Is the Ordos Block Archean or Paleoproterozoic in age? Implications for the Precambrian evolution of the North China Craton

Abstract

The Ordos Block is a large but poorly exposed crustal segment in the western part of the North China Craton. Little is known about its Precambrian basement rocks and their evolution because of an extensive cover by younger sedimentary rocks. We report SHRIMP zircon ages and Hf-in-zircon isotopic compositions for five samples recovered from drill holes that penetrated into the Ordos basement. Based on these data, two age groups of rocks can be distinguished: an early Paleoproterozoic group that is represented by one sample from the northern margin of the Ordos Block and a late (or middle-late) Paleoproterozoic group consisting of the remaining four samples. The early Paleoproterozoic sample contains zircon cores and metamorphic rims with ages of >2.4 Ga and >2.28 Ga, respectively. The cores have Hf (t) values of ؊8.8 to 6.2 and Hf crustal model ages of 2606 to 3221 Ma. The remaining rocks of late (or middle-late) Paleoproterozoic age contain zircons that may also show a core-rim structure, but with the cores having ages of ϳ2.08 Ga and the metamorphic rims recording ages of ϳ1.9 Ga. The zircon cores have Hf (t) values of ؊9.1 to 10.1, and Hf crustal model ages of 2039 to 3068 Ma. Combined with data from earlier studies, we draw the conclusion that late Paleoproterozoic metasedimentary rocks are widespread in the Ordos basement. There is no evidence from our samples of an Archean component, and this calls into question the prevailing view that the Ordos basement is an Archean cratonic block. The fact that the Ordos basement was involved in a widespread late Paleoproterozoic tectono-thermal event indicates that most current models for the tectonic evolution of the western portion of the North China Craton need to be revised.

Linking the Alxa Terrane to the eastern Gondwana during the Early Paleozoic: Constraints from detrital zircon U–Pb ages and Cambrian sedimentary records

“…Although many ages similar to the Neoarchean age peak (2517 Ma) of the Xiangshan Group (Fig. 9I) were reported from the Alxa Terrane and the North China Terrane (Myrow et al, 2010;Hughes et al, 2011); E, the Collie and Perth Basins, Western Australia (Cawood and Nemchin, 2000;Veevers et al, 2005); F, Modern sands of Yangtze River (Rino et al, 2008;Safonova et al, 2010); G, the western Ordos, North China (Darby and Gehrels, 2006;Hu et al, 2012;Wan et al, 2013); H, South China ; I, this study; and J, Modern sands of Australia (Cawood et al, 2003;Condie et al, 2009). All data have concordances between 90% and 110%.…”

Upper Permian Junggar and Upper Triassic Ordos lacustrine source rocks in Northwest and Central China: Organic geochemistry, petroleum potential and predicted organofacies

“…By the end of 2012, proved reserves of 21.47 × 10 8 t of oil and 3.27 × 10 12 m 3 of natural gas have been estimated by the Changqing Oilfield Company of PetroChina (COCP), ranking the Ordos Basin among the biggest oil and gas field in the Central China (Yang et al 2012;Zou 2013). The basin has formed as an intraplate depression on the North China Craton during Mesozoic to Cenozoic, and overlied the Paleoproterozoic crystalline basement (Liu et al 2008;Wan et al 2013). It is ringed by a series of synchronous, poly-phase orogens, i.e.…”

“…It is ringed by a series of synchronous, poly-phase orogens, i.e. the Yishan Orogen to the north, Qinling Orogen to the south, Lvliang Orogen to the east and LiupanHelan Orogens to the west (Wan et al 2013;Yang et al 2005), and can be subdivided into six regional structural units (Fig. 3b).…”

Paleoproterozoic S-type granites in the Helanshan Complex, Khondalite Belt, North China Craton: Implications for rapid sediment recycling during slab break-off

“…The Paleoproterozoic Khondalite Belt is probably wider than presently mapped, given that Late Paleoproterozoic sedimentary rocks and metamorphism have been revealed in the Ordos Block from drill core samples in recent years (Hu et al, 2012;Wan et al, 2013b). Irrespective of the width that is ultimately defined, however, the Khondalite Belt must represent a suture zone.…”