Multiple mantle sources of the Early Permian Panjal Traps, Kashmir, India

Abstract

The Early Permian Panjal Traps of northern India are the volcanic remnants of continental rifting that led to the formation of the Neotethys Ocean and the ribbon-like continent Cimmeria. The Traps are one of at least five major mafic eruptions of flood basalts during the Late Palaeozoic however their origin and petrogenesis are poorly constrained. Basalts from the Kashmir Valley were collected and analyzed for chemical and isotopic (Sr, Nd) compositions in order to characterize their mantle source and evaluate the petrogenetic processes related to opening of the Neotethys Ocean. Samples collected from the eastern side (Guryal Ravine, Pahalgam, PJ3) of the Kashmir Valley are chemically similar to mildly alkaline to tholeiitic, within-plate flood basalts. The TiO 2 contents (TiO 2 ‫؍‬ 0.8 to 3.1 wt.%), La/Yb N values (La/Yb N ‫؍‬ 1.8 to 6.1) and Nd (t) values ( Nd (t) ‫؍‬ ؊5.3 to ؉1.3) along with partial melt modeling indicates that the basalts were likely derived from a spinel peridotite source. In contrast, samples collected from the western side (PJ4) of the Kashmir Valley (Buta Pathri) are more primitive in composition and show evidence for clinopyroxene fractionation. The basalts from the western side of the Kashmir Valley have higher Mg# (Mg# ‫؍‬ 60 to 78) values and Nd (t) values ( Nd (t) ‫؍‬ ؉0.3 to ؉4.3) suggesting they were derived by slightly higher amounts of partial melting and from a more depleted spinel peridotite source. The changing bulk composition of the basalts from 'enriched OIB-like' on the eastern side to 'depleted MORB-like' compositions on the western side is likely due to the changing nature of the Panjal rift from a nascent continental setting to one transitioning to a mature ocean basin. In comparison to Pangaean and post-Pangaean flood basalt provinces, the Panjal Traps are more chemically similar to the flood basalts from the post-Pangaean provinces that are associated with plate separation.

The initial break-up of Pangæa elicited by Late Palæozoic deglaciation

“…The primary melt compositions and mantle potential temperature estimates were calculated using PRIMELT3 24 . The major elemental data of each sample was entered into PRIMELT3 and calculated using an Fe 2 O 3 /TiO 2 ratio of 0.5 and 1.0, pressure of 1 bar, H 2 O = 0 wt% and the lowest possible FeO content.…”

“…Calculations parameters are summarized in Dataset S2. ( b ) The variability of ε Nd (t) of Early to Middle Permian mafic volcanic rocks from west to east across the Himalaya 19 21 24 36 37 39 70 .…”

“…The rifting of Cimmeria and accompanying magmatism are thought to be related to a regional-scale mantle-plume 19 20 21 . However, geochemical and structural studies of the Panjal Traps (Kashmir), the single largest contiguous outcropping of Early Permian flood basalts associated with Cimmerian rifting, suggest they are related to passive extension that propagated eastward 22 23 24 . In contrast, Early Permian basaltic rocks in Oman (west) and Tibet (east) are each thought to be derived by a mantle-plume and that the Panjal Traps are either an eastern or western extension of rift propagation 19 20 21 25 .…”

The Early Permian Woniusi Flood Basalts from the Baoshan Terrane, SW China: Petrogenesis and Geodynamic Implications

“…During this time a series of intra-plate, basaltic rocks were emplaced within the Tethyan Himalaya domains of Pakistan, India and China and they are considered to be parts of a Large Igneous Provine (LIP) associated with the breakup of Gondwana (Ernst and Buchan, 2001;Zhu et al, 2010;Liao et al, 2015;Shellnutt et al, 2015;Xu et al, 2016;Zhang and Zhang, 2017;Wang et al, 2019). The Panjal Traps, Abor, Nar-Tsum, Bhote Kosi, and Selong volcanic groups and Qiangtang mafic dykes and flood basalts are amongst the many occurrences of the Late Carboniferous to Early Permian basaltic rocks within the Himalaya (Bhat et al, 1981;Garzanti et al, 1999;Chauvet et al, 2008;Zhu et al 2010;Ali et al 2012;Zhai et al 2013;Shellnutt et al, 2014Shellnutt et al, , 2015Xu et al, 2016;Zhang and Zhang, 2017;Liu et al, 2018;Wang et al, 2019). Recent studies have also documented large volumes of Late Carboniferous to Early Permian flood basalts and mafic dykes in the Jinji (Wang et al, 2004;Ali et al, 2013;Liao et al, 2015) and Shidian (Huang et al, 2012;Ali et al, 2013) areas in the Baoshan terrane, SW China.…”

“…The formation of continental LIPs has also significant implications for continental growth, rifting and breakup (Wang et al, 2008;Bryan and Ferrari, 2013). Previous work suggests the extensive Late Carboniferous to Early Permian basaltic rocks throughout the Himalaya are likely the volcanic expressions of passive lithosphere extension on the northern margin of East Gondwana whereas others suggest they could be the products of basaltic magmatism induced by mantle plume activity (Chauvet et al, 2008;Zhu et al, 2010;Zhai et al, 2013;Shellnutt et al, 2014Shellnutt et al, , 2015Liao et al, 2015;Xu et al, 2016;Zhang and Zhang, 2017;Wang et al, 2019). Consequently, the origin and tectonic implications of this magmatism remain unclear.…”