4:00 PM - 4:15 PM
[SIT26-09] Early Cretaceous to Paleocene magmatism in the Sikhote-Alin area and their implications for Paleo-Pacific plate subduction and continental evolution
Keywords:continental arc, paleo-pacific plate subduction, Northeast Aisa, Sikhote-Alin, continental evolution
In general, the data show a cycle of arc magmatism that started from the early Cretaceous to Paleocene in Sikhote-Alin. Zircon U-Pb geochronology of igneous rocks indicate a major population of granitoids that had ages of 135-57 Ma; a small population of volcaniclastic rocks were dated at 55-53 Ma. Three magmatic episodes with distinct geochemical characteristics were recognized: 135-120 Ma, 110-100 Ma and 100-57 Ma. The 135-120 Ma granitoids are dominated by S-type granites; zircons with inherited cores were frequently observed in this episode. The 110-100 Ma episode has mostly I-type granites, whereas the 100-57 Ma magmatism had I-type granites that show greater degrees at fractional crystallization than the other groups. Some magmatic rocks with 67-57 Ma and ~100 Ma were A2 type granites, suggesting that two periods of intraplate magmatism could had occurred within this subduction setting. The La/Yb ratio and Nd isotopic ratios of the granitoids remained relatively similar during the Cretaceous and even showed a La/Yb ratio decrease in the late Cretaceous, implying that the Andean subduction margin crustal thickening model (Haschke et al., 2002) may not applicable to the Sikhote-Alin area.