Paleoproterozoic tectonic evolution of the Trans-North China Orogen: Toward a comprehensive model

Abstract

In this contribution we present a reconstruction of the overall lithotectonic architecture, from inner zones to external ones, of the Paleoproterozoic Trans-North China Orogen, within the North China Craton. Moreover, forward thermobarometrical modelling on a kyanite-bearing gneiss yields a reliable prograde P-T-t-D path. In addition, 40 Ar/ 39 Ar dating on rocks from distinct litho-tectonic units helps us to distinguish several tectono-metamorphic events during the orogenic development. Considering these results, we propose a geodynamic model involving three cratonic blocks, namely the Western, Fuping and Eastern Blocks, separated by two oceans, the Lüliang and Taihang Oceans. The opening of oceanic basins occurred around 2.2-2.3 Ga. After the westward subductions of oceanic lithosphere, the Trans-North China Orogen was built up through a polyphase tectonic evolution within the period 1900-1800 Ma. The first event (D1) corresponded to the emplacement of lower and upper nappes herein called the Orthogneiss-and-Volcanite Unit (OVU) and the Low-Grade-and-Mafic Unit (LGMU), respectively. The syn-metamorphic D1 deformation (1880 ± 10 Ma) is characterized by a NW-SE stretching and mineral lineation with a top-to-the SE sense of shear. During ongoing compression of the thickening orogenic crust, a second deformation event D2 (1850 ± 10 Ma) was responsible for (1) syn-anatectic lateral flow and exhumation of the orogenic root and (2) folding of the middle and upper parts of the orogenic wedge that consequently acquired a fan-type geometry. The late D3 (1830 ± 10 Ma) and D4 (1810 ± 10 Ma) events are related to late-orogenic normal and strike-slip shearing, respectively. In our present state of knowledge, the Paleoproterozoic Trans-North China Orogen might be regarded as the assemblage of two continent-continent collisional belts, both of which are characterized by nappe stacking accommodated by top-to-the E/SE ductile shearing. Continental subduction, crustal thickening, partial melting of overthickened crust, exhumation of HP rocks and deposition of syn-orogenic detrital basins are typical features of modern collisional-type orogens.

Reinterpretation of metamorphic age of the Hengshan Complex, North China Craton

“…1.91 Ga for garnet amphibolite [47], two groups of monazite Th-U-Pb age of 1.92-1.93 Ga and 1.82-1.85 Ga [18,47] for metapelites in the Wutai Group, and also two groups of monazite age of 1.92-1.94 Ga from grain cores and 1.85-1.88 Ga or younger from grain rims for metapelites in the Lüliang Group [18,48]. So far, the younger age group is mostly interpreted to represent the peak metamorphic stages of amphibolite and granulite facies, coeval with the collision between the Eastern and Western Blocks [12,14,15,18,23,48,49]. However, it contradicts the thermal modelling results of England and Thompson [50] that different grades of rock with one P-T array share a same age at peak stages.…”

Geochemistry of metamafic dykes from the Quanji massif: Petrogenesis and further evidence for oceanic subduction, Late Paleoproterozoic, NW China

“…The first one occurred at 1.90-1.95 Ga and the second at 1.85-1.80 Ga, respectively (e.g., Chen et al, 2013aChen et al, , 2009Chen et al, , 2007Zhang et al, 2011;Wang, 2009;Lu et al, 2008;. These metamorphism are characterized by medium-P/T type and thus are believed to result from collision of the Quanji massif to other unknown continental blocks or massifs in the NW China (Chen et al, 2013a and references therein), and at the same time, coevally consistent with the timing and natures of the processes involving the amalgamation of the North China Craton, which was linked to the assembly of Columbia supercontinent worldwide (Zhao and Zhai, 2013;Meert, 2012;Mohanty, 2012;Rogers, 2012;Trap et al, 2012;Zhao G C et al, 2004Zhao G C et al, , 2002a. However, little evidence for arc-related tectonic setting has been reported to support oceanic subduction in the previous studies.…”

Paleoproterozoic Granulites in the North China Craton and Their Geological Implications

“…Their P-T paths comprise a near-isothermal decompression, following the clockwise P-T path (Liu and Liang 1997;Zhao et al 1999;Qian et al 2013). The metamorphic ages are 1965-1800 Ma Trap et al 2007Trap et al , 2012Qian et al 2013). …”