New 40Ar/39Ar age constraints on the Late Palaeozoic tectonic evolution of the western Tianshan (Xinjiang, northwestern China), with emphasis on Permian fluid ingress

Abstract

International audienceLaser-probe dating of mylonite whole-rock samples from the North Tianshan—Main Tianshan fault zone that cross-cuts the North Tianshan domain's southern margin yielded 40Ar/39Ar spectra with 255–285 Ma ages. Biotite from an undeformed, Early Carboniferous granite, which cuts the steep mylonitic foliation in the Proterozoic basement of the Yili arcs's southern margin, gave a 263.4 ± 0.6 Ma plateau age (1σ). Pre-Carboniferous metasediments overlying this basement yielded plateau ages (1σ) of 253.3 ± 0.3 (muscovite) and 252.3 ± 0.3 (biotite) Ma. The Permian ages of mylonites date movement on these ductile, dextral strike-slip shear zones, whereas the mica ages are interpreted by recrystallisation as a result of fluid flow around such transcurrent faults. We propose that the Tianshan's Permian syn-tectonic bimodal magmatism was created in a non-plume-related Yellowstone-like extensional–transtensional tectonic regime. Gold mineralisation, tracing aqueous flow in the crust, peaked in Permian time and continued locally into the Triassic. The picture is emerging that a convective fluid system partly driven by magmatic heat, existed in a strongly fractured and weakened crust with an elevated heat flow, leading to regional-scale isotope resetting. We suggest that surprisingly young isotopic ages in the literature for early orogenic (ultra)high-pressure metamorphism are similarly due to fluid-mediated recrystallisation

Tectonic evolution of the South Tianshan orogen and adjacent regions, NW China: geochemical and age constraints of granitoid rocks

“…The clockwise rotation of the Tarim block is interpreted to have created the large-scale strike-slip movement between the Yili and Tarim blocks in Early Permian times (Wang et al 2007a). This Permian movement is in agreement with the timing of other transcurrent faults in the Tianshan orogen (Shu et al 1999;Laurent-Charvet et al 2002, 2003Charvet et al 2007;Jong et al 2008).…”

“…However, the zircon rim age of 233-226 Ma is interpreted to be due to the fluidmediated recrystallization of zircons (Jong et al 2008). A U-Pb age of 291 Ma obtained on zircons from the western Tianshan rodingites, which are greenschist-facies retrograde products of former eclogites , further indicate that the Triassic ages for eclogites cannot be related to the collision of the Tarim and Yili-Central Tianshan plates.…”

“…Some authors have suggested a Late Paleozoic age (e.g. Allen et al 1992;Gao et al 1998Gao et al , 2006Gao and Klemd 2003;Charvet et al 2007;Solomovich 2007;Wang et al 2007b;Jong et al 2008;Li et al 2008), whereas others have proposed a Triassic collision age (e.g. Li et al 2002;Zhang et al 2007a, b;Xiao et al 2008).…”

Universal Elemental Homology in Glyptocystitoids, Hemicosmitoids, Coronoids and Blastoids: Steps Toward Echinoderm Phylogenetic Reconstruction in Derived Blastozoa

“…The tectonics and ophiolite belts of northern Xinjiang and especially the Hoxtolgay area and how these may relate to the Central Asian Orogenic Belt have not been foci of our research. Such matters can be approached through contributions made by Li et al (1991), Huang et al (1995), Aitchison (2001, 2004), Xiao et al (2008) and de Jong et al (2009). Reconstructions hypothesized for the Central Asian Orogenic Belt (Windley et al, 2007;Xiao et al, 2010) would locate the Hongguleleng Formation at approximately 25 to 30 degrees north, a more tropical setting than the previous palaeogeographic reconstructions reported by Waters et al (2003).…”

Late Paleozoic paleogeographic reconstruction of Western Central Asia based upon paleomagnetic data and its geodynamic implications

“…Though sinistral motions have been described in Kirghizstan (Mikolaichuk et al, 1995), the timing of deformation is badly constrained. More to the East, a dextral kinematics of the fault has been better described and the deformation is dated between 265 Ma and 250 Ma (Ar-Ar dating; de Jong et al, 2009;Wang et al, 2010). Its well preserved linear shape allows to estimate an Euler pole position at ca.…”