2016-12-23T18:52:10

[1] We defined a new global moving hot spot reference frame (GMHRF), using a comprehensive set of radiometric dates from arguably the best-studied hot spot tracks, refined plate circuit reconstructions, a new plate polygon model, and an iterative approach for estimating hot spot motions from numerical models of whole mantle convection and advection of plume conduits in the mantle flow that ensures their consistency with surface plate motions. Our results show that with the appropriate choice of a chain of relative motion linking the Pacific plate to the plates of the Indo-Atlantic hemisphere, the observed geometries and ages of the Pacific and Indo-Atlantic hot spot tracks were accurately reproduced by a combination of absolute plate motion and hot spot drift back to the Late Cretaceous ($80 Ma). Similarly good fits were observed for Indo-Atlantic tracks for earlier time (to $130 Ma). In contrast, attempts to define a fixed hot spot frame resulted in unacceptable misfits for the Late Cretaceous to Paleogene (80-50 Ma), highlighting the significance of relative motion between the Pacific and Indo-Atlantic hot spots during this period. A comparison of absolute reconstructions using the GMHRF and the most recent global paleomagnetic frame reveals substantial amounts of true polar wander at rates varying between $0.1 /Ma and 1 /Ma. Two intriguing, nearly equal and antipodal rotations of the Earth relative to its spin axis are suggested for the 90-60 Ma and 60-40 Ma intervals ($9 at a 0.3-0.5 /Ma rate); these predictions have yet to be tested by geodynamic models.Citation: Doubrovine, P. V., B. Steinberger, and T. H. Torsvik (2012), Absolute plate motions in a reference frame defined by moving hot spots in the

Cenozoic convergence between the Indian and Asian plates produced the archetypical continental collision zone comprising the Himalaya mountain belt and the Tibetan Plateau. How and where India-Asia convergence was accommodated after collision at or before 52 Ma remains a long-standing controversy. Since 52 Ma, the two plates have converged up to 3,600 AE 35 km, yet the upper crustal shortening documented from the geological record of Asia and the Himalaya is up to approximately 2,350-km less. Here we show that the discrepancy between the convergence and the shortening can be explained by subduction of highly extended continental and oceanic Indian lithosphere within the Himalaya between approximately 50 and 25 Ma. Paleomagnetic data show that this extended continental and oceanic "Greater India" promontory resulted from 2,675 AE 700 km of North-South extension between 120 and 70 Ma, accommodated between the Tibetan Himalaya and cratonic India. We suggest that the approximately 50 Ma "India"-Asia collision was a collision of a Tibetan-Himalayan microcontinent with Asia, followed by subduction of the largely oceanic Greater India Basin along a subduction zone at the location of the Greater Himalaya. The "hard" India-Asia collision with thicker and contiguous Indian continental lithosphere occurred around 25-20 Ma. This hard collision is coincident with far-field deformation in central Asia and rapid exhumation of Greater Himalaya crystalline rocks, and may be linked to intensification of the Asian monsoon system. This two-stage collision between India and Asia is also reflected in the deep mantle remnants of subduction imaged with seismic tomography.continent-continent collision | mantle tomography | plate reconstructions | Cretaceous T he present geological boundary between India and Asia is marked by the Indus-Yarlung suture zone, which contains deformed remnants of the ancient Neotethys Ocean (1, 2) (Fig. 1). North of the Indus-Yarlung suture is the southernmost continental fragment of Asia, the Lhasa block. South of the suture lies the Himalaya, composed of (meta)sedimentary rocks that were scraped off now-subducted Indian continental crust and mantle lithosphere and thrust southward over India during collision. The highest structural unit of the Himalaya is overlain by fragments of oceanic lithosphere (ophiolites).We apply the common term Greater India to refer to the part of the Indian plate that has been subducted underneath Tibet since the onset of Cenozoic continental collision. A 52 Ma minimum age of collision between northernmost Greater India and the Lhasa block is constrained by 52 Ma sedimentary rocks in the northern, "Tibetan" Himalaya that include detritus from the Lhasa block (3). This collision age is consistent with independent paleomagnetic evidence for overlapping paleolatitudes for the Tibetan Himalaya and the Lhasa blocks at 48.6 AE 6.2 Ma ( Fig. 2; SI Text) as well as with an abrupt decrease in India-Asia convergence rates beginning at 55-50 Ma, as demonstrated by India-Asia plate circuits ...