Geochemical characteristics and genetic discussion of Middle Jurassic granodiorite in the Erdaohe area,Jilin Province
The Middle Jurassic granodiorite in the Erdaohe area includes medium-coarse-grained granodiorite,medium-fine-grained granodiorite,and tonalite.The Middle Jurassic granodiorite is peraluminous calc-alkaline rock,characterized by a relative-ly high degree of magmatic fractional crystallization and has the features of"I"type granite.Most of the trace elements show good correlations,with significant enrichments of Rb,Th,U,La,and Zr,and depletions of Nb,P,and Ti.It indicates that the rock mass may be new crust accreted at the continental margin.The chondrite-normalized rare-earth element distribution curve belongs to the light-rare-earth-element-enriched type,with relatively flat heavy-rare-earth elements,representing the characteristics of crustal remelting;the distribution curve is right-leaning,with obvious fractionation and a relatively high degree of crystallization differentiation.It is Europium-depleted type,but the total amount of rare-earth elements is relatively close.The tectonic environ-ment of the Middle Jurassic granodiorite should be granite at the subduction-related active plate margin,belonging to the magmatic emplacement product of the pre-plate-collision-mantle-derived differentiation type,and is volcanic-arc granite.
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