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The heterogeneous orogenic lithospheric mantle: whole rock and mineral geochemical evidence from early Paleozoic mafic intrusives in the Qilian orogen, China.

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Title: The heterogeneous orogenic lithospheric mantle: whole rock and mineral geochemical evidence from early Paleozoic mafic intrusives in the Qilian orogen, China.
Authors: Chen, Qi1 (AUTHOR), Dai, Li-Qun1,2,3 (AUTHOR) lqdai@ustc.edu.cn, Zhao, Zi-Fu1,2,3 (AUTHOR) zfzhao@ustc.edu.cn, Zheng, Yong-Fei1,2 (AUTHOR), Zhou, Yao1 (AUTHOR)
Source: Contributions to Mineralogy & Petrology. Nov2022, Vol. 177 Issue 11, p1-21. 21p.
Subjects: Regolith, Mafic rocks, Subduction zones, Igneous rocks, Strontium isotopes, Minerals, Orogenic belts
Geographic Terms: China
Abstract: Mantle heterogeneity is caused by recycling of crustal materials into the mantle, and mafic arc magmatism provides important imformation on the nature of crust–mantle interaction. Here we undertake an integrated study of whole rock major-trace elements and Sr–Nd–Hf isotopes, in-situ zircon U–Pb ages and Hf–O isotopes as well as mineral major-trace elements and clinopyroxene Sr isotopes for mafic intrusives in the Qilian orogen. The studied Jinyuan and Jishishan mafic igneous rocks show consistent zircon U–Pb ages of ca. 448–450 Ma. They all display arc-like trace element distribution patterns, relatively depleted Sr–Nd isotope compositions, and variably high zircon O isotopes. In comparison, the Jinyuan mafic igneous rocks have less depleted Sr–Nd–Hf and higher O isotope compositions than the Jishishan mafic rocks. These geochemicial features indicate they originated from a heterogeneous orogenic lithospheric mantle source, which resulted from the incorporation of variable crustal materials into the mantle. Model calculations confirm that the heterogeneous mantle source would be generated by reaction of the mantle wedge peridotite with different proportions of the subducting Proto–Tethyan oceanic crust-derived aqueous solutions and sediment-derived hydrous melts. Partial melting of the heterogeneous mantle source would generate different batches of mafic melts, which led to magma mixing and recharge processes prior to emplacement as evidenced by mineral compositional zonings. Therefore, in addition to heterogeneous crust–mantle interaction during oceanic subduction, magmatic processes such as magma recharge and mixing may also contribute to the petrogenesis of arc igneous rocks above the oceanic subduction zone. [ABSTRACT FROM AUTHOR]
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Abstract:Mantle heterogeneity is caused by recycling of crustal materials into the mantle, and mafic arc magmatism provides important imformation on the nature of crust–mantle interaction. Here we undertake an integrated study of whole rock major-trace elements and Sr–Nd–Hf isotopes, in-situ zircon U–Pb ages and Hf–O isotopes as well as mineral major-trace elements and clinopyroxene Sr isotopes for mafic intrusives in the Qilian orogen. The studied Jinyuan and Jishishan mafic igneous rocks show consistent zircon U–Pb ages of ca. 448–450 Ma. They all display arc-like trace element distribution patterns, relatively depleted Sr–Nd isotope compositions, and variably high zircon O isotopes. In comparison, the Jinyuan mafic igneous rocks have less depleted Sr–Nd–Hf and higher O isotope compositions than the Jishishan mafic rocks. These geochemicial features indicate they originated from a heterogeneous orogenic lithospheric mantle source, which resulted from the incorporation of variable crustal materials into the mantle. Model calculations confirm that the heterogeneous mantle source would be generated by reaction of the mantle wedge peridotite with different proportions of the subducting Proto–Tethyan oceanic crust-derived aqueous solutions and sediment-derived hydrous melts. Partial melting of the heterogeneous mantle source would generate different batches of mafic melts, which led to magma mixing and recharge processes prior to emplacement as evidenced by mineral compositional zonings. Therefore, in addition to heterogeneous crust–mantle interaction during oceanic subduction, magmatic processes such as magma recharge and mixing may also contribute to the petrogenesis of arc igneous rocks above the oceanic subduction zone. [ABSTRACT FROM AUTHOR]
ISSN:00107999
DOI:10.1007/s00410-022-01970-1