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ABSTRACT

Plate tectonic reconstructions play a pivotal role in unravelling the complexity of the evolution of the Indian plate during its longest voyage and provide a platform to address long-standing geologic and paleobiogeographic questions in a geodynamic context. The northward drift of the Indian plate from its original Gondwana home in the late Paleozoic to its current position in Asia since the early Cenozoic provides a unique natural laboratory for tracking its changing geography, climate, tectonics, and vertebrate evolution for the past 300 m.y. Lithologic indicators of climate indicate a progressive amelioration of the climate of India with time, from Early Permian Ice Age through cooler temperate to warmer temperate climate in the Late Permian. By the Triassic, a more tropical monsoon-type climate prevailed, and India continued within the subtropical to tropical climates during its northward journey until its collision with Asia. In the Pangean world from the Late Permian to the Late Jurassic, India exchanged tetrapod fauna both with Gondwana and Laurasia without any physical barrier. During that time, India was pivotal in the emergence of major groups of tetrapods such as squamates, sauropods, and early mammals. For nearly 100 m.y., the Indian plate drifted from Gondwana until its collision with Asia ca. 55 Ma, during which time there were shifting roles of dispersal and vicariance that shaped the Indian paleobiogeography in time and space.

With the breakup of Gondwana in the Late Jurassic, India began to disintegrate into a smaller plate, becoming partially isolated during the Early Cretaceous Period but possibly retained a biotic link with Africa via Madagascar. Circa 80 Ma as the Indian plate collided with the Kohistan-Ladakh (KL) arc, Arabia collided with the Oman arc; the dual collision formed a continuous accreted terrane—the Oman-Kohistan-Ladakh (OKL) arc, which served as a biotic filter bridge between India and Africa. India also established another circumpolar filter bridge during the Late Cretaceous via emergent Ninetyeast Ridge and Antarctica to exchange tetrapod fauna with South America. The biotic connectivity with Africa and South America resolved one of the greatest conundrums of Indian paleobiogeography, namely the lack of endemism among Late Cretaceous Indian tetrapods. The northward motion of the Indian plate is recorded from ocean magnetic anomalies and two spectacular linear-hotspot trails left by the Réunion and Kerguelen plumes, respectively, in the Indian Ocean since the Cretaceous. After the accretion of the OKL arc, the active subduction shifted farther north from the Indus suture to the Shyok suture.

At the Cretaceous–Paleogene (K/PG) boundary, India was ground zero for two catastrophic events—the Shiva impact and the Deccan volcanism, which have been linked to the dinosaur extinction. At the same time, Seychelles was separated from India. During the Late Cretaceous (ca. 67 Ma), the Indian plate suddenly accelerated its motion to 20 cm/yr between two transform faults that facilitated the northward movement like the parallel tracks of a rail line—the Owen-Chaman fault on the west and the Wharton Ridge–Sagaing fault on the east. As a result, the Neotethyan plate, bordered by these two transform faults, became a separate oceanic plate called the Kshiroda plate. India continued acceleration during the Paleocene as a passenger ship with a mobile gangplank of the OKL arc, carrying its impoverished Gondwana fauna. During this time India exchanged tetrapod fauna with northern Africa and Europe via the Spain-Morocco corridor.

Despite several decades of investigations, inferences of the timing and nature of collisions between India and Asia remain controversial. A pronounced global warming took place during the Paleocene–Eocene thermal maximum (PETM), when India collided with Asia; this warming caused significant tectonic changes and tetrapod radiation. India slowed down dramatically to 5 cm/yr during its initial collision, and its tetrapods underwent an explosive evolution in response to a new ecological opportunity resulting in the Great Indo-Eurasian Interchange. As India joined with Eurasia, Indian tetrapod fauna became highly diverse and acquired European heritage. The earliest clades of frogs, agamids, and several clades of placental mammals such as bats, artiodactyls, whales, perissodactyls, primates, and lagomorphs appeared abruptly on the Indian subcontinent in the paleoequatorial region during the Early Eocene and dispersed rapidly in the Holarctica province, thus strengthening the “out-of-India” hypothesis. Our results suggest that terrestrial faunas could have dispersed to or from Europe during the initial collision via the Kohistan-Ladakh arc corridor.

The postcollisional tectonics during the Neohimalayan stage created the world’s highest, youngest, and most tectonically active mountain belt on Earth—the Himalayan Mountains–Tibetan Plateau. As India converged with Asia, the Nanga Parbat syntaxis (NPS) and Namcha Barwa syntaxis (NBS) functioned like two prongs of a rigid, V-shaped indentor that produced the uniform curvature of the Himalayan arc, squeezed the Tibetan block, and resulted in the formation of the Altyn Tagh and the Karakoram strike-slip faults. The channel-flow model explains a genetic relationship between the uplift of the Tibetan Plateau and the unusual metamorphic rocks of the Higher Himalaya. Such a drastic change in topography has fundamentally influenced regional and global climate.

During the Neohimalayan tectonic uplift, the intensity of monsoon increased with exhumation of the Himalaya. A foreland basin developed in front of the Lesser Himalaya, where rich Siwalik vertebrates thrived in the floodplains of the Siwalik River from Miocene to Pleistocene mimicking the Serengeti ecosystem. The Siwalik megafauna suffered greatly during the Late Pleistocene extinction. The antecedent Himalayan rivers began to emerge along the Indus-Tsangpo suture zone in the early collision stage and modified in concert with the rise of the Himalaya. The present-day drainage systems of the Himalayan river systems were reorganized, fragmented, and rerouted from the ancient Siwalik River because of tectonic forces.

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