Net growth of the continental crust during the process of accretionary orogeny: Constraints from igneous rocks, southern margin of the middle section of the Central Asian Orogenic Belt

Accretionary orogens function as major sites for the generation of continental crust, but the growth model of continental crust remains poorly constrained. The Central Asian Orogenic Belt, as one of the most important Phanerozoic accretionary orogens on Earth, has been the focus of debates regarding the proportion of juvenile crust present. Using published geochemical and zircon Hf-O isotopic data sets for three belts in the Eastern Tianshan terrane of the southern Central Asian Orogenic Belt, we first explore the variations in crustal thickness and isotopic composition in response to tectono-magmatic activity over time. Steady progression to radiogenic zircon Hf isotopic signatures associated with syn-collisional crustal thickening indicates enhanced input of mantle-derived material, which greatly contributes to the growth of the continental crust. Using the surface areas and relative increases in crustal thickness as the proxies for magma volumes, in conjunction with the calculated mantle fraction of the mixing flux, we then are able to determine that a volume of ∼14−22% of juvenile crust formed in the southern Central Asian Orogenic Belt during the Phanerozoic. This study highlights the validity of using crustal thickness and zircon isotopic signatures of magmatic rocks to quantify the volume of juvenile crust in complex accretionary orogens. With reference to the crustal growth pattern in other accretionary orogens and the Nd-Hf isotopic record at the global scale, our work reconciles the rapid crustal growth in the accretionary orogens with its episodic generation pattern in the formation of global continental crust.

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Geochronology and geochemistry of Late Devonian-Carboniferous igneous rocks in the Songnen-Zhangguangcai Range Massif, NE China: Constraints on the late Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt

Gondwana Research ◽

10.1016/j.gr.2018.01.007 ◽

2018 ◽

Vol 57 ◽

pp. 119-132 ◽

Cited By ~ 6

Author(s):

Peng Guo ◽

Wen-Liang Xu ◽

Zhi-Wei Wang ◽

Feng Wang ◽

Jin-Peng Luan

Keyword(s):

Tectonic Evolution ◽

Orogenic Belt ◽

Igneous Rocks ◽

Central Asian Orogenic Belt ◽

Late Paleozoic ◽

Late Devonian ◽

Ne China ◽

Central Asian

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A mid-Palaeozoic ocean–continent transition in the Mazongshan subduction–accretion complex, Beishan, NW China: new structural, chemical and age data constrain the petrogenesis and tectonic evolution

Geological Magazine ◽

10.1017/s0016756820000114 ◽

2020 ◽

Vol 157 (11) ◽

pp. 1877-1897 ◽

Cited By ~ 1

Author(s):

J.-X. Wang ◽

K.-X. Zhang ◽

Brian F. Windley ◽

B.-W. Song ◽

X.-H. Kou ◽

...

Keyword(s):

Continental Crust ◽

Early Carboniferous ◽

Orogenic Belt ◽

Central Asian Orogenic Belt ◽

Published Data ◽

Zircon Age ◽

The North ◽

Tectonic History ◽

Central Asian ◽

Tectonic Mélange

AbstractAccretionary orogens contain key evidence for the conversion of oceanic to continental crust. The late tectonic history and closure time of the Palaeo-Asian Ocean are recorded in the Mazongshan subduction–accretion complex in the southern Beishan margin of the Central Asian Orogenic Belt. We present new data on the structure, petrology, geochemistry and zircon U–Pb isotope ages of the Mazongshan subduction–accretion complex, which is a tectonic mélange with a block-in-matrix structure. The blocks are of serpentinized peridotite, basalt, gabbro, basaltic andesite, chert and seamount sediments within a matrix that is mainly composed of fore-arc-trench turbidites. U–Pb zircon ages of two gabbros are 454.6 ± 2.5 Ma and 434.1 ± 3.6 Ma, an andesite has a U–Pb zircon age of 451.3 ± 3.5 Ma and a tuffaceous slate has the youngest U–Pb zircon age of 353.6 ± 5.1 Ma. These new isotopic ages, combined with published data on ophiolitic mélanges from central Beishan, indicate that the subduction–accretion of Beishan in the southernmost Central Asian Orogenic Belt lasted until Late Ordovician – Early Carboniferous time. Structure and age data demonstrate that the younging direction of accretion was southwards and that the subduction zone dipped continuously to the north. Accordingly, these results record the conversion of oceanic to continental crust in the southern Beishan accretionary collage.

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