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Petrogenesis of Songshugou dunite body in the Qinling orogenic belt, Central China: Constraints from geochemistry and melt inclusions

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Science China Earth Sciences 2005年第8期48卷 1146-1157页

作者： SU Li1,2. SONG Shuguang3.& ZHOU Dingwu1 1. key laboratory of {2. dynamics of the {3. of education, Department of Geology, northwestern university, xi’an 710069, China 2. The Geological Lab Center, China university of Geosciences (Beijing), Beijing 100083. China 3. key laboratory of Orogenic Belts of the {3. of education, Department of Geology, Peking university, Beijing 100871, China key laboratory of {2. {3. of the {3. of education Department of Geology Northwestern University Xi’an China The Geological Lab Center China University of Geosciences (Beijing)Beijing China key laboratory of Orogenic Belts of the {2. of {3. Department of Geology Peking University Beijing China

The Songshugou dunite body, which occupies an area of about 2. km2. is the largest ultramafic massif in the eastern Qinling orogenic belt, Central China. The major compo-nent of this body is dunitic rocks including mylonitic dunite and coarse-grained dunite; they oc-cupy about 95 vol% of the total body. Petrography, mineral composition, major and trace ele-ments and primitive melt inclusions have been investigated in this paper; all revealed that this dunite body is the product of melt-rock interaction by porous percolation flow. In comparison with dunite sills or veins in harzburgite from the basal part of Oman ophiolite, this dunite body is characterized by lower contents of Al2.3. CaO and HREE but higher content of highly incom-patible elements and Zr and Hf. The LREE enriched patterns and primitive mantle normalized spidergrams of trace elements are also different from the Oman dunite. Combining with melt in-clusions observed in olivines, we conclude that this dunite body is the product of large- scale porous percolation flow of high-MgO melts within depleted mantle peridotites. The high-MgO magma, in essence, was most probably produced at the hot head of an upwelling mantle plume. The occurrence of the Songshugou dunite body is closely associated with the activity of mantle super-plume in Neo-Proterozoic era in the Yangtze Craton.

关键词： Songshugou dunite body, geochemistry, melt inclusion, mantle plume, Qinling orogenic belt.

Ultrahigh pressure (>7 GPa) gneissic K-feldspar (-bearing) garnet clinopyroxenite in the Altyn Tagh, NW China: Evi- dence from clinopyroxene exsolution in garnet

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Science China Earth Sciences 2005年第7期48卷 1000-1010页

作者： LIU Liang1,3. CHEN Danling1, ZHANG Anda1, SUN Yong1, WANG Yan1, YANG Jiaxi1,2.& LUO Jinhai1 1. key {3. of {2. dynamics of the {3. of education of China, northwest university, xi’an 710069, China 2. College of Earth Science and Land Resources, Chang’an university, xi’an 710054, China 3. The {3. of Orogen and Basin of the {3. of education, Peking university, Beijing 100871, China key laboratory of {2. {3. Ministry of Education of China Northwest University Xi'an 710069 China laboratory of Orogen and Basin Ministry of Education Peking University Beijing 100871 China College of Earth Science and Land Resources Chang'an University Xi'an 710054 China

The exsolution of clinopyroxene and rutile in coarse-grain garnet is found in the gneissic K-feldspar(-bearing) garnet clinopyroxenite from Yinggelisayi in the Altyn Tagh, NW China. The maximum content of the exsolved clinopyroxene in the garnet is up to >5% by volume. The reconstructed precursor garnet (Grt1) before exsolution has a maximum Si content of 3.061 per formula uint, being of supersilicic or majoritic garnet. The peak-stage metamorphic pressure of >7 GPa is estimated using the geobarometer for volume percentage of exsolved pyroxene in garnet and the Si-(Al+Cr) geobarometer for majoritic garnet, and the temperature of about 1000℃ using the ternary alkali-feldspar geothermometer and the experimental data of ilmen- ite-magnetite solid solution. The protoliths of the rocks are intra-plate basic and intermediate ig- neous rocks, of which the geochemical features indicate that they are probably the products of the evolution of basic magma deriving from the continental lithosphere mantle. The rocks are in outcrops associated with ultrahigh pressure garnet-bearing lherzolite and ultrahigh pressure garnet granitoid gneiss. All of these data suggest that the ultrahigh pressure metamorphic rocks in the Altyn Tagh are the products of deep-subduction of the continental crust, and such deep- subduction probably reaches to >2.0 km in depth. This may provide new evidence for further discussion of the dynamic mechanism of the formation and evolvement of the Altyn Tagh and the other collision orogenic belts in western China.

关键词： Altyn Tagh gneissic K-feldspar (-bearing) garnet clinopyroxenite clinopyroxene exsolution in garnet ultra-high pressure metamorphism.

Ultra-high pressure metamorphism of granitic gneiss in the Yinggelisayi area, Altun Mountains, NW China

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Science China Earth Sciences 2004年第4期47卷 338-346页

作者： LIU Liang, SUN Yong, LUO Jinhai, WANG Yan, CHEN Danling & ZHANG Anda The key laboratory of {2. {3., {3. of education,Department of Geology, northwest university, xi抋n 710069, China The key laboratory of {2. {3. Ministry of Education Department of Geology Northwest University Xi’an China

A study on petrography and mineral chemistry of granitic gneiss from the Yinggeli-sayi area in the Altun Mountains of the northwestern China demonstrates that the granitic gneiss experienced a complicated multi-stage metamorphism. The peak-stage mineral assemblage is garnet+perthite(before exsolution)+titanite(before exsolution)+kyanite+zoisite +quartz/ coesite clinopyroxene with minor apatite and rutile. The exsolution of rod-like plagioclase +amphibole is contained within the core part of coarse-grained titanite, and the Si value per unit formula of the titanite is estimated to be 1.03.1}1.047, which implies that the titanite contains Si with six-fold coordination and the precursor titanite is hence of supersilicic titanite and suggests that the CaSi2.5 component in the titanite is 3.1%—4.7%. The P-T condition of peak metamorphism is estimated to be 3.7—4.3.Pa at 1000. High-Al titanite inclusions are also found in the garnet. All of these suggest that the granitic gneiss underwent UHP metamorphism. The granitic gneiss has SiO2.content (> 70%), Al2.3.(12.58%—14.08%), high K2. content (>5%) with Na2./K2. ratio of 0.4—0.6, LREE-enriched patterns with (La/Yb)N ratio of 4.3.9.1 and large negative Eu anomaly (d Eu = 0.06—0.59), which indicate that the protolith of the granitic gneiss is the product of anatexis of the middle or upper crustal rock. The UHP granitic gneiss, together with the inter-beds of UHP metamorphic garnet lherzolite and garnet-bearing intermediate-basic gneiss in the outcrops, suggests that they all might undergo continental deep subduction, which will have im-portant bearing for further discussion of the dynamic mechanism of the formation and exhuma-tion of the rocks in this region.

关键词： Altun Mountains, granitic gneiss, supersilicic titanite, UHP metamorphism, continental deep subduction.

Identification of 3.5 Ga detrital zircons from Yangtze craton in south China and the implication for Archean crust evolution

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Progress in Natural Science:Materials International 2006年第6期16卷 663-666页

作者： LIU xiaoming, GAO Shan, LING Wenli, YUAN Honglin and HU Zhaochu (National key laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China {{3. of Geosciences, Wuhan 43.074, China key laboratory of {3. dynamics, Department of Geology, northwest university, xi' an 710069, China) National key laboratory of Geological Processes and Mineral Resources Faculty of Earth Sciences China University of Geosciences Wuhan 430074 China key laboratory of {2. {3. Department of Geology Northwest University Xi'' an 710069 China

The LA-ICP-MS U-Pb dating of hundreds of detrital zircon grains from the Sinian sandstones of Liantuo formation and tillites of Nantuo formation at Sanxia area in Yichang identified 3.19-3.08 Ma zircon grains. Their 2.7Pb/2.6Pb and 2.6Pb/2.8U ages show excellent agreement (concordia degree 99%-100% ). Their CL images exhibit well-developed oscillatory zoning and the Th/U ratios are within 0.46-0.76, implying that they are igneous zircons which formed during middle-early Archean. These zircons are the oldest ones discovered in Yangtze craton until now. However, the detrital zircons with ages older than 3. 3.Ga in the metamorphic rocks of Kongling group were not found by further investigation, which suggests the presence of crust older than high-grade metamorphic Kongling terrain in Yangtze craton.

关键词： early Archean detrital zircon zircon dating Yangtze craton.

Formation of the Permian basalts and implications of geochemical tracing for paleo-tectonic setting and regional tectonic background in the Turpan-Hami and Santanghu basins,xinjiang

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Science China Earth Sciences 2006年第6期49卷 584-596页

作者： ZHOU Dingwu1,2. LIU Yiqun1,2. xiNG xiujuan1, HAO Jianrong1, DONG Yunpeng1 & OUYANG Zhengjian1 1. key laboratory of {2. dynamics, {3. of education, northwest university Department of Geology, northwest university, xi’an 710069, China 2. Geoinformation Science & Engineering College, SDUST, Qingdao 2.6510, China key laboratory of {2. {3. Ministry of Education Northwest University Xi’an China Geoinformation Science & Engineering College SDUST Qingdao China Department of Geology Northwest University Xi’an China

The Turpan-Hami and Santanghu basins are the late Paleozoic-Mesozoic-Cenozoicreworked intracontinental basins that superposed on the folded basement of the Paleozoic orogenicbelt. ^(40)Ar/^(3.)Ar geochronological study of the basalts developed in the basins reveals that theformation period is Permain (2.3.2.6 Ma). From geochemical comparison of the basalts, theSantanghu basalts exhibit a strong depletion in Nb and Ta, and a selective enrichment in HFSE,reflecting that the source region is influenced by the subducted components related to subduction ofthe ancient oceanic crust and characterized with ''lagged arc volcanic rocks''. In contrast, theTurpan-Hami basalts show a slight depletion in Nb and Ta, high Th/Ta ratio, similar to the basaltsformed in an intracontinental ex-tensional zone or in an initial rift. Combined with the formationperiod of the ophiolite and ophiolite melange zones and regional magmatic activities occurring onthe post-orogenic extensional background in northern xinjiang, it can be inferred from thesegeochemical characteristics that the tectonic background for forming the Turpan-Hami and Santanghubasins is closely related to the regional extension after the continent-continent collisionalorogeny. The basalts of the two basins came from different sources on the post-orogenic extensionalbackground of the similar basin-forming {2.. Although the settings are all intracontinentalrift, the source for the Santanghu basalts is obviously subjected to the metasomatism of thesubducted components, implying the existence of the previous subduction.

关键词： xinjiang, Tu-Ha basin, Santanghu basin, basalt, postorogeny, tectonic setting, extensional background.

Cenozoic volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, China: Petrochemical evidence for partial melting of the mantle-crust transition zone

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Acta Geochimica 2007年第3期26卷 305-311页

作者： LAI Shaocong, QIN Jiangfeng, LI Yongfeng, and LIU xin State key laboratory of {{3. dynamics, Department of Geology,{3., xi’an 710069, China State key laboratory of {2. {3. Department of Geology Northwest University Xi’an China

Neogene volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, are represented by a typical intermediate-basic and intermediate alkaline rock association, with latite-trachyte as the main rock type. The results of chemical analysis are: SiO2.52.–62., Al2.3.15%, Na2./K2.>1 and MgO3.3.%. In addition, the volcanic rocks are LREE-enriched with LREE/HREE=10–13. (La/Yb)N=15–19, and show a weak negative Eu anomaly with δEu=0.71–0.89. The close relationship between Mg# and SiO2.and the co-variation of the magmatophile elements and ultra-magmatophile elements such as La/Sm-La and Cr-Tb indicate that this association of volcanic rocks is the product of comagmatic fractional crystallization. The rock association type and lower Sm/Yb values (Sm/Yb=3.2.–3.97) imply that this association of volcanic rocks should have originated from partial melting of spinel lherzolite in the lithospheric mantle. On the other hand, the weak negative Eu anomaly and relative depletion in Nb, Ta and Ti reflect the features of terrigenous magma. So the Neogene Belog Co alkaline volcanic rocks should be the result of partial melting of the special crust-mantle transition zone on the Qinghai-Tibet Plateau.

关键词： major and trace elements Cenozoic volcanic rock mantle-crust transition zone Qinghai-Tibet Plateau

Pediculate Brachiopod Diandongia pista from the Lower Cambrian of South China

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Acta Geologica Sinica(English Edition) 2003年第3期77卷 288-293页

作者： ZHANG Zhifei, HAN Jian, ZHANG xingliang, LIU Jianni and SHU DeganEarly Life Institute and key laboratory for {{3. dynamics of the {3. of education,northwest university, xi’an, Shaanxi 710069 E-mail: zhangelle@*** Wang Si’en and xie Guanglian NW Univ xian Early Life Inst Xian 710069 Peoples R China NW Univ xian Key Lab Continental Dynam Minist Educ Xian 710069 Peoples R China

The Chengjiang Lagerstatte has been celebrated for prolific soft-bodied fossils. Based on specimens recently excavated in the Chengjiang Lagerstatte by the Early Life Institute, northwest university, Diandongia pista Rong, 1974, is directly revealed to be a pediculate brachiopod, assigned to the Family Botsfordiidae, as is further confirmed by the exceptionally preserved vascular system including dorsal and ventral mantle canals. These specimens described herein exhibit some peculiarities, notably the extremely thin and long pedicles, which suggest that Diandongia is epifaunal rather than burrowing brachiopod. A study of this group of animals indicates that they may be vital to understand the relationship between the lingulids and the remaining brachiopods, and the character evolution of the early Cambrian brachiopods.

关键词： Chengjiang Lagerstatte soft-bodied fossils mantle canals character evolution Cambrian China

Response to“Discussion on the systematic position of the Early Cambrian priapulomorph worms”

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Science Bulletin 2006年第2期51卷 250-256页

作者： HAN Jian1 & HU Shixue2.1. Department of Geology and key laboratory for {2. Dynam- ics of the education {3., northwest university, xi’an 710069, China 2. Yunnan Geological Institute, Kunming 650011, China Department of Geology and key laboratory for {2. {3. of the {3. ministry Northwest University Xi’an China Yunnan Geological Institute Kunming China

A response by Han Jian & Hu Shixue to a letter to the editor about their article 'Systematic Position of the Early Cambrian priapulomorph worms' in the 2.04 issue is presented.

关键词： Response to Discussion on the systematic position of the Early Cambrian priapulomorph worms

Discovery of ultrahigh-pressure magnesite-bearing garnet lherzolite (>3.8 GPa) in the Altyn Tagh, northwest China

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Chinese Science Bulletin 2002年第11期47卷 881-886页

作者： LIU Liang, SUN Yong, xiAO Peixi, CHE Zicheng, LUO Jinhai, CHEN Danling, WANG Yan, ZHANG Anda, CHEN Liang & WANG Yonghekey {3. of {2. dynamics of the {3. of education, northwest university, xi’an 710069, China The northwest Institute of key laboratory of {2. {3. of the {3. of education Northwest University Xi’an China The northwest Institute of Geology and Mineral Resources Xi’an China

Magnesite-bearing garnet Iherzolite from the Altyn Tagh, associated with garnet pyroxenite, and garnet-bearing felsic gneiss, crops out as lenses in Proterozoic gneiss about 100 km east of the Jianggelasayi River. The garnet Iherzolite, together with the eclogite in western Jianggelasayi, composes a high-pressure to ultrahigh-pressure metamorphic belt in the southern margin of the Altyn Tagh. Parageneses of minerals from magnesite-bearing garnet Iherzolite indicate that the rock evolved a multi-stage metamorphism. The peak-stage metamorphism produces an assemblage of Grt+Ol+Opx+Cpx±Mgs, in which A12.3.content of Opxis very low (0.3.-0.66wt%). The calculated P-T condition of the peak stage is *** and 880-970°C, some exsolution rods of clinopyroxene and rutile occur in the Grt and magnesite is rimed by dolomite and orthopyroxene, all implying that the peak stage was a UHP metamorphic process. Together with regional geological studies, isotopic dating and the discovery of coesite inclusions in

关键词： garnet lherzolite magnesite UHP metamorphism Altyn Tagh Mountains.