Abstract:Abstract:Geophysical survey of Dongpo rock mass on the south bank of Yarlung Zangbo River in western Tibet was carried out using multiple methods, and the inversion of aeromagnetic survey anomaly precisely positioned by ground magnetic survey revealed the range of the deep magnetic body in Dongpo rock mass; seismic reflection survey delineated the weak reflection places under the rock mass with reflected wave characteristics different from those of outcropping ophiolite body; meanwhile,as confirmed by MT method, the low-resistivity bodies under the rock mass are at the roughly identical places. The outcropping ophiolite body extends downward, resembling a pot bottom as a whole, and its middle part is characterized by low resistivity and weak reflected wave. In addition, magnetic minerals are relatively developed at the depths of 1.5km-3.0 km, which might be the very section of chromium-bearing rock mass having strong mineralization and alteration; the similar characteristics were observed in the Luobusha mining area, and hence these places are favorable for ore prospecting.

Abstract:Abstract: Investigating rotational deformation of the southeastern margin of the Tibet is the key to understanding how and why the Tibet material extruded to the southeast. Until now there are two sets of strata used to study the rotational deformation on the southeastern margin of the Tibet: the Jurassic-Eocene and the Miocene-Quaternary strata. Paleomagnetic studies of the Jurassic-Eocene strata indicate widespread clockwise rotational deformation, similar studies of the Miocene-Quaternary strata suggest multiple deformation patterns, including clockwise rotation, counter-clockwise rotation and also no rotation. However, it is still not well constrained as to the timing and degree of rotational deformation on the southeastern margin of Tibet. Two sets of strata (the Paleocene-Eocene and Pliocene-Quaternary sediments) are well exposed in the Yanyuan basin, Sichuan Province. Magnetostratigraphic studies indicate an age of >3.6-0.6 Ma for the Pliocene-Quaternary strata. Declination data suggest that the Pliocene-Quaternary sediments experienced counter-clockwise rotation (-14.4°), and the Paleocene-Eocene deposits underwent notable clockwise rotation (10°-21.5°). As the age of the youngest strata that experienced clockwise rotational deformation on the southeastern margin of Tibet is the Eocene, the clockwise rotational deformation likely occurred during a time interval between the Eocene and the Miocene. The counter-clockwise rotational deformation recorded in the Yanyuan basin happened before 3.6 Ma with an average rotational rate of 4°/Ma. Since anisotropy of magnetic susceptibility (AMS) data indicate that the Pliocene-Quaternary sediments underwent no compressional deformation at all, the counter-clockwise rotational deformation was initiated most likely by strike-slip faults around the Yanyuan basin.

Abstract:Abstract: In this paper, the authors conducted zircon LA-ICP-MS U-Pb dating and Lu-Hf analysis of the alkali-feldspar granite in Tama of Xietongmen region along the middle Gangdise magmatic belt. The results suggest that the weighted mean ages of two samples are (40.02±0.39)Ma and (40.65±0.32)Ma for the pluton, respectively. In essence, the two ages are of the same geological significance in that they both represent the crystallization age or emplacement age of the alkali-feldspar granite. Zircon Lu-Hf analytical data reveal that values of 176Hf/177Hf vary from 0.282633 to 0.282878 (averaging 0.282765), and the values of εHf（t） range from -4.08 to 4.15 (0.28 on average) , with the peak values of εHf（t）varying from -1 to 1. TDMC model ages are from 822 Ma to 1373 Ma (averaging 1075 Ma) with peak model ages being ca.1000-1200 Ma. The obvious feature is that the values of the εHf（t）show alternating positive and negative values, corresponding to a small value and indicating the crustal-mantle contamination process, which resulted from partial melting of the ancient crust. Combined with geological setting and study results, the authors consider that the alkali-feldspar granite might have generated from the slab break off of the Neo-Tethys oceanic crust, which led to upwelling of the asthenosphere and further induced the partial melting and recycling of the ancient crust. During the process, the mantle materials played a vital role in forming the alkali-feldspar granite in the study area.

Abstract:Abstract: Early Cretaceous granites are widely distributed in northern Gangdise, Tibet. The Zhaduding intrusive body, which belongs to monzogranite in lithology, is widely distributed and occurs in the form of batholith, being a typical case of the granites. Petrogeochemically it is characterized by high SiO2 (70.05%-74.97%) and K2O (4.09%-5.35%), low CaO (0.93%-2.19%), TiO2 (0.22%-0.52%) and Al2O3 (12.81%-14.24%). Moreover, it belongs to metaluminous or weak peraluminous (A/CNK=0.99-1.06) high-K calc-alkaline series. The rocks are characterized by high REE content (∑REE=199.36×10-6-247.91×10-6), rich LREE relative to HREE (LREE/HREE=5.82-6.88), and significant negative Eu anomalies (δEu=0.30-0.45). Chondrite-normalized REE patterns exhibit V-type with slight right-oblique feature. Trace elements show that the rocks are enriched in Rb, Th, K, Zr and Hf and depleted in Nb, Ta, Sr, Ba, P and Ti, with average (Zr+Nb+Ce+Y) 427.63. Bulk-rock?zircon?saturation?temperature (828-838°C) shows that the temperature of magma formation was pretty high. The petrogeochemical characteristics show that the Zhaduding rock body is A-type granite. The LA-ICP-MS zircon U-Pb age of 103.8±1.0Ma indicates that Zhaduding rock body was formed in late Early Cretaceous, and is located in the post-collisional A2-type granite area in discrimination diagrams. It was formed by a certain degree of mixing of the lithosphere mantle and the crustal partial melts, resulting from asthenosphere material upwelling in the post-collision extensional setting.

Abstract:Abstract: Studies of petrology and geochemistry indicate that the Baluntai diorite is the high-K calc-alkaline diorite. The rocks, which have the data Na2O+K2O=4.14%-7.05%, Al2O3 ＝14.62%-17.35%, (La/Yb)N with an average of 10.46, are characterized by enrichment of large ion lithophile elements (LILE, such as K, Rb, Ba, and Pb) and light REE but depletion of high field strong elements (HFSE, like Nb, Ta, and Ti)，and were probably produced in an island arc settings. LA-ICP-MS zircon U-Pb dating shows that the Baluntai diorite was formed at (430.1±1.1)Ma. In-situ zircon Hf analyses show that zircons from Baluntai diorite have εHf(t) values from -12.7 to –7.6 and tDM2 model ages of 1895 Ma to 2219 Ma. Combined with Hf isotope analytical results and regional geological data, it is held that the Baluntai diorite resulted from partial melting of the Tianshan crystalline basement in response to northward subduction of South Tianshan Ocean during the Early Silurian. The isotopic ages of the Baluntai diorite body represent the upper age limit of the Wuwamen ophiolite.

Abstract:Abstract: Located in the central part of Yarlung Zangbo Suture Zone (YZSZ), the Saga ophiolite is mainly composed of peridotites, gabbro, diabase and lava. This paper reports a suite of alkaline basalts to the south of the Saga ophiolite, which extends in NWW direction and crops out 1~3km in width. This suite of basaltic lavas has vesicular/ amygdaloid structure and porphyric texture with phenocrysts of plagioclase (15 modal %-20 modal.% in content) and clinopyroxene (~5 modal % in content). The plagioclase is albite and the clinopyroxene is titaniferous diopside (TiO2=1.46wt.％). Based on the composition and TAS diagram, the authors hold that the lava belongs to alkaline basalt. The lava shows the characteristics of low SiO2, high TiO2 ,K2O and Al2O3 content as well as enrichment of large ion lithophile elements ( LILE ) (Rb, Ba, Th ) and high field strength elements ( HFSE ) ( Zr, Hf, Nb, Ta ). The rare earth elements (REE) content of the basalt is higher (∑REE=266.93×10-6), with a strong fractionation between LREE and HREE （( Ce/Yb )N = 7.30-14.18）. The chemical characteristics are similar to features of continental rift volcanic rocks. This study shows that garnets exist as residual minerals in the source. In addition, at the early stage of magmatism, there existed crystallization fractionation of olivine, clinopyroxene and other mafic minerals. U-Pb dating of zircons by LA-ICP-MS yielded a wide range of ages. The youngest group has average age of (54.2±1.4)Ma，with εHf（t） being -11-+1.7, and has the Mesoproterozoic two-stage model age, indicating that these zircons were captured from the crust and the lava had not formed until early Eocene.

Abstract:Abstract: The tectonic setting of western Qinling orogenic belt was studied through the research on the petrogeochemical characteristics and U-Pb age of zircon from Dawulu quartz-diorite and Laodou granitic-diorite using LA ICP-MS. These two kinds of rocks belong to peraluminous calc-alkaline middle rocks. Trace element studies suggest that the rocks are predominately characterized by enrichment of LILE elements such as Rb, Th and U and other light rare-earth elements, depletion of Ba ,K, Nb, Sr, P, and low Sr and Y, suggesting typical characteristics of Himalaya-type granite. REE data indicate that the light rare earth elements were abundant, and heavy rare-earth elements are poor in these rocks. The light and heavy rare -earth fractionation is obvious. δEu has a weak negative anomaly. U-Pb age of zircon indicates that the weighted average ages of both Dewulu quartz-diorite and Laodou granitic diorite are (245.8±1.7) Ma and (243.4±1.9) Ma, (241.4±2.1) Ma, (38.2±1.7)Ma and (241.4±1.6) Ma respectively, which suggests that these two intrusions formed at the earlier stage of Indosinian. It is pointed out that Laodou granitic diorite and Dewulu quartz diorite were derived from the different sources which came from the different depths, and the emplacement and accumulation were from multiple origins. The Laodou granitic diorite and Dewulu quartz diorite are projected into the range of arc magma. The tectonic setting research suggests that the western Qinling lies in the continental-to-continental collision in the earlier Indosinian period, and hence this region is favorable in search for porphyry Cu-Au deposits, skarn Cu-Au deposits and epithermal Cu-Au-Sb deposits.

Abstract:Abstract: Mesozoic intermediate-acid intrusive rocks in Hushan intrusion of Tongling area belong to the high potassium (K) calc-alkaline series, with main rock types being quartz monzodiorite and granodiorite porphyry. LA-ICP-MS zircon U-Pb dating of Hushan intrusion shows that the emplacement age of quartz monzodiorite and granodiorite porphyry are (143.2±1.2)Ma and (145.3±1.2)Ma respectively, belonging to Late Jurassic-Early Cretaceous. These data are consistent with eastern China’s J-K magmatic event. In addition, Hushan body has experienced two times of magma intrusion activities. The age of early granodiorite porphyry (145.3±1.2)Ma is consistent with the age of Yaoshan granodiorite porphyry (146.0±0.9) Ma in the Tongling ore district, and the age of late quartz monzodiorite (143.2±1.2)Ma is consistent with that of Tongguanshan and Tianebaodanshan (142±1)Ma,(141.7±1)Ma). From the study of geochemistry and plagioclase-hornblende thermobarometry, the authors conclude that the magma crystallization temperature and the corresponding pressure varied in the range of 768~838°C and 3.44×108 ~5.42×108 Pa, respectively. Hushan intrusion was derived from the mixture of the mantle magma and crustal magma, with their corresponding depths being 11~18 km.

Abstract:Abstract: With the method of U-Pb isotope dating of detriatal zircon from Middle Jurassic Mohe Formation, the authors detected that detrital zircon ages are clustered in the range of 1425-170 Ma, which suggests that the basement of Mohe Basin has complex provenance. The provenance of Mohe Basin is mainly made up of Mesoproterozoic metamorphic volcanic rocks with the detrital zircon age of 1425-1064 Ma, Neoproterozoic metamorphic intrusive rock with the detrital zircon age of 888-550 Ma, Cambrian-Ordovician metamorphic supracrustal rock and metamorphosed plutonic intrusive rock with the detrital zircon age of 517-441 Ma, Permian-Carboniferous intrusive rock with the age of 327-252 Ma, and Triassic and Middle Jurassic intrusive rock with the age of 250-170 Ma. These data correspond?to the ages of geological bodies on the south margin of the basin, which shows that the source of the basin was from the Middle Proteronic -Middle Jurassic geologic body in the south, with the youngest age of detrital zircon being 17 Ma. It is therefore held that the lower sedimentary limit of the Mohe Formation is not earlier than early Middle Jurassic. The results achieved by the authors provide new evidence for the study of the evolution of Mohe Basin

Abstract:Abstract: On the southern margin of the Qinling orogenic belt, there exists a multitude of Early Paleozoic mafic volcanic rocks, and the syenite porphyry veins in the Qiaomaichong gold deposit were intruded in NW direction into mafic volcanic rocks in the study area. By means of studying new zircon LA-ICP-MS U–Pb age and Hf-isotope, whole-rock major and trace elements of syenite porphyry veins in the Qiaomaichong gold deposit and the mafic country rock, the authors tried to constrain the age and petrogenesis and geodynamic background of the siliceous veins. It is revealed that the intrusion of the syenite porphyry can be divided into two phases, and the corresponding two zircon samples of syenite porphyry have 206Pb / 238U weighted average ages of (415±7) Ma and (477±6) Ma respectively. The former age belongs to the Late Silurian, whereas the latter to the Early Ordovician. Veins have a high SiO2 (>75%) content, σ=1.59，and A/CNK=1.28, which suggests peraluminous alkaline siliceous shear veins. The εHf (t) values are all positive, and vary in a large range ( 3.4 to 11.8) , which suggests that almost all the matter came from the depleted mantle source, exhibiting a crust-mantle mixing feature. The mafic rocks have a high amount of REE (149.62×10-6-321.55×10-6), and are strongly enriched in light rare earth elements , showing a high degree of differentiation. Research shows that this area was within plate tectonic cleavage in the early Paleozoic, so the mantle asthenosphere upwelling of magma formed mafic rocks. Then the veins brought the Au from deep crust into the surface crust in the invasion process, thus providing material of Au sources for pre-concentration of Au and later shear mineralization. The determination of the age of the formation of veins has a great significance for the study of late stage gold enrichment.

Abstract:Abstract: In this paper, the authors studied the andsites in Rongna ore block, Tiegelong Cu (Au-Ag) deposit, Duolong ore concentration area, Tibet, and used the zircon U-Pb data and petrogeochemistry of andsites to identify the petrogenetic age and tectonic setting of the andsites. The weighted average age of zircon U-Pb is 110.1±0.7 Ma (MSWD=2.3) , which represents the petrogenesis age. An analysis of the whole rock sample shows that SiO2 values are 59.5%-61.48%, Al2O3 values are 16.14%-17.11% and Na2O+K2O values are 6.02%-6.63%; Mg# is of intermediate value. LILE such as Ba, Rb, Th, K are rich, HFSE such as Ta, Nb, P, Ti are relatively poor and characterized by Rb positive anomaly and obvious Zr, Hf negative anomalies. Petrological and geochemical studies show that the andesites are high potassium calc-alkaline rocks exhibiting the characteristics of Andean-type active continental margin volcanic rocks. They resulted probably from partial melting of subducted oceanic slab as well as miscibility with crustal material during the upward migration of the magma in the case that subducted oceanic slab didn’t interact with the mantle. They were the magma products of the northward subduction of Bangong Co-Nujiang Ocean and Lhasa and the collision collage process of Qiangtang terrane. In combination with other dating data and drilling core catalog data, the authors hold that the formation of andesites was later than the rock-forming and ore-forming stage of the Tiegelongnan high sulfur epithermal Cu (Au-Ag) deposits, which seems to have been the important condition for the preservation of the ore deposit.

Abstract:Abstract: The Yarlung Zangbo suture zone (YZSZ) , which separates Eurasia in the north from the Indian plate in the south, can be divided into eastern, central and western segments. The western part is further divided into Dajiweng-Saga ophiolite zone in the north and Daba-Xiugugabu ophiolite zone in the south. The studied Cuobuzha ophiolite is located in the north part of the western YZSZ. The mantle peridotites mainly consists of harzburgites and associatd dikes or veins of gabbro in the massif. The characteristics of the mineral show that the Fo values of the olivine in mantle peridotites are high, and all of the olivines are forsterites; in addition, the orthopyroxenes are mainly enstatites, the clinopyroxenes are endiopsides and diopsides. Chrome spinels are characterized by high Al (Cr#=22-39) and high Mg# (60-70). The harzburgite in Cuobuzha has similar distribution patterns of rare earth elements, characterized by their slight depletion of LREE and weak enrichment of HREE with (La/Yb)N being 0.11-0.60. Fractional melting modeling indicates that harazburgites may be the residues from 15%-22% melting. However, the LREE values of the Cuobuzha peridotites are higher than the calculated LREE values. In combination with their enrichment of large ion lithophile elements (LILE, e.g., Rb and Sr) and high field strength elements (HFSE, e.g., Ta, Hf and Ti) , the authors hold that these rocks originated from partial melting of mantle source and was later modified by fluids and melts in a suprasubduction zone mantle wedge. Comparative study of the western YZSZ suggests that the tectonic setting of the two ophiolitic subbelts are similar to each other, and the tectonic emplacement probably resulted in the differences between them.

Abstract:Abstract: The ophiolitic peridotites constitute an important part of the ophiolite in that they not only record the experienced plate tectonic events but also offer help to discuss the composition of the mantle and the effect of the deep mantle. The Purang ophiolite located in the western part of Yarlung Zangbo suture zone is characterized by containing a large mantle peridotite massif ca.600km2 in area. In order to discuss the petrogenesis and tectonic significance of the Purang peridotite massif, the authors sampled a section of about 10 km across the massif in the eastern part of the Purang mantle peridotite massif. Based on a detailed field survey and mineralogical and geochemical analysis of systematically selected mantle peridotite samples, the authors have achieved some results: (1) The lithofacies distribution of the Purang ophiolite peridotites has been determined. The profile across the massif shows that harzburgites form the main part of the Purang peridotite massif, the harzburgites are mainly located within the peridotite massif, the banded lherzolites are mainly distributed at the edge of the peridotite massif, and the ratio of the exposed area of harzburgites to that of lherzolites is about 4:1; (2) Based on olivine-spinel associations and the formulae based on the reaction of 6Fe2SiO4+O2= 3Fe2Si2O6+2Fe3O4, the oxygen fugacity values have been calculated (?log(fo2)FMQ range from-1.11 to+0.45), which are significantly higher than the fO2 value obtained using the V content, indicating a reducing tectonic setting; (3) The Purang peridotites are not the simple residues of partial melting and might have experienced later melts metasomatism. According to the whole rock geochemistry and oxygen fugacity values, this paper argues that the later metasomatic melts were probably derived from the lower partial melting magma formed in a mid-ocean ridge setting; (4) The Purang ophiolite peridotites show similar bulk geochemical features and oxygen fugacity characteristics to the modern mid-ocean ridge abyssal peridotites. It is thus held that the Purang ophiolite peridotites formed in a mid-ocean ridge tectonic setting, without imprints of supra-subduction zone setting. The two stage evolution model (MOR→SSZ) of the peridotites from the Yarlung Zangbo suture zone needs to be reexamined.

Abstract:Abstract: The peridotites in Darbute ophiolite consist mainly of harzburgite and minor dunite, lherzolite and dunite and exhibit strong alteration. The major elements of clinopyroxene, orthopyroxene, olivine and spinel of harzburgite show the characteristics of both abyssal peridotite and SSZ peridotite, which is identical to the features of the trace elements of clinopyroxene obtained from the LA-ICP-MS in-situ analysis, while lherzolite is similar to abyssal peridotite. Oxygen fugacities recorded by olivine-spinel of harzburgite equilibrium are +0.96 log units below and -0.14 log units above the FMQ buffer, overlapping the range from MOR to SSZ harzburgite, or from back arc basin peridotite to island arc peridotite. The plot of Ga-Ti-Fe3+# of spinels indicates that the origin of dunite was related to the interaction between peridotite and island arc tholeiite, and the harzburgite was probably the residue after the interaction between peridotite and MOR melt and the interaction between peridotite and hydrous melt at the SSZ environment. The values of ∑REE of harzburgite and dunite are lower than those of C1 chondrite, and display the enriched LREE and the U-type REE pattern，which implies the fluid/melt-rock reaction. Taking into account the above data, the authors hold that the Darbute ophiolite was probably formed in the back arc spreading ridge and influenced by subducted fluid/melt.

Abstract:Abstract: The Wuwamen ophiolite is located on the southern margin of Middle Tianshan Mountains, Xinjiang. In this paper, petrology, mineralogy and geochemistry of the ultramafic rocks from Wuwamen ophiolite were studied to constrain their origin and tectonic setting. The ultramafic rocks from Wuwamen ophiolite are serpentinized lherzolites composed of olivine (Fo=89.1-90.6), orthopyroxene (Wo0.4-2.4En87.2~90.7Fs8.9-10.9; Mg#=89.0-91.0), clinopyroxene (Wo49.1-51.3En16.0~48.4Fs0.9-4.3; Mg#=90.2-92.1) and spinel (Mg#=71.8-77.5; Cr#=9.3-13.4). They are characterized by relatively lower content of MgO (37.74%-41.34%), and higher content of Al2O3 (2.58%-3.39%), CaO (2.23%-3.68%) and TiO2 (0.05%-0.11%). The ultramafic rocks are also depleted in rare earth elements (REE; total REE = 1.73×10?6-4.63×10?6) and incompatible elements (e.g., Rb=0.4×10?6-1.39×10?6, Zr=0.73×10?6-3.28×10?6, Hf=0.04×10?6-0.11×10?6), and enriched in compatible elements (e.g., Cr=2516×10?6-2793×10?6, Co=84.6×10?6-119×10?6, Ni=1641×10?6-2261×10?6). These data indicate that the ultramafic rocks from Wuwamen ophiolite are residues of mantle rocks after low degrees (ca. 5%-10%) of partial melting in a Mid-Ocean-Ridge (MOR) environment.

Abstract:Abstract: Zetang ophiolite is mainly composed of peridotite, gabbro and basalt. Hornblende gabbro, which was intruded into the peridotite, comprises amphibole, prehnite+pumpellyite and minor Fe-Ti oxides. The amphibole in hornblende gabbro is brown euhedral with homogeneous interference color and has higher Al2O3 (7.0%-11.0%), TiO2 (1.0%-2.5%), as well as Na2O (1.0%-1.9%) values than the amphibole of metasomatic genesis, implying that the amphibole is of primary magmatic origin. The Fe-Ti oxides consist of magnetite (TiO2=1.2%-13.2%; Fe2O3=40.6%-61.4%; FeO=31.1%-43.6%) and ilmenite (TiO2=36.2%-50.8%; Fe2O3=2.5%-24.6%; FeO=33.0%-43.7%). The ilmenites always exhibit trellis and sandwich textures or are closely spaced (composite type) in the magnetite host. The oxygen fugacities (expressed as -logfo2) of the Fe-Ti oxides calculated by ilmenite-magnetite geothermobarometry are 12.4-22.8 (approximately NNO+1), indicating that the presence of high water activities during crystallization. The positive εHf(t) values (+11.0 to +19.8) of the sample suggest that it came from depleted mantle (DM). The hornblende gabbro is characterized by high Al2O3 (20.4%-22.4%) and TiO2 (1.0%-1.5%), low MgO (4.1%-5.5%) values, similar to features of high-alumina basalt (HAB). The hornblende gabbro might have been formed by evolved mantle-derived hydrous magma rich in volatile, Ti and Al2O3. However, the sample shows depleted light rare earth element (LREE) patterns, which is different from features of HAB in the subduction zone. The rocks were probably formed by partial melting of mantle wedge induced by dehydration of serpentinized subducted oceanic lithosphere.

Abstract:Abstract: Listwanite is a suite of silica-carbonate alteration products which are formed when CO2-bearing hydrothermal fluids meet and react with serpentinized mafic and ultramafic rocks. This alteration product is of great importance for its economic significance. Gold, mercury, magnesite and base metal deposits are often associated with listwanite. In China, Not enough attention has been paid to the petrogenesis of listwanite and related mineralization. This paper reports the study of listwanite occurring along the northeast edge of Baer ophiolite in the western part of the Yarlung Zangbo?suture (YZSZ). Baer ophiolite lies in Ngari Prefecture of southwest Tibet. The Baer listwanite crops out along the northeast boundary of the ophiolite with a width of ca. 20 meters and stretches a few kilometers in NWW direction. Based on the features of spinel under optical microscope, the authors recognized two stages of listwanite: Stage I listwanite contains spinel relicts while Stage II listwanite rarely contains spinel relicts. This means Stage II listwanite experienced more intense alteration. Geochemically, Baer listwanite is mainly composed of SiO2, MgO and CO2. 8 samples (containing 3 Stage I samples and 5 Stage II samples) show variation of major oxides, and the MgO/SiO2 ratios are not consistent, which implies that the listwanization was not an iso-chemical process. Baer peridotite and two stages of listwanites show similar trace elements distribution patterns. Both stages of listwanites show little enrichment of the LREE related to the protolith. From peridotite to two stages of listwanites, the behavior of HREE might have experienced depletion followed by slight enrichment. All samples show positive Sr anomalies and their values go up stage by stage. The values of Au and Hg in both stages of listwanites show that they have not been subjected to Au and Hg mineralization.

Abstract:Abstract: The Zhongzaohuo mafic dyke swarms in East Kunlun are principally composed of dioritic porphyrite with minor lamprophyre, porphyritic diabase, and diabase. The LA-ICP-MS zircon U-Pb dating indicates that the mafic dykes were emplaced at (249±1) Ma. The mafic dykes are enriched in LILE and depleted in HFSE. The rocks have higher total REE，with slightly enriched LREE (∑REE=99.9×10-6~173.9×10-6 ，(La/Yb)N=3.5~9.3). Source region analysis shows that mafic magma resulted from the fluid from subducted ocean crust and the mantle metasomatism, and partial melting played a dominant role in magma evolution，while crustal contamination and fractional crystallization played a limited role in magmatic differentiation. Tectonic setting analysis shows that the formation of the rocks was related to subduction; in combination with the tectonic evolution of East Kunlun, the authors hold that the formation process of mafic dyke swarms in this paper is as follows: in early Triassic, as the result of northward subduction of Paleo-Tethys Ocean, fluids from the subduction slab were dehydrated and mantle peridotite experienced metasomatism, which promoted the mantle peridotite partial melting into mafic magma; the magma was affected by the dynamic background of the back-arc extension, and then it migrated upward to the upper crust along the fissures to form the mafic dykes.

Abstract:Abstract: This paper reports the discovery of unusual mantle mineral group in the mantle peridotites of Dongbo ophiolite, which lies in the western part of the Yarlung Zangbo suture zone. The Dongbo ophiolite consists mainly of harzburgite, with a small amount of lherzolite and dunite, pyroxenite and gabbro dikes cutting across the harzburgite. Geochemical characteristics suggest that the Dongbo mantle peridotite was derived from mid-ocean ridge (MOR) but modified in a suprasubduction zone (SSZ) environment. Some grains of diamond and other unusual minerals, such as moissanite, were recovered by standard mineral separation techniques from a 693 kg sample of harzburgite. The presence of diamond, native Cr, Au, Fe, Si and Cu, together with the moissanite, indicates a strong reducing environment. The authors also found a lot of alloys, oxides, sulfides, silicates, fluoride and some other materials. These mineral assemblages recovered from the Dongbo harzburgite are very similar to those of Luobusa and Purang harzburgite, which gives evidence to the ophiolite-type diamond.

Abstract:Abstract: The mineral assemblage of such minerals as diamond and moissanite has been discovered in several mantle peridotites in Yarlung Zangbo ophiolite belt. The authors collected 526 kg harzburgite rocks from Zedang mantle peridotite for artificial heavy mineral research so as to further investigate the physical and chemical environment of these unusual minerals. Diamond, moissanite and more than 30 other mineral species were discovered, similar to the result of other mantle peridotite in the Yarlung Zangbo ophiolite belt. These unusual minerals show that high pressure, super-reduction conditions and numerous continental crust materials existed in mantle peridotite, suggesting that ancient crust might have experienced continental deep subduction or lithosphere delamination into mantle or even into mantle transition zone (410-660 km) at the early stage; subsequenty these crustal materials were modified in an environment of high pressure and super-reduction in the deep mantle, and surged upward to shallow crust by mantle plume or mantle convection process. Unusual minerals were trapped within the mantle peridotite in such a recycling process. It is of great significance to understend crust mantle exchange and deep mantle dynamics for comprehensive research on mineralogy of unusual mineral assemblages in mantle peridotite.

Abstract:Abstract: Diamond and other deep mantle minerals, previously found in the Mesozonic Tibet and the early Paleozoic Polar Ural, Russia, are now found in ophiolite mantle peridotite chromite. Hence the traditional opinion holding shallow origin of ophiolite and chromite should be reconsidered. In order to find out the distribution of diamond and other deep mantle minerals in different orogenic ophiolite chromites and to investigate the formation processes of the Hegenshan podiform chromitites, the authors carried out mineralogical study of chromitites in the Hegenshan ophiolite, Inner Mongolia. Approximately 2000 kg of mainly disseminated chromitite ore were collected from Hegenshan No. 3756 orebody. By mineral separation, preliminary studies identified more than 30 mineral species in addition to diamonds and moissanite. The other minerals include minerals of oxides, sulfides, silicates, and other compounds. This study demonstrates that the formation and tectonic setting of Hegenshan ophiolite and the chromitites deserve reevaluation.

Abstract:Abstract: The Zedang mafic-ultramafic body crops out in the eastern Yarlung Zangbo suture zone of Tibet. This massif consists of mantle peridotite, gabbro, diabase and volcanic rocks. The mantle peridotites are mostly harzburgite, lherzolite and minor harzburgite with chromite. A dike-like bodies of dunite are also present. The Fo values of olivine vary in the range of 89.62-91.84 and all olivines belong to forsterite. The orthopyroxenes are enstatite, and the En values vary from 87.82 to 90.32. Clinopyroxenes are mainly endiopside and diopside, and the En values of clinopyroxene vary in the range of 44.12-50.02. The spinels have Cr# values from 17.00 to 93.59. The aluminum-rich spinels are of harzburgite and lherzolite. The PGE content of Zedang peridotites (16.67×10-9-32.59×10-9) is similar to that of primary mantle. The mineral-chemistry indicates that the lherzolite is abyssal peridotite and the harzburgite is fore-arc peridotite. The Cr# of spinel, Mg# of olivine and high Os（3.50×10-9-7.75×10-9）imply that Zedang peridotites were formed by partial-melting. The positive slope of PGE patterns and high Pd/Ir are consistent with the opinion that the Zedang peridotites were influenced by melts/fluids which were enriched with PPGE. The mineralogy and PGE geochemistry of the Zedang peridotites suggest that they formed originally at a mid-ocean ridge（MOR) and were later modified by suprasubduction zone（SSZ）melts.

Abstract:Abstract: Podiform chromitite is the main source of chromium, and is a kind of important strategic material of extreme shortage in China; therefore, the study of chromitite and peridotite has become the first way to solve the long-term dependence on imports. In this study, the authors focused on the main ultramafic body and chromitite from Yarlung Zangbo ophiolite belt. On the basis of field geological work, the authors summarized the sequence of ophiolite, mineral composition, geochemistry, Re-Os isotopic composition and other characteristics, so as to discuss the formation of chromite and mantle peridotite. Some conclusions have been reached: (1) The ophiolite in different segments of Yarlung Zangbo suture zone exhibits quite different rock assemblages, with different tectonic evolution backgrounds, which proves the heterogeneity of Tethys evolution; (2) There are two types of high aluminum and high chrome chromitie found in western YZSZ, and the mineral chemical characteristics of chrome spinel have recorded traces of different tectonic settings, mineralogy and geochemistry; (3) The mineralogy and geochemistry of mantle peridotites peridotite and chromite have both the features of deep mantle peridotite and the island arc mantle peridotite, suggesting multi-processes of rock/melt reaction and partial melting; (4) The podiform chromite formation experienced multiple stages, from the early subduction to the mantle transition zone; driven by plume / mantle convection, the materials migrated onto the top of the transition zone, where they condensed and consolidated, and reacted with harzburgite in the emplacement process under a subduction zone environment; (5) The diamond and other UHP minerals extensively exist in all of the Yarlung Zangbo suture zone, with the western part bearing similarity to Luobusha in that they both experienced the same tectonic setting and ore mineralization, thus having potential for further prospecting.

Abstract:Abstract: The eclogite in the Lhasa block mainly consists of garnet, omphacite, phengite, epidote and rutile. The garnet in the eclogite has no visible zonation and a homogeneous core. The Xpy and Xgr decrease from core to rim. Most of the omphacites show weak zonation. The Jd value increases from core to rim. The growth of some narrow barroisite rods along omphacite cleavage may reflect retrograde processes. The phengite included in garnet has higher Si value than that in the matrix. The authors applied for the first time the phase equilibrium simulation method to the study of this common eclogite in the Lhasa block. P-T pseudosection of sample 13SD43 was employed in the NCKMnFMASHTO system. The maximum Xpy in the core of garnet and the maximum Si value in phengite were used to determine the peak metamorphic condition of 610℃，32Kbar, with a peak mineral assemblage of g+o+law+phn+ru. With the help of phase equilibrium and petrography research, several metamorphic evolution processes of the eclogite could be recognized. Studies show that the eclogites in the Lhasa block probably experienced UHP metamorphism and rapid exhumation to the middle crust, which might have provided new evidence for the existence of the suture zone in the Lhasa block.

Abstract:Abstract: The garnet-bearing mica-quartz schist of Sumdo UHP belt in Lhasa block occurs as country rocks of eclogite, and is mainly composed of garnet, muscovite, albite, chlorite, quartz and minor rutile and sphene. Garnet displays an obvious compositional zonation where Xprp increases from the core to the mantle and then decreases in the rim, whereas Xsps decreases gradually from the core to mantle, with the trend of declining following rising in the rim, indicating that garnet composition profiles from core to mantle have preserved the prograde growth zoning and were partially reset during retrogression. The model system MnNCKFMASHO was chosen to calculate P-T and P-M(H2O) pseudosections of the garnet-bearing mica-quartz schist. Garnet isopleth thermobarometry involved plotting compositional isopleths of garnet as contours on a P-T pseudosection, with the combination of contours of saturated H2O content, thus obtaining estimated peak P-T conditions of 27 kbar, 523/580 ℃ and peak mineral assemblages of g-jd-cr-law (+phn +q/coe+H2O). The compositional profile of garnet from the core to the mantle and contouring of the H2O content saturated indicate that prograde metamorphic evolution represents a cold subduction stage with heating with the increasing pressure, and the rocks experienced blueschist-facies to eclogite-facies metamorphism during this stage. P-M(H2O) pseudosections and isopleth of saturated H2O content could be used to assess evolution of mineral assemblages in terms of changes in water content during decompression, which shows that garnet-bearing mica quartz schist experienced an early isothermal decompression process and was then followed by a cooling with decompression evolution during the late stage. Amphibolite-facies to epidote-amphibolite-facies metamorphism occurred during early stage and was followed by greenschist-facies metamorphism. The isothermal decompression of garnet-bearing mica-quartz schist probably represents a fast tectonic exhumation. Albite was likely to replace early jadeite at this stage. A comparison with the P-T path and contact relationship in the field of garnet-bearing mica-quartz schist and eclogite shows evidently that garnet-bearing mica-quartz schist and the eclogite it hosted experienced similar subduction and exhumation processes.

Abstract:Abstract:The newly found staurolite-bearing garnet amphibolites in Nyingchi complex of the Lhasa Block have the mineral assemblage of garnet, amphibole, staurolite, chlorite, plagioclase, mica and minor ilmenite and apatite. The cores of the garnet in the garnet amphibolite are extremely rich in Mn (XSps=0.12-0.15) and poor in Fe (XAlm=0.45-0.50), whereas their rims are relatively Mn poor (XSps=0.01-0.03) and Fe rich (XAlm=0.60-0.65), implying that the core and the rim of the garnets belong to two metamorphic generations. Xpy increases and Xgr decreases from the garnet core to the rim, indicating characteristics of prograde metamorphic zonation. The amphibole growing at different metamorphic stages have obvious composition differences. Staurolite, as an uncommen aluminium-rich mineral in the metabasite, has also recorded different metamorphic processes in their microstructures. In combination with the garnet compositional profile, it is possible to calculate the P-T evolution by phase diagram. The authors modeled the pseudosection of the staurolite-bearing garnet amphibolite under the model system of Mn-NCKMASHO, using Perple-X program with the help of Xpy and Xgr isopleths of the garnet, and obtained the peak metamorphic condition of 620oC and 12kbar. The peak mineral assemblages are garnet, amphibole, staurolite and mica. In the meanwhile, the clockwise P-T path has also been demonstrated by the microstructures in the staurolites, suggesting that the staurolite-bearing garnet amphibolites have experienced three stages of metamorphism.

Abstract:Abstract: Based on the newly acquired and reprocessed seismic data, in combination with drilling data, gravity and magnet inversion and onshore and offshore correlation, the authors studied the geological characteristics of Mesozoic and Cenozoic strata in southern East China Sea Shelf Basin. With sedimentary center in the east, the Mesozoic strata of great thickness are distributed extensively over such uplift areas as Taibei, Guanyin and Yandang. The Cenozoic strata are thicker in the east and west than in the central part in the study area. The southern East China Basin was a marginal depression basin in Mesozoic, with a western boundary of Jurassic on the east side of Yandang uplift, and that of Cretaceous on the west side of Oujiang Sag. More marine facies marks were found in drilling analysis, which shows that the transgression from south to north and from east to west happened in Jurassic, and that from east to west occurred in Cretaceous, in consideration of surrounding sedimentary environments. Source rocks of Lower Jurassic, Lower Cretaceous, Paleocene, Eocene, Oligocene and Miocene are well developed in the study area, so there exists a great hydrocarbon potential in the study area.

Abstract:Abstract: Currently, the oil and gas exploration of global volcanic reservoirs has entered into an important stage. For an objective assessment of the status and prospects of global volcanic reservoirs, a systematic review is necessary. Based on extensive literature analysis, the research process of global volcanic reservoirs as a whole can be divided into four stages: the casually discovering stage (prior to 1949), the low speed progress stage (1950 to 1979), the partial success stage (1980 to 1999) and the mature stage (2000 to the present). An analysis shows that Jatibarang oil and gas field (Indonesia), Xushen gas field (China), Kelameili gas field (China), Changqing gas field (China), Kudu gas field (Namibia) and some other fields are typical large volcanic oil and gas fields in the world. In terms of the frequency of occurrence in different strata, the major distribution of volcanic reservoirs is in the Cenozoic and Mesozoic (especially in the Jurassic, Cretaceous, Paleogene and Neogene), followed by the Upper Paleozoic. From a global perspective, all kinds of volcanic rocks have the chances to form effective reservoirs. In some cases, the discovery of volcanic reservoirs may change the traditional understanding about the basements of some basins, and hence the oil and gas exploration of these basins should be conducted towards deeper strata.At present, key areas for the exploration of volcanic reservoirs are as follows in turn: Cenozoic volcanic reservoirs in circum-Pacific tectonic domain, Late Paleozoic volcanic reservoir in Paleo-Asian Ocean tectonic domain, volcanic reservoirs in Tethys tectonic domain (such as the surrounding Mediterranean) and so on.

Abstract:Abstract: On the basis of collecting and testing about 416 couples of rice seeds and the cultivated soil samples from Suxichang typical area of Jiangsu Province, a series of geochemical data related to Cd distribution and other relative elements concentrations since 2011 was obtained. By studying and analyzing these data, the authors confirmed that rice uptake of Cd from soil is mainly controlled by such geochemical factors as cadmium, zinc, selenium, pH, organic matter (OM) and cation exchange capacity (CEC) within the cultivated soil. Some conclusions have been reached: 1) When the pH is lower than 7.0 in soil and BCF (Bioconcentration Factor) is larger than 10% in milled rice, there exists obvious positive correlative relationship between Cd concentration of milled rice and Cd and Zn content within soil, and their correlation coefficients are above 0.67; bioactivity of cadmium in farmland soils is higher in most cases; there exists more significant correlative relationship between Cd of rice and bioavailable Cd of soil than total Cd within soil if cadmium content from the cultivated soil reflects only exchangeable and weak acid-soluble fraction, with the correlation coefficient larger than 0.7; 2) Se, OM and CEC could inhibit the rice uptake of Cd from the cultivated soil, and there exists a significant negative correlation between Cd concentration of milled rice and Se, OM and CEC concentrations within the soil under some limited conditions, with the correlation coefficients being less than -0.5; 3) Soil acidification could stimulate the increase of Cd content in the milled rice, when Cd concentration of milled rice is larger than 0.2mg/kg and its OM is equal to 2.5%~6.5%, and there yet exists significant negative correlation between Cd concentration of milled rice and pH in the cultivated soil, with the correlation coefficient smaller than -0.6; 4) the Cd distribution in different rice organs is not uniform, from the roots to the upper rice organs, the Cd content in rice gradually reduced, and it is obvious that root rice organs could play a greater role in absorption of Cd from the cultivated soil during the rice growth.