Thermal event records in SE China coastal areas: Constraints from monazite ages of beach sands from two sides of the Taiwan strait

摘要

CHIME ages of > 460 detrital monazites from beach sands from SE China (Chinmen Island) and W Taiwan were determined in order to deduce the major tectonothermal events affecting the coastal areas of SE China. Additional 360 monazites from estuarine sediments of the Minjiang River (eastern China), metamorphic rocks from Chinmen Island and sedimentary rocks from W Taiwan were also dated. Ages of the Chinmen beach monazites (245-80Ma) reveal that they are derived from adjacent gneisses and mixed with sediment from the Jiulongjiang River (SE China). Some large, euhedral monazites contain older cores (similar to 220Ma) and younger rims (137-124Ma), demonstrating that overgrowth on inherited Indosinian grains occurred at the time of gneiss formation (137Ma). Monazites of W Taiwan fall into two age groups, one in the Paleoproterozoic (1900-1650Ma) and the other spanning the Phanerozoic (530-120Ma). Based on similar ages of Phanerozoic monazites from the Minjiang River and W Taiwan, monazites of the latter group are inferred to be derived mainly from this river, hence the Paleoproterozoic monazites are most probably derived from Cathaysia basement exposed in the drainage basin of the Wuyishan (NW Fujian). Along with monazite ages of the two-mica schist, sediments from the uplifted Changle-Nanao shear zone (CNSZ) constitute only a minor component of deposits in W Taiwan. The age frequency distribution of Phanerozoic monazites from W Taiwan, which shows peaks at 450-430, 360-350, similar to 275 and similar to 245Ma suggests the existence of Caledonian, Hercynian and Indosinian crust beneath the immense Yanshanian cover of the SE China coastal area. (c) 2006 Elsevier B.V. All rights reserved.