Petrogenesis and geochemical evidence from early Jurassic intrusive rocks and their implications for subduction of the Paleo-Pacific Plate in the Yanbian area, Northeast China

Subduction of the Paleo-Pacific Plate plays a key role in the Early Jurassic magmatism evolution in the Yanbian area, Northeast China. In this paper, zircon U-Pb ages, whole-rock geochemical, and Sr-Nd-Hf isotopic compositions are presented. The Early Jurassic gabbros, diorite enclaves, granodiorites, and granites ages range from 183 to 189 Ma. They are characterized by enrichment in large-ion lithophile elements and depletion in high-field strength elements. The gabbros are classified as low-and medium-K tholeiitic, granodiorites and granites are high-K calc-alkaline I-type, and diorite enclaves are calc-alkaline transitional series. The gabbros have zircon [epsilon] Hf(t) values of 6.81-9.89, whole-rock [.sup.87]Sr/[.sup.86][Sr.sub.(i)] = 0.7043-0.7044, and [epsilon] Nd(t) from 2.72 to 2.80. The diorite enclaves have zircons with [epsilon] Hf(t) values of 8.26-12.80, whole-rock [.sup.87]Sr/[.sup.86][Sr.sub.(i)] = 0.7051, and [epsilon] Nd(t) from 0.96 to 1.09. The granodiorites and granites have zircon [epsilon] Hf(t) values of 7.59-12.87, whole-rock [.sup.87]Sr/[.sup.86][Sr.sub.(i)] = 0.7042-0.7066, and [epsilon]Nd(t) from 2.33 to 2.61. These data indicate that gabbroic magmas were derived from partial melting of a depleted mantle wedge metasomatized by subduction-related fluids. The basaltic magma underplated and heated the juvenile crust, whereas the granodiorites and granites might be the product of fractional crystallization of a mixture of basaltic and felsic magmas or derived from partial melting of the juvenile lower crust. Our data constrain the petrogenesis of these Early Jurassic intrusive rocks which are attributed to subduction of the Paleo-Pacific Plate beneath Eurasia continent in northeastern China. Key words: Early Jurassic, intrusive rocks, petrogenesis, Paleo-Pacific Plate subduction, Sr-Nd-Hf isotope, Yanbian area
1. Introduction Understanding the generation and emplacement of granitic magmas is necessary to deduce the internal structure, formation, and evolution of continental crust (Pearce 1983; Barbarin 1999; Condie and Kroner [...]