Yan, Maoqiang, Li, Guomeng, Shi, Wenjie, Huizenga, Jan Marten, Turlin, François, Xu, Chongwen, Moritz, Robert, and Wei, Junhao (2024) Recognizing crystal accumulation in plutonic system: Evidence from mafic microgranular enclaves in Early Silurian Qingshan granodiorite, North Qilian Orogenic Belt, NW China. Lithos, 468-469. 107518.

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Abstract

Granitoids are the primary constituents of the continental crust; recognizing and quantifying the effects of crystal accumulation in evolved magmas is a challenging task. Here we present whole-rock chemical, Sr-Nd isotopic, zircon U-Pb geochronological, and Hf isotopic data as well as EPMA and in-situ LA-ICP-MS analyses of amphiboles from Qingshan granodiorite and mafic microgranular enclaves (MMEs) from the North Qilian Orogenic Belt (NQOB). The MMEs and granodiorite have identical crystallisation ages (ca. 434 Ma), the same mineral assemblage, but different mineral modal proportions as the MMEs comprise more amphibole. The MMEs and granodiorite have indistinguishable and depleted zircon Hf (εHf (t) values of 6.1–8.3, and 6.4–9.1, respectively) and whole-rock Sr-Nd isotopic compositions, i.e. (87Sr/86Sr)i values of 0.70514–0.70913 and 0.70207–0.70552, respectively; and εNd(t) values of 0.27–2.23 and 0.21–2.39, respectively. The occurrence of idiomorphic amphibole grains, low MREEs and HREEs concentration, low Mg# values of equilibrium melts (AEMs), and decreasing Zr/Hf ratios indicate that Qingshan MMEs represent cumulates formed at a thermal boundary layer between the ascending conduits and the wall rocks. The Qingshan granodiorite was formed by partial melting of subducted oceanic crust with crustal materials during southward subduction of the North Qilian Ocean, followed by further amphibole-dominated fractionation by compaction without crystal deformation. We propose a model of southward subduction with the back-arc basin for the tectonic evolution of the western NQOB. Both the subduction- and collision-related granitoids of the NQOB have played a vital role in continental crust growth.

Item ID:	81696
Item Type:	Article (Research - C1)
ISSN:	1872-6143
Keywords:	Amphibole; Crystal accumulation; Cumulate; Mafic magmatic enclaves (MMEs); North Qilian Orogenic Belt; Continental crust growth
Copyright Information:	© 2024 Elsevier B.V. All rights reserved.
Date Deposited:	01 Mar 2024 03:02
FoR Codes:	37 EARTH SCIENCES > 3703 Geochemistry > 370399 Geochemistry not elsewhere classified @ 50% 37 EARTH SCIENCES > 3705 Geology > 370503 Igneous and metamorphic petrology @ 50%
SEO Codes:	28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280107 Expanding knowledge in the earth sciences @ 100%
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