Proterozoic–Mesozoic history of the Central Asian orogenic belt in the Tajik and southwestern Kyrgyz Tian Shan: U-Pb,⁴⁰Ar/³⁹Ar, and fission-track geochronology and geochemistry of granitoids

Research Article| March 01, 2017 Proterozoic–Mesozoic history of the Central Asian orogenic belt in the Tajik and southwestern Kyrgyz Tian Shan: U-Pb, 40Ar/39Ar, and fission-track geochronology and geochemistry of granitoids Alexandra Käßner; Alexandra Käßner † 1Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany †[email protected] Search for other works by this author on: GSW Google Scholar Lothar Ratschbacher; Lothar Ratschbacher 1Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany Search for other works by this author on: GSW Google Scholar Jörg A. Pfänder; Jörg A. Pfänder 1Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany Search for other works by this author on: GSW Google Scholar Bradley R. Hacker; Bradley R. Hacker 2Department of Geological Sciences, University of California, Santa Barbara, California 93106-9630, USA Search for other works by this author on: GSW Google Scholar George Zack; George Zack 1Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany Search for other works by this author on: GSW Google Scholar Benita-Lisette Sonntag; Benita-Lisette Sonntag 1Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany Search for other works by this author on: GSW Google Scholar Jahanzeb Khan; Jahanzeb Khan 1Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany Search for other works by this author on: GSW Google Scholar Klaus P. Stanek; Klaus P. Stanek 1Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany Search for other works by this author on: GSW Google Scholar Mustafo Gadoev; Mustafo Gadoev 3Institute of Geology, Tajik Academy of Sciences, 734063 Dushanbe, Tajikistan Search for other works by this author on: GSW Google Scholar Ilhomjon Oimahmadov Ilhomjon Oimahmadov 3Institute of Geology, Tajik Academy of Sciences, 734063 Dushanbe, Tajikistan Search for other works by this author on: GSW Google Scholar GSA Bulletin (2017) 129 (3-4): 281–303. https://doi.org/10.1130/B31466.1 Article history received: 30 Nov 2015 rev-recd: 05 Jul 2016 accepted: 10 Aug 2016 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alexandra Käßner, Lothar Ratschbacher, Jörg A. Pfänder, Bradley R. Hacker, George Zack, Benita-Lisette Sonntag, Jahanzeb Khan, Klaus P. Stanek, Mustafo Gadoev, Ilhomjon Oimahmadov; Proterozoic–Mesozoic history of the Central Asian orogenic belt in the Tajik and southwestern Kyrgyz Tian Shan: U-Pb, 40Ar/39Ar, and fission-track geochronology and geochemistry of granitoids. GSA Bulletin 2017;; 129 (3-4): 281–303. doi: https://doi.org/10.1130/B31466.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Multimethod geochronology (U-Pb zircon; 40Ar/39Ar hornblende, biotite, feldspar; apatite fission track) on granitoids, gneisses, and Cenozoic intramontane basin clastics of the Gissar-Alai ranges, South Tian Shan collisional belt, west of the Talas-Fergana fault, elucidates a history of Neoproterozoic magmatism, late Paleozoic magmatism and metamorphism, and Mesozoic–Cenozoic thermal reactivation. Zircon-core and grain-interior U-Pb ages of ca. 2.7–2.4, 2.2–1.7, 1.1–0.85, and 0.85–0.74 Ga tie the early evolution of the Gissar-Alai ranges to that of the Tarim craton. At least part of the Gissar range crystalline basement—the Garm massif—shows U-Pb zircon crystallization ages of ca. 661–552 Ma (median ca. 609 Ma), again suggesting a Tarim craton connection. Tarim collided with the Middle Tian Shan block at ca. 310–305 Ma, completing the protracted formation of the South Tian Shan collisional belt. The massive Gissar range granitoids intruded later (ca. 305–270 Ma), contemporaneous with peak Barrovian-type metamorphism in the Garm massif rocks. Major- and trace-element compositions suggest that the Gissar granitoid melts have continental arc affinity. Zircon εHf and whole-rock εNd values of –2.1 to –6.9 and –2.7 to –7.2, respectively. and Hf-isotope crustal model and Nd-isotope depleted mantle model ages of ca. 1.0–1.2 and ca. 1.1–2.2 Ga, respectively, suggest significant input of Precambrian crust in the Gissar granitoid and Garm orthogneiss melts, consistent with the U-Pb ages of inherited and detrital zircons. The distinct ca. 661–552 Ma Garm gneiss crystallization ages and the ca. 1.0–2.2 Ga model ages (and the lack of 2.4–3.4 Ga model ages) tie the Garm gneisses and the reworked crust of the Gissar range to the northern rim—the Kuqa and Kolar sections—of the Tarim craton, suggesting a united Karakum-Tarim craton. Although about contemporaneous with widespread postcollisional magmatism in the entire Tian Shan, the large volume and short duration of the Gissar range magmatism, including crustal thickening and prograde metamorphism during Tarim craton–Middle Tian Shan block collision, and formation and closure of an oceanic back-arc basin (the Gissar basin), indicate its origin in a distinct setting. Combined, this likely resulted in midcrustal melting and upper-crustal batholith emplacement. Mafic dikes and pipes intruded at ca. 256–238 Ma (median ca. 241 Ma); the source region of the parental melts was within the asthenospheric mantle. The simplest interpretation for these basanites is that they were part of the Tarim flood basalt province; this would extend this province westward from the Tarim craton into the southwestern Tian Shan and imply that the relatively short-lived flood basalt event (ca. 290–270 Ma) was followed by much less voluminous but longer-lasting hotspot magmatism. The 40Ar/39Ar and detrital apatite fission-track dates outline post–Gissar-Alai range granitoid emplacement cooling, Cimmerian collision events at the southern margin of Asia, Late Cretaceous crustal extension and local magmatism, and early Cenozoic shortening and burial in the far field of the India-Asia collision. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

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