Late Permian High-Ti Basalt in Western Guangxi, SW China and Its Link With the Emeishan Large Igneous Province: Geochronological and Geochemical Perspectives

Jian Jiang,Xingjun Shi,Changming Li,Tianguo Wang,Chenguang Zhang,Renyu Zeng

doi:10.3389/feart.2021.729955

Abstract

High-Ti (Ti/Y) flood basalts are widely distributed in the Late Permian Emeishan large igneous province (LIP), SW China, and their spatial distribution and genetic mechanism are important to reveal the role of plume-lithosphere interactions in the LIP origin. Western Guangxi is located on the eastern edge of Emeishan LIP. To explore the genesis of the high-Ti basalt in western Guangxi and any genetic link with the Emeishan LIP, we performed whole-rock geochemical and Sr-Nd isotope and zircon U-Pb-Hf isotope analyses on the Longlin basalts from western Guangxi. The results indicate that the Longlin basalt from Tongdeng area has relatively high SiO2 but low MgO and TFe2O3 contents. The rocks have zircon εHf(t) = −0.42 to 6.41, whole-rock (87Sr/86Sr)i = 0.707167–0.707345, and εNd(t) = −2.5 to −2.14. In contrast, the Longlin basalt from Zhoudong area has relatively low SiO2 but high MgO and TFe2O3 contents. The rocks have whole-rock (87Sr/86Sr)i = 0.706181–0.706191 and εNd(t) = −0.57 to 0.69. Four Longlin basalt samples display LREE enrichments and HREE depletions, and with indistinct δEu and δCe anomalies. LA-ICP-MS zircon U-Pb dating on three Longlin basalt samples (from different localities) yielded consistent weighted average age of 257.9 ± 2.6 Ma (MSWD = 0.55), 259.5 ± 0.75 Ma (MSWD = 3.0), and 256.7 ± 2.0 Ma (MSWD = 0.68), indicating a Late Permian emplacement. Considering the similar age and geochemical features between the Longlin basalt and Emeishan flood basalts, we interpret that the former is spatially, and temporally associated with the Emeishan LIP. Geochemical features show that the high-Ti basalts in western Guangxi resemble Deccan-type continental flood basalts (CFBs), which were derived by decompression melting of the mantle plume. Combined with previous geochemical studies, we suggest that the difference in Ti content and Ti/Y ratio in CFBs are related to the depth and melting degree of mantle source, in which high-Ti features may have been linked to low degree of partial melting in the deep mantle.

Highlights

Large igneous provinces (LIPs) are formed by voluminous mafic rocks emplaced in a short period of time, and are generally considered to be mantle plume-related but not directly related to normal ocean spreading and subduction (Coffin and Eldholm, 1994; Courtillot and Renne, 2003; Acocella, 2021), recent works suggested that interaction between mantle plumes and subducting/subducted slabs may be plausible (Xu et al, 2019; Xu et al, 2021)
1) Longlin basalts from different places in western Guangxi yielded similar Late Permian zircon U-Pb ages, i.e., 257.9 ± 2.6 Ma (Tongdeng), 259.5 ± 0.75 Ma (Xiaoren), and 256.7 ± 2.0 Ma (Zhoudong), coeval with the Emeishan flood basalt emplacement
2) Element and Sr-Nd-Hf isotope geochemistry show that the Longlin basalts were formed from low-degree partial melting in the spinel–garnet transition zone at depths of 75–85 km

Summary

Introduction

Large igneous provinces (LIPs) are formed by voluminous mafic (and minor felsic) rocks emplaced in a short period of time, and are generally considered to be mantle plume-related but not directly related to normal ocean spreading and subduction (Coffin and Eldholm, 1994; Courtillot and Renne, 2003; Acocella, 2021), recent works suggested that interaction between mantle plumes and subducting/subducted slabs may be plausible (Xu et al, 2019; Xu et al, 2021). Petrogenesis of LIPs, such as the role of plume-lithosphere interaction in the origin of the continental flood basalts (CFB), and the origin of the high-Ti (Ti/ Y), and low Ti mafic magmatism, has attracted much research attention (Fodor, 1987; Peate et al, 1999; Lai et al, 2012). The Emeishan LIP is located in the western margin of the Yangtze craton and the eastern margin of the Tibetan plateau, SW China, and likely related to Late Permian mantle plume processes (Chung and Jahn, 1995; Li et al, 2008; Zhang, 2009). Complex tectonic events in the Sanjiang fold belt had strongly deformed the original distribution of the Emeishan LIP rock units (Xu et al, 2013).

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