Primary magmas and mantle sources of Emeishan basalts constrained from major element, trace element and Pb isotope compositions of olivine-hosted melt inclusions

Abstract

Olivine-hosted melt inclusions within lava retain information regarding the lava"s primary magma compositions and mantle sources. Thus, they can be used to infer the nature of the mantle sources of large igneous provinces, which is still not well known and of the subject of debate. We have analyzed the chemical compositions and Pb isotopic ratios of olivine-hosted melt inclusions in the Dali picrites, Emeishan Large Igneous Province (LIP), SW China. These are the first in-situ Pb isotope data measured for melt inclusions found in the Emeishan picrites and allow new constraints to be placed on the source lithology of the Emeishan LIP. The melt inclusions show chemical compositional variations, spanning low-, intermediate-and high-Ti compositions, while their host whole rocks are restricted to the intermediate-Ti compositions. Together with the relatively constant Pb isotope ratios of the melt inclusions, the compositional variations suggest that the low-, intermediate-and high-Ti melts were derived from compositionally similar sources. The geochemical characteristics of melt inclusions, their host olivines, and whole-rocks from the Emeishan LIP indicate that Ca, Al, Mn, Yb, and Lu behave compatibly, and Ti, Rb, Sr, Zr, and Nb behave incompatibly during partial melting, requiring a pyroxenite source for the Emeishin LIP. The wide range of Ti contents in the melt inclusions and whole-rocks of the Emeishan basalts reflects different degrees of partial melting in the pyroxenite source at different depths in the melting column. The Pb isotope compositions of the melt inclusions and the OIB-like trace element compositions of the Emeishan basalts imply that mixing of a recycled ancient oceanic crust (EM1-like) component with a peridotite component from the lower mantle (FOZO-like component) could have underwent solid-state reaction, producing a secondary pyroxenite source that was subsequently partially melted to form the basalts. This new model of pyroxenite melting could explain the geochemical variations among the low-, intermediate-and high-Ti basalts for the Emeishan LIP and challenges the prevailing belief that the source of the Emeishan basalts is peridotite- .

Melt Diversity and Magmatic Evolution in the Dali Picrites, Emeishan Large Igneous Province

“…Picritic rocks predominately occur in the inner zone of the Emeishan LIP (Hanski et al, ; Li et al, , ; Ren et al, ; Song et al, ; Tao et al, ; M. Wang et al, ; Zhang et al, ) and mainly occur as stocks, dikes, or lava flows. In addition, some picritic flows crop out in the Song Da distinct (Figure , Anh et al, ; Hanski et al, ; Li et al, ; Wang et al, ).…”

Early Cretaceous high-Ti and low-Ti mafic magmatism in Southeastern Tibet: Insights into magmatic evolution of the Comei Large Igneous Province

“…1996; Peate 1992; Peate and Hawkesworth, 1996;Xu et al, 2001Xu et al, & 2004Xiao et al, 2004;Ewart et al, 2004;Ren et al, 2017). These characteristics have led to vastly different petrogenetic models that attempt to explain the relationship between the high-Ti and low-Ti series, which can be summarized as: (1) different source regions, including complex interactions between plume, lithosphere, and asthenosphere (Walker et al, 1990;Hergt et al, 1991;Lightfoot et al, 1993;Gibson et al, 1995Gibson et al, & 1996; (2) different degrees of partial melting of a mantle plume source (Fodor et al, 1987;Xu et al, 2001Xu et al, & 2004Lai et al, 2012;Ren et al, 2017); (3) different degrees of crustal contamination (Shellnutt et al, 2011); or (4) the collective effects of all of the above factors (Petrini et al, 1987;Xiao et al, 2004;Ewart et al, 2004;Wang et al, 2007).…”

“…These characteristics have led to vastly different petrogenetic models that attempt to explain the relationship between the high-Ti and low-Ti series, which can be summarized as: (1) different source regions, including complex interactions between plume, lithosphere, and asthenosphere (Walker et al, 1990;Hergt et al, 1991;Lightfoot et al, 1993;Gibson et al, 1995Gibson et al, & 1996; (2) different degrees of partial melting of a mantle plume source (Fodor et al, 1987;Xu et al, 2001Xu et al, & 2004Lai et al, 2012;Ren et al, 2017); (3) different degrees of crustal contamination (Shellnutt et al, 2011); or (4) the collective effects of all of the above factors (Petrini et al, 1987;Xiao et al, 2004;Ewart et al, 2004;Wang et al, 2007). In much of the cited work, TiO 2 content and Ti/Y ratio have been viewed as critical criteria for classifying mafic rocks and as indicators of their source characteristics (Cox et a., 1967(Cox et a., & 1988Peate et al, 1992;Gibson et al, 1995Gibson et al, & 1996Xu et al, 2001Xu et al, & 2004.…”

“…TiO 2 content and Ti/Y ratio have long been viewed as important parameters to reflect the geochemical characteristics of mafic rocks (Peate et al, 1992;Xu et al, 2001Xu et al, & 2004Ren et al, 2017). In terms of whole-rock TiO 2 and MgO contents, the Dala diabase can be subdivided into two series: a high-Mg/low-Ti series and a low-Mg/high-Ti series (Fig.…”

“…A number of flood basalt provinces (e.g., the Paraná, the Karoo and the Emeishan basalts) host contemporaneous high-Ti and low-Ti basaltic magmas (Cox et al, 1967(Cox et al, & 1988Gibson et al, 1995Gibson et al, & 1996Xu et al, 2001Xu et al, & 2004Ren et al, 2017). The Dala diabase pluton also hosts high-Ti and low-Ti series rocks.…”