Response to the Magmatic Process of Mantle Plume with Basalt in the Shawan Area
A large area of Permian basalt is exposed near Shawan District,Leshan City,which is an important part of Emeishan large igneous province.Petrological and geochemical analysis show that the basalts are mainly dense massive pyroxene basalts,oblique porphyry basalts and trachyte basalts.The major elements indicate that basalts belong to high-titanium tholeiite series.The normalized rare earth element pattern of chondrites for basalts in the Shawan area exhibits right-dipping patterns with LREE enrichment and a high degree of fractionation of light and heavy rare earth elements.The normalized trace element distribution map of the primordial mantle shows that they are enriched in large ion lithophile elements(LILE)such as Th、U etc,but depleted in trace elements related to fluids(Sr and P)with negative Eu anomalies.It is similar to the ocean island basalts(OIB)and high-titanium basalts that erupted in the late period near Binchuan,Yunnan,suggesting that the basalts around Emeishan were formed in an intraplate rift environment induced by a mantle plume.The magma originated from the low-degree partial melting of the garnet peridotite and the separation and crystallization of plagioclase,and weak crustal contamination occurred during the ascent.The geochemical comparison between the basalts in the intermediate zone and the basalts in the inner zone of the large igneous province reveals that the basalts in Shawan area are the product of late magmatism in the large igneous province,and the main body is characterized by the edge of the mantle plume itself.
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