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Time scale of an early to mid-Paleozoic orogenic cycle of the long-lived Central Asian Orogenic Belt, Inner Mongolia of China: Implications for continental growth

Abstract:

We present a detailed, new time scale for an orogenic cycle (oceanic accretion-subduction-collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical arc-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497-477Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473-470Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461-450Ma), high-Mg adakite and adakite were produced by slab melting and subsequent interaction of the melt with the mantle wedge; (4) death, caused by subduction of a ridge crest (ca. 451-434Ma) and by ridge collision with the ophiolite (ca. 428-423Ma). The evolution of the magmatic arc exhibits three major coherent phases: arc volcanism (ca. 488-444Ma); adakite plutonism (ca. 448-438Ma) and collision (ca. 419-415Ma) of the arc with a passive continental margin. The northern orogen, a product of ridge-trench interaction, evolved progressively from coeval generation of near-trench plutons (ca. 498-461Ma) and juvenile arc crust (ca. 484-469Ma), to ridge subduction (ca. 440-434Ma), microcontinent accretion (ca. 430-420Ma), and finally to forearc formation. The paired orogens followed a consistent progression from ocean floor subduction/arc formation (ca. 500-438Ma), ridge subduction (ca. 451-434Ma) to microcontinent accretion/collision (ca. 430-415Ma); ridge subduction records the turning point that transformed oceanic lithosphere into continental crust. The recognition of this orogenic cycle followed by Permian-early Triassic terminal collision of the CAOB provides compelling evidence for episodic continental growth.