Title: GEOCHEMICAL CHARACTERISTICS AND GENESIS OF THE EARLY MESOZOIC VOLCANIC ROCKS IN WEST LIAONING AREA
Abstract: The Early Mesozoic volcanic rocks in West Liaoning,northeastern China consist of trachyandesite-andesite-dacite-trachydacite,which are close to calc-alkaline and high-K calc-alkaline series.The volcanic rocks have high Al (Al_2O_3≥15.16%),high Na (Na_2O/K_2O≥1.13)and SiO_2≥56.99%.The distinct characteristics of volcanic rocks are strongly fractionated REE(La/Yb≥14.89),which have low Yb and Y(Yb≤1.90×10~(-6),Y≤17.51×10~(-6)),and absence of Eu negative anomaly(0.78~0.97),indicating obvious depletion of Rb,Th,Nb,P,ZrTi elements,and relative enrich ment of Ba,K,Sr and REE,as well as low Rb/Sr ratios(≤0.15)and high Sr/Y ratios(≥35.16).The volcanic rocks belong to high Sr,low Yb and low Y rocks,which are obviously different from normal island arc calc-alkaline volcanic rocks.Study of the petrology and geochemistry showed that the Early Mesozoic volcanic rocks have similar geochemical characteristics to adakite,and are recognized as adakite-like rocks.The isotopic data of Pb,Sr and Nd from the Early Mesozoic volcanic rocks showed that the volcanic rocks were derived from the partial melting of ancient intermediate-basic metamorphic rocks in the lower crust,with great depth of volcanic source.The formation environment of volcanic rocks is of compressional setting,related with collision-super collision of North China and Siberia plate,and not related with the westward subduction of the Paleo-Pacific plate.The volcanic rocks were resulted probably from the delamination of lower crust.The recognition of the adakite-liks identification of Early Mesozoic is of important geological significance in discussion of magma derivation,crust-mantle process and geodynamics.
Publication Year: 2003
Publication Date: 2003-01-01
Language: en
Type: article
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Cited By Count: 2
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