Abstract:From south to north, three parallel metamorphic imbricated slices compose the Sulu high to ultrahigh pressure metamorphic terrane. They are high pressure (HP) slice, very high pressure (VHP) slice, and ultrahigh pressure (UHP) slice, separated by ductile shear zones. Using 40Ar/39Ar and whole rock Rb-Sr techniques, the authors analyzed micas from amphibolite facies rocks in the UHP slice and from greenschist facies rocks in the HP slice to constrain the timing of exhumation of the Sulu HP-UHP metamorphic belt. Together with previous results from zircon U/Pb, whole rock Sm-Nd and Rb-Sr measurements, the data obtained show that peak metamorphism and subsequent exhumation in the UHP zone occurred in 240～220 Ma and 220～200 Ma, respectively. In the HP zone, however, peak metamorphism and the onset of exhumation occurred earlier than 258 Ma and in 258～240 Ma, respectively. These data have led us to propose a newmodel for the formation and exhumation of the Sulu HP-UHP rocks. In this model,sequential subduction and exhumation of different parts of the Yangtze slab occurred in different periods, depending upon vertical variations in the physical properties of the subducted continental crust.

Abstract:The A'nyemaqen ophiolite belt marks the suture after closure of the paleo-Tethys. In this region, four types of volcanic rocks related to ocean-floor spreading and plate subduction have been recognized.They are, from south to north, oceanic floor basalt (OFB), island arc volcanic rocks (IAV), back arc basin lavas (BAB) and post---collision volcanic rocks (PCV).The plate tectonic regime suggests the subduction sense from south to north. The spreading of the A'nyemaqen oceanic basin started at least as early as late Carboniferous (308Ma) and the closure probably took place during early Triassic. The IAV, BAB and PCV were formed respectively in late Permian (260 Ma), in early-middle Triassic, and in late Triassic. Several large-sized ductile sinistral strike slip fault zones, extending hundreds to thousands of kilometers along the suture or in the north, were initially formed during early to late Triassic.They include the South Margin Fault Zone of East Kunlun (200～220 Ma), the Altyn Tagh Fault Zone (220～230 Ma), and the North Qaidam Fault Zone（240～250 Ma）.These strike slip faults were most likely genetically related to the oblique subduction and collision of the paleo-Tethyan ocean basin, particularly in the period of exhumation of subducted plate or uplift of the overthrust plate, a period when post-collision magmatism and volcanism were active.

Abstract:The Emeishan Large Igneous Province comprises voluminous flood basalts and spatially associated mafie-ultramafic intrusions. In the Pan-Xi region, SW China, a number of gabbroic intrusions are dated at -260 Ma, same as the previous reported ages for the ELIP, and host .some giant Fe-Ti-V oxide deposits. Unlike the oxide deposits in classic layered intrusions, such as the Bushveld Complex, those in the Pan-Xi region occur as layers and/or lenses within the gabbros and are generally concentrated in the lower parts of the intrusions. Available geochemical evidence suggests that the intrusions were formed from highly evolved Fe-Ti-Vrich ferrogabbroic or ferropicritic magmas. The magmas were further enriched in Fe-Ti-V after separation of Si-rich magmas which formed the syenitic intrusions. Ore textures and associated mineral assemblages indicate that the orebodies were formed by late-stage crystallization of V-rich titanomagnetite from oxide liquids. The abundant accessory hydrous phases suggest that addition of fluide from upper crustal rocks might have induced the separation of the immiscible oxide melts and subsequently gave rise to the oxide orebodies.

Abstract:Free SiO-2 is represented by quartz, coesite and stishovite polymorphs. Quartz widely occurs in different rocks of the earth's crust, whereas coesite and stishovite are only formed under high pressures and temperatures. Since olivine is silica-unsaturated, quartz and olivine never coexist in the same rock. Therefore, in mantle peridotite and other ultramafic rocks, primary quartz can never be found. Recently, free SiO-2 (quartz and coesite) was discovered from podiform chromitites in mantle peridotites of Luobusa ophiolite, Tibet. High-pressure and high-temperature phase equilibrium experiments show that silicates such as olivine and pyroxene will be decomposed into simple oxides like FeO (wustite), MgO (periclase) and SiO-2 (stishovite) beneath the lower mantle (>670 km). It is thus thought that the free silica (quartz and coesite) associated with mantle minerals was possibly derived from the lower mantle and that mantle plume might have been the mechanism for transporting these minerals to the shallow part of the ophiolitic mantle.

Abstract:Haxiu quartz diorite is outcropped along the western Jinshajiang suture zone, and a study of its genesis and emplacement time can provide isotope geochronological evidence for the plate subduction and collision along the Xijinwulan_Jinshajiang suture zone. According to major element discrimination, it should belong to the IAG type formed during plate subduction. The 40Ar/39Ar dating results of hornblende show that its emplacement time is ～216.4 Ma, suggesting a product of Late Indo-Sinian magmatism. A study of its origin and age shows that, along the Jinshajiang suture zone, the plate collision didn't start and the subduction of the oceanic crust still continued in Late Triassic.

Abstract:Two kinds of mantle peridotites are recognized in Rutog at the westernmost part of the Bangong Lake - Nujiang ophiolite mélange in Tibet. One is a brecciform harzburgite, composed of about 80% olivine with Fo 90.76～91.84, 91.09 on average, 15% orthopyroxene with Mg# 90.97～91.41, 91.16 on average, 2% clinopyroxene with Mg# 93.24～94.60, 93.96 on average, and 3% magnetite and light brown chromium spinel with Cr# 0.20～0.25, 0.23 on average (lower than 0.60), and characterized by low MgO (41.41%～42.02%), high Al2O3 (1.63%～1.94%), CaO (1.34%～1.60 %) and Ti (133.04～134.52 μg/g), and depletion of REE with ΣREE being 0.17～0.22 times that of chondrite. Major and trace element characteristics indicate that the brecciform harzburgite is restite resulting from 10%～15% partial melting of primitive mantle. The other type is massive harzburgite without clinopyroxene, composed of about 85% olivine, 13% orthopyroxene, and 2% magnetite and red_brown chromium spinel with Cr# 0.69～0.74, 0.71 on average (higher than 0.60). In contrast to the brecciform harzburgite, the massive harzburgite is characterized by high MgO (42.96%～44.69%), low Al2O3 (0.23%～0.61%), CaO (0.08%～0.11%) and Ti (68.55～68.82 μg/g), and considerable depletion of REE, with ΣREE being 0.03～0.05 times that of chondrite. Major and trace element characteristics suggest that the massive harzburgite is restite formed by 30%～40% partial melting of the primitive mantle. It is preliminarily held that the brecciform harzburgite is restite of ancient oceanic lithosphere emplacement in the orogeny zone, and that the massive harzburgite is restite formed by another partial melting of residual peridotites during the subduction of ancient oceanic lithosphere. They are typical mantle peridotites of MOR- and SSZ-type ophiolite, respectively, and consistent with the two types of lavas in Bangong Lake ophiolite mélange, i.e., P-MORB and Boninite.

Abstract:The ultramafic_mafic dyke swarms on the southern piedmont of the Tongbai orogenic belt in Suizhou-Zaoyang area consists of two remarkably different types: troctolitic dyke (sill) swarms and metamorphosed mafic dyke ones. The troctolitic dyke swarms did not experience any metamorphism, so its emplacement age might be not earlier than that of the HP-UHP metamorphism (220～240 Ma), belonging probably to the product of late- to post-orogenic magmatism. Nevertheless, the metamorphosed mafic dyke swarms are geochemically very similar to Late Proterozoic basalt of Huashan Group in the area and are thus likely to be acognate phase. The troctolitic dyke swarms consist chiefly of olivine, plagioclase, orthopyroxene and clinopyroxene with minor phlogopite. Olivine is chrysolite (Fo72～78). Plagioclase crystals are mainly bytownite with minor labradorite.Clinopyroxene includes augite and diopside. The TiO2 content of phlogopite (3.36%) is high and indicates a Ti-rich variety. The olivine-augite equilibrium tempera-tures mainly range from 1 120 to 1 165℃, and the crystallization temperatures of augites range from 971 to 1?079℃. The rocks are characterized by high Al203 (17.25%～20.20%), MgO (9.56%～15.30%) and MgO/FeO* (1.26～1.76), and low TiO2 (0.33%～0.58%) and alkaline (Na2O+K2O=1.64%～2.23%). The transitional element contents (Cr=70～125 μg/g, Ni=251～518 μg/g, Co=54～75 μg/g) and the Mg numbers (Mg#=54～67) are relatively high in the rocks, which may approximately represent partial melting of the parental magma in the upper mantle. The rare earth element contents of the troctolitic swarms are low (ΣREE=18.66～35.42 μg/g) and are characterized by relative strong fractionation between LREE and HREE ［(La/Yb) N=4.4～4.7］ and especially by prominent features of strong Ba, Sr and Eu positive anomalies (Eu/Eu*=1.31～1.49), thus suggesting relative enrichment of Ca-plagioclase in the swarms. There exist no HFS (high field strength) elements (Nb, Ta, U, Th, Zr, Hf) anomalies in the troctolitic dyke swarms. Such phenomena are quite different from geochemical characteristics of the enrichment-type upper mantle indicated by the early Paleozoic basalt in the area, but similar to the features of Paleogene basaltic rocks in the orogenic belt, the foreland and the backland. It is thus considered that, with the delamination of the mountain root, intense interaction occurred between the subcontinental lithospheric mantle and the lower mantle. The development of troctolitic dyke (sill) swarms means a strong extensional event in the back part of the subducted plate after the delamination of the mountain root.

Abstract:The authors made an anisotropic analysis of shear waves obtained from broadband seismic experiments along the Yecheng (Xinjiang)-Ali (Tibet) profile. The result reveals the anisotropic characteristics in the upper mantle of western Tibet. The anisotropy is generally in NE direction and the orientation only varies insignificantly, being identical with the anisotropic direction in Tibetan Plateau and northern Tarim. The northward movement of Indian plate plays a key role in forming the shear wave anisotropy within the lithosphere of this region. The anisotropy in all blocks of Tibetan Plateau remains stable in a large EW-trending area. The original anisotropy in the lithosphere of each block stretches northeastward. Bangong-Nujiang faulted belt, as the boundary between Qiangtang block and Lhasa block, is mainly a boundary at the surface. In depth, the anisotropy in Indian lithosphere remains unchanged over Bangong-Nujiang fault belt, both in the western segment and in the central segment of Tibetan Plateau.

Abstract:As a result of protracted granitic magmatism （～150 myr）in the extinct Mesozoic Sierran continental arc, California, the metasedimentary framework rocks had undergone up to amphibolite facies intermediate- to high-grade metamorphism and partial melting of labile wall rocks within the proximity of invading plutons. These partial melting processes resulted in the formation of a number of migmatite complexes in the southern Sierra Nevada batholith. Such well-preserved migmatite complexes provide a natural laboratory to investigate the geochemistry of metasediment-derived melts. Rare earth element geochemistry data on the Goat Ranch migmatite complex, one of the best preserved migmatite complexes, show that the leucosomes, migmatites, and metapelites have: (1) pronounced negative Ce anomalies; (2) subparallel chondrite-normalized REE distribution patterns; (3) leucosomes have lower LREE contents than those in migmatites and pelites; and (4) contrary to the migmatites and pelites, leucosomes have various Eu anomalies. The Isabella metapelites contain a fair amount of graphite as shown in whole rock dissolution experiments and petrographic observations, which suggest that they are strongly reduced metasediments. A similar conclusion was alsoreached from previous studies on mineral geochemistry of biotites from these rocks and adjacent granitoids. These data and previous Sr, Nd isotopic compositiondata on the leucosomes, migmatites and metapelites demonstrate that pronounced negative Ce anomalies in leucosomes were inherited from their source rocks, not due to differential dissolution or fractionation crystallization of accessory phases (e.g. apatite, monazite or zir- con) during partial melting of metapelites. The finds from this study also suggest that if sediments with Ce anomalies above a subduction zone are introduced into the island arc magma source regime via either subduction or subduction erosion, and participate in island arc magmatism, then sediment-derived melts can contribute to the formation of those arc magmas with negative Ce anomalies.

Abstract:The anorthositic rocks in southern part of Korean peninsula occur as a long belt, intruding the ca . 2.0 Ga old Precambrian basement rocks of the Yeongnam massif. Although they have simple rock types (anorthosite and gabbroic anorthosite) comparable to well known massif-type anorthosites worldwide, they possess several important differences such as layered structure, amphibole rather than pyroxene as a mafic phase, and no orthopyroxene megacrysts. Theage of intrusion was not available previously. We have applied Rb-Sr and Sm-Nd isotope systematics to investigate the age and origin of these rocks. One foliated gabbroic anorthosite defines a Sm-Nd mineral isochron age of 1678±90 Ma. This age is tentatively interpreted as the emplacement age because of apparently closed-system behavior of Sm-Nd system in these rocks during greenschist-facies metamorphism of presumably Mesozoic age. This age agrees with the age range (1.1 to 1.7 Ga) reported for the occurrence of Proterozoic massif-type anorthosites, suggesting that origin of the anorthositic rocks might be explained in the context of so-called Proterozoic anorthosite event. Significance of the anorthositic magmatism to the tectonic history of the Precambrian basement rocks in southern Korea Peninsula is discussed. εNd(t) values of whole rocks range -1.6 to -5.2, while initial 87Sr/86 Sr ratios vary from 0.704 to 0.706. These data are interpreted as the result of assimilation of crustal material during crystallization of presumed anorthositic magma of mantle origin, although possible lower crustal source can not be excluded.

Abstract:The dip angles of eclogite and retrograde metamorphic eclogite type foliations in 100～2 950 m core of the CCSD main hole are obviously steeper than the angles of gneiss type foliations, with the former angles being generally 55 or so and the latter around 28 . Foliations of gneiss type locally dissect foliations of eclogite type, and hence foliations of these two types might have been formed in different periods. The contact relation between the twotypes of rocks is that of ductile shear zone formed during SEE-NWW ductile shearing at the main exhumation stage of Su-Lu terrane. Foliation attitude of eclogite and retrograde metamorphic eclogite plays a certain role in controlling attitude of miniature faults in eclogite type rocks, whereas foliation attitude of gneiss type exerts a relatively weak role in controlling attitude of miniature faults in gneiss type rocks. Brittle deformation in the main hole mainly reflects deformational characteristics of the SEE-NWW extensional tectonic stress field since Cretaceous. The striation plunging of miniature normal faults in 100～1 620m core of the main hole is predominantly in SEE direction, and this evidently results from deformation of this stage.

Abstract:Metallic and intermetallic compounds of Fe-group elements from Luobusa ophiolite chromitites were studied by X-ray diffraction (XRD) analysis. The results indicate that they belong to four mineral species. These minerals are intergrown with such minerals as UHP mineral wustite and platinum-group minerals. Formed under the strong reduction condition of great depth, these minerals are similar to the earth's core in chemical composition. It is thus held that the iron-group minerals might have been derived from the mantle or the core of the earth.

Abstract:In the present paper, the authors analyzed the earthquake mechanism solutions (M4.6～8.5) during 1933～2003 for the study of the extensional tectonic movement at the surface of the Tibetan Plateau and its relative dynamics. The results show that a lot of normal fault type earthquakes are concentrated in the central part of the Tibetan Plateau with the elevation greater than 4 000 m. Many earthquakes are pure normal fault events. Their focal mechanism solutions show that the strike directions of faults are almost in the N-S direction. The dislocation slip vectors of the normal fault type events have large components in the E-W direction, suggesting the extensional motions in nearly E-W direction in the high elevation area of the plateau. The tensional forces in theE-W or WNW-ESE directions are predominant in this region, and may result in theabove extensional tectonic motions. The dynamics for extensional motions can be attributed to the gravitational collapse of the rising plateau and the stress of its surrounding areas. Around the Tibetan Plateau, earthquakes caused by reverse and strik-slip faulting are predominant on the north and west margins (except for the east margin), and the Himalayan Mountains. Horizontal stress field innearly NE or NNE direction dominates the tectonic motions along all margins. The tectonic forces from the relative movement between the Indo_Australian and Eur-sian plates cause P-axes to line up in the NE-SW direction in the western China.

Abstract:The native Si-Fe alloy minerals from podiform chromitites of Luobusha ophiolite in the Yarlung Zangbo suture zone were examined by a new Gandolfi method using SMART APEX CCD X-ray diffractometer.The powder diffraction pattern shows that the minerals are composed of FeSi, FeSi2 and native silicon. The association of these minerals suggests that the crystallization order of the mineral may be from early to late FeSi→FeSi2→ native silicon, accompanied by gradually increasing deoxidization.

Abstract:The cores, measurements of physical properties, well-logging and VSP data obtained from the Chinese Continental Scientific Drilling (CCSD) hole can be used to calibrate seismic reflectors and raise the reliability of seismic interpretation. Measurements of physical properties indicate that the rutile-bearing eclogite, due to its very high seismic velocity and density, can produce reflections and gravity anomalies. Numerical modeling demonstrates that the arch reflectors appearing at the CCSD site result jointly from the eclogites and the penetrating late shatter zone. Southeast of the CCSD main hole, there are quite a few such reflectors, implying that eclogite bodies exist in the extension direction of the surface eclogite body.

Abstract:The U-Pb ages of zircon from Cishan granite were determined by LA-ICP-MS (Laser ablation-inductively coupled plasma_mass spectrometer). The ages of 199～149 Ma from 8 grains indicate the Jurassic formation of the granite, which can thus be termed Yanshanian granite. The ages of 2 110～2?467 Ma (2 252±41 Ma in average) from 4 grains of Early Paleozoic inherited zircon show that the source of the granite contains materials from Early Paleozoic Fenzishan Group. The formation ages of the granite provide important evidence for the origin of the Nanzhangjia gold deposit.

Abstract:Bulk rock chemistry of Hujialing garnet clinopyroxenite inRizhao of the Sulu ultrahigh-pressure metamorphic belt is rich in fusible composition and low in refractory composition when compared with that of the primary mantle. Whole rock has 44.04％～50.50％ SiO2，high MgO（12.77％～18.73％），high CaO/Al2O3 (1.6～8.0)，low alkali and Mg# 74.82～86.13), which shows that the rock has an affinity to alumina-depleted komatiite. The REE partition pattern has the form of clinopyroxne and relative HREE depletion withe（Gd/Yb)N being 3.51～5.87. The total PGE concentration varies in a wide range of 19.18×10-9 ～59.44×10-9and is higher than that of xenolith and Alpine type peridotites with （Pd/Ir)N of 8.58～11.07. All of these characteristics indicate that the magma which produced the garnet clinopyroxenite was formed mainly by melting of the clinopyroxene from the mantle source with residual garnet. The phases of the rock before exhumation might have been clinopyroxene+garnet.The high concentration and positive slope of PGE suggest that their distribution was controlled by a high degree of partial melting and that magma was sulfur-unsaturated without sulfide segregation.

Abstract:The HP metamorphic belt along the southern margin of Sulu terrane is made up of a middle temperature-high pressure metamorphic slice and alow temperature-high pressure metamorphic slice. The former slice consists of gravel-bearing phengite feldspar quartzite, mica feldspar quartz schist, marble-phosphate rock and phengite albite quartz schist in upward succession, whereas the latter consists of feldspar quartz schist and albite quartz schist. In schists, the end_member component of plagioclase is albite, the feldspar phenocrysts have features of volcanic crystal fragments, and the zircon has magmatic rhythm crystallization zoning and high Th/U ratio (＞0.5). In addition, the schists exhibit high SiO2 and Na2O+K2O, low CaO, enrichment of LREE with strong fractionation, depletion of HREE with weak fractionation, δEu between 0.13 and 0.47, and significant negative Nb, P and Ti anomalies. The schists are plotted in the alkaline field in a SiO2 versus A·R discrimination diagram, in the A-type field in a (K2O+Na2O)/CaO versus Zr+Nb+Ce+Y discrimination diagram. The schists in the medium temperature-high pressure metamorphic slice and in the low temperature_high pressure metamorphic slice are plotted in the peraluminous field and the metaluminous field respectively in a A/CNK versus A/NK discrimination diagram. It is thus considered that the protoliths of the three sorts of schists are acid volcanic rocks, and that the rock type and genetic type of the volcanic rocksare peraluminous to metaluminous alkaline rhyolite and A type igneous rocks, respectively. According to the major and trace element discrimination diagrams, the volcanic rocks were formed in an extensional plate environment and might have been an accessory product during the breakup of Rodinia continent and the formation of Yangtze intracontinental rift in Neoproterozoic.

Abstract:Two FeCrNi spherules were discovered in the main hole of CCSD. They are about 200 μm in size. Their chemical compositions are Fe 71.07%～73.68％, Cr14.55%～16.79％ and Ni 9.91%～11.47％,totally 98.2%～99.65％.The spherules contain oxide inclusions, with elements of Cr, Mn, Ti, Al, Fe, Si, and O. X-ray diffraction analysis shows that the spherules, having molecular formulaof Fe0.74Cr0.16Ni0.10,is polycrystalline and of the cubic system, with space group of Fm3m, cell parameter of a ＝0.360?3 nm, Z=4 and density of 7.828 g/cm3. The polished faces of the spherules are white gray in color and have metallic luster. The hardness of the spherules is about 4.026Hm. The reflectance of spherule is 56％～63％, with S546 of 56％. The spherules were probably produced by cooling of melted FeCrNi metallic droplets which trapped oxygen and was thus oxidized.

Abstract:The garnet migmatitic granite (GMG) was formed by partial melting of Ga-Bi gneiss within Ga-Bi gneiss complex of Archaean khondalites in Daqingshan area, Inner Mongolia, in the process of subhorizontal shearing and granulite facies metamorphism. The GMG mainly inherited mineral composition and geochemical features from the Ga-Bi gneiss, while its difference from Ga-Bi gneiss in textures and geochemistry (especially REE) indicates the process of partial melting and evolution. In spite of its small bodies, GMG shows heterogeneity in mineral composition, textures and geochemistry, and can be divided into two types, of which the former has high K2O and low Na2O, CaO, showing apparently positive anomalies and Low ∑REE, whereas the latter has low K2O and high Na2O,CaO, assuming negative Eu anomalies and high ∑REE. It is suggested that the development of the two types of GMG is related to the gradual separation of partial melts from the solid residue during the partial melting and subsequent flowing. The relative lack in the former and enrichment in the latter of the restite and relic minerals, especially the REE behavior-controlling refractory minerals such as garnet, monazite, apatite and zircon, caused the difference in REE distribution of the two types of GMG. The available data suggest that the GMG was developed in Neoarchaean and is hence quite different from the Paleoproterozoic anatexis_derived garnet-bearing granite in Sanggan area.