Abstract The Dongjun Pb‐Zn‐Ag deposit in the northern part of the Great Xing'an Range (NE China) consists of quartz‐sulfide vein‐type and breccia‐type mineralization, related to granite porphyry. Hydrothermal alteration is well‐developed and includes potassic‐silicic‐sericitic alteration, phyllic alteration and propylitic alteration. Three stages of mineralization are recognized on the basis of field evidence and petrographic observation, demarcated by assemblages of quartz‐pyrite‐arsenopyrite (early stage), quartz‐polymetallic sulfide (intermediate stage) and quartz‐carbonate‐pyrite (late stage). Zircon LA‐ICP‐MS U‐Pb dating indicates that the granite porphyry was emplaced at 146.7 ± 1.2 Ma (Late Jurassic). Microthermometry and laser Raman spectroscopy shows that ore minerals were deposited in conditions of intermediate temperatures (175–359°C), low salinity (0.5–9.3 wt% NaCl eqv.) and low density (0.60–0.91 g/cm 3 ). Ore‐forming fluids were derived largely from magmatic hydrothermal processes, with late‐stage addition of meteoric water, belonging to a H 2 O‐NaCl‐CO 2 ± CH 4 system. The δ 34 S V‐CDT values range from 0.75‰ to 4.70‰. The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb values of the ore minerals are in the ranges of 18.240–18.371, 15.542–15.570, and 38.100–38.178, respectively. Data for the S and Pb isotopic systems indicate that the ore‐forming metals and sulfur were derived from Mesozoic magma. Based on the geological characteristics and geochemical signatures documented in this study, we conclude that the Dongjun deposit is a mesothermal magmatic hydrothermal vein‐type Pb‐Zn‐Ag deposit controlled by fractures and related to granite porphyry, in response to Late Jurassic tectonic–magmatic–hydrothermal activity. We further conclude that fluid immiscibility, fluid mixing and fluid‐rock interactions were the dominant mechanisms for deposition of the ore‐forming materials.
Research Article| March 01, 2013 Tertiary basin evolution along the northeastern margin of the Tibetan Plateau: Evidence for basin formation during Oligocene transtension Weitao Wang; Weitao Wang † 1State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China †E-mail: weitaoww@gmail.com. Search for other works by this author on: GSW Google Scholar Eric Kirby; Eric Kirby 2Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA Search for other works by this author on: GSW Google Scholar Zhang Peizhen; Zhang Peizhen 1State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Zheng Dewen; Zheng Dewen 1State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Zhang Guangliang; Zhang Guangliang 1State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Zhang Huiping; Zhang Huiping 1State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Zheng Wenjun; Zheng Wenjun 1State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Chai Chizhang Chai Chizhang 3Ningxia Hui Autonomous Region Institute of Seismology, China Earthquake Administration, Yinchuan 750001, China Search for other works by this author on: GSW Google Scholar GSA Bulletin (2013) 125 (3-4): 377–400. https://doi.org/10.1130/B30611.1 Article history received: 23 Sep 2011 rev-recd: 22 Jun 2012 accepted: 15 Jul 2012 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Weitao Wang, Eric Kirby, Zhang Peizhen, Zheng Dewen, Zhang Guangliang, Zhang Huiping, Zheng Wenjun, Chai Chizhang; Tertiary basin evolution along the northeastern margin of the Tibetan Plateau: Evidence for basin formation during Oligocene transtension. GSA Bulletin 2013;; 125 (3-4): 377–400. doi: https://doi.org/10.1130/B30611.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The development of high topography associated with the Indo-Asian collision plays a central role in ongoing debates over the linkages between development of the Tibetan Plateau and climate. In northeastern Tibet, the widespread appearance of coarse terrestrial sediment during the Oligocene is commonly interpreted to herald the development of a foreland basin in response to crustal thickening along the present-day margin of the plateau. However, a lack of direct observations relating sediment accumulation to fault activity leaves this interpretation uncertain. Here, we present new stratigraphic observations along the northern margin of the Longzhong basin that provide insight into the tectonic setting of basin development. A combination of field and subsurface observations, including the geometry of basin-bounding faults, sedimentary provenance, paleoflow direction, isopach and sedimentary facies distribution patterns, constrains basin evolution from the Middle Tertiary through Quaternary time. Our results suggest that NE-SW extension across normal faults controlled development of accommodation space in the northern Longzhong basin during the Oligocene to early Miocene. Continued sediment accumulation from the mid-Miocene through Pliocene occurred in a broad, shallow basin, consistent with thermal subsidence following extension. Basin inversion initiated between 10 Ma and 6 Ma, associated with the development of the modern Haiyuan fault system. Our results imply that the onset of Tertiary sedimentation in the Longzhong basin does not represent a developing foredeep associated with a nascent Tibetan Plateau, but rather reflects transtensional deformation inboard of extensional basins along the East Asian margin. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The Lower Urgen molybdenum deposit (44,856 t Mo @ 0.141%), situated in the northern Great Xing’an Range, is a newly discovered porphyry molybdenum deposit. Mineralization is characterized by veinlet-disseminated- and vein-type quartz–sulfide orebodies primarily occurring in the cupola of the Early Cretaceous granite porphyry stock. In this study, we present a detailed description of the ore geology, molybdenite Re-Os dating, H-O-S-Pb isotopic compositions, and fluid inclusion (FI) analyses including petrography, laser Raman, and microthermometry to precisely constrain the timing of ore formation, the origin of ore-forming fluids and materials, as well as the metal precipitation mechanism. Molybdenite Re-Os dating yielded two model ages of 141.2 ± 1.5 and 147.7 ± 1.7 Ma, coeval with the regional Late Jurassic–Early Cretaceous molybdenum metallogenesis. The hydrothermal process can be divided into three stages: the quartz–molybdenite(–pyrite) stage, quartz–polymetallic sulfide stage, and quartz–carbonate stage. Four types of FIs were distinguished for quartz, including two-phase liquid-rich (L-type), saline (S-type), CO2-rich (C1-type), and CO2-bearing (C2-type) FIs. Microthermometric data showed that the homogenization temperatures and salinities from the early to late stages were 240–430 °C, 5.0–11.9, and 30.1–50.8 wt% NaCl equiv.; 180–280 °C and 3.0–9.1 wt% NaCl equiv.; and 120–220 °C and 0.2–7.9 wt% NaCl equiv., respectively, suggesting a decreasing trend. H-O isotopic compositions indicate that the ore-forming fluids were initially of magmatic origin with the increasing incorporation of meteoric water. S-Pb isotopic compositions indicate that the ore-forming materials originated from granitic magmas, and the mineralization is genetically related to the ore-bearing granite porphyry stock in the deposit. Fluid immiscibility and fluid–rock interaction are collectively responsible for the massive deposition of molybdenite in stage 1, whereas fluid mixing and immiscibility played a critical role in the deposition of polymetallic sulfide in stage 2.
In the northern and central Great Xing ' an Range, there exist widespread Late Mesozoic volcanic rocks, of which the petrogenesis and geodynamic setting remain controversial. These rocks are composed of andesite, trachyandesite, basaltic andesite, and rhyolite. This study presents new data of zircon U–Pb dating, Hf isotopic composition, and whole‐rock geochemistry of the Late Jurassic intermediate‐mafic volcanic rocks within the northern Great Xing'an Range. In addition, the geochronological and geochemical data for the Late Mesozoic intermediate‐mafic rocks within the northern and central Great Xing'an Range are summarized for constraining the geochronological framework, petrogenesis, and geodynamic setting of the large‐scale Late Mesozoic volcanism in this region. The intermediate‐mafic volcanic rocks are enriched in large‐ion lithophiles and light rare earth elements and are depleted in high‐field‐strength elements such as Nb, Ta, and Ti, with positive ε Hf ( t ) values (+0.7 to +15.4). The data indicate that the volcanic rocks were derived from the partial melting of a mantle wedge that was modified by previously subducted slab‐derived fluids. These Late Mesozoic intermediate‐mafic volcanic rocks record a post‐collisional lithospheric extensional setting resulting from the closure of the Mongol‐Okhotsk Ocean.
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