Assembly of the Pamirs: Age and origin of magmatic belts from the southern Tien Shan to the southern Pamirs and their relation to Tibet

Abstract

Magmatic rocks and depositional setting of associated volcaniclastic strata along a north‐south traverse spanning the southern Tien Shan and eastern Pamirs of Kyrgyzstan and Tajikistan constrain the tectonics of the Pamirs and Tibet. The northern Pamirs and northwestern Tibet contain the north facing Kunlun suture, the south facing Jinsha suture, and the intervening Carboniferous to Triassic Karakul–Mazar subduction accretion system; the latter is correlated with the Songpan‐Garze–Hoh Xi system of Tibet. The Kunlun arc is a composite early Paleozoic to late Paleozoic‐Triassic arc. Arc formation in the Pamirs is characterized by ∼370–320 Ma volcanism that probably continued until the Triassic. The cryptic Tanymas suture of the southern northern Pamirs is part of the Jinsha suture. A massive ∼≤227 Ma batholith stitches the Karakul–Mazar complex in the Pamirs. There are striking similarities between the Qiangtang block in the Pamirs and Tibet. Like Tibet, the regional structure of the Pamirs is an anticlinorium that includes the Muskol and Sares domes. Like Tibet, the metamorphic rocks in these domes are equivalents to the Karakul–Mazar–Songpan‐Garze system. Granitoids intruding the Qiangtang block yield ∼200–230 Ma ages in the Pamirs and in central Tibet. The stratigraphy of the eastern Pshart area in the Pamirs is similar to the Bangong‐Nujiang suture zone in the Amdo region of eastern central Tibet, but a Triassic ocean basin sequence is preserved in the Pamirs. Arc‐type granitoids that intruded into the eastern Pshart oceanic‐basin–arc sequence (∼190–160 Ma) and granitoids that cut the southern Qiangtang block (∼170–160 Ma) constitute the Rushan‐Pshart arc. Cretaceous plutons that intruded the central and southern Pamirs record a long‐lasting magmatic history. Their zircons and those from late Miocene xenoliths show that the most distinct magmatic events were Cambro‐Ordovician (∼410–575 Ma), Triassic (∼210–250 Ma; likely due to subduction along the Jinsha suture), Middle Jurassic (∼147–195 Ma; subduction along Rushan‐Pshart suture), and mainly Cretaceous. Middle and Late Cretaceous magmatism may reflect arc activity in Asia prior to the accretion of the Karakoram block and flat‐slab subduction along the Shyok suture north of the Kohistan‐Ladakh arc, respectively. Before India and Asia collided, the Pamir region from the Indus‐Yarlung to the Jinsha suture was an Andean‐style plate margin. Our analysis suggests a relatively simple crustal structure for the Pamirs and Tibet. From the Kunlun arc in the north to the southern Qiangtang block in the south the Pamirs and Tibet likely have a dominantly sedimentary crust, characterized by Karakul–Mazar–Songpan‐Garze accretionary wedge rocks. The crust south of the southern Qiangtang block is likely of granodioritic composition, reflecting long‐lived subduction, arc formation, and Cretaceous‐Cenozoic underthrusting.

Geometry of the Pamir‐Hindu Kush intermediate‐depth earthquake zone from local seismic data

“…It consists of roughly E-W trending structural belts that reflect a history of successive terrane accretion. These are commonly referred to as Northern (Paleozoic subduction-accretion complex), Central (Mesozoic platform rocks), and Southern (mostly Mesozoic metasediments) Pamir [Burtman and Molnar, 1993;Schwab et al, 2004;Mechie et al, 2012]. Correlation of the terranes and the sutures separating them from their counterparts in Tibet [e.g., Yin and Harrison, 2000] and Afghanistan [Burtman and Molnar, 1993] indicates a relative northward displacement of the entire Pamir by about 300 km.…”

“…However, lower continental crustal rocks do not typically contain any significant amount of hydrated minerals [Rudnick, 1995;Rudnick and Fountain, 1995] and should therefore predominantly deform aseismically at mantle depths. In a delamination scenario for the Pamir, the southern and central Pamir's origin from accreted volcanic arcs [Schwab et al, 2004] may provide preserved fluid reservoirs in hydrated rocks that are now released as these rocks are transported to greater depth. Alternatively, concepts of shear instabilities by thermal runaway [Kelemen and Hirth, 2007;John et al, 2009] have been proposed for the generation of intermediate-depth earthquakes.…”

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

“…In particular, the Cretaceous arc-type granitoids in the Central and Southern Pamir have been linked to equivalents in Tibet. However, the details of such correlations are still debated (e.g., Schwab et al, 2004;Robinson, 2009).…”

“…The domes cover up to 30 % of the Pamir and expose crystalline basement and metamorphic rocks (Vlasov et al, 1991;Brunel et al, 1994;Schwab et al, 2004;Robinson Schmidt et al, 2011;Stübner et al, 2013) The Kurgovat Dome of the Northern Pamir consists of high-grade metamorphosed Triassic rocks. The domes in the Central Pamir (Yazgulom, Sarez, Muskol and Shatput domes; Fig.…”

“…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).…”