气候变化领域集成服务门户(CCPortal): Oligocene High-MgO Alkali Basalts in Central Tibet: Implications for Magma-Mush Mixing and Mantle Processes

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DOI	10.1093/petrology/egad091
	Oligocene High-MgO Alkali Basalts in Central Tibet: Implications for Magma-Mush Mixing and Mantle Processes
	Qi, Yue; Wang, Qiang; Wei, Gang-Jian; Zhang, Xiu-Zheng; Dan, Wei; Yang, Zong-Yong; Hao, Lu-Lu; Hu, Wan-Long
发表日期	2024
ISSN	0022-3530
EISSN	1460-2415
卷号	65 期号:1
英文摘要	High-MgO (>9 wt %) basaltic rocks can be primary magmas and are used to constrain the geochemistry and temperature of the mantle. However, high MgO contents can also result from mixing between evolved melts and antecrysts or xenocrysts, and thus, the whole-rock composition might not represent the solidified equivalents of primary magma. Whether such mixing with crystals can result in erroneous interpretations of mantle processes remains unclear. This study presents a petrological and geochemical investigation of the post-collision high-MgO (>9 wt %) Lugu volcanic rocks in the southern Qiangtang terrane, central Tibet. The Lugu volcanic rocks comprise porphyritic and intersertal alkali basalts. Zircon U-Pb ages and Ar-40/Ar-39 dating suggest that the two types of alkali basalts were erupted at c. 29 Ma. Based on detailed petrographic observations and geochemical analysis, the porphyritic alkali basalts may represent near-primary melts, which are characterised by low SiO2 contents (40.9-45.1 wt %), high CaO/Al2O3 ratios (1.1-1.5), and arc-like trace element patterns. We suggest these basalts were derived by partial melting of enriched garnet peridotite (>3 GPa) in the presence of H2O and CO2. These geochemical features are different from those of the c. 30-Ma (ultra)-potassic rocks in the Qiangtang terrane, indicating that a heterogeneous lithospheric mantle existed beneath the Qiangtang terrane during the Oligocene. In contrast, although the intersertal alkali basalts have high MgO contents (>9 wt %), evidence from mineral chemistry indicates that the whole-rock compositions of the intersertal alkali basalts represent mixtures of evolved residual melts and cumulate crystals. They were the product of polybaric fractional crystallisation and the subsequent mixing of crystals and residual melts in a magmatic plumbing system. Furthermore, when intersertal alkali basalts are assumed to be primary melts, they would have been derived by partial melting of shallow (similar to 2.5 GPa) CO2-poor pyroxenite or peridotite. These conditions are different from interpretations of the nature of the mantle source and melting conditions for porphyritic alkali basalts. Our results highlight that the interpretation of petrogenetic processes should be preceded by detailed mineralogical investigations.
关键词	high MgO rocks mush mantle heterogeneity central Tibet
英文关键词	OXYGEN FUGACITY; U-PB; VOLCANIC-ROCKS; IGNEOUS ROCKS; ISOTOPIC CHARACTERISTICS; LIQUID EQUILIBRIA; CRUSTAL STRUCTURE; WORKING REFERENCE; QIANGTANG BLOCK; ZIRCON
WOS研究方向	Geochemistry & Geophysics
WOS记录号	WOS:001139890600002
来源期刊	JOURNAL OF PETROLOGY
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/282802
作者单位	Chinese Academy of Sciences; Guangzhou Institute of Geochemistry, CAS; Chinese Academy of Sciences; University of Chinese Academy of Sciences, CAS
推荐引用方式 GB/T 7714	Qi, Yue,Wang, Qiang,Wei, Gang-Jian,et al. Oligocene High-MgO Alkali Basalts in Central Tibet: Implications for Magma-Mush Mixing and Mantle Processes[J],2024,65(1).
APA	Qi, Yue.,Wang, Qiang.,Wei, Gang-Jian.,Zhang, Xiu-Zheng.,Dan, Wei.,...&Hu, Wan-Long.(2024).Oligocene High-MgO Alkali Basalts in Central Tibet: Implications for Magma-Mush Mixing and Mantle Processes.JOURNAL OF PETROLOGY,65(1).
MLA	Qi, Yue,et al."Oligocene High-MgO Alkali Basalts in Central Tibet: Implications for Magma-Mush Mixing and Mantle Processes".JOURNAL OF PETROLOGY 65.1(2024).