Cretaceous magmatic migration and flare-up in Pamir-Karakoram

The Pamir-Karakoram terrain contains abundant Cretaceous granitoids, and minor coeval volcanic rocks and mafic intrusions, which represent a wide (ca. 400 km) continental arc developed during northward subduction of Neo-Tethys oceanic lithosphere. However, little is known of the tectonic controls on the magmatic flare-ups and their implications for crustal thickening. In this paper, we report new zircon U-Pb age and Hf isotope data for Cretaceous biotite granites, two-mica granites and mafic microgranular enclaves (MMEs) from the large-scale granitic batholiths in Pamir. These and previously published results show there were four episodes of Cretaceous magmatism (124-108, 107-103, 102-92, and 80-70 Ma). The Cretaceous arc migrated progressively landward from Karakoram to Central Pamir with a maximum arc-trench distance of ca. 400 km during the first magmatic episode (124-108 Ma). The igneous rocks are mainly S-type granites with enriched zircon Hf isotopic compositions (& epsilon;Hf(t) = -19.8 to -5.4), indicating derivation by partial melting of metasedimentary units. A magmatic flare-up at 105 & PLUSMN; 2 Ma generated voluminous I-type granites and minor mafic igneous rocks that cover ca. 30% of the study area. The I-type granites have higher zircon & epsilon;Hf(t) values (-19.0 to -2.0) as compared with those of the earlier S-type granites, which reflect the addition of mantle-derived materials (ca. 30%). The third episode of magmatism (102-92 Ma) generated mainly intermediate-silicic volcanic rocks, which are geochemically similar to I-type granites and have & epsilon;Hf(t) values of -15.0 to -1.5. The final episode of magmatism (80-70 Ma) was dominated by alkaline and mafic igneous rocks formed in a post-collisional setting, which have variable & epsilon;Hf(t) values of -6.6 to 10.5. Our study highlights that the Early Cretaceous magmatic flare-up in the Pamir-Karakoram terrain was related to foundering of the flat-slab of Neo-Tethys oceanic lithosphere that was previously subducted, which induced voluminous underplating of mantle-derived magma in the lower crust. This process had a key role in crustal thickening in the Pamir-Karakoram terrain prior to the Cenozoic India-Asia collision.

Automated summary

This study reports the zircon U-Pb age and Hf isotope data for granites and mafic intrusions from the Pamir-Karakoram terrain, revealing four episodes of magmatism between 124-70 million years ago. These magmatic events were associated with the subduction of Neo-Tethys oceanic lithosphere and played a key role in crustal thickening in the region.