Latest Cretaceous Himalayan tectonics: Obduction, collision or Deccan-related uplift?

Abstract

Diverging interpretations and incompatible scenarios have been proposed for the early stages of Himalayan history. Numerous researchers have postulated that northern India was involved in ophiolite obduction, arc–continent, or continent–continent collision during the Late Cretaceous or Early Paleocene, but firm geological evidence was never produced. In this article we argue against orogenic events predating the Late Paleocene, when the Neotethys Ocean was still open. The Tethys Himalayan sedimentary record testifies to anorogenic evolution, primarily controlled by dynamic uplift of the passive margin prior to the massive outburst of Deccan lavas and eventually followed by thermal subsidence. Major stratigraphic gaps in pelagic sediments suggest that such tectono-magmatic episode started to affect the base of the Indian Plate in the Campanian or possibly even in the Santonian, 10 to 20Ma before the climax of Deccan flood-basalt eruptions. The abrupt increase in siliciclastic supply and accumulation rates recorded in sedimentary basins all around the Indian subcontinent during the Maastrichtian was followed by progradation of coastal quartzarenites along the northern Indian margin in the Early Paleocene. Sandstones derived from the rejuvenated craton and uplifted inner continental margin in the south are dominantly but not exclusively quartzose. Felsitic volcanic rock fragments and Cr-spinels, many of which with the same geochemical fingerprint as Deccan spinels and newly found throughout the Maastrichtian to Danian succession, resisted the combined effect of subequatorial weathering and subsequent diagenesis, and testify that detritus from Deccan basalts reached the Indian passive margin as far as South Tibet. At the close of the Early Paleocene India drifted away from the Seychelles block, and thermal subsidence led to widespread carbonate deposition along the Tethys Himalaya. This article illustrates how mega-events of magmatic upwelling followed by lithospheric cooling may control passive-margin sedimentation and stratigraphic patterns, as occurred in northern India first in the Early Cretaceous and next in the latest Cretaceous/Paleocene.