Geochemistry, zircon geochronology and Lu-Hf isotopic characteristics of the Sudi monzogranite in the Western Sichuan: Implications for tectonic setting of the Songpan-Ganze terrane

This paper is the result of geological survey engineering.

Objective It is of great significance to find out the geochemical and tectonic evolution characteristics of granite in the southeast of the Songpan-Ganze terrane for searching for rare metal minerals in this area.

Methods we have carried out field geological survey and conducted whole-rock geochemistry and zircons LA-(MC)-ICP-MS U-Pb and Lu-Hf isotope analyses on the monzogranite of the Sudi pluton in the southeast part of the Songpan-Ganze terrane.

Results The results show that the samples were medium-high potassium, sodium rich and calcium deficiency. The values of AR were 1.44-1.83 and values of A/CNK were 0.98-1.16, which were medium-high potassium calcareous alkaline series. The rocks show relatively enriched large ion lithophile element (LILE), negative high field-strength elements (HFSE), and high REE content (the total amount of REE = 157.16×10^-6-187.88×10^-6) with the LREE enrichement (LREE/HREE = 6.26-9.46) and weak negative Eu anomaly europium anomaly (δEu = 0.62-0.74). The results of zircon U-Pb dating were (221.1±1.5) Ma (MSWD=0.30, n=22) and (214.5±1.5) Ma (MSWD=0.22, n=22), indicating that the primitive magma of the Sudi pluton crystallized in the middle of the Late Triassic. Its zircon Lu-Hf isotope ε_Hf(t) and T_DM2 are -6.56--4.12 and 1.67-1.51 Ga.

Conclusions According to the comprehensive analysis, we believe that the monzogranite in Sudi pluton is a typical I-type granite and it may be formed by the upwelling and emplacement of the initial magma from the lower crust in the middle of Late Triassic in the process of orogenic collision to post-collisional extensional tectonic setting. The southeastern margin of Songpan-Ganze terrane was under post-collisional orogenic environment in Late Triassic.