale mineralization.     

http://www.sciencedirect.com/science/article/pii/S1674987111000570

Mid-Cretaceous strata within the Tintina Trench.3 km west of the community of Ross River, contain evidence of deposition in two distinct,alternating,fluvial settings.Coal-bearing,mud-dominated strata are commonly associated with high-constructive sandy channel systems,with extensive overbank. levee and splay deposits.Channels are between 3 and 30 m wide and 0.4-7 m thick.They show repetitive development of side and in-channel bar-forms,as well as up-channel widening of the rivers by selective erosion of associated overbank and levee deposits.Levees extended for several hundred metres away from the channels.In this setting low-angle inclined stratification and epsilon cross stratification may reflect lateral migration of crevasse channels or small streams.The paucity of exposure prevents recognition of the channels as products of multiple channel anastomosed systems or single channel high-constructive systems. Gravel-dominated strata,inter-bedded with,and overlying coal-bearing units,are interpreted as deposits of wandering gravel-bed rivers,with sinuosity approaching 1.4.In most exposures they appear to be dominated by massive and thin planar-bedded granule to small pebble conglomerates,which would traditionally be interpreted as sheet-flood or longitudinal bar deposits of a high-gradient braided stream or alluvial fan.Architectural analysis of exposures in an open-pit shows that the predominance of flat bedding is an artefact of the geometry of the roadside exposures.In the pit the conglomerates are dominated by large scale cross stratification on a scale of 1-5.5 m.These appear to have developed as downstream and lateral accretion elements on side-bars and on in-channel bars in water depths of 2-12 m.Stacking of strata on domed 3rd order surfaces suggests development of longitudinal in-channel bar complexes similar to those observed in parts of the modern Rhone River system.Mudstone preserved in some of the channels reflects intervals of channel abandonment or avulsion.Minimum channel width is from 70 to 450 m.     

http://www.sciencedirect.com/science/article/pii/S1674987112000035

The well SK-I in the Songliao Basin is the first scientific borehole targeting the continental Cretaceous strata in China.Oval concretions,thin laminae and beds of dolostone are found intercalated within mudstone and organic-rich black shale in the Nenjiang Formation of Campanian age.Low ordered ferruginous dolomite is composed of euhedral-subhedral rhombs with cloudy nucleus and light rims formed during the diagenesis.which are typical features of replacement.The heavy carbon isotopes (δ¹³C_PDB-1.16-16.0) are results of both the fermentation of organic matter by microbes and degassing of carbon dioxide during the period of diagenesis,and the presence of light oxygen isotopes(δ¹⁸O_Pdb- 18.53～-5.1) is a characteristic feature of fresh water influence which means the carbonate may have been altered by ground water or rainwater in the late diagenesis.Marine water incursions into the normally lacustrine basin have been proved by both the salinity of Z value and the occurrence of foraminifera in the same strata where dolomite occurs.Pyrite framboids observed by SEM are usually enclosed in the dolomite crystals or in the mudstones,supporting the sulfate reducing bacteria（SRB）.The formation of both dolomite and pyrite are associated with marine water incursions,which not only supply magnesium ion for dolomite,but also result in limited carbonate precipitation in the basin.The presence of pyrite tramboids indicates the development of an anoxic environment associated with salinity stratification in the lake.The dolomite in the Nenjiang Formation is the results of marine water incursions,diagenetic replacement of calcareous carbonate and sulfate reducing bacteria（SRB）.     

http://www.sciencedirect.com/science/article/pii/S1674987114000322

The Central Hebei Basin （CHB） is one of the largest sedimentary basins in the North China Craton, extending in a northeast-southwest direction with an area of 〉350 km2. We carried out SHRIMP zircon dating, Hf-in-zircon isotopic analysis and a whole-rock geochemical study on igneous and metasedi- mentary rocks recovered from drill holes that penetrated into the basement of the CHB, Two samples of gneissic granodiorite （XG1-1） and gneissic quartz diorite 048-1） have magmatic ages of 2500 and 2496 Ma, respectively. Their zircons also record metamorphic ages of 2.41-2.51 and ～2.5 Ga, respec- tively. Compared with the gneissic granodiorite, the gneissic quartz diorite has higher REE contents and lower Eu/Eu＊ and （La/Yb）n values. Two metasedimentary samples （MG1, H5） mainly contain ～2,5 Ga detrital zircons as well as late Paleoproterozoic metamorphic grains. The zircons of different origins have eHf （2.5 Ga） values and Hf crustal model ages ranging from 0 to 5 and 2.7 to 2,9 Ga, respectively, Therefore, ～2.5 Ga magmatic and Paleoproterozoic metasedimentary rocks and late Neoarchean to early Paleoproterozoic and late Paleoproterozoic tectono-thermal events have been identified in the basement beneath the CHB. Based on regional comparisons, we conclude that the early Precambrian basement beneath the CHB is part of the North China Craton.     

Geochronology and Sr–Nd–Hf isotopic composition of the granites, enclaves, and dikes in the Karamay area, NW China: Insights into late Carboniferous crustal growth of West Junggar

New whole-rock major and trace elements,and zircon U-Pb and Hf-Nd isotope compositions are reported for the Karamay dikes,enclaves,and host granites in the West Junggar,NW China.Zircon U-Pb dating of the Karamay pluton yields an age of 300.7 ± 2.3 Ma for the enclave and 300.0 ± 2.6 Ma for the host granite,which was intruded by dike with an age of 298 Ma.The host granites exhibit relatively low SiO_2 contents and A/CNK and Ga/Al ratios,low initial ~(87)Sr/~(86)Sr ratios(0.703421—0.703526) and positive εHf(t)(5.5—14.1) and εNd(t)(7.3—8.1) values with a young model age,suggesting that they are I-type granites and were mainly derived from a juvenile lower crustal source.The enclaves and dikes belong to an andesitic calc-alkaline series and have high MgO concentrations at low silica content and positive εNf(t)(7.6-13.2,14.2-14.9) and εNd(t)(6.8-8.3,~6.9) values.They are enriched in LILEs(Rb,Ba and U) and LREE and depleted in HFSEs(Nb and Ta) with insignificant negative Eu anomalies,indicating that the melts were derived from an enriched lithospheric mantle modified by subducted oceanic crust-derived melts and minor fluids,followed by fractional crystallization.The Karamay host granites and enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and lithospheric mantle-derived magmas,and were intruded by the unmixed dikes subsequently.The upwelling mantle through a slab window in an island arc environment might have triggered partial melting of the lithospheric mantle and its subsequent interaction with the granitic magma,further suggesting that the ridge subduction played an important role in the crustal growth of West Junggar.     

Southern East Siberia Pliocene–Quaternary faults: Database, analysis and inference

This paper presents the first release of an Informational System（IS）devoted to the systematic collection of all available data relating to Pliocene-Quaternary faults in southern East Siberia,their critical analysis and their seismotectonic parameterization.The final goal of this project is to form a new base for improving the assessment of seismic hazard and other natural processes associated with crustal deformation.The presented IS has been exploited to create a relational database of active and conditionally active faults in southern East Siberia（between 100°-114° E and 50°-57° N）whose central sector is characterized by the highly seismic Baikal rift zone.The information within the database for each fault segment is organized as distinct but intercorrelated sections（tables,texts and pictures,etc.）and can be easily visualized as HTML pages in offline browsing.The preliminary version of the database distributed free on disk already highlights the general fault pattern showing that the Holocene and historical activity is quite uniform and dominated by NE-SW and nearly E-W trending faults;the former with a prevailing dip-slip normal kinematics,while the latter structures are left-lateral strike-slip and oblique-slip（with different proportion of left-lateral and normal fault slip components）.These faults are mainly concentrated along the borders of the rift basins and are the main sources of moderate-to-strong（M≥5.5）earthquakes on the southern sectors of East Siberia in recent times.As a whole,based on analyzing the diverse fault kinematics and their variable spatial distribution with respect to the overall pattern of the tectonic structures formed and/or activated during the late Pliocene-Quaternary,we conclude they were generated under a regional stress field mainly characterized by a relatively uniform NW-SE tension,but strongly influenced by the irregular hard boundary of the old Siberian craton.The obtained inferences are in an agreement with the existing models of the development of     

http://www.sciencedirect.com/science/article/pii/S1674987111000545

By applying the ’theory of synchronization’ from the science of complexity to studying the regional regularity of ore formation within the Nanling region of southern China,a characteristic target-pattern regional ore zonality has been discovered.During the early and late Yanshanian epoch(corresponding respectively to the Jurassic and Cretaceous periods),two centers of ore formation emerged successively in the Nanling region;the former is mainly for rare metals(W,Sn,Mo,Bi,Nb) and one rare-earth element (La) and was generated in the Jurassic period;whereas the latter is mainly for base metals(Cu,Pb,Zn,Sb, Hg),noble metals(Au,Ag),and one radioactive element(U) and was generated in the Cretaceous period. Centers of ore formation were brought about by interface dynamics respectively at the Qitianling and Jiuyishan districts in southern Hunan Province.The characteristic giant nonlinear target-pattern regional ore zonality was generated by spatio-temporal synchronization process of the Nanling complex metallo-genic system.It induced the collective dynamics and cooperative behavior of the system and displayed the configuration of the regional ore zonality.Then dynamical clustering transformed the configuration into rudimentary ordered coherent structures.Phase dynamics eventually defined the spatio-temporal structures of the target-pattern regional ore zonality and determined their localization and distribution.A new methodology for revealing regional ore zonality is developed,which will encourage further investigation of the formation of deep-seated ore resources and the onset of large-scale mineralization.     

http://www.sciencedirect.com/science/article/pii/S1674987111001356

A total of 103 surface sediment samples collected from the water depth range of 15—3300 m along Vijaydurg-Karwar stretch of central west coast of India were analyzed for foraminiferal content. Relict benthic foraminiferal assemblage was noted within 50—135 m water depth.The relict benthic foraminiferal assemblage that includes Amphistegina,Operculum and Alveolinetta in sediment samples within the water depth of 85—135 m indicates presence of coral reef at this depth during Early Holocene. The presence of barnacle fouling on Relict foraminifera at 60—90 m confirms the paleo-shoreline. The shallow depth zone is characterized by presence of agglutinated relict foraminifera.The agglutinated forms indicate freshwater influx,which eventually increased the sea level and subsequently deteriorated the paleo-coral reef.     

The final collision of the CAOB: Constraint from the zircon U–Pb dating of the Linxi Formation, Inner Mongolia

The Linxi Formation occupies an extensive area in the eastern Inner Mongolia in the Central Asian Orogenic Belt(CAOB).The Linxi Formation is composed of slate,siltstone,sandstone and plant,lamellibranch microfossils in the associated strata.Major and trace element data(including REE) for sandstones from the formation indicate that these rocks have a greywacke protolith and have been deposited during a strong tectonic activity.LA-ICPMS U—Pb dating of detrital zircons yield ages of 1801 to 238 Ma for four samples from the Linxi Formation.425—585 Ma,together with the ~500 Ma age for the metamorphism event previously determined for Northeast China,indicates that their provenance is the metamorphic rocks of Pan-African age that have a tectonic affinity to NE China.A few older zircons with U-Pb ages at 1689-1801 Ma,1307-1414 Ma,593-978 Ma are also present,revealing the Neoproterozoic history of NE China.The youngest population shows a peak at ca.252 Ma,suggesting that the main deposition of the Linxi Formation was at late Permain.Moreover,the ca.250 Ma zircon grains of all four samples yield weighted mean ~(206)Pb/~(238)U ages of 250 ± 3 Ma,248 ± 3 Ma,249 ± 3 Ma,and 250 ± 2 Ma,respectively.These ages,together with the youngest zircon age in the sample ZJB-28(ca.238 Ma),suggest that the deposition of the Linxi Formation extended to the early Triassic.Combining with previous results,we suggest that the final collision of the Central Asian Orogenic Belt(CAOB) in the southern of Linxi Formation,which located in the Solonker-Xra Moron-Changchun suture,and the timing for final collision should be at early Triassic.     

The boring billion? – Lid tectonics, continental growth and environmental change associated with the Columbia supercontinent

The evolution of Earth＇s biosphere,atmosphere and hydrosphere is tied to the formation of continental crust and its subsequent movements on tectonic plates.The supercontinent cycle posits that the continental crust is periodically amalgamated into a single landmass,subsequently breaking up and dispersing into various continental fragments.Columbia is possibly the first true supercontinent,it amalgamated during the 2.0-1.7 Ga period,and collisional orogenesis resulting from its formation peaked at 1.95-1.85 Ga.Geological and palaeomagnetic evidence indicate that Columbia remained as a quasi-integral continental lid until at least 1.3 Ga.Numerous break-up attempts are evidenced by dyke swarms with a large temporal and spatial range; however,palaeomagnetic and geologic evidence suggest these attempts remained unsuccessful.Rather than dispersing into continental fragments,the Columbia supercontinent underwent only minor modifications to form the next supercontinent （Rodinia） at 1.1 -0.9 Ga; these included the transformation of external accretionary belts into the internal Grenville and equivalent collisional belts.Although Columbia provides evidence for a form of ‘lid tectonics’,modern style plate tectonics occurred on its periphery in the form of accretionary orogens.The detrital zircon and preserved geological record are compatible with an increase in the volume of continental crust during Columbia＇s lifespan; this is a consequence of the continuous accretionary processes along its margins.The quiescence in plate tectonic movements during Columbia＇s lifespan is correlative with a long period of stability in Earth＇s atmospheric and oceanic chemistry.Increased variability starting at 1.3 Ga in the environmental record coincides with the transformation of Columbia to Rodinia; thus,the link between plate tectonics and environmental change is strengthened with this interpretation of supercontinent history.     

http://www.sciencedirect.com/science/article/pii/S1674987113000315

The Panzhihua gabbroic intrusion,part of the plumbing system of the Emeishan large igneous province, intruded late-Proterozoic dolomites and marls about～263 Ma ago.The dolomites in the contact aureole were converted to brucite marbles and a diverse suite of forsterite,diopside and garnet skarns.The variation in mineralogy is explained in part by differences in the composition of the protolith,particularly the proportion of silica minerals and clay,and in part by transfer of elements from intruding magmas.The trace element compositions of most marbles and skarns are very similar to those of unmetamorphosed dolomites and marls,but some contain high Si,Ti,and Fe contents that are interpreted to have come from a magmatic source.Three brucite marbles sampled～10 m from the contact of the intrusion and named "enriched brucite marble" have trace element compositions very different from their dolomitic protolith:their rare earth elements are strongly enriched whereas levels of Nb-Ta,Zr-Hf and Ti are very low.These characteristics resemble those of carbonate liquid in equilibrium with silicate liquid or more probably with silicate minerals in the case of Panzhihua,a similarity we take to indicate that the sample underwent partial melting.Samples taken up to 300 m from the contact contain brucite indicating that high temperatures persisted well into the country rocks.However,other samples collected only tens of metres from the contact are only slightly recrystallized indicating that conditions in the aureole were highly variable.We suggest that temperatures within the aureole were controlled by conduction of heat from the main intrusion and by supply of additional heat from abundant small dykes within the aureole.Circulation of fluids derived from deeper levels in the aureole flushed the carbon dioxide from the dolomite,lowering temperature needed to partially melt carbonate to the temperatures attained near the intrusion.Irregular but extensive heating destabilized the carbonates of the aureole and decarbonation reactions associated with carbonate breakdown and melting emitted a large volume of CO₂,with potential impact on global climate.     

http://www.sciencedirect.com/science/article/pii/S1674987112000643

Incipient charnockites represent granulite formation on a mesoscopic scale and have received considerable attention in understanding fluid processes in the deep crust.Here we report new petrological data from an incipient charnockite locality at Rajapalaiyam in the Madurai Block,southern India,and discuss the petrogenesis based on mineral phase equilibrium modeling and pseudosection analysis. Rajapalaiyam is a key locality in southern India from where diagnostic mineral assemblages for ultrahigh-temperature（UHT） metamorphism have been reported.Proximal to the UHT rocks are patches and lenses of charnockite（Kfs + Qtz + Pl + Bt + Opx + Grt + Ilm） occurring within Opx-free Grt-Bt gneiss（Kfs + Pl + Qtz + Bt + Grt + Ilm + Mt） which we report in this study.The application of mineral equilibrium modeling on the charnockitic assemblage in NCKFMASHTO system yields a p-T range of～820℃and～9 kbar.Modeling of the charnockite assemblage in the MnNCKFMASHTO system indicates a slight shift of the equilibrium condition toward lower p and T（～760℃and～7.5 kbar）. which is consistent with the results obtained from geothermobarometry（710—760℃,6.7—7.5 kbar）. but significantly lower than the peak temperatures（>1000℃） recorded from the UHT rocks in this locality,suggesting that charnockitization is a post-peak event.The modeling of T versus molar H₂O content in the rock（M（H₂O）） demonstrates that the Opx-bearing assemblage in charnockite and Opxfree assemblage in Grt-Bt gneiss are both stable at M（H₂O） = 0.3 mol%-0.6 mol%.and there is no significant difference in water activity between the two domains.Our finding is in contrast to the previous petrogenetic model of incipient charnockite formation which envisages lowering of water activity and stabilization of orthopyroxene through breakdown of biotite by dehydration caused by the infiltration of CO₂-rich fluid.T-X_Fe³⁺（= Fe₂O₃/（FeO + Fe₂O₃） in mole） pseudosections suggest that the oxidation condition of the rocks played a major role on the stability of orthopyroxene:Opx is stable at X_Fe³⁺ <0.03 in charnockite.while Opx-free assemblage in Grt-Bt gneiss is stabilized at X_Fe³⁺ >0.12.Such low oxygen fugacity conditions of X_Fe³⁺ <0.03 in the charnockite compared to Grt-Bt gneiss might be related to the infiltration of a reduced fluid（e.g.,H₂O + CH₄） during the retrograde stage.     

http://www.sciencedirect.com/science/article/pii/S1674987111000387

Fluid flow is an integral part of hydrothermal mineralization,and its analysis and characterization constitute an important part of a mineralization model.The hydrodynamic study of mineralization deals with analyzing the driving forces,fluid pressure regimes,fluid flow rate and direction,and their relationships with localization of mineralization.This paper reviews the principles and methods of hydrodynamic studies of mineralization,and discusses their significance and limitations for ore deposit studies and mineral exploration. The driving forces of fluid flow may be related to fluid overpressure,topographic relief,tectonic deformation, and fluid density change due to heating or salinity variation,depending on specific geologic environments and mineralization processes.The study methods may be classified into three types,megascopic(field) observations, microscopic analyses,and numerical modeling.Megascopic features indicative of significantly overpressured (especially lithostatic or supralithostatic) fluid systems include horizontal veins,sand injection dikes,and hydraulic breccias.Microscopic studies,especially microthermometry of fluid inclusions and combined stress analysis and microthermometry of fluid inclusion planes(FIPs) can provide important information about fluid temperature,pressure,and fluid-structural relationships,thus constraining fluid flow models.Numerical modeling can be carried out to solve partial differential equations governing fluid flow, heat transfer,rock deformation and chemical reactions,in order to simulate the distribution of fluid pressure, temperature,fluid flow rate and direction,and mineral precipitation or dissolution in 2D or 3D space and through time.The results of hydrodynamic studies of mineralization can enhance our understanding of the formation processes of hydrothermal deposits,and can be used directly or indirectly in mineral exploration.     

http://www.sciencedirect.com/science/article/pii/S1674987113001345

Many elongated, lenticular plutons of porphyritic granitoids are distributed mainly near the southern and northern margin of the Chhotanagpur Gneissic Complex （CGC） which belongs to the EW to ENE-WSW tending 1500 km long Proterozoic orogenic belt amalgamat ng the North and South Indian cratonic blocks. The late Grenvillian （1071 ±64 Ma） Raghunathpur porphyritic granitoid gneiss （PGG） batholith comprising alkali feldspar granite, granite, granodiorite, tonalite, quartz syenite and quartz monzonite intruded into the granitoid gneisses of southeastern part of CGC in the Purulia district, West Bengal and is aligned with ENE-WSW trending North Purulia sr~ear zone, Mineral chemistry, geochemistry, physical condition of crystallization and petrogenetic model of Raghunathpur PGG have been discussed for the first time. The petrographic and geochemical features （including major and trace- elements, mineral chemistry and S7Sr/S6Sr ratio） suggest these granitoids to be classified as the shosh- onitic type. Raghunathpur batholith was emplaced at around 800 ~C and at 6 kbar pressure tectonic discrimination diagrams reveal a post-collision tectonic setting while structural studies reveal its emplacement in the extensional fissure of North Purulia shear zone. l＇he Raghunathpur granitoid is compared with some similar granitoids of Europe and China to draw its petrogenetic model. Hybridi- zation of mantle-generated enriched mafic magma and crustal magma at lower crust and later fractional crystallization is proposed for the petrogenesis of this PGG. Mafic magma generated in a post-collisional extension possibly because of delamination of subducting slab. Raghunathpur batholith had emplaced in the CGC during the final amalgamation （~ 1.0 Ga） of the North and South Indian cratonic blocks. Granitoid magma, after its generation at depth, was transported to its present level along megadyke channel, ways within shear zones.