Abstract:

The granitoid rocks in Taili area, western Liaoning Province, are mainly composed of granitic gneiss, porphyritic granitic gneiss and biotite adamellite, and were once regarded as the Neoarchean granite. According to the occurrence sequence of various types of granitic rocks, the authors consider that the massive/gneissic biotite adamellite, located in south and north sides of the study region, intruded into granitic gneiss and porphyritic granitic gneiss as the apophysis or dike. Geochemical characteristics indicate that the biotite adamellite belongs to metaluminous-weakly peraluminous I-type granite, and shows volcanic arc granite characteristics. Zircons in the biotite adamellite are of complex origin. A large number of inherited zircons coexist with neonatal zircons. Neonatal zircons with obvious characteristics of magmatic crystallization are characterized by oscillating growth zonation and high Th/U values (0.15-1.70). Weighted average ages of two samples by LA-ICP-MS zircon U-Pb are (153.7±2.0) Ma and (153.7±4.7) Ma, respectively. The results show that the biotite adamellite belongs to the Late Jurassic granitoid plutons with source rock as meso-basic volcanic rocks of the lower crust. The origin of the biotite adamellite is tectonically linked to the subduction of the paleo-Pacific plate to the Asian continent.

Key words: Taili area of western Liaoning Province, biotite adamellite, zircon U-Pb geochronology, geochemistry, Late Jurassic