关键词: 地球化学, 锆石U-Pb年代学, 后造山花岗岩, 晚中生代, 延边地区

Abstract:

The Liudong pluton is located in the southern Helong area of Yanbian area, the southwest segment of Gudonghe fault and north margin of Longgang block. It’s composed of monzonitic granite. Systematic researches on petrography and geochronology have been carried out to determine the emplacement age and tectonic environment of the pluton. The LA-ICP-MS zircon U-Pb dating yields the weighted mean age of (118.63±0.69) Ma and (118.58±0.87) Ma for N-6 and N-7 sample, respectively. The rock is weak peraluminous and belongs to the high potassium calc-alkaline series, characterized by high Si (70.30%-76.30%), high alkali (7.82%-8.52%), high aluminum (12.30%-15.50%) and low titanium (0.16%-0.29%), with A/CNK value of 1.03-1.11. Such geochemical characteristics as DI （87.99-94.89）and SI(2.39-5.31) indicate the rock experienced a highly fractionated evolving stage. The rock is of LREE enrichment (LREE/HREE=3.46-8.09) and HREE depletion ((La/Yb)_N=10.59-33.94). The Liudong pluton is characterized by the strong enrichment in large ion lithophile elements (LILE), such as Cs, Pb, Ba, K, depletion in high field-strength elements (HESE), such as Nb, Ta, Ti, and P, and middle negative Eu anomalies (δEu=0.63~0.92). Combining petrography, geochronology, rock geochemical characteristics, and regional geological material, it can be concluded that the Liudong pluton belongs to the highly fractionated high-potassium calc-alkaline I-type granite and emplaced in the transferring stage from a post-orogenic to an extensional tectonic setting.

Key words: geochemistry, zircon U-Pb geochronology, post-orogenic granite, Late Mesozoic period, Yanbian area