Characteristics of granodiorite in the Litang area of Sichuan and its volcanic arc magmatism accretionary wedge

This paper is the result of geological survey engineering.

Objective By finding out the age and geochemical characteristics of granodiorites in Lazhagashan area, this paper discusses the age, genesis and tectonic background of granodiorites, so as to provide a basis for the study of subduction-accretion processes in the Ganzi-Litang Ocean Basin.

Methods Our project carried out systematically study the petrography, LA-MC-ICP-MS zircon U-Pb chronology and rock geochemistry from the granodiorites in subduction accretion complex of Ganzi-Litang ophiolite melange belt.

Results The granodiorites contain a large amount of femic mineral such as amphibole, biotite, and a large number of dioritic enclaves and surrounding rock xenoliths. The intrusive rocks were formed in the Late Triassic ((207.2±1.5)Ma), and are I-type calc-alkaline quasi-aluminous granites with enriched in large-ion-lithophile elements (LILE), such as Rb, Ba, K, Th and U, depleted in high-field-strength elements (HFSE), such as Nb, Ta, P, Zr and Ti. It shows a right-leaning pattern of enrichment of light rare earth and depletion of heavy rare earth. It is a typical volcanic arc granite showing strong enrichment of LREE and depletion of HREE, with negative Eu anomaly.

Conclusions Combined with the regional geological data and the research results of this paper, it is considered that the Lazhagashan granodiorite in Litang area is closely related to the westward subduction of the Ganzi-Litang Ocean resulted in the expansion of the accretionary complex in the eastern margin of the Zhongza block, which is the product of melting accretionary complex into different types of magma mixing.