SHRIMP U-Pb geochronology of the detrital zircons from the Longshoushan Group and its tectonic significance

Abstract

Sixty-two geologically meaningful U-Pb dates were obtained by using SHRIMP technique for the detrital zircons in three metasedimentary rocks from stratigraphically uppermost parts of the Longshoushan Group in the present study. Eighty percents of these dates range from 1.7 Ga to 2.2 Ga with a peak at 1.8-2.0 Ga and twenty percents from 2.3 Ga to 2.7 Ga. The youngest detrital zircon is dated at 1724±19 Ma which is interpreted as the maximum depositional age of the metasedimentary rocks. Therefore, the age for the diagenesis and lithification of the original sedimentary rocks of the Longshoushan Group before the metamorphism must be younger than 1724±19 Ma. Comparison of the age histograms of these detrital zircons with the ages of the igneous rocks on the surrounding older massifs suggests that the sediments of the Longshoushan Group were most likely derived from the Alaxa Block and Tarim Craton. This implies that the affinity between Alaxa Block and Tarim Craton was strong and that they might have been a unified craton during middle-early Proterozoic time.

An Early Permian (ca. 280Ma) silicic igneous province in the Alxa Block, NW China: A magmatic flare-up triggered by a mantle-plume?

“…However, the petrogenesis and the tectonic setting of these granitoids, and their relationship to the broadly contemporaneous Tarim LIP are unclear. In this contribution, we present in situ zircon U-Pb age and Hf-O isotope data and whole-rock element and Nd-Sr isotope data for two newly .8 Ga (Gong et al, 2011;Tung et al, 2007). The Mesoproterozoic medium-to low-metamorphic grade Alxa Group (Geng et al, 2007) was unconformably covered by Neoproterozoic un-metamorphosed to very low-grade metamorphosed sedimentary sequences (NMBGMR (Nei Mongol Bureau of Geology and Mineral Resources), 1991; Chen et al, 2004).…”

From Subduction to Collision in the Northern Tibetan Plateau: Evidence from the Early Silurian Clastic Rocks, Northwestern China

“…In e and f, ARC p island-arc basalt; CFB p continental flood basalt; LIP p large igneous province; MORB p mid-ocean ridge basalt; OIB p ocean-island basalt; SSZ p suprasubduction zone. (BGMRQP 1991;Xia et al 1995Xia et al , 2003Zhang et al 1997;Mao et al 1999Mao et al , 2000Wang et al 2005a;Chen 2007;Yu et al 2010), 1.1-0.8 Ga (2) for the Central Qilian Block (Guo et al 2000;Wan et al 2000Wan et al , 2001Gehrels et al 2003b;Tung et al 2007a;Wang et al 2007;Xu et al 2007;Yong et al 2008a;Xue et al 2009), and 2.1-1.7 and 2.6-2.4 Ga (3 and 4, respectively) for the North China Craton (Krö ner et al 1988;Wan et al 2003;Darby and Gehrels 2006;Tung et al 2007b;Li et al 2008). Taylor and McLennan (1985).…”

“…Potential ophiolitic source rocks within the North Qilian Belt are represented by the Jiugequan, Dachadaban, and Yushigou-Dongcaohe ophiolites, which were emplaced during the Cambrian to Early-Middle Ordovician within/between the back (Xu et al 2010); e, Central Qilian Block granitic intrusions (Guo et al 2000;Wan et al 2000Wan et al , 2001Gehrels et al 2003b;Tung et al 2007a;Wang et al 2007;Xu et al 2007;Yong et al 2008a;Xue et al 2009); f, metasedimentary basement of the Central Qilian Block (Gehrels et al 2003a;Tung et al 2007a;Xu et al 2007); g, detrital zircons from the basement of the North China Craton (Krö ner et al 1988;Wan et al 2003;Darby and Gehrels 2006;Tung et al 2007b;Li et al 2008 (Xia et al 2003) and the high-Crcontent rocks of the Dachadaban ophiolite (Chen et al 1995;Zhang et al 1998b). The average value of Shuiquan samples, representing the continent provenances ), was calculated with Dachadaban ophioliteprovenance average value to generate two-end-member mixing lines, accounting for the high Cr/Th and Cr/V ratios of some samples from the Lujiaogou Formation.…”

Paleoproterozoic Multiple Tectonothermal Events in the Longshoushan Area, Western North China Craton and Their Geological Implication: Evidence from Geochemistry, Zircon U–Pb Geochronology and Hf Isotopes

“…The main outcropping stratum of the area are the LS Group, the late Mesoproterozoic Dunzigou Group [29] and the Neoproterozoic-Cambrian Hanmushan Group [30,31]. As the basement rock, the LS Group is exposed in a long narrow belt about 500 km long and 30 km wide bounded by [38][39][40] • N latitude and 99-103 • E longitude in the LS area [32]. It is in unconformable contact with the overlying strata of the Dunzigou Group.…”

“…It is in unconformable contact with the overlying strata of the Dunzigou Group. The LS Group underwent deformation, regional metamorphism and migmatization [32]. It mainly consists of schlieren and homogenic migmatites, marble, biotite-plagioclase gneiss, granulites, quartz schist, amphibolite and pyroclastic rock.…”