Mantle Potential Temperature Estimates and Primary Melt Compositions of the Low-Ti Emeishan Flood Basalt

J G Shellnutt,Thuy T Pham

doi:10.3389/feart.2018.00067

Abstract

The Late Permian Emeishan large igneous province (ELIP) is considered to be one of the best examples of a mantle plume derived large igneous province. One of the primary observations that favour a mantle plume regime is the presence of ultramafic volcanic rocks. The picrites suggest primary mantle melts erupted and that mantle potential temperatures (TP) of the ELIP were > 200oC above ambient mantle conditions. However, they may represent a mixture of liquid and cumulus olivine and pyroxene rather than primary liquids. Consequently, temperature estimates based on the picrite compositions may not be accurate. Here we calculate mantle potential temperature (TP) estimates and primary liquids compositions using PRIMELT3 for the low-Ti (Ti/Y < 500) Emeishan basalt as they represent definite liquid compositions. The calculated TP yield a range from ~1400oC to ~1550oC, which is consistent with variability across a mantle plume axis. The primary melt compositions of the basalts are mostly picritic. The results of this study indicate that the Emeishan basalt was produced by a high temperature regime and that a few of the ultramafic volcanic rocks may be indicative of primary liquids.

Highlights

Continental flood basalt provinces and oceanic plateaux are the remnants of atypical mantle melting in anorogenic tectonic settings (White and McKenzie, 1989, 1995; Coffin and Eldholm, 1994; Jerram and Widdowson, 2005)
The significant volume (>105 km3) of primarily mafic volcanic rocks in flood basalt provinces is thought to be related to anomalous thermal conditions associated with deep mantle upwelling (Richards et al, 1989; Griffiths and Campbell, 1990; Ernst and Buchan, 2003; Ernst et al, 2005)
The distinction between mantle plume-derived and non-mantle plume-derived may have implications for biological evolution as the five major mass extinctions (Ordovician-Silurian, Late Devonian, Permian-Triassic, Triassic-Jurassic and Cretaceous-Paleogene) are contemporaneous with flood basalt eruptions of which the three youngest are thought to contemporaneous with mantle plume derived flood basalts (Rampino and Stothers, 1988; Wignall, 2001; Courtillot and Renne, 2003; Phipps Morgan et al, 2004; Self et al, 2005; Sobolev et al, 2011; Rampino and Caldeira, 2018)

Summary

Introduction

Continental flood basalt provinces and oceanic plateaux are the remnants of atypical mantle melting in anorogenic tectonic settings (White and McKenzie, 1989, 1995; Coffin and Eldholm, 1994; Jerram and Widdowson, 2005). There are a number of geochemical, geological, and geophysical criteria used to identify mantle plume-derived continental flood basalt provinces in the geological record (Ernst and Buchan, 2003; Xu et al, 2004; Ernst et al, 2005; Campbell, 2007; Bryan and Ferrari, 2013). Ultramafic volcanic rocks are commonly found in the lower volcanic sequences of flood basalt provinces, generated by high degrees of melting under high mantle temperatures, and provide a clear record of the thermal regime (Herzberg and O’Hara, 2002; Kamenetsky et al, 2012). The plutonic units consist of ferroan alkalic granites (A-type), ore-bearing layered mafic-ultramafic intrusions and mafic dykes (Shellnutt and Zhou, 2007; Shellnutt et al, 2008; Pang et al, 2010; Li et al, 2015)

Methods

Results

Discussion

Conclusion