Exhumational history of the north central Pamir

Abstract

[1] The Pamir plateau forms a prominent tectonic salient along the western end of the Tibet-Tarim margin. Despite its tectonic significance, relatively little is known about the timing of major Cenozoic tectonic events in the Pamir. Here we present new apatite and zircon (U/Th)-He ages, bulk rock geochemistry, and Al-in-hornblende barometry results from the Karakul graben, a prominent north-south oriented rift basin located ∼50 km south of the Main Pamir Thrust. Although cooling ages do not record the onset of extension, graben-bounding normal faults provide exposures of otherwise slowly eroding rocks which record two Cenozoic thermal events. Existing geochronology and new results suggest that granitic rocks in the Karakul region were shallowly emplaced, cooled very quickly through ∼300°C, and have experienced less than 10 km of exhumation since the late Triassic. A long period of relatively slow exhumation throughout much of the late Mesozoic and Cenozoic was punctuated by two periods of accelerated exhumation during the middle Eocene (∼50-40 Ma) and early Miocene (∼25-16 Ma). We interpret the first period of accelerated exhumation as a result of tectonic uplift and subsequent erosion due to the northward propagation of the India-Asia collision. We attribute the second period of rapid exhumation to a renewed phase of tectonism and plateau uplift in the Pamir, perhaps related to a break off event along the down-going Indian plate at ∼25 Ma or to the onset of slip along the nascent Karakoram fault.

Rates of river incision across the main tectonic units of the Pamir identified using optically stimulated luminescence dating of fluvial terraces

“…Situated at the western end of the India-Asia collision zone, the Pamir have experienced some of the highest deformation rates on the planet (e.g., Burtman and Molnar, 1993;Pegler and Das, 1998;Reigber et al, 2001;Ducea et al, 2003;Wheeler et al, 2005). The topography of the Pamir is dominated by a series of Oligo-Miocene domes (Hubbard et al, 1999;Ducea et al, 2003;Schwab et al, 2004;Amidon and Hynek, 2010). The timing and mechanism of dome exhumation and the distribution of neotectonic activity are a focus of research in the Pamir (e.g., Schmidt et al, 2011;Schneider et al, 2013;Sippl et al, 2013;Stübner et al, 2013).…”

Early middle Miocene tectonic uplift of the northwestern part of the Qinghai–Tibetan Plateau evidenced by geochemical and mineralogical records in the western Tarim Basin

“…However, it is not clear whether these signals are the direct result of regional tectonic changes (i.e., uplift of the surrounding mountain ranges) or regional climate change. The two may very well be linked, especially in the Miocene, during which coincident exhumation occurred in the Pamir, Tianshan, and Kunlun mountains (Amidon and Hynek 2010;Lukens et al 2012;Jolivet et al 2001Jolivet et al , 2003.…”

“…The mountains around the Tarim Basin have undergone multiple phases of uplift based on extensive and coincident exhumation records in the Pamir, Tianshan, and Kunlun (Amidon and Hynek 2010;Sobel and Dumitru 1997;Sobel et al 2006;Jolivet et al 2001Jolivet et al , 2003. Amidon and Hynek (2010) attributed the first period of tectonic uplift to the northward propagation of the deformation related to the India-Eurasia collision during middle Eocene, based on apatite and zircon (U/Th)-He ages in the Pamir.…”

“…Amidon and Hynek (2010) attributed the first period of tectonic uplift to the northward propagation of the deformation related to the India-Eurasia collision during middle Eocene, based on apatite and zircon (U/Th)-He ages in the Pamir. The second period is associated with a renewed phase of tectonics and plateau uplift in the Pamir (Amidon and Hynek 2010;Lukens et al 2012) and in the Tianshan during the late Oligocene to middle Miocene (Sobel and Dumitru 1997;Sobel et al 2006;Li and Peng 2010;Heermance et al 2008). Meanwhile, the Kunlun strike-slip fault was also active in the Miocene at around 15 Ma (Jolivet et al 2001(Jolivet et al , 2003.…”

Geological evolution of Central Asian Basins and the western Tien Shan Range

“…Deformation along the fault trace during the Late Oligocene-Early Miocene (e.g. Hendrix et al 1994;Sobel & Dumitru 1997;Sobel et al 2006a;Heermance et al 2008;Amidon & Hynek 2010;Wei et al 2013;Bande et al 2015a) and again in the Late Miocene (e.g. Bullen et al 2003;Heermance et al 2008;Macaulay et al 2014) can be linked to the evolution of the Pamir (Bande et al 2015b).…”