U-Pb ages of detrital zircons from deep-water Well LS33A at Lingnan Low Uplift of the Qiongdongnan Basin and their geological significances

Abstract

U-Pb ages of detrital zircons from Well LS33A at Lingnan Low Uplift of the Qiongdongnan Basin (QDNB) are measured with LA-ICP-MS technique. Th/U ratios of detrital zircons mostly with oscillatory zoning are higher than 0.1, indicating a magmatic origin. Zircon U-Pb data of the Yacheng Formation yield an age range from 95.8 to 387.9 Ma, with two major clusters of 95-106 Ma and 214-237 Ma, representing Yanshanian and Indosinian, respectively. U-Pb age range of the Yinggehai-Ledong Formations varies widely from 87 to 2 490 Ma, exhibiting four remarkable age peaks of 88 Ma, 146 Ma, 208 Ma and 386 Ma on age spectrum. The variation in zircon age assemblage reveals that in provenance. Based on synthesizing seismic data, heavy mineral assemblages, geochemical data and zircon U-Pb ages, the main conclusions are as follows. There existed frequent fault-block activities in study area during the Yacheng deposition of Early Oligocene, which controlled the wedge-shaped disorderly fillings, and sediments chiefly came from the southern exposed tectonic uplift area of the QDNB. As it entered post-rifting stage and transgression continued, the provenance from the Pliocene to the Quaternary expanded to far- and multi-source realm, with Hainan Island, Red River and Indo-China Peninsula being source areas. The Proterozoic metamorphic basement, which supplied main material sources for the Yacheng Formation of Well LS33A, existed in the southern tectonic uplift area. Two large-scale magmatic activities, occurring in the southern uplift area in the Indosinian (214-237 Ma) and Yanshanian (95-106 Ma), not only destroyed the original metamorphic basement, but also provided an acidic magmatic provenance to study area.