Accretionary tectonics of the Western Kunlun Orogen, China: A Paleozoic-Early Mesozoic, long-lived active continental margin with implications for the growth of Southern Eurasia

Abstract

Our new SHRIMP U-Pb zircon ages from the Western Kunlun Orogen allow us to constrain the history of an active continental margin developed on the southern boundary of the Tarim block from the Ordovician to the Triassic. A 492 ± 7-Ma dacite from Yixieke extrusive rocks that contain 220 ± 5-Ma reheated zircons is interpreted as an intraoceanic arc complex that accreted to the Tarim block. The Yirba granodiorite has a continental arc geochemical signature, a 471 ± 5-Ma U-Pb crystallization age, and 491 ± 3-Ma inherited zircons. It formed during the first, early Paleozoic stage of an active continental margin arc that was juxtaposed to the south against the Kudi high-grade gneiss complex, the Buziwan ophiolite, and the Yixieke volcanic and sedimentary rocks. Zircons from a paragneiss in the Kudi gneiss complex range in age from 398 ± 12 to 1345 ± 31 Ma; the oldest reflect protolith ages of a gneissic continental block (incorporated into the trench), and the youngest may represent the age of a refoliated high-grade fabric created during accretion. The Buziwan ophiolite occupies a thrust sheet tectonically overlying the Kudi gneiss complex. A leuco-gabbro pegmatite, with a zircon age of 403 ± 7 Ma and ca. 490-Ma inherited zircons, and the North Kudi granite, with a zircon age of 408 ± 7 Ma, were emplaced during the second mid-Paleozoic stage of the active continental margin. The Akarz subduction-related granite that has a 214 ± 1-Ma zircon crystallization age formed during the final, early Mesozoic stage of the active margin. The long-lasting active continental margin in the western Kunlun forms a key, well-documented section of the Andean-type margin that extends from the Caucasus to the Qinling. © 2005 by The University of Chicago. All rights reserved.