Source provenance
Searle, M.P., Rex, A.J., Tirrul, R., Rex, D.C., Barnicoat, A. & Windley, B.F. (1989). Metamorphic, magmatic, and tectonic evolution of the central Karakoram in the Biafo-Baltoro-Hushe regions of northern Pakistan. In: Malinconico, L.L. & Lillie, R.J. (eds) Tectonics of the Western Himalayas. Geological Society of America Special Paper 232, 47-73.
Cited by 1 unit (1 published) · 0 field-level citations · 2 revision notes.
Central Karakoram (northern Karakoram terrane, Karakoram batholith, Karakoram metamorphic complex). The Baltoro Plutonic Unit (BPU) — biotite monzogranite to two-mica +/- garnet leucogranite and pegmatite-aplite, mildly peraluminous — is the youngest phase of the composite Karakoram batholith, a postcollisional crustal melt with U-Pb age 21 +/- 0.5 Ma and K-Ar mica cooling ages 11.7-5.25 Ma. Older subduction-related phases: Jurassic Hushe complex, Cretaceous (82-75 Ma) Muztagh Tower metagranitoids. Four metamorphic phases M1-M4 (M2 Barrovian kyanite-garnet ~550 C/5.5 kbar; Mango Gusar granite 37.0+/-0.8 Ma; M4 <5 Ma along the Main Karakoram Thrust).
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Units citing this source
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- Age: Searle et al. (1989): the Baltoro Plutonic Unit (BPU) — biotite monzogranite to two-mica ± garnet leucogranite and pegmatite-aplite of mildly peraluminous affinity — is the youngest magmatic phase of the composite Karakoram batholith, with a U-Pb crystallisation age of 21 ± 0.5 Ma and K-Ar mica cooling ages of 11.7–5.25 Ma. It is a postcollisional crustal melt derived from deep crustal levels (petrogenesis distinct from the High Himalayan leucogranites), emplaced after the India–Eurasia collision along the southern Karakoram.
- Geological significance: Searle et al. (1989): thermal effects of BPU emplacement define the M3 metamorphism of the central Karakoram (andalusite-cordierite at Mitre Peak indicating ≤3.75 kbar / ~12.5 km depth; sillimanite-grade melt pods at Paiyu), overprinting the regional syntectonic Barrovian M2 (kyanite-garnet, ~550 °C / 5.5 kbar). Older subduction-related phases of the batholith include the Jurassic Hushe complex and the Cretaceous (82–75 Ma) Muztagh Tower metagranitoids; the M2-cutting Mango Gusar two-mica granite is 37.0 ± 0.8 Ma.