Genesis of high-Ni olivine phenocrysts of the Dali picrites in the Central Emeishan large igneous province

Wen-Chang Cai,Zhao-Chong Zhang,Jiang Zhu,Rong-Hao Pan,M Santosh

doi:10.1017/s0016756820001053

Abstract

AbstractThe Emeishan large igneous province (ELIP) in SW China is considered to be a typical mantle-plume-derived LIP. The picrites formed at relatively high temperatures in the ELIP, providing one of the important lines of argument for the role of mantle plume. Here we report trace-element data on olivine phenocrysts in the Dali picrites from the ELIP. The olivines are Ni-rich, and characterized by high (>1.4) 100×Mn/Fe value and low (<13) 10 000×Zn/Fe value, indicating a peridotite-dominated source. Since the olivine–melt Ni partition coefficient (KDNiol/melt) will decrease at high temperatures and pressures, the picrites derived from peridotite melting at high pressure, and that crystallized olivines at lower pressure, can generate high concentrations of Ni in olivine phenocrysts, excluding the necessity of a metasomatic pyroxenite contribution. Based on the Al-in-olivine thermometer, olivine crystallization temperature and mantle potential temperature (TP) were calculated atc. 1491°C andc. 1559°C, respectively. Our results arec. 200°C higher than that of the normal asthenospheric mantle, and are consistent with the role of a mantle thermal plume for the ELIP.

Highlights

Large igneous provinces (LIPs) are characterized by voluminous volcanic sequences (>105 km2; >105 km3) erupting over a short period of time (1–5 Ma), and their formation is generally related to mantle plumes (Richards et al 1989; Campbell & Griffins, 1990; Chung & Jahn, 1995; Campbell, 2005)
The role of high-temperature primary magmas in the Emeishan large igneous province (ELIP) remains contentious. We investigate this aspect based on petrology and mineral chemistry of olivine phenocrysts from Dali picrite in the inner zone of the ELIP, with a view to evaluate the nature of the mantle source and the conditions of melting
The picritic lavas mainly occur in the central ELIP such as those in the Dali and Binchuan districts, and these areas are considered to represent the centre of the mantle plume (Zhang et al 2006; Hanski et al 2010; Kamenetsky et al 2012; Li et al 2015; Ren et al 2017; Wu et al 2018)

Summary

Introduction

Large igneous provinces (LIPs) are characterized by voluminous volcanic sequences (>105 km2; >105 km3) erupting over a short period of time (1–5 Ma), and their formation is generally related to mantle plumes (Richards et al 1989; Campbell & Griffins, 1990; Chung & Jahn, 1995; Campbell, 2005). The association of picrites with LIPs provide one of the important lines of evidence in favour of a relatively high-temperature plume source (He et al 2003; Hanski et al 2004; Ali et al 2005; Campbell, 2005, 2007; Zhang et al 2006; Shellnutt, 2014; Santosh et al 2018; Condie & Puetz, 2019). Some studies recorded picritic rocks in the inner zone of the ELIP (Hanski et al 2010; Kamenetsky et al 2012; Yu et al 2017; Yao et al 2019), which were thought to have formed at relatively high temperatures (Xu et al 2001; Zhang et al 2004, 2006; Shellnutt & Pham, 2018).

Geological setting

Analytical methods

Mineral chemistry of olivine and Cr-spinel

Discussion

Findings

Conclusions