Geochronology,geochemistry And Tecyonic Setting Of The Granites From Huangtudaban In Solun Area,Inner Mongol

In this paper,the Huangtudaban granites from Solun area in the central-southern Great Xing'an Range area were investigated.Based on the field geological survey and the measured section,we undertook the petroraphical,chronological,geochemical and Lu-Hf isotopic analyses of the Huangtudaban granites pluton in this region,with an aim to determine their age,and further reveal their petrogenesis and tectonic settings.1.The Huangtudaban granites of Solun area are mainly composed of monzogranite,syenogranite,and granite porphyry,with minor alkali-felspar granite.The granites are characterized by high silicon,alkali-rich,magnesium-depleted,and calcium-deficient,They are metaluminous-to weakly peraluminous and belong to the high-K calc-alkaline series with A/CNK values of 0.9 to 1.39.2.The LA-ICP-MS zircon U-Pb dating shows that the monzogranite and granite porphyry in the Solon area formed in the Early Cretaceous,with ages of 125.9±3.7 Ma for and 129.9±2.3 Ma,respectively.3.The petrographic and geochemical characteristics have revealed that most of the Huangtudaban biotite granites are highly fractionationed I-type granites.The chondrite-normalized REE patterns indicate these granitoids are enriched in the light rare earth elements?LREE?relative to the heavy rare earth elements?HREE?,with weak to obvious Eu anomalies.These granites are relatively enriched in in large ion lithophile elements?LILEs;e.g.,Rb,Th,U,K?and relatively depleted in high field strength elements?HFSEs;e.g.,Nb,Ta,Ti,P?as well as Ba and S.The granites are mostly characterized by low-Sr and high-Yb,and they are belong to Nanling granites woich formed in the normal or thin crust thickness environment.The residual phase is mainly plagioclase and hornblende.4.The zircons from Huangtudaban granites have initial ¹⁷⁶Hf/¹⁷⁷Hf ratios of 0.282866to 0.282994,and relatively high?_Hf?t?values?+5.80⁺10.70?,and corresponding two-stage model age is from 804 and 502 Ma,reflecting that their primary magma was derived from partial melting of Neoproterozoic to Phanerozoic newly accreted mafic crustal material.5.The Huangtudaban granites are formed in the post-orogenic extensional environment and likely to be related to the lithospheric extension caused by the closure of the Mongo-Okhotsk Ocean.