Yu S.-Y.,Hebei United University |
Xu Y.-X.,Hebei United University |
Xu Y.-X.,CAS Institute of Geology and Geophysics |
Guo Z.-L.,No. 706 Geological Team |
And 4 more authors.
Northwestern Geology | Year: 2011
Situated in the middle part of the Central Asian Orogenic Belt (CAOB), the Altay orogenic belt (AOB) is an important metallogenic belt in China. Many economic deposits are distributed along southern margin of the AOB, e.g. Kaktal Pb-Zn deposit, Mengku iron deposit, Abagong iron deposit, and Tiemuerte Pb-Zn deposit, etc. , which all occur in the Kangbutiebao Formation stratum comprising low grade metamorphosed volcanic rocks. Using the LA-ICP-MS zircon U-Pb method, we obtain that the age of granite is 412. 7±0. 78Ma and that of andesitic tuff is 411. 2±3. 4Ma age, representing the eruption time of the granite and the meta-andesitic tuff at the Supute Anticline. This age indicates that an intense volcanic activity may occur in the early Devonian in the Supute Anticline in the southern margin of the Altay, suggesting an active continental margin setting during this time. They belong to the same event of product and have the same dynamic background with the extensive development of volcanic in this area. The Result provides important theoretical basis for the study of the Paleozoic tectonic evolution at Supute anticline and the Southern margin of Altay.
Zhou Q.,CAS Institute of Geology and Geophysics |
Zhou Q.,University of Chinese Academy of Sciences |
Qin K.,CAS Institute of Geology and Geophysics |
Tang D.,CAS Institute of Geology and Geophysics |
And 2 more authors.
Acta Petrologica Sinica | Year: 2013
The Koktokay No. 3 pegmatitic rare-element deposit with perfect and world-famous concentric internal zones is the largest pegmatite of the Altai orogen belt, hosting about 100,000 pegmatites. The micas and feldspars show different features of structure and composition in 9 internal zones. The micas belong to muscovite through I-VIII zones and lepidolite in inner zones. From outer to inner, muscovites occur in vellow-green middle to fine grains, white or green middle-coarse-huge grains and white or green book assemblages. Lepidolites occur in middle-fine scaly or wedge-shaped assemblages. There are chemical zoning, disequilibrium and metasomatic structures of micas in backscattered images. The feldspars from the Koktokay No. 3 pegmatite include K-feldspar, albite and some plagioclase. The K-feldspars occur in massive and albites occur in saccharoidal, blade and slice from outer to inner, 'lire micas of the Koktokay No. 3 pegmatite contain high Li(249 × 10-6 ∼ 35932 × 10-6) , Rb( 1240 × 10 -6 ∼ 22825 × 10-6) , Cs(35. 9 × 10-6 ∼ 13980 × 10 -6 ) , Ta( 13. 3 × 10-6 ∼ 447 × 10-6 ) , low K/Rb values (4. 23 ∼ 59. 4 ) and K/Cs values ( 6. 53 ∼ 2368 ) and the K-feldspare contain low K/Rb values (35. 4 ∼ 1865). Also, from outer to inner, Li, Hb, Cs, F and Ta contents increase and K/Rb values decrease. Thus, the Koktokay No. 3 pegmatite is a highly evolutionary pegmatite with increasing fractionation from outer to inner. The oscillation changes of major and trace element contents of micas and feldspars from continuous adjacent zones are possibly controlled by melt-immiscible process with minor effect of mineral crystallization and fractionation. Also, the melt-immiscible process possibly results in the internal zonation of the Koktoka No. 3 pegmatite. There are significant differences of compositions( FeO, Li, Hb, Cs, F, Ta contents and K/Rb and K/Cs values) and structures( disequilibrium and metasomatic) of micas and feldspars between outer zones( I- IV)and inner zones ( V-VIII). Compared with outher zones, inner zones show more fractionation features and contain more fluid, suggesting that the system transformed from melt stage( outer zones) to instable melt-fluid stage (inner zones). On account of field work, a pressure-relief event results in the the system abrupt change between zone IV and zone V and contributes to more fluid exoslution and the formation of melt-fluid stage.
Deng Y.,Hefei University of Technology |
Yuan F.,Hefei University of Technology |
Zhou T.,Hefei University of Technology |
Xu C.,Hefei University of Technology |
And 2 more authors.
Geoscience Frontiers | Year: 2015
Mineral chemistry, whole-rock major oxide, and trace element compositions have been determined for the Tuerkubantao mafic-ultramafic intrusion, in order to understand the early Paleozoic tectonic evolution of the West Junggar orogenic belt at the southern margin of the Central Asian orogenic belt. The Tuerkubantao mafic-ultramafic intrusion is a well-differentiated complex comprising peridotite, olivine pyroxenite, gabbro, and diorite. The ultramafic rocks are mostly seen in the central part of the intrusion and surrounded by mafic rocks. The Tuerkubantao intrusive rocks are characterized by enrichment of large ion lithophile elements and depleted high field strength elements relative to N-MORB. In addition, the Tuerkubantao intrusion displays relatively low Th/U and Nb/U (1.13-2.98 and 2.53-7.02, respectively) and high La/Nb and Ba/Nb (1.15-4.19 and 37.7-79.82, respectively). These features indicate that the primary magma of the intrusion was derived from partial melting of a previously metasomatized mantle source in a subduction setting. The trace element patterns of peridotites, gabbros, and diorite in the Tuerkubantao intrusion have sub-parallel trends, suggesting that the different rock types are related to each other by differentiation of the same primary magma. The intrusive contact between peridotite and gabbro clearly suggest that the Tuerkubantao is not a fragment of an ophiolite. However, the Tuerkubantao intrusion displays many similarities with Alaskan-type mafic-ultramafic intrusions along major sutures of Phanerozoic orogenic belts. Common features include their geodynamic setting, internal lithological zoning, and geochemistry. The striking similarities indicate that the middle Devonian Tuerkubantao intrusion likely formed in a subduction-related setting similar to that of the Alaskan-type intrusions. In combination with the Devonian magmatism and porphyry mineralization, we propose that subduction of the oceanic slab has widely existed in the expansive oceans during the Devonian around the Junggar block. © 2015, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.
Wang C.,Xinjiang Institute of Ecology and Geography |
Wang C.,CAS Institute of Geology and Geophysics |
Wang C.,University of Chinese Academy of Sciences |
Qin K.,Xinjiang Institute of Ecology and Geography |
And 6 more authors.
Acta Petrologica Sinica | Year: 2015
Located in the Koktokay pegmatitic ore cluster, eastern Altay, the Arskartor Be-Nb-Mo deposit is a large beryllium deposit, bearing gemstone and associated with Nb, Mo, and Ga mineralization. Rare-mental mineralization was developed both in granite and pegmatite, with sulfides like molybdenite and pyrite formed in the late stage, which is unique in Altai pegmatite province. A study of LA-ICP-MS zircon U-Pb dating combined with Hf isotope analysis on the muscovite-albite granite, beryllium-mineralized muscovite-albite granite and striped pegmatite is conducted, Re-Os dating of molybdenite from different zones of pegmatite is carried out as well. Weighted mean 206Pb/238U ages of zircon are 219.2 ±2.9Ma, 222.6 ±4.6Ma and 218.2 ± 3.9Ma respectively, molybdenite Re-Os age is 218.6 ± 1.3Ma, indicate that the formation of granite followed by pegmatite, and a short evolution history of the granitic-pegmatite system. The εHf(t) values are - 0.72 ∼ + 1.33, - 0.36 ∼ + 1.99 and - 0.45 ∼ + 0.38, with tDMC values of 1298 ∼ 1169Ma, 1279 ∼1130Ma and 1282 ∼ 1229Ma, respectively, implying that the source area for granite and pegmatite are similar and from the crustal material of Pre-Cambrian micro-continental blocks probably. The granite and pegmatite were formed by melting of thickened crust under an intra-plate tectonic setting during the post-orogenic stage. We infer the Arskartor pegmatite is LCT type from the association of mineralized elements, source material and tectonic setting. Characteristics of geology, geochemistry and geochronology imply that the muscovite-albite granite was the parent pluton for pegmatite.
Deng Y.-F.,Hefei University of Technology |
Deng Y.-F.,Xinjiang Institute of Ecology and Geography |
Yuan F.,Hefei University of Technology |
Yuan F.,Xinjiang Institute of Ecology and Geography |
And 7 more authors.
Journal of Asian Earth Sciences | Year: 2015
New U-Pb zircon ages and geochemical data including whole rock major and trace element concentrations, PGE and radiogenic isotopes are used to investigate the magma evolution processes and the sulfide saturation history of the Ural-Alaskan type Tuerkubantao mafic-ultramafic intrusion in southern Altai orogen. The Tuerkubantao intrusion consists of dunite, wehrlite, olivine pyroxenite, gabbro and diorite. Igneous zircons from a gabbro in the intrusion yielded a LA-ICP-MS U-Pb age of 370.3 ± 4.8 Ma, indicating that the intrusion was emplaced in the Late Devonian. The intrusive rocks are characterized by enrichment of large ion lithophile elements and depleted high field strength elements relative to N-MORB, which is similar to the Devonian Ural-Alaskan type intrusions in southern Altai orogen and different from Devonian volcanic rocks from ophiolites in West Junggar. The Tuerkubantao intrusive rocks have restricted (87Sr/86Sr)t ratios (0.70396-0.70453) and a large range of εNd(t) (-2.84 to +3.80). The trace elements and isotope compositions are comparable with those of the volcanic rocks along the Pacific margins of the Americas. The calculated parental magma of the Tuerkubantao rocks has a high-Mg basaltic composition with ~9.12 wt% MgO and ~7.02 wt% FeOT. It is proposed that the primary magma was generated from partial melting of metasomatized lithospheric mantle triggered by upwelling of asthenosphere at an active continental margin. The Cu/Pd ratios in gabbros (9.26 × 105-32.8 × 105) are obviously higher than those of the wehrlites (1.18 × 104-1.95 × 104), indicating that gabbros in the intrusion have experienced sulfide segregation, whereas sulfide saturation did not occur in the wehrlites. © 2015 Elsevier Ltd.