Early Palaeozoic high-Mg basalt-andesite suite in the Duobaoshan Porphyry Cu deposit,NE China: Constraints on petrogenesis,mineralization, and tectonic setting |
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| Institution: | 1. Key Laboratory of mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Institutions of Earth Science, Chinese Academy of Sciences, China;3. University of Chinese Academy of Sciences, Beijing 100049, China;1. Department of Geosciences, Biogeology, University of Tübingen, Hölderlinstrasse 12, 72074 Tübingen, Germany;2. Senckenberg Research Centre for Human Evolution and Paleoenvironment, University of Tübingen, Hölderlinstrasse 12, 72076 Tübingen, Germany;3. Instituto de Investigaciones Arqueológicas y Paleontológicas del Cuaternario Pampeano (INCUAPA-CONICET), Universidad Nacional del Centro de la provincia de Buenos Aires, Del Valle 5737, B7400JWI Olavarría, Buenos Aires, Argentina;4. Museo Municipal de Ciencias Naturales Pachamama, Santa Clara del Mar, Argentina;5. Universidad Nacional de Mar del Plata, Argentina;6. Div. Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque, 1900 La Plata, Argentina;7. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja (CRILAR), Provincia de La Rioja, UNLaR, SEGEMAR, UNCa, CONICET, Entre Ríos y Mendoza s/n, 5301 Anillaco, La Rioja, Argentina;1. College of Earth Sciences, Jilin University, Changchun 130061, China;2. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong;1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;3. Department of Applied Geology, Curtin University, G.P.O. Box U1987, Perth, Western Australia 6845, Australia;4. Key Laboratory of Computational Geodynamics, Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | High-Mg basalt-andesite suites are extremely rare in the modern Earth but genetically important for indicating essential crust-mantle interactions, ascertaining critical geodynamic settings, and understanding the formation of porphyry copper deposits. Secondary ion mass spectrometry (SIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating and geochemistry document an early Palaeozoic high-Mg basalt-andesite suite from the Duobaoshan porphyry Cu deposit, eastern Central Asian Orogenic Belt (CAOB). Dating results reveal that the Duobaoshan high-Mg basalt and andesite erupted ca. 506 Ma and ca. 485 Ma, respectively. These high-Mg samples are typical subduction-related volcanic rocks with SiO2 contents of 47.73 to 55.16 wt%, high MgO (6.08 to 10.82 wt%), and high Mg# (58 to 67) and feature enrichments in large ion lithophile elements (LILEs) and depletions in high field strength elements (HFSEs). The samples have juvenile whole-rock initial 87Sr/86Sr ratios of 0.70272 to 0.70451, ?Nd(t) of 4.8 to 8.7 (average 7.23), and zircon ?Hf(t) of 7.3 to 15.9. Additionally, they have high Sr (average 619.36 ppm) and low Y (average 11.92 ppm) and Yb (average 1.21 ppm) contents that show affinity with adakitic high-Mg basalts and andesites worldwide. These high-Mg, depleted mantle-like isotopic and adakitic geochemical features imply a depleted mantle source variably assimilated by slab-derived melts under a sustained subduction tectonic setting. We also propose that the Duobaoshan high-Mg basalt-andesite suite, as the parental source magma, fertilized the overlying Duobaoshan porphyry Cu deposit by providing water, copper, and sulphur and high oxygen fugacity. A comprehensive comparison of the post-ore volcanic rocks shows that they might have originated from the slab-derived fluid metasomatized depleted mantle wedge, which had different properties from the mantle that produced the pre- and syn-ore volcanic intrusive rocks. The post-ore volcanic rocks underwent little crustal evolution en route to the surface during a reworked subduction event, which indicates a relatively immature island arc environment. |
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