Geochemistry of the continental basalts within the Tethyan Himalaya of Lahul-Spiti and SE Zanskar, northwest India

Abstract

The intrusive continental basalts of the Tethyan Himalaya are not necessarily comagmatic feeder dykes or the hypabyssal equivalents of the middle Permian Panjal Traps flows associated with the Permo-Mesozoic rifting of the Tethys, as is generally considered. A comparative study of basic rocks from SE Zanskar, NW Spiti and Upper Lahul shows the coexistence of geochemically different basalts in this region. The Panjal Traps of SE Zanskar and NW Spiti are tholeiitic continental flood basalts (CFB). They originated from an ‘enriched’ P-MORB-type magma which underwent a limited evolution by fractional crystallization and probable crustal contamination. In the adjacent Upper Lahul area, the Baralacha La Dyke Swarm shows a close spatial association with Lower Carboniferous transtensional synsedimentary faults. These dykes consist of tholeiitic to alkalic basalts, belonging to a comagmatic suite that evolved mainly by fractional crystallization. Geochemical data indicate that the Panjal Traps and the dykes are not comagmatically related. These characteristics imply either the coexistence, in the studied area, of contemporaneous but chemically different magmas or temporally unrelated magmatic events. The Baralacha La Dyke Swarm could be associated with a Lower Carboniferous transtensional tectonic event, related to an early phase of Permian rifting of Neo-Tethys.

Subduction, peak and multi-stage exhumation metamorphism: Traces from one coesite-bearing eclogite, Tso Morari, western Himalaya

“…Preserved structures indicate subaerial as well as subaqueous eruptions of the volcanic rocks. Carbonates, especially calcite, oxides (titanite and Fe-oxides), white and dark mica were found in rarely modified source rocks beside greenschist-facies minerals (Vannay and Spring, 1993). The investigated eclogite sample and counterparts in the Kaghan Valley, Pakistan have been interpreted to be metamorphosed equivalents of the Panjal Trap basalts (Honegger et al, 1982;Wilke et al, 2010a).…”

Evidence for pre-Cretaceous history and partial Neogene (19–9Ma) reequilibration in the Karakorum (NW Himalayan Syntaxis) from 40Ar–39Ar amphibole dating

“…This phase started with rifting in the Carboniferous to the Early Permian. From the Middle Permian (275 Ma) to the Upper Triassic (200 Ma), the end of rifting coincided with proxism effusion of continental flood basalts at 210 Ma (Vannay and Spring, 1993). In the Western Himalaya (Pakistan and India), eruption of tholeiitic lavas of more than 1000 km 2 (Panjal Traps) occurred during the Permian (Honegger et al, 1982).…”

Exhumation history of the NW Indian Himalaya revealed by fission track and 40Ar/39Ar ages

“…Berthelsen, 1953;Virdi et al, 1978;Baud et al, 1982Baud et al, , 1984Gaetani et al, 1985Gaetani et al, , 1990Garzanti et al, 1986Garzanti et al, , 1987Guillot et al, 1995;Spring, 1993;Spring et al, 1993a,b;Vannay, 1993;Vannay and Spring, 1993;Steck et al, 1998;Steck, 2004, 2008). The Permian to Tertiary sediments of this nappe stack were deposited on the North Indian Tethyan shelf.…”