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Guo L.S.,Peking University | Guo L.S.,China Earthquake Administration | Liu Y.L.,Peking University | Liu H.F.,Tibet Institute of Geological Survey | And 3 more authors.
Acta Petrologica Sinica | Year: 2011

Molang intrusion, located north of Sangye Temple, Zedang Town, represents the middle part of the Gangdese magmatic belt. Lithological assemblage is composed principally of pyroxene diorite, diorite, granodiorite and K-feldspar granite. Detailed LA- ICP-MS zircon U-Pb geochronological and petrogeochemical studies are presented in this paper. Granodiorite and K-feldspar granite were emplaced at57Ma and characterized by high SiO 2(70. 1% -74. 4% ) , low to high K2O (1. 3% ∼5. 2% ) , and low MgO (0. 2% ∼ 1. 2% ) contents as well as distinctly negative Eu and Sr anomalies. The Zr/Nb-Zr and AFM-CFM diagrams indicate derivation of the granodiorite and K-feldspar granite by low-degree partial melting of juvenile crust and metagreywacke. In contrast, pyroxene diorite, diorite were crystallized at 52 ∼54Ma and characterized by low SiO 2(53. 2% -58. 6% ) , middle to high K 2O ( 1. 3% ∼2. 5% ) , and high MgO (3.2% ∼ 3. 9%) contents with weakly to obviously negative Eu and Sr anomalies. These characteristics are analogous to those of the intermediate to basic intrusions of the Quxu batholith. We suggest that they were produced by magma mixing between mantle-derived materials and partial melts derived from remelting of juvenile crust.

Guo L.,Chinese Institute of Crustal Dynamics | Guo L.,Peking University | Liu Y.,Peking University | Liu Y.,Wuhan University | And 5 more authors.
Lithos | Year: 2013

The Gangdese belt, Tibet, records the opening and closure of the Neo-Tethyan ocean and the resultant collision between the Indian and Eurasian plates. Mesozoic magmatic rocks generated through subduction of the Tethyan oceanic slab constitute the main component of the Gangdese belt, and play a crucial role in understanding the formation and evolution of the Neo-Tethyan tectonic realm. U-Pb and Lu-Hf isotopic data for tonalite and granodiorite from the Xietongmen-Nymo segment of the Gangdese belt indicate a significant pulse of Jurassic magmatism from 184Ma to 168Ma. The magmatic rocks belong to metaluminous medium-K calc-alkaline series, characterized by regular variation in major element compositions with SiO2 of 61.35%-73.59%, low to moderate MgO (0.31%-2.59%) with Mg# of 37-45. These magmatic rocks are also characterized by LREE enrichment with concave upward trend in MREE on the chondrite-normalized REE patterns, and also LILE enrichment and depletion in Nb, Ta and Ti in the primitive mantle normalized spidergrams. These rocks have high zircon εHf(t) values of +10.94 to +15.91 and young two-stage depleted mantle model ages (TDM2) of 192Ma to 670Ma. The low MgO contents and relatively depleted Hf isotope compositions suggest that the granitoid rocks were derived from the partial melting of the juvenile basaltic lower crust with minor mantle materials injected. In combination with the published data, it is suggested that northward subduction of the Neo-Tethyan slab beneath the Lhasa terrane began by the Late-Triassic, which formed a major belt of arc-related magmatism. © 2013 Elsevier B.V.

Wang Z.,Peking University | Wang Z.,China University of Geosciences | Liu Y.,Peking University | Liu Y.,Nanjing University | And 4 more authors.
Ore Geology Reviews | Year: 2012

We have determined the ages of the ore-bearing Bangpu porphyries and the age of formation of an associated Mo-Cu ore deposit using the LA-ICPMS zircon U-Pb and the molybdenite Re-Os methods. Zircons from two adamellite porphyries give ages of 14.07 ± 0.08. Ma and 14.96 ± 0.16. Ma, and zircons from a diorite porphyry give an age of 15.30 ± 0.25. Ma. The ages of three molybdenite samples are 14.96 ± 0.23. Ma, 15.08 ± 0.23. Ma and 16.61 ± 0.23. Ma. Light Rare Earth Elements (LREE) are enriched in the ore-bearing adamellite, which is shoshonitic and peraluminous, while Heavy Rare Earth Elements (HREE) and Y are strongly depleted, indicating an adakitic affinity. In contrast to other deposits formed in the post-collisional Gangdese belt, the Rb/Sr ratio in Bangpu is high, demonstrating more crustal contamination. The geochemistry of the ore-bearing diorite porphyry differs significantly from that of the ore-bearing adamellite. The diorite porphyry displays a reverse slope in its REE (Rare Earth Element) pattern, and is shoshonitic and metaluminous. The geochronology and geochemistry of both ore-bearing rocks indicate that the Bangpu ore deposit is related to two different source regions in a post-collisional environment. The metallic minerals formed mainly during the older diorite porphyry stage, but they were recycled and reactivated during adamellite magmatism. The sources of the mineralising fluids, and the evolution of the northern GPCB (Gangdese Porphyry Copper Belt), where the Bangpu ore deposit is located, are more complex than in the southern GPCB. © 2012 Elsevier B.V.

Chen R.,Peking University | Liu Y.,Peking University | Guo L.,Chinese Institute of Crustal Dynamics | Wang Z.,Peking University | And 4 more authors.
Acta Geologica Sinica | Year: 2014

We have determined the ages of the ore-bearing Tinggong porphyries and the Eocene granites using the LA-ICPMS zircon U-Pb method. Zircons from one adamellite porphyry and two diorite porphyries yield ages of 15.54+0.28 11a, 15.02+0.25 1Ia and 14.74+0.22 Ma, respectively. The ages of two granites are 50.48±0.71 Ma and 50.16±0.48 1Ia. Light Rare Earth Elements (LREE) are enriched in the ore-beating adamellite porphyries, which are high-K caic-alkaline and metaluminous, while Heavy Rare Earth Elements (HREE) and Y are strongly depleted, indicating an adakitic affinity. The Large Ion Lithophile Elements (LILE) of the adamellite porphyries are highly enriched, whereas some High Field Strength Elements (HFSE) are depleted. The diorite porphyry in this study is chemically similar to the adamellite porphyries, except that the Mg5 of the diorite porphyry is a little higher, demonstrating more mantle contamination. Four samples from different rocks are selected for in situ zircon Hf isotopic analyses. The samples show positive E111(t) values and young Hf model ages, indicating their derivation from juvenile crust. However, the adamellite porphyry and diorite porphyry formed in the Miocene exhibit more heterogeneous Hf isotopic ratios, with lower EH (t values than the granites formed in the Eoccne, suggesting the involvement of old Indian continent crust in their petrogenesis. The geochronology and geochemistry of the adamellite porphyries and the diorite porphyries indicate that they formed from the same source region in a post-collisional environment, but contaminated by crust and mantle materials in different ratios. The metallic minerals formed mainly during the older adamellite porphyry stage, but they were recycled and reactivated by the diorite porphyry intrusion. © 2014 Geological Society of China.

Chen J.,CAS Guangzhou Institute of Geochemistry | Chen J.,Chinese Academy of Sciences | Xu J.,CAS Guangzhou Institute of Geochemistry | Xu J.,Chinese Academy of Sciences | And 6 more authors.
Ore Geology Reviews | Year: 2015

Porphyry Cu (-Mo-Au) deposits occur not only in continental margin-arc settings (subduction-related porphyry Cu deposits, such as those along the eastern Pacific Rim (EPRIM)), but also in continent-continent collisional orogenic belts (collision-related porphyry Cu deposits, such as those in southern Tibet). These Cu-mineralized porphyries, which develop in contrasting tectonic settings, are characterized by some different trace element (e.g., Th, and Y) concentrations and their ratios (e.g., Sr/Y, and La/Yb), suggesting that their source magmas probably developed by different processes. Subduction-related porphyry Cu mineralization on the EPRIM is associated with intermediate to felsic calc-alkaline magmas derived from primitive basaltic magmas that pooled beneath the lower crust and underwent melting, assimilation, storage, and homogenization (MASH), whereas K-enriched collision-related porphyry Cu mineralization was associated with underplating of subduction-modified basaltic materials beneath the lower crust (with subsequent transformation into amphibolites and eclogite amphibolites), and resulted from partial melting of the newly formed thickened lower crust. These different processes led to the collision-related porphyry Cu deposits associated with adakitic magmas enriched by the addition of melts, and the subduction-related porphyry Cu deposits associated with magmas comprising all compositions between normal arc rocks and adakitic rocks, all of which were associated with fluid-dominated enrichment process. In subduction-related Cu porphyry magmas, the oxidation state (fO2), the concentrations of chalcophile metals, and other volatiles (e.g., S and Cl), and the abundance of water were directly controlled by the composition of the primary arc basaltic magma. In contrast, the high Cu concentrations and fO2 values of collision-related Cu porphyry magmas were indirectly derived from subduction modified magmas, and the large amount of water and other volatiles in these magmas were controlled in part by partial melting of amphibolite derived from arc basalts that were underplated beneath the lower crust, and in part by the contribution from the rising potassic and ultrapotassic magmas. Both subduction- and collision-related porphyries are enriched in potassium, and were associated with crustal thickening. Their high K2O contents were primarily as a result of the inheritance of enriched mantle components and/or mixing with contemporaneous ultrapotassic magmas. © 2015 Elsevier B.V.

Leng Q.-F.,Chengdu University of Technology | Tang J.-X.,Chinese Academy of Geological Sciences | Zheng W.-B.,Chinese Academy of Geological Sciences | Zheng W.-B.,China University of Geosciences | And 4 more authors.
Geology in China | Year: 2015

The Lakange porphyry Cu-Mo deposit in the Gangdise metallogenic belt of central and southern East Lhasa block within the Tethys tectonic domain is one of the key deposits in the Tibet Plateau geological survey project evaluation in recent years. Reus isotopie dating technique was applied for determination of mineralization events, and eight molybdenite samples were analyzed for Re-Os isotopie compositions, with the model ages obtained ranging from (13.20±0.20) Ma to (13.64±0.21) Ma, and the isochron age being(13.12±0.44)Ma which represents the metallogenic age of the Lakange porphyry Cu-Mo deposit, indicating Miocene. The Re content of the molybdenite is 343.6 × 10-6-835.7 × 10-6, with an average of 557.8 × 10-6, suggesting that the metallogenic material originated from a source with mantle components. The Lakange porphyry Cu-Mo deposit was formed in a stretching background of India-Asia continental collision orogenic collision, the age (17-12 Ma) is identical with ages of numerous porphyry-skarn mineralization systems in the eastern of Gangdise metallogenic belt, and is 2-3 Ma younger than ages of the porphyry-skarn copper polymetallic deposits in the same ore concentration area, such as Jiama, Qulong and Bangpu, with the formation controlled by the same metallogenic geodynamics setting.

Chen L.,Jiangxi University of Science and Technology | Chen H.,Jiangxi University of Science and Technology | Wang B.,Chengdu Center | Wu K.,Jiangxi University of Science and Technology | And 6 more authors.
Acta Geologica Sinica | Year: 2013

This paper presents a description of the river terrace at Tangjia Village in Lhasa, Tibet. Selected types of phytolith and pollen were used as proxies to study the paleoclimate in the stndy area. Ancient climate and vegetation changes since 10 ka BP were examined. The results demonstrated that between 10.2 and 8.9 ka BP, the dominating phytolith was the cold type and the dominating vegetation type was grassland-forest. This indicated that the climate changed from cool-humid to cool-dry and later turned back into a cool-humid climate. Between 8.9 and 8.1 ka BP, the main types of phytoliths were tooth, dumbbell, and polyhedral. This suggests that the vegetation consisted of forest-grassland and the period's climate had become warmer. Between 8.1 and 6.7 ka BP, the warm index of phytolith assembelage gradually increased, whereas the spore and pollen assembelage revealed that the vegetation was forest with hardwood. This suggested that the paleoclimate was warmest in this period. The herbaceous vegetation increased gradually, indicating that the climate had become colder since 7.5 ka BP. Between 6.7 and 4.6 ka BP, cold type phytolith such as tooth and cap were found. Simultaneously, the pollen assembelage indicated that the vegetation shifted from grassland to forest and then turned hack into grassland. This implies that the climate fluctuated from cold-dry to coolhumid. Between 4.6 and 1.9 ka BP, the dominate type of phytolith was cold type and its warm index was in the range 0.04-0.28, suggesting a herhaceous vegetation cover and indicating that the climate was cold. The phytolith warm index from 1.9 ka BP revealed that the climate was continuously decreasing, and most of the pollen assembelage consisted of Chcnopodiaceae and Arteinisia. This conclusion is in agreement with the phytolith result that indicates that the climate was becoming colder and colder.

Xie Y.-W.,Regional Geological Survey Party | Liu H.-F.,Tibet Institute of Geological Survey | Qiangba Z.-X.,Regional Geological Survey Party | Jiang G.-W.,Tibet Institute of Geological Survey
Geological Bulletin of China | Year: 2010

Original Chaqupu Formation of Early-Middle Triassic in the Quesang area of Lhasa is composed by the lower part carbonate rocks which contain abundant Early-Middle Triassic fossils and the upper part volcanic rocks with no information on paleontology or chronology. Based on their stratigraphic overlying relationship, the volcanic rocks were determined as the upper part of Chaqupu Formation, and its age was determined to be Early-Middle Triassic, which has become a classical formation sequence locally and been widely used. Recendy, SHRIMP U-Pb zircon dating was carried on the zircons of basaltic andesites of the volcanic rocks in the upper part of original Chaqupu Formation. The dating results show that these rocks were formed in Early Triassic (248 Ma±4 Ma), so the original Chaqupu Formation is a inversion tectonic, and the volcanic rocks used be under the carbonate rocks and contact conformably with Lielonggou Formation of Permian, which is a trustworthy evidence of the continuous deposition in this area from Permain to Triassic and further shows that this area existed magmatic activities in Early Triassic. The determination of the sequence of Chaqupu Formation has important significances in studying the evolution process of the Gangdise area.

Zhang J.,Chengdu University of Technology | Zhang J.,Tibet Institute of Geological Survey | Duo J.,Tibet Institute of Geological Survey | Xia D.,Tibet Julong Copper Ltd | And 3 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2013

Nearby the Qulong gaint porphyry Cu-Mo deposit at the Gangdese belt in Tibet, there are two typical skarn Cu deposits. The Zhibula deposit is 2 km south and Langmujiaguo is 4 km southeast to the Qulong deposit. It's reported that the Re-Os isotopic age of the molybdenite dating from Langmujiaguo skarn deposit is (17.11±0.55) Ma. Combined with the published dating data from Qulong and Zhibula, a conclusion can be drawn that those deposits in the Qulong area were derived from the common magmatic hydrothermal mineralization and they may belong to a complete porphyry-skan ore-forming system. More attention should be paid to the porphyry deposits and the adjacently skarn deposits during geological prospecting and exploration at Gangdese belt.

Zhang W.,Guangdong Institute of Gelogical Survey | Chen L.-K.,Wuhan University | Chen L.-K.,Tibet Institute of Geological Survey | Zhang G.,Guangdong Institute of Gelogical Survey
Wutan Huatan Jisuan Jishu | Year: 2010

Regional geochemical survey with the main purpose of mineral exploration was carried out in Chongjiang area of Tibet, and the geochemical data was gotten, which was integrity in Systematic and standardized, multi-parameter ( 13 types of data). The most direct expression way of geochemical data was analyzing geochemical map, and one of the foundation map of geochemical was integrated-anomaly map. The key compilation is to determination of element association and main elements. From example of compilation integrated-anomaly in Chongjiang Area, the authors discussed in detail on the problem of the compilation of Geochemical Integrated-anomaly Map, which provides a scientific basis in anomaly filtration and anomaly inspection.

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