Indexed on: 22 Oct '16Published on: 21 Oct '16Published in: Sedimentary Geology
The South China Block was subject to widespread tectonic and magmatic events during the middle Ordovician to earliest Devonian which are collectively called the Wuyi-Yunkai orogeny. Two different hypotheses were formulated about the origin of the orogeny: collisional orogenesis and intracontinental orogenesis. Ages of 215 detrital zircons were obtained from quartz sandstones in the Lower Devonian Danlin Formation exposed in Dushan County, south Guizhou Province. The results show that the detrital zircons came from multiple source areas but with little indication of the Wuyi-Yunkai orogeny. The detrital zircons of early Paleozoic age account only for 1.9% of all samples. These zircons range from 476 to 402 Ma and originated from the early Paleozoic granite situated east of Dushan County. The mean 206Pb/238U age of the two youngest detrital zircons was 404 Ma, which constrains the maximum depositional age of the Danlin Formation. The detrital zircons are mostly within Neoproterozoic age (59.5%) and in the range 997 to 557 Ma. The zircon age pattern, morphology, trace element characteristics combined with paleogeographic reconstruction interpret that these detrital zircons were supplied from igneous rocks in the Neoproterozoic Sibao and Danzhou Groups within the west Jiangnan Orogen to the east of the study area. Mesoproterozoic zircons made up 20.9% of the grains and range from 1569 to 1055 Ma; the ages of most of these zircons coincide with those of zircons indicating the Grenvillian orogeny (1300–1000 Ma) in the Cathaysia Plate. The detrital zircon age data reveal that the study area was located in an intracontinental tectonic setting, both before and after the Wuyi-Yunkai orogeny. Therefore, the Cathaysia Plate was not separated from the Yangtze Plate by an ocean and the study area received sediments primarily from the Cathaysia Plate located to the southeast since the middle Ordovician. By the early Devonian, the sediments were supplied by the west Jiangnan Orogen. Although a source change was caused by Wuyi-Yunkai orogeny, our data imply that this orogeny represented an intracontinental event rather than an orogenesis involving subduction-collision and joining of the Yangtze and Cathaysia Plates during the early Paleozoic.