Academy of Geological science

Beijing, China

Academy of Geological science

Beijing, China
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Liu S.,Academy of Geological science | Tsunogae T.,University of Tsukuba | Li W.,Peking University | Shimizu H.,University of Tsukuba | And 4 more authors.
Lithos | Year: 2012

The Inner Mongolia Suture Zone (IMSZ, incorporating the Khondalite Belt) forms part of an accretionary orogen developed during the Paleoproterozoic collision between the Yinshan Block and Ordos Blocks within the North China Craton (NCC). The granulites within the IMSZ are characterized by high-temperature (HT) to ultrahigh-temperature (UHT) metamorphism with diagnostic mineral assemblages for UHT conditions preserved in some localities such as Tuguiwula and Wuchuan. We report here a new locality in Heling'er, located within the southern domain of the IMSZ where spinel-garnet-sillimanite-bearing granulites record UHT metamorphic conditions. The prograde assemblages occurring as inclusions in porphyroblastic minerals in these rocks include sillimanite+quartz+spinel, whereas coarse grained garnet+sillimanite+quartz+spinel+cordierite+plagioclase+K-feldspar+magnetite+ilmenite represent the peak assemblages. The retrograde stage is marked by orthopyroxene and cordierite rims developed on garnet and spinel. Biotite marks the final hydration stage of the high-grade metamorphism. Spinel and quartz occur in direct contact, with the spinel showing low Zn, Cr, and Fe 3+. Application of Ti-in-zircon and ternary feldspar geothermometers yields temperatures up to ~940°C for the peak stage. Mineral phase equilibria modeling based on the bulk chemistry and mineral assemblages shows that the peak assemblage of garnet+plagioclase+spinel+cordierite+sillimanite+quartz+ilmenite+magnetite was stabilized at 1030°C at 6.5-7.5kbar, thus we infer a 940-1030°C temperature range for peak metamorphism in these rocks. The newly discovered UHT rocks in Heling'er, dated as 1.92Ga, together with the two previously reported UHT localities at Tuguiwula and Wuchuan, suggest that the Paleoproterozoic UHT metamorphism occurred on a regional scale within the IMSZ, probably in association with the subduction-accretion-collision tectonics and the incorporation of the NCC within the Columbia supercontinent. © 2012 Elsevier B.V.

Santosh M.,China University of Geosciences | Santosh M.,Kochi University | Tsunogae T.,University of Tsukuba | Tsunogae T.,University of Johannesburg | And 5 more authors.
Precambrian Research | Year: 2014

Sri Lanka, the 'pendant' of Gondwana, is a collage of distinct crustal blocks that preserve important records of major Neoproterozoic tectonothermal events. Here, we present the petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes on a suite of meta-igneous rocks including granodiorite, diorite and garnet amphibolite from the Kadugannawa Complex (KC), granodiorite from the Wanni Complex (WC) and mafic granulites, gabbros and garnet-bearing charnockite from the Highland Complex (HC) along a NW-SE transect. The regional metamorphic peak P- T conditions were estimated from garnet-clinopyroxene-plagioclase-quartz assemblage in the metagabbro as 830-860. °C and 9.4-9.8. kbar. Slightly lower temperature ranges of 700-780. °C were obtained from garnet amphibolite, metagranodiorite and metadiorite, corresponding retrograde conditions. Trace element and rare earth element patterns as well as Rb-Y-Nb and Rb-Yb-Ta discrimination plots show volcanic arc affinity for the granodiorite, diorite and garnet charnockite suggesting that the protoliths of the rocks were formed from felsic to intermediate arc magmas. The mafic granulites and magnesian metagabbro also suggest volcanic arc affinity and indicate subduction-related mafic magmatism and magma underplating. The garnet-bearing metagabbro shows N-MORB signature, whereas the garnet amphibolite displays oceanic island alkali basalt affinity. These rocks therefore represent accretion of the remnants of oceanic lithosphere during the subduction-collisional event. Zircons in a metadiorite and the surrounding metagranodiorite from the KC yield ages of 980±16Ma to 916±57Ma marking early Neoproterozoic magmatism followed by metamorphism at 532±18Ma. Zircons in the garnet amphibolite from this complex show extensive metamorphic recrystallization yielding a weighted mean 206Pb/238U age of 520.7±6.6Ma. From the WC, zircons in a metagranodiorite define three groups of weighted mean 206Pb/238U ages at 805±12Ma (emplacement of the magmatic protolith), 734.0±4.6Ma (Cryogenian thermal event) and 546.0±5.7Ma (latest Neoproterozoic-Cambrian metamorphism). Zircons from the HC record multiple late Neoproterozoic-Cambrian thermal events with weighted mean 206Pb/238U ages of 576.8±9.3Ma and 523.0±7.1Ma (metagabbro) and 579±10Ma, 540.4±6.0Ma and 511.1±5.9Ma (garnet charnockite), 553.0±3.2Ma (mafic granulite), and 539.1±4.4Ma (mafic granulite sill). Lu-Hf data reveal dominantly positive e{open}Hf(t) values for zircons in the metadiorite and metagranodiorite from the KC (-1.1 to 7.2) and Hf crustal model ages (TDM C) in the range of 1206-1733Ma suggesting a mixed source from both juvenile and Paleo-Mesoproterozoic components. However, zircons in the garnet amphibolite from this complex show dominantly negative e{open}Hf(t) values (mean -16.5) with TDM C in the range of 2356-2828Ma suggesting reworked Neoarchean-Paleoproterozoic crustal source. Zircons in metagranodiorite of the WC also possess negative e{open}Hf(t) values (mean -6.2) with TDM C in the range of 1799-2498Ma suggesting reworked Paleoproterozoic crust as the magma source. The HC rocks also preserve distinct imprints of reworking of older crust. The zircon e{open}Hf(t) values in mafic granulite show a tight cluster from -2.2 to 0.1 with TDM C in the range of 1501-1651Ma suggesting a mixed source from both juvenile Neoproterozoic and reworked Mesoproterozoic components. Zircons in the metagabbro from this complex show negative e{open}Hf(t) values (mean -6.3) and TDM C of 1847-1978Ma. Zircons in the garnet charnockite also display highly negative e{open}Hf(t) values (mean -17.7) and older TDM C) (mean 2614Ma) suggesting reworked Paleoproterozoic crust. Zircons in the mafic granulite sample show negative e{open}Hf(t) values (mean -14.1) and TDM C between 2263 and 2790Ma indicating that the source material for the magma evolved from the Neoarchean-Paleoproterozoic crust. In summary, the 916-980Ma ages from the KC represent arc magmatism during early Neoproterozoic, followed by the 805Ma granodioritic magma emplacement in the WC. Repeated thermal events during mid and late Neoproterozoic are also recorded from the Wanni and Highland Complexes, culminating in Cambrian high-grade metamorphism that reached ultrahigh-temperature conditions. We propose a model of double-sided subduction during the Neoproterozoic, where the Wanni Complex to the west and the Vijayan Complex to the east represent continental arcs, culminating in collision along the HC during late Neoproterozoic-Cambrian. © 2014 Elsevier B.V.

Su J.,Hohai University | Su J.,Chinese Academy of Geological Sciences | Dong S.,Academy of Geological science | Zhang Y.,Chinese Academy of Geological Sciences | And 4 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2014

The Sichuan (Chuan)-Guizhou (Qian)-Hunan (Xiang) tectonic belt (CQXTB) can be divided into four different sub-belts. The Xuefengshan tectonic belt (XTB), one of the four sub-belts, is the most particular and hotly debated on its genetic mechanism, because it's just located in the gravity gradient belt of South China block, and the thickness of lithosphere changes greatly along the both sides of the XTB. The structural styles of CQCTB are analyzed. The geological basement of XTB shows a flower style and constitutes a thick-skinned structure together with Chuan-Qian fold belt, as a whole. The XTB is characterized by compressive-twisting features and its basement uplifts to the maximum height in the Yuanma basin. The lithosphere thickness of South China is also transformed with time. Referring to the deep seismic reflection profile, the authors draw the deep and shallow structure profile maps of the QXTB. Based on the different coupling styles between middle-upper crust and lower crust, the authors discussed the deformation process of the lower crust. The lower crust's downward bidirectional subduction under the XTB forms a root without subduction into the mantle. Meanwhile, the lithosphere is bended due to the thickening of crust. After then, the lower crust and upper mantle probably depressed due to Rayleigh-Taylor instability of dense subcrustal lithosphere, where the lower crust and upper mantle sank into the asthenosphere mantle. Finally, under the extensional tectonic background, the asthenosphere rose, which resulted in the delamination of lithosphere at the east of XTB during the Late Mesozoic Era.

Ren Y.,Jilin University | Wang H.,Jilin University | Qu W.,Academy of Geological science | Zhao H.,Jilin University | Chu G.,Hunchun Zijin Mining Industrial Co.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2011

To obtain the exact metallogenic age of Xiaoxi nancha copper gold deposit, the quartz-molybdenite vein newly discovered in the Beishan ore block is studied and dated by Re-Os isotopic dating of molybdenite. The quartz molybdenite vein is parallel to adjacent lode copper gold ore bodies, which indicates that both are controlled by the common structure system. The dominant metal minerals in molybdenum ore is molybdenite which is occasionally cut by later pyrite and chalcopyrite. Due to the intergrowth of different metal minerals, the lode molybdenum mineralization in Xiaoxi nancha deposit is clearly earlier than major copper gold metallogenic stage. Accordingly, it can be concluded that the lode molybdenum mineralization belongs to early metallogenic stage of copper gold mineralization. Six samples of molybdenite for Re-Os isotopic dating are analyzed. The model ages vary from 109.2±3.4 Ma to 110.8±4.0 Ma, average 109.9±3.9 Ma, and a good isochron age of 111.1±3.1 Ma. These results are consistent with new isotopic dating of granitic intrusions related to copper gold mineralization in this deposit. It indicates that the large copper gold mineralization took place in late Yanshanian periods and both the granites and copper gold mineralization were generated under extensive active continental margin resulted from the obliquely subduction of Pacific Ocean slab. Moreover, petrological & geochemical characters, isotopic dating of ore forming intrusions as well as low content of Re in molybdenite demonstrate that granitic intrusions and copper gold mineralization were derived from deep source, mainly upper mantle.

He B.Z.,Chinese Academy of Geological Sciences | Jiao C.L.,Sinopec | Xu Z.Q.,Chinese Academy of Geological Sciences | Cai Z.H.,Chinese Academy of Geological Sciences | And 2 more authors.
Acta Petrologica Sinica | Year: 2011

Based on regional seismic profiles, core and drill data of well in Tangguzibas depression, Tarim basin, we research the three-layer configuration of two unconformities, the one occurred between Early Silurian to Late Ordovician ( S/O3, T7° seismic reflection horizon) , the others emerged between Late Devonian to Silurian (D3d/S, T 6 seismic reflection horizon). The structure deformation underlying unconformities, the distribution of configuration type of unconformities, the compositions and provenance of elementary sediment gravels overlying unconformities have been analyzed. Three-layer configuration studies have established that the unconformity of Middle Caledonian ( S/O3 ) was an area angular unconformity, presented middle angle monocline or fold between unconformities to its underlying strata on obduction slabs of thrust faults, and the distribution of configuration type of unconformities were controlled by a series of thrust faults with NEE-SWW trending. It' s unique to Tangguzibas depression, difference to the other tectonic units in Tarim basin. The unconformity configuration of Late Caledonian ( D3d/S) was also an angular ones, formed angular unconformity with northward erosion mainly, the part influenced by thrust fault with NEE-SWW trending and inherited development, to form superimpose unconformities. The sandstones and gravels of early deposits overlying on two unconformities had obvious differences, the former deposited varies of sedimentary gravel from passive margin and near provenance and, the later deposited gavels are far provenance relatively, from passive margin and continental island are During Late Ordovician, tectonic of Tangguzibas controlled mainly by Altun and West Kunlun collision orogenic action, response more to Altun orogenic action, while affected by West Kunlun and Altun collision orogenic action from Middle Silurian to Late Devonian. The fault system trending NEE which controlled configuration of unconformities has been comparability to South Altun Fault (SAF) on regional stress field, active phase and intensity. The three-layer configuration of unconformity on Middle and Late Caledonian movement responded on dynamic process of Early Paleozoic tectonic movement, and provide evidences for that Altun and West Kunlun orogenic action happened, developed and ended off.

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