Permian Tectonic Evolution in Southwestern Khanka Massif： Evidence from Zircon U-Pb Chronology, Hf isotope and Geochemistry of Gabbro and Diorite

• Published in: Acta geologica Sinica (Beijing) Vol. 85; no. 6; pp. 1390 - 1402
• Main Authors: Huahua, CAO, Wenliang, XU, Fuping, PEI, Xingzhou, ZHANG
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.2011; Wiley Subscription Services, Inc; College of Earth Sciences, Jilin University, Changchun, Jilin 130061, China
• Edition: English ed.
• Subjects: arc-continent collision; geochemistry; Hf同位素; Khanka Massif; Permian magmatism; the Paleo-Asian ocean; 二叠纪; 区域构造演化; 地块; 地球化学证据; 辉长岩; 锆石U-Pb年龄; 闪长岩; geochemistry; Khanka Massif; arc-continent collision; the Paleo-Asian ocean; Permian magmatism
• ISSN: 1000-9515; 1755-6724
• DOI: 10.1111/j.1755-6724.2011.00594.x

Laser ablation-inductively coupled plasma mass spectrometry （LA-ICP-MS） zircon U-Pb dating and geochemical data for the Permian gabbros and diorites in the Hunchun area are presented to constrain the regional tectonic evolution in the study area. Zircons from gabbro and diorite are euhedral-subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios （0.26-1.22）, implying their magmatic origin. The dating results indicate that the gabbro and diorite formed in the Early Permian （282-2 Ma） and in the Late Permian （255-3 Ma）, respectively. In addition, the captured zircons with the weighted mean age of 279-4 Ma are also found in the diorite, consistent with the formation age of the gabbro within uncertainty. The gabbros belong chemically to low-K tholeiitic series, and are characterized by low rare earth element （REE） abundances, fiat REE pattern, weak positive Eu anomalies （JEu）, and depletion in high field strength elements （HFSEs, Nb, Ta, and Ti）, similar to the high-aluminum basalts from island arc setting. Initial Hf isotopic ratios of zircons from the gabbro range from ＋7.63 to ＋14.6, suggesting that its primary magma could be mainly derived from partial melting of a depleted lithospheric mantle. The diorites belong to middle K calc-alkaline series. Compared with the gabbros, the diorites have higher REE abundance, weak negative Eu anomalies, and more depletion in HFSEs （Nb, Ta, and Ti）, similar chemically to the volcanic rocks from an active continental margin setting. Initial Hf isotopic ratios and Hf two-stage model ages of zircons from the diorite range from ＋11.22 to ＋14.17 and from 424 to 692 Ma, respectively, suggesting that its primary magma could be mainly derived from partial melting of the Early Paleozoic and/or Neoproterozoic accretted lower crust. Taken together, it is suggested that geochemical variations from the Early Permian gabbros to the Late Permian diorites reveal that the subduction of the Paleo-Asian oceanic plate beneath the Khanka Massif and collision between the arc and continent （Khanka Massif） happened in the late stage of the Late Paleozoic.