Earth Science Frontiers ›› 2023, Vol. 30 ›› Issue (3): 340-365.DOI: 10.13745/j.esf.sf.2022.9.2

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Processes and mechanism of lithospheric thinning in the eastern North China Craton during the Early Cretaceous: Evidence from the Beidashan pluton, Liaoning Province

LUO Niangang1,2(), GAO Lianfeng1,*(), ZHANG Zhenguo1, YIN Zhigang1, CUI Jianyu2, WU Junfei3, XING Jie1, DING Kai1, GAO Chenyang1, WANG Yue1   

  1. 1. College of Mining Engineering, Liaoning Technical University, Fuxin 123000, China
    2. Liaoning Provincial Geological and Mineral Survey Institute Co., Ltd., Shenyang 110031, China
    3. Inner Mongolia Pingzhuang Coal Industry (Group) Co., Ltd., Chifeng 204000, China
  • Received:2022-04-12 Revised:2022-07-13 Online:2023-05-25 Published:2023-04-27

Abstract:

The North China Craton (NCC) experienced pervasive lithospheric thinning in the Early Cretaceous, but the thinning process and thinning mechanism are still controversial. To shine a new light on the thinning events this paper focuses on the Beidashan Pluton of Liaoning Province, eastern NCC to conduct detailed field geological survey, combined with laboratory research including petrographical, geochemical, U-Pb zircon chronological and Lu-Hf isotopic analyses, so as to explore the formation age, source area and petrogenesis of the Beidashan pluton. The lithology of the Beidashan pluton is porphyritic biotite monzogranite which has a weighted mean age of 117.1±1.4 Ma by zircon U-Pb dating. The quasi peraluminous porphyritic biotite monzogranite is rich in silicon (69.15%-69.87%) and alkali (8.46%-8.66%) and poor in magnesium (0.80%-0.90%) and calcium (2.03%-2.04%), and is enriched in large ion lithophile elements (LILEs) (Rb, Th, K, Ba) and depleted in high field strength elements (HFSEs) (Nb, Ta, Ti). The rare earth element (REE) pattern is right-leaning, showing a steep linear slope for light REE (LREE) and flattening of heavy REE (HREE). The zircon saturation temperature of granite melt (763.14-768.87℃) is clearly lower than that of A-type granite (> 800 ℃). The above characteristics generally represent high-k, calc-alkaline I-type granitoids. Zircon εHf(t) values range from -21.49 to -19.04, and the two-stage Hf model ages (tDM2) range between 2536-2383 Ma, indicating the monzogranite is mainly derived from partial melting of Paleproterozoic ancient basaltic crust. According to the chronological and petrogeochemical analyses, the Beidashan pluton was formed under regional extensional environment caused by slab roll-back of the paleo-Pacific plate during the Early Cretaceous, and the upwelling asthenosphere caused large-scale delamination of the deep lithosphere of the North China Craton resulting in lithospheric thinning.

Key words: porphyaceous biotite monzonitic granite, geochemistry, geochronology, Lu-Hf isotope, lithospheric thinning, Beidashan pluton

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