Abstract
This study focuses on the mafic–ultramafic lavas of the Early Carboniferous outcrop in Mangxin, southwestern Yunnan, China. Picrites with 26–32 wt% MgO and a quenched texture are the most significant components of this rock association. This article divides the Mangxin picrites into two types. The mantle potential temperature (T p ) of these picrites is higher than the T p range of mid-ocean ridges and reaches that of mantle plumes. According to the geochemical characteristics, the Type-1 picrites probably formed from the melting of the mantle plume head and were contaminated by ambient depleted mantle, whereas the Type-2 picrites formed from the melting of mantle plume tails. These plume-related mafic–ultramafic rocks in Mangxin and the ocean island basalt (OIB)-carbonate rock associations in many areas of the Changning–Menglian belt provide significant evidence for the improvement of previous models of the Palaeotethyan oceanic plateau.
Highlights
Ultramafic lavas are generated by high degrees of partial melting (>10–15%) in the mantle [Herzberg and O’Hara, 2002]
We cannot ignore picritic magmas that were produced by island-arc regimes, such as the Aleutians, Kamchatka, Solomon Islands and Canada [Cameron and Nisbet, 1982, Kamenetsky et al, 1995, Milidragovic et al, 2016, Schuth et al, 2004], the preferred tectonic environment of ultramafic lavas is still related to mantle plumes based on the abnormal thermal conditions that are required by their high-Mg characteristics [Herzberg and O’Hara, 1998, Thompson et al, 2001]
The Type-1 picrites are depleted in light rare earth elements (REEs) and exhibit similar patterns to those of N-MORB; in particular, the curve of sample MX01 perfectly matches the curve of N-MORB except for the negative Ce anomaly, which could be related to the alteration of olivine [Frisby et al, 2016, Niu, 2004]
Summary
Ultramafic lavas are generated by high degrees of partial melting (>10–15%) in the mantle [Herzberg and O’Hara, 2002]. We cannot ignore picritic magmas that were produced by island-arc regimes, such as the Aleutians, Kamchatka, Solomon Islands and Canada [Cameron and Nisbet, 1982, Kamenetsky et al, 1995, Milidragovic et al, 2016, Schuth et al, 2004], the preferred tectonic environment of ultramafic lavas is still related to mantle plumes based on the abnormal thermal conditions that are required by their high-Mg characteristics [Herzberg and O’Hara, 1998, Thompson et al, 2001]. The purpose of this article is to utilize this rare geological record of Mangxin picrites, further analyse their characteristics, and discuss their petrogenesis and tectonic significance
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