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Geological Society, London, Special Publications; 1993; v. 74; p. 237-249;
DOI: 10.1144/GSL.SP.1993.074.01.17
© 1993 Geological Society of London

Tethyan Himalaya

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

J. C. Vannay & L. Spring

Institut de Minéralogie et de Pétrographie, Université de Lausanne, 1015 Lausanne, Switzerland

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.





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