Rifting, subduction and collisional records from pluton petrogenesis and geochronology in the Hindu Kush, NW Pakistan

Abstract

New U-(Th)/Pb geochronology and geochemical analyses of plutonic bodies in the Hindu Kush range, NW Pakistan, provide insight on the crustal growth and tectonic evolution of the southern Eurasian margin. These new data outline a protracted magmatic history that spans the Cambrian to the Neogene (ca. 538 to 23 Ma) and record a variety of petrogenetic associations variably influenced by within plate, volcanic arc, and collision tectonic environments. The Kafiristan pluton (538 ± 4 to 487 ± 3 Ma) yields geochemical signatures consistent with extensional plutonism and rifting of the Hindu Kush terrane from Gondwana. The Tirich Mir (127 ± 1 to 123 ± 1 Ma) and Buni-Zom (110 ± 1 to 104 ± 1 Ma) plutons have geochemical signatures that can be attributed to a subduction related continental volcanic arc system that developed along the southern margin of Eurasia in the Mesozoic. The Garam Chasma pluton, the youngest body in the study area (27.3 ± 0.5 to 22.8 ± 0.4 Ma), yields a geochemical signature consistent with widespread anatexis during crustal thickening related to the development of the Himalaya. The present geochemical and geochronological analysis from the Hindu Kush have produced important new constraints on the timing of tectonic events and variable tectonic settings along the south Eurasian margin before and after the continued India-Asia collision.

Mesozoic to Cenozoic tectono‐metamorphic history of the South Pamir–Hindu Kush (Chitral, NW Pakistan): Insights from phase equilibria modelling, and garnet–monazite petrochronology

“…Guillot et al., ; Rutte, Ratschbacher, Khan, et al., ) or to the Tethyan Himalaya–Lhasa microcontinent collision and subsequent oceanic slab flattening (Van Hinsbergen et al., ). Peak metamorphism is reached at 580–600°C and ˜0.6 GPa for the staurolite schist, and 700–750°C and 0.7–0.8 GPa for the sillimanite migmatites. Late Oligocene (28–23 Ma) crustal anatexis, which culminated in the intrusion of the Garam Chasma leucogranite (27–23 Ma; for example, Faisal et al., ). Rocks in the Chitral area underwent near‐isothermal decompression/exhumation (over 0.1 GPa; 3–7 km).…”

“…Moreover, based on geochemical data, it has been demonstrated that the Cretaceous magmatic intrusions represent the development of an Andean‐style arc along the southern Eurasian margin due to the northward subduction of the Neotethys ocean (Figure b; for example, Chapman, Scoggin, et al., ; Faisal et al., ; Kapp, DeCelles, Gehrels, Heizler, & Ding, ; Robinson, ; Schwab et al., ). This magmatism occurred from 130 to 95 Ma in the Karakoram (Aminov et al., ; Debon, Le Fort, Dautel, Sonet, & Zimmermann, ; Fraser et al., ; Heuberger et al., ; Robinson, ), and to 105 Ma in the North Lhasa (Tibet; Chen et al., ; Sui et al., ; Zhu et al., ), with a high‐flux event between 110 and 105 Ma.…”

“…Crystallization of the pluton has been constrained by U-Pb zircon geochronology to 127-114 Ma (Faisal et al, 2016;Heuberger et al, 2007;Hildebrand et al, 2001). This timing is similar to the crystallization of the Karakoram batholith to the east .…”

“…While on a broad scale the pluton intrudes the Karakoram–Hindu Kush boundary (Figure a), in the Chitral region it appears partially bounded along its eastern margin by the TMFZ (Figure b; Hildebrand et al., ; Zanchi et al., ). Crystallization of the pluton has been constrained by U–Pb zircon geochronology to 127–114 Ma (Faisal et al., ; Heuberger et al., ; Hildebrand et al., ). This timing is similar to the crystallization of the Karakoram batholith to the east (Searle et al., ).…”

“…This allows the direct study of the tectonic evolution of metamorphic and magmatic rocks residing at mid‐crustal conditions, and the crustal foundering that affected its root zone during this time (Hacker et al., ; Kooijman, Smit, Ratschbacher, & Kylander‐Clark, ), especially in the Central Pamir and Karakoram blocks (Fraser, Searle, Parrish, & Noble, ; Mahéo, Blichert‐Toft, Pin, Guillot, & Pêcher, ; Palin, Searle, Waters, Horstwood, & Parrish, ; Rolland, Mahéo, Guillot, & Pêcher, ; Rolland, Villa, Guillot, Mahéo, & Pêcher, ). Only a few studies, however, have examined the detailed timing of deformation and metamorphism in the South Pamir, including the Hindu Kush region, which has been shown to preserve a potentially more complex and longer history of magmatism and metamorphism than the adjacent Karakoram block (Aminov et al., ; Chapman, Robinson, et al., ; Chapman, Scoggin, et al., ; Faisal, Larson, Camacho, & Coutand, ; Faisal, Larson, Cottle, & Lamming, ; Faisal, Larson, King, & Cottle, ; Hildebrand, ; Hildebrand, Noble, Searle, Waters, & Parrish, ; Hildebrand, Searle, Shakirullah, Khan, & Van Heijst, ).…”