Ce Wang

Redefinition and Formation Age of the Tanjianshan Group in Xitieshan Region, Qinghai

: The Tanjianshan Group, which was previously divided into a, b, c and d formations, has been controversial for a long time. It mainly distributes in the northern margin of Qaidam Basin and is an important early Paleozoic greenschist facies metamorphic volcanic sedimentary rock formation. Detailed field investigation and zircon LA-ICPMS U-Pb dating of the key strata suggest that the original lower part of a Formation (a-1) versus the original middle upper of d Formation (d-3 and d-4), the original upper part of a Formation (a-2) and b Formation versus the original lower part of d Formation (d-1 and d-2) of Tanjianshan Group are contemporaneous heterotopic facies volcanicclasolite deposit, respectively. The former formations formed during the middle-late Ordovician (463–458 Ma), while the latter ones formed in the late Ordovician (about 445 Ma). The original c formation of Tanjianshan Group, which formed after 430 Ma, is similar to the Maoniushan Formation of Kunlun Mountains and north Qaidam Basin. According to the rules of stratigraphic division and naming, new stratum formations of Tanjianshan Group are re-built and divided into Duancenggou (O1–2td), Zhongjiangou (O2–3tz) and Xitieshan (O3tx) formations. The original c Formation is separated from Tanjianshan Group and is renamed as the Wuminggou Formation (S3-D1w), which shows a discordant contact with underlying Tanjianshan Group and overlying Amunike Formation (D3a). The zircon U-Pb age frequency spectrogram of Tanjianshan Group indicates three prominent peaks of 430 Ma, 460 Ma and 908 Ma, which is consistent with the metamorphic and magmatic crystallization ages obtained from para- and orthogneisses in north Qaidam HP-UHP metamorphic belt, implying that strong Caledonian and Jinningian tectonic and magmatic events have ever happened in North Qaidam.

Detrital Zircon Provenance of Pliocene Yinggehai Formation in the Ledong Gas Field of the Yinggehai‐Song Hong Basin

Over the past decades, a number of hydrocarbon reservoirs have been discovered in the deepwater area of the Yinggehai-Song Hong Basin, South China Sea. The NW-oriented Yinggehai-Song Hong Basin, located on the continental shelf at water depths of 50-200 m in the northwestern South China Sea, is one of the largest Cenozoic pull-part basins in the world. The previous studies illustrated that three major source terrains were involved in the basin, including Red River (southern Yangtze Block), central Vietnam (Eastern Indochina Blcok) and Hainan Island (Cathaysia Block) (Xie, 2009). The provenance of Pliocene Yinggehai Formation in the southeast of the basin is still controversial due to there is no reliable data to identify the source regions. Recently, the studies of modern river sediments around the basin have shown that detrital zircon populations derived from the Red River are fundamentally different to those derived from central Vietnam and Hainan Island (Hoang et al., 2009; Yan et al., 2011; Wang et al., 2014). Therefore, the method of detrital zircon U-Pb dating could be used to constrain the provenance of the Yinggehai Formation. In this study, sandstone sample (LD30-1) was collected from the drill core in the Ledong gas field in order to determine the provenance of the Yinggehai Formation in this area. U-Pb geochronologic analysis of detrital zircon grains extracted from the sample using a laser ablation inductively coupled mass spectrometer yields ages ranging from Archean to Cenozoic (Fig.1D). The sample have two major age peaks at ca. 234 Ma and 430 Ma, with subordinate peaks at ca. 98 Ma, 158 Ma, 2526 Ma and a “broad” age group between 750 Ma and 1060 Ma. The Late Jurassic-Cretaceous zircon grains with age peaks at ca. 98 Ma and ca. 158 Ma are consistent with the ages of Yanshanian granites which mainly present in the Hainan Island (Wang et al., 1991; Yan et al., 2011) and could be regarded as the symbol of the Hainan (Wang et al., 2014). The Late Early Cretaceous adakitic intrusive rocks and volcanic rocks (around 100 Ma) have been discovered in the southeast of the Baisha Fault (Jia et al., 2009; Wang et al., 2011). Abundant ages of around 234 Ma are consistent with the ages of the “HercynianIndosinian Movements”. The ages well developed in the surrounding source areas and probability related to Indochina and South China collision and subsequent lateral extrusion of Indochina (Şengör et al., 1988; Lu et al., 1999; Lepvrier et al., 2008). The early Paleozoic grains related to Caledonian Orogen in South China with peak at ca. 430 Ma are widely distributed in Yangtze and Indochina Block but rare and poorly understand in Hainan Island. These zircons in this sample are younger than those in the Indochina (Fig. 1), thus, we suggest that they were derived from southern Yangtze through the Red River. The Neoproterozoic grains (750-1060 Ma) corresponding to the tectonic event termed “Jinningian Movement” are rare or absent in other source areas and can be interpreted as a signature of the Yangtze Craton. Neoproterozoic magmatism, including granites, volcanic rocks and ophiolites, occurred sporadically around the Yangtze Block (Lu, 1999; Zhou et al., 2006; Xiao et al., 2007), which probably produced by a mantle plume that marked the pre-breakup of Rodinia and subsequent migration of South China. In addition, a number of ages around 2526 Ma has been suggested to the basement sedimentary sequences of the Yangtze Craton. During the Pliocene, the majority of sediment was supplied from the northwest delivered by the “Red River delta”. The source region WANG Ce, LIANG Xinquan, FU Jiangang, ZHOU Yun, JIANG Ying and DONG Chaoge, 2015. Detrital Zircon Provenance of Pliocene Yinggehai Formation in the Ledong Gas Field of the Yinggehai-Song Hong Basin. Acta Geologica Sinica (English Edition), 87(supp.): 279-280.

Research advance in sediment provenance of the Qiongdongnan Basin

Sediment provenance study, as an important part of basin analysis, is a key for source area definition, paleogeographic reconstruction, sediment transport route identification, and tectonic evolution (Haughton et al., 1991; Morton et al., 1999; Fontanelli et al., 2009; Cawood et al., 2012). The Qiongdongnan Basin (QDNB), lies in the northwestern passive continental margin of the South China Sea, neighbouring Hainan Island on the north and Yinggehai Bain on the west, is a hydrocarbon-rich Cenozoic extensional rifted basin. The basin orientating NE-SW, with length of 250-450 km and width of 150-200 km, and can be subdivided into four units, including the Central Depression, Central Uplift, Northern Depression and Southern Uplift. The investigation of the possible source terranes and transport pathways of sediments is of crucial factor in establishing reservoir presence and hydrocarbon exploration (Tsikouras et al., 2011; Chen et al., 2015). In this article, the research progress of sedimentary provenance is reviewed in details from the conventional methods transferred to advanced analysis in the QDNB. In last decades, many methods have been used in provenance study of the QDNB, and concentrated in the Central Depression. Previous studies of provenance are mainly based on the traditional ways, including heavy minerals, seismic, mineralogical and geochemical studies (e.g. Yao et al., 2008; Cao et al., 2013; Li et al., 2015; Liu et al., 2015). These studies illustrated that several major source terranes were involved in the basin, including Hainan Island, southern Cathaysia and central Vietnam (eastern Indochina Blcok), several uplifts (e.g. Yongle, Shenhu, Xisha), and even Red River (southern Yangtze Block). Yao et al. (2008) based on the seismic data and