Two Contrasting Exhumation Scenarios of Deeply Subducted Continental Crust in North Pakistan

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2022-02, Vol.23 (2), p.n/a
• Main Authors: Zhang, Dingding, Ding, Lin, Chen, Yi, Schertl, Hans‐Peter, Qasim, Muhammad, Jadoon, Umair Khan, Wang, Houqi, Li, Jinxiang, Zhang, Liyun, Yue, Yahui, Xie, Jing
• Format: Article
• Language: English
• Subjects: Amphibolite facies; Amphibolites; Continental crust; Cooling; eclogite; Exhumation; Metamorphism; Mountains; Paleoceanography; Paleogene; Plates; Rutile; Sedimentary facies; UHP; Uplift; U‐Pb dating; western Himalayan syntaxis
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2021GC010193

In Western Himalayan Syntaxis, the India‐Asia continental collision occurred at ca. 50 Ma, while its uplift history and exhumation mechanism are still in dispute despite decades of studies. A new type of eclogite was found in Naran, located ca. 30 km southwest of the Upper Kaghan Valley. Phase equilibrium calculations and thermobarometer performed on the Naran eclogite documented the peak‐P metamorphic condition of 720–780°C at 2.4–2.8 GPa. Two further exhumation stages were identified with the first one at high‐P granulite‐facies conditions of 750–800°C at 1.6–1.9 GPa, and the second at amphibolite‐facies conditions of 550–630°C at 0.5–0.8 GPa. SIMS U‐Pb dating of metamorphic zircons yielded an age of 46 ± 2 Ma, which is interpreted to constrain the high‐P metamorphism age along the northwestern margin of the Indian plate. SIMS U‐Pb dating of rutile yielded a cooling age of 26 ± 3 Ma, which is interpreted as cooling age in the amphibolite facies. The average speculated exhumation rate of the Naran massif (∼3 mm a−1) was much lower than that recovered from the Upper Kaghan Valley massif (86–143 mm a−1). The tectonic and metamorphic evolution of the whole Western Himalayan Syntaxis shows the difference in temporal and spatial change within the Paleogene era, indicating the inconsistent exhumation histories of the continental slices. Such a multi‐slice exhumation process was probably related to the closure of the Neo‐Tethys ocean and the break‐off of the Indian lithospheric slab. Key Points Naran eclogite underwent peak metamorphism at ca. 46 Ma with PT conditions of 710–770°C, 2.2–2.8 GPa U‐Pb dating of rutile indicated cooling age of ca. 26 Ma with PT conditions of 580–630°C and 0.6–0.8 GPa Naran eclogite represents a new type of HP rock sequence with a much lower exhumation rate (3 mm a−1) than Kaghan eclogite (30–143 mm mm a−1)