Tectonic Implications of Detrital Zircon Ages From Lesser Himalayan Mesozoic‐Cenozoic Strata, Pakistan

Abstract

We carried U‐Pb‐Hf geochronology of the clastic sequence covering upper Mesozoic‐Cenozoic period. The upper Mesozoic sequence is overlain unconformably by the Cenozoic strata, marking regional K‐T boundary, which is mapped as angular unconformity. This angular relationship may strongly indicate a compressional orogenic event that occurred during the Late Cretaceous. Late Cretaceous Kohistan‐Karakoram collision and ophiolite emplacement may account for the development of this compression along the northern Indian margin. The U‐Pb‐Hf isotopic analyses of the upper Mesozoic and lower Cenozoic sequence (Hangu Formation and Lower Patala Formation) are similar to the Tethyan and Lesser Himalayan signatures, which indicate the Indian‐plate provenance. The two younger Cretaceous grains recorded in the Hangu Formation might be derived from the Indian‐plate volcanic rocks and/or Tethyan Himalayan volcanic rocks. The absence of ophiolitic age component in the precollision sequence may indicate that these ophiolites are not exposed until final India‐Eurasia collision. The major shift in provenance is recorded in the upper part of the Patala Formation, where the presence of disconformity and the appearance of <100 Ma detrital zircons indicate the contribution of Eurasian source (i.e., Kohistan‐Ladakh arc; KLA), which is further supported by the ɛHf(t) signatures. Upsection, the contribution from Eurasian source increased in the Early Middle Eocene Kuldana Formation. Therefore, we suggest that the provenance mixing close to Paleocene‐Eocene boundary indicates that the India‐Eurasia collision in the north Pakistan occurred at ∼56–55 Ma and subsequent exhumation increased the contribution of the northern (Eurasian) provenance in the upsection.

Balanced Cross‐Sections and Numerical Modeling of the Lithospheric‐Scale Evolution of the Hindu Kush and Pamir

“…We rely on a recent estimate of ∼3,150 km of India-Asia convergence along the western syntaxis since 56 Ma, which we assume to be the time of contact (Ingalls et al, 2016, their Figure 2b). This compares with the van Hinsbergen et al (2011) equivalent estimate of ∼3,500 km from their preferred Model A. Provenance analysis from the Pakistan Himalaya confirm India-Asia contact and formation of a foreland basin by 56-55 Ma (Ding et al, 2016;Qasim et al, 2018).…”

“…This compares with the van Hinsbergen et al. (2011) equivalent estimate of ∼3,500 km from their preferred Model A. Provenance analysis from the Pakistan Himalaya confirm India‐Asia contact and formation of a foreland basin by 56–55 Ma (Ding et al., 2016; Qasim et al., 2018).…”

Synchronous Sedimentation in Gonjo Basin, Southeast Tibet in Response to India‐Asia Collision Constrained by Magnetostratigraphy

“…(2017) proposed a diachronous collision model to explain the broad range of collision ages. According to our statistics (Table in the supporting information), several studies from the past 2 decades propose that the India‐Asia collision occurred during the early Paleogene (65–50 Ma) and imply a diachronous collision that first occurred in the central Himalaya at 65–59 Ma (e.g., L. Ding et al., 2005; Hu et al., 2015; L. Ma et al., 2017; Orme et al., 2015; Wu et al., 2014) and then progressed westwards initiating at 56–54 Ma in the NW Himalaya (e.g., Clementz et al., 2011; L. Ding, Qasim, et al., 2016; Green et al., 2008; Najman et al., 2016; Qasim et al., 2018), and eastwards where collision initiated at ∼50 Ma (e.g., Baral et al., 2018; H. Ding, Zhang, et al., 2016; B. Zhu et al., 2005). Meanwhile, Early Cenozoic continental sediments deposited contemporaneously or soon after the onset of India‐Asia collision provide an obvious target for gaining insight into growth of the Tibetan Plateau (Studnicki‐Gizbert et al., 2008).…”

“…Ma et al, 2017;Orme et al, 2015;Wu et al, 2014) and then progressed westwards initiating at 56-54 Ma in the NW Himalaya (e.g., Clementz et al, 2011;L. Ding, Qasim, et al, 2016;Green et al, 2008;Najman et al, 2016;Qasim et al, 2018), and eastwards where collision initiated at ∼50 Ma (e.g., Baral et al, 2018;H. Ding, Zhang, et al, 2016;B.…”

Lithospheric Deformation and Active Tectonics of the NW Himalayas, Hindukush, and Tibet

“…In the NW Himalayas, the Zangbo suture bifurcates into a northern suture, termed as the main Karakoram thrust (MKT), and a southern suture, termed as the main mantle thrust (MMT), bounding the Kohistan-Ladakh island arcs towards north and south, respectively ([12]; Figure 2). The timing of collision along northern (MKT) and southern (MMT) sutures is recorded as~90 and~55 Ma, respectively [1,11,29].…”