Phanerozoic evolution of the Inner Mongolia–Daxinganling orogenic belt in North China: constraints from geochronology of ophiolites and associated formations

Abstract

The Inner Mongolia–Daxinganling Orogenic Belt (IMDOB), located between the North China and South Mongolia Blocks, consists of several ENE–WSW- to NE–SW-trending zones including dismembered ophiolite blocks, metamorphic rocks and granitoids. Although numerous studies have been carried out on this belt, its tectonic evolution has been a subject of controversy, chiefly because of the lack of reliable geochronological data. Based on a synthesis of newly published geochronological data and our unpublished data for the IMDOB, we define two oceanic basins: Ondor Sum and Hegenshan. The former, probably the main one, was initiated during the Ordovician (>467 Ma) period, whereas the latter, representing a back-arc basin, opened on a pre-Permian basement at, or earlier than, Early Permian times (c. 295 Ma). These two oceanic basins were separated by a magmatic arc (Sunid–Baolidao), and were probably closed simultaneously when the final orogenesis of the IMDOB occurred during the Triassic period (240–220 Ma). Importantly, the Triassic timing of the final orogenesis of the IMDOB due north of the North China Craton is essentially coeval with that of the Qinling–Dabie–Su–Lu orogenic belt on the southern margin of the North China Craton. It is inferred that this two-sided subduction–collision scenario in the Triassic may have contributed to the Mesozoic lithospheric thinning event of the North China Craton, although the details are unclear.

End-Permian to mid-Triassic termination of the accretionary processes of the southern Altaids: implications for the geodynamic evolution, Phanerozoic continental growth, and metallogeny of Central Asia

“…Recently acquired SHRIMP U-Pb zircon crystallization ages of the Hegenshan ophiolitic rocks include a basaltic dike at 298 ± 9 Ma (Table 2) (Jian et al 2007(Jian et al , 2008Miao et al 2007Miao et al , 2008, a cumulate gabbro at 295 ± 15 Ma (Jian et al 2007(Jian et al , 2008Miao et al 2007Miao et al , 2008, and a massive basalt has a whole-rock 40 Ar/ 39 Ar age of 293 ± 1 Ma interpreted as the time of formation ). An 40 Ar/ 39 Ar age of 242 ± 2 Ma on a meta-mafic dike by Robinson et al (1999) was interpreted to be represent the emplacement time of the ophiolite .…”

“…An 40 Ar/ 39 Ar age of 242 ± 2 Ma on a meta-mafic dike by Robinson et al (1999) was interpreted to be represent the emplacement time of the ophiolite . Moreover, a granodiorite intruded into a Hengenshan serpentinized harzburgite, has a weighted mean SHRIMP U-Pb zircon age of 244 ± 4 Ma ( Table 3) (Jian et al 2007(Jian et al , 2008Miao et al 2007Miao et al , 2008 interpreted as the emplacement age of a granitic crustal melt derived from tectonically and/or magmatically thickened crust shortly after closure of the Paleoasian Ocean. Wang and Liu 1986;Tang 1990;Tang and Yan 1993;Hsü et al 1991;IMBGMR 1991;Chen et al 2000;Badarch et al 2002 andXiao et al 2003a).…”

“…For clarity, late Mesozoic-Cenozoic strata are not shown. Some middle to late Paleozoic isotopic ages of ophiolitic melanges are shown (modified after Miao et al 2007Miao et al , 2008. Insert is a simplified map of Asia showing the study area and the general tectonic divisions in southern Mongolia (modified after Lamb and Badarch 1997;Lamb et al , 2008 Int J Earth Sci (Geol Rundsch) (2009) 98:1189-1217 1199…”

“…The polarity of subduction in the eastern part of the Altaids has proved less controversial. It has long been widely accepted that there was northward subduction under the Uliastai active continental margin (Ş engör et al 1993;Ş engör and Natal'in 1996a;Miao et al 2007;Windley et al 2007;Chen et al 2009). Xiao et al (2003b) proposed that there was southward subduction under a narrow accretionary wedge in front of the North China craton, although without evidence of a continental margin magmatic arc.…”

“…Late Paleozoic geochronological data from subduction-accretion complexes in the southern Altaids in Inner Mongolia and adjacent areas (modified afterMiao et al 2007), which predate the terminal collisional processes…”