Pre-Late Eocene position of the Lüchun-Jinping microblock in western Yangtze Craton: constraints from Eocene-Oligocene lamprophyres in southeastern Tibet

Shen, Yang, Zheng, Yuan-Chuan, Hou, Zeng-Qian, Huizenga, Jan, Zhang, Ai-Ping, Wang, Zi-Xuan, Li, Xin, Xu, Pei-Yan, Wu, Chang-Da, and Liu, Si-Qi (2022) Pre-Late Eocene position of the Lüchun-Jinping microblock in western Yangtze Craton: constraints from Eocene-Oligocene lamprophyres in southeastern Tibet. Lithos, 414-415. 106622.

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The tectono-magmatic history of the Lüchun-Jinping microblock and its possible affinity with the Yangtze Craton are important elements for the reconstruction of Cenozoic plate tectonics in southeastern Tibet. In order to constrain the affinity and decipher the pre-Cenozoic paleopositon of the Lüchun-Jinping microblock, we focused on the petrogenesis of Eocene-Oligocene lamprophyres in the Lüchun-Jinping microblock. The lamprophyres yield zircon Usingle bondPb ages of 34.7–33.3 Ma and exhibit potassic-ultrapotassic features with elevated K2O/Na2O (1.4–4.0) ratios. They are characterized by high concentrations of compatible elements (e.g., Cr = 187–692 ppm, Ni = 31–218 ppm), large-ion-lithophile elements and light rare-earth elements enrichment, high-field-strength elements depletion, and high radiogenic isotopic values, i.e. (87Sr/86Sr)i = 0.7063–0.7078 and εNd(t) = −3.9 to −2.4. Combined with the low Nb/U ratios, these features suggest that the lithospheric mantle source was metasomatized by subduction-related fluids beneath the Lüchun-Jinping microblock. The relatively high Rb/Sr ratios and high heavy rare-earth element contents indicate that these lamprophyres were derived from partial melting of a phlogopite-bearing lherzolite within the spinel stability field. The parental magmas have experienced fractional crystallization of olivine and clinopyroxene during emplacement. Comprehensive comparisons between the lamprophyres from the Lüchun-Jinping microblock and the potassic-ultrapotassic mafic rocks from the western Yangtze Craton indicate that the Lüchun-Jinping microblock can be regarded as a dismembered part of the western Yangtze Craton due to continental extrusion and Cenozoic sinistral displacement. The compositional trends of the potassic-ultrapotassic mafic rocks suggest that the palaeogeographic position of the Lüchun-Jinping microblock was near the Dali area (west of the Binchuan) and close to the Jinshajiang suture zone before the Cenozoic.

Item ID: 72399
Item Type: Article (Research - C1)
ISSN: 1872-6143
Keywords: Lamprophyres; Geochemistry; Lithospheric mantle; Paleoposition; Lüchun-Jinping microblock; Southeastern Tibet
Copyright Information: © 2022 Elsevier B.V. All rights reserved.
Date Deposited: 03 Jun 2022 00:09
FoR Codes: 37 EARTH SCIENCES > 3703 Geochemistry > 370302 Inorganic geochemistry @ 40%
37 EARTH SCIENCES > 3705 Geology > 370503 Igneous and metamorphic petrology @ 30%
37 EARTH SCIENCES > 3705 Geology > 370511 Structural geology and tectonics @ 30%
SEO Codes: 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280107 Expanding knowledge in the earth sciences @ 100%
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