Tran Trong Hoa

Intraplate extension prior to continental extrusion along the Ailao Shan-Red River shear zone

Left-lateral movement of the Ailao Shan–Red River shear zone lends support to the hypothesis of continental extrusion resulting from the collision of India with Asia. Our new observations from northwestern Yunnan, China, and northwestern Vietnam on different sides of the shear zone demonstrate that the sinistral offset was ∼600 km according to correlations of Permian-Triassic flood basalt successions and late Paleogene highly potassic mafic magmas. We conclude that the shear was propagating on the South China continental margin and does not correspond to a suture between South China and Indochina. Furthermore, the highly potassic magmas were emplaced from ca. 40 to 30 Ma, before the shear movement, which was caused by the late Oligocene to early Miocene (ca. 27–22 Ma) extrusion activity. This suggests that a late Eocene to early Oligocene intraplate extension, possibly induced by delamination of thickened continental lithosphere, took place in northwestern Yunnan (or eastern Tibet) as a response to the India-Asia collision. This extension, and sea-floor spreading of the South China Sea that began ca. 30 Ma, could have accounted for the initiation of the Ailao Shan–Red River shear zone.

Geochemical and Sr-Nd isotopic characteristics of granitic rocks from northern Vietnam

Abstract Five major felsic igneous suites from northern Vietnam, with ages from mid-Proterozoic to early Cenozoic, were studied. Representative granitic rocks from the Posen Complex (mid-Proterozoic) and the Dienbien Complex (late Permian to early Triassic) show geochemical characteristics similar to those of calc-alkaline to high-K calc-alkaline I-type granites. However, the former, located in the South China block, has significantly higher initial Nd isotopic ratios [eNd(T)=+0.7 to +1.5] and older Nd isotopic model ages (TDM∼1.7 Ga) than the latter [eNd(T)=−4.7 to −9.7; TDM∼1.3–1.5 Ga] which were emplaced south of the Song Ma Suture and thus in the Indochina block. The generation of both complexes may be attributed to subduction-related processes that occurred in two distinct crustal provenances with different degrees of mantle inputs. On the other hand, Jurassic to Cretaceous granitic rocks from the Phusaphin Complex, contemporaneous rhyolites from the Tule Basin, and late Paleogene granitic rocks from the Yeyensun Complex, all exposed in the South China block between the Ailao Shan–Red River shear zone and the Song Ma Suture, display geochemical features similar to those of A-type granites with intermediate eNd(T) values (+0.6 to −2.8) and younger TDM ages (0.6–1.1 Ga). These magmas are suggested to have been generated as a consequence of intraplate extension in the western part of the South China block (Yunnan), and to have been transported to their present position by mid-Tertiary continental extrusion along the Ailao Shan–Red River shear zone related to the India–Asia collision. Overall, the isotopic and model age data, reported in this study indicate that in northern Vietnam, the most important crust formation episode took place in the Proterozoic. Likewise, repeated mantle inputs have played a role in the petrogenesis of Phanerozoic granitic rocks.

The Khao Que-Tam Tao gabbro-granite massif, Northern Vietnam: A petrological indicator of the Emeishan plume

New data obtained on the Khao Que-Tam Tao gabbro-granite pluton (Northern Vietnam) are discussed. It was established that this pluton was formed at the Permian-Triassic boundary (250.5 ± 3.2 Ma, 40Ar/39Ar isotopic age). Morphologically, it represents a hypabyssal fracture intrusion. The first stage was marked by the intrusion of the picrobasaltic melt, the differentiation of which resulted in the formation of the layered peridotite-gabbro series and the quartz-bearing monzodiorites and granophyres in its endocontact at the final stage. At the second stage, the Khao Que peridotite-gabbro massif was broken in its central part by a fault, along which the Tam Tao granodiorite-granite massif was localized. Numerical simulation using the COMAGMAT program for the basic system and geochemical estimates for the granite system allow the statement that the mafic and granitic melts evolved independently, and their final products were quartz-bearing monzodiorite and granophyre, on the one hand, and aplites and pegmatites, on the other hand. The compositional correlation of the Permian-Triassic magmatic associations in Northern Vietnam (the Nui Chua gabbro pluton and the Khao Que-Tam Tao gabbro-granite and Pia Bioc granite plutons) and in Southeast China (flood basalts) allows these complexes to be regarded as a part of a single large igneous province produced by the Emeishan plume activity.

Stanniferrous granites of Vietnam: Rb-Sr and Ar-Ar isotope age, composition, sources, and geodynamic formation conditions

Stanniferrous granite-leucogranite massifs in Vietnam to which the bedrock and placer commercial deposits of cassiterite are associated (Timtuc etc.) are of late Cretaceous age (∼85 Ma by Rb-Sr and Ar-Ar isotope dating). These massifs are presented by stocks and fracture intrusions (to 100 km2 in area) of simple homodromic structure: biotite granites ⇒ two-mica and muscovite leucogranites ⇒ topaz-containing aplites ⇒ rare-metal pegmatites.

Mineralogical characteristics of arsenopyrite and pyrite in Bo Va and Nam Quang gold-sulfide deposits (Northeast Vietnam)

Crystal morphology and chemical composition of arsenopyrite and pyrite in the Nam Quang and Bo Va deposits of the Song Hien basin (Northeast Vietnam) are studied in detail. Arsenopyrite crystals often form elongated crystals. Their chemical composition are relatively poor in As, but rich in S with S/As ratios often > 1.1, impurity elements such as Ni, Co, Sb, and sometimes containing gold (up to 0.02 wt.%). Pyrite is characterized by the stoichiometric composition, but contains relatively high arsenic and sometimes contain gold. The correlation between the concentration of As and Au in pyrite has been recorded. The morphology and chemical composition of arsenopyrite and pyrite of Bo Va and Nam Quang deposits can be correlated to those in the Au-sulfide deposits in black shale in Kazastan and southestern China. References Trần Trọng Hoa (chủ bien), 1996: Xây dựng mo hinh điều tra, sử dụng hợp lý, bảo vệ moi trường trong qua trinh khai thac tai nguyen khoang sản quý hiếm tỉnh Cao Bằng. Lưu trữ Viện Địa chất, Ha Nội. Trần Trọng Hoa, Polyakov G.V., Trần Tuấn Anh, Borisenko A.S., Izokh A.E., Balyakin P.A., Ngo Thị Phượng, Phạm Thị Dung, 2011: Hoạt động magma va sinh khoang nội mảng miền Bắc Việt Nam. Nxb. Khoa học Tự nhien va Cong nghệ, 368tr. Trần Trọng Hoa, Nevolko P., Ngo Thị Phượng, Trần Tuấn Anh, Phạm Thị Dung, Bui Ấn Nien, Nguyễn Xuân Huyen, Nguyễn Thuy Dương, Vũ Hoang Ly, Trần Văn Hiếu, 2013: Cac tụ khoang vang-sulfide trong cac thanh tạo lục nguyen - carbonat rift Song Hiến, ÐBVN. Tuyển tập Bao cao KHCN toan quốc năm 2013. ISBN: 978-604-59-0693-4; tr.131-140. Nong Thế Tang (chủ bien), 1996: Bao cao Khảo sat va tim kiếm đanh gia vang gốc Nam Quang, Bảo Lạc, Cao Bằng. Lưu trữ Trung tâm Thong tin lưu trữ Địa chất, Ha Nội. Chen M.H., Mao J.W., Bierlein F.P., Norman T., Uttley P.J., 2011: Structural features and metallogenesis of the Carlin-type Lannigou gold deposit, Guizhou Province, China. OreGeol. Rev.43 (1), 217-234. Fleet, M.E., Mumin, A.H., 1997: Gold-bearing pyrite and arsenopyrite from Carlin Trend gold deposits and laboratory synthesis: American Mineralogist, v. 82, p.182-193. Kovalev K.R., Kalinin Yu.A., Naumov E.A., Kolesnikova M.K., Korolyuk V.N., 2011: Gold-bearing arsenopyrite in eastern Kazakhstan gold-sulfide deposits. Russian Geology and Geophysics 52, 178-192. Kovalev K.R., Kalinin Yu.A., Polynov V.I., Kydyrbekov E.L., Borisenko A.S., Naumov E.A., Netesov M.I., Klimenko A.G., and Kolesnikova M.K., 2012: ISSN 1075-7015, Geology of Ore Deposits, vol. 54, No.4, 254-275. Peters S.G., HuangJ.Z., Li Z.P., JingC.G., 2007: Sedimentary rock-hosted Au deposits of the Dian-Qian-Guiarea, Guizhou, Yunnan Provinces, and Guangxi District, China. Ore Geol. Rev.31,170-204. Volkova A. V. , Genkina A. D. , and Academician of the RAS Goncharovb V. I., 2006. New data on invisible gold in disseminated sulfide ores of the Natalka deposit. Vol. 409A, No 6, pp. 879-883. Zhong H.R., Chao S.W., Wu B.X., Zhi T.G., Hofstra A.H., 2002: Geology and geochemistry of Carlin- type gold deposits in China Mineralium Deposita 37:378-39. Zhou T.H., Goldfarb R.J., Phillips G.N., 2002: Tectonics and metallogeny of gold deposits in China. Mineralium Deposita 37, 249-282.