KT boundary plate reconstruction showing the paleopositions of India, Laxmi Ridge, Seychelles, and Madagascar. During the Shiva impact, there was plate reorganization in the northwest Indian Ocean when the Central Indian Ridge jumped more than 500 km northward to form the Carlsberg Ridge, thus initiating the rifting between India and Seychelles. At the same time an extinct ridge in the East Arabian Basin (EAB) between Laxmi Ridge and the Shiva crater jumped 500 km westerly to West Arabian Basin (WAB) between Seychelles and Laxmi Ridge. A-E represent different fracture zones (modified from Hartnady 1986; Talwani and Reif 1998; Dyment 1998). 

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... the Shiva bolide. These authors noticed that composition of these cosmic spinels from the Pacific is markedly different from those found in western Europe and the South Atlantic. We believe the compositional variations of cosmic spinels in KT boundaries indicate two impact sources: Chicxulub structure for the European and Atlantic distribution and the Shiva structure for the source of the Pacific impact debris. As the vapor cloud would progress downrange from the Shiva structure toward the Pacific, the earliest and highest temperature phases would drop as airborne particles, first at Meghalaya and then over the Pacific (Fig. 18). Wetherill and Shoemaker (1982) summarized the current knowledge of Earth-crossing and Earth-orbit- ing asteroids. They listed three large asteroids that exceed 10-km in diameter: Sisyphus (~11 km), Eros (~20 km), and Ganymed (~40 km). Using the crater scaling method (Grieve and Cintala 1992), we esti- mate that a 40-km diameter asteroid (having a mass of 10 16 kg) about the size of Ganymed, striking at a speed of 15 km/s, could have created the Shiva crater with a 500 km diameter and ~10 6 km 3 of impact melt produced by three distinct stages (Elkins-Tanton and Hager 2005), as discussed earlier. The impact of a large bolide into the Earth may have set in motion a very complex array of events with intriguing consequences. For typical terrestrial impact velocities of 15-25 km/s, the impacting body penetrates the target rock approximately 2-3 times its radius and transfers most of its kinetic energy to the target (Grieve 1987). Impact of the bolide may have produced a vast transient crater 50 km deep and 250 km across, which quickly collapsed under the force of the gravity, leaving a basin 500 km wide and 7 km deep. The energy from the 10-km-diameter Chicxulub bolide is estimated to be about 10 24 Joules, equivalent to the explosion of 100 trillion tons of TNT, or about 10,000 times greater than the explosive energy of the world’s entire nuclear arsenal (Frankel 1999; Grieve 1990). If so, the Shiva bolide (~40 km diameter) would generate so much energy that it could create isostatic instability leading to uplift, possibly resulting in shattering of the lithosphere, rifting, volcanism, and other rearrangement of the interior dynamics of the planet. Thus, the Shiva impact not only created the largest crater on Earth, but also initiated several other geodynamic anomalies. Some authors have suggested relationships between large impacts and phenomena such as magnetic reversals and plate movements (Clube and Napier 1982), but these suggestions remain un- proven. The Shiva provides for the first time tangible evidence linking large impact with seafloor spreading and evolution and jumping of nearby spreading ridges. It appears that both the Shiva impact and adjacent spreading centers such as the Carlsberg Ridge and Laxmi Ridge are part of a single thermal system. The Shiva impact produced cratering and associated tectonic rebound/collapse effects sufficient to locally dis- rupt the entire lithosphere and cause a major change in plate stress patterns such that stress would propagate quite rapidly away from the immediate region of the impact. It caused major changes in the Indian plate motion and lithospheric stress patterns. The impact might have important consequences on the evolution and propagation of nearby spreading ridges around the Shiva crater in the northwestern Indian Ocean. Whereas Late Cretaceous magnetic lineations in other oceans show no obvious signs of disturbances at the Tertiary boundary, the end-Cretaceous Indian plate boundary in the Indian Ocean provides evidence of major tectonic reorganization at or shortly after magnetostratigraphic chron 29R that might be linked to the Shiva impact. The effects of major plate tectonic changes at about chron 29R, when the Seychelles rifted from India, were not confined to the northwestern Indian Ocean; they are also observed over an extensive segment of former African plate boundary in the southwestern Indian and Southern Atlantic oceans, involving both the Antarctic and South American plates. In the Agulthus Basin, a westward ridge jump of more than 800 km occurred at the KT boundary time between the African and South American plates (Hartnady 1986). India-Seychelles Rifting .—A new rift between Indo-Somalia and Seychelles was formed near the KT boundary (65 Ma) coinciding with the Shiva impact (Chatterjee and Scotese 1999). At this time the Central Indian Ridge (CIR) jumped 500 km northward from its location in the Madagascar Basin to a new location between the Seychelles and Indo-Somalia to form the Carlsberg Ridge. The Mascarene basin spreading center became extinct as a possible response of this emplacement. This ridge jump (>500 km) caused a sliver of continent to split off from Indo- Greater Somalia, forming the Seychelles microcontinent. It resulted in sudden transfer of the Seychelles and Mascarene bank to the African plate (Fig. 19). This ridge jump may be linked to the Shiva impact on the trailing edge of the Indo-Seychelles block (Hartnady 1986). This impact may have formed a large lithospheric crack between India and Seychelles and initiated the creation of the Carlsberg Ridge, triggering readjustments along the Indian-African and Antarctic-African plate boundaries (Chatterjee and Rudra 1996; Hartnady 1986). Hartnady (1986) specu- lates that anomaly 29 may appear near the base of the steep microcontinental slope of Seychelles. If these identifications are correct, then rifting occurred just before chron 29 and may correspond to chron 29R (KT boundary). At present, there is a time lag (~2 Ma) between the impact (29R) and its subsequent expression in chron 28R of the rifting of the Carlsberg Ridge. Laxmi Basin .—The Laxmi Ridge, an enigmatic continental sliver in the Arabian Sea, about 700 km long and 100 km across, occurs west of the Shiva crater (Figs. 3, 19). Although the origin of Laxmi Ridge is still controversial, gravity and seismic data indicate that it is quite different from a typical oceanic ridge and is probably continental in origin (Dyment 1998; Talwani and Reif 1998). It formed two basins, one on each side: the East Arabian Basin (EAB) and the West Arabian Basin (WAB). In the East Arabian Basin, a short duration of seafloor spreading commenced from the A28-A33 interval of geomagnetic chron, which finally ceased around 65 Ma (Bhattacharya et al. 1994). At the same time, with the extinction of the East Arabian Basin spreading center, the ridge suddenly jumped more than 500 km westerly to the West Arabian Basin on the other side of the Laxmi Ridge, as a possible response to the Shiva impact (Talwani and Reif 1998). This ridge jump is synchronous with the Mascarene Basin jump of the Carlsberg Ridge. In the West Arabian Basin, regular sea-floor spreading anomalies have been identified; the oldest anomaly was chron 28R. Apparently, the opening of the East Arabian Basin commenced around 84 Ma and ceased around 65 Ma, when the spreading center jumped from east to west of the Laxmi Ridge to the West Arabian Basin. The age relationship between the Shiva impact and the cessation and westerly jump of the spreading of the Laxmi Ridge is intriguing. We speculate that the sudden westerly jump of the Laxmi Ridge at KT boundary time may be linked to the Shiva impact, which readjusted the plate tectonic framework of the Arabian seafloor coinciding with the northerly jump of the Central Indian Ridge. Origin of the Deccan Traps .—The Deccan traps are one of the largest continental volcanic provinces of the world. It consists of more than 2 km of flat- lying basalt lava flows and covers an area of 500,000 km 2 , roughly the size of the State of Texas. Estimates of the original area covered by the Deccan lava flows including the Seychelles-Saya De Malha Bank are as high as 1,500,000 km 2 (White and McKenzie 1989). The Deccan traps are flood basalts similar to the Co- lumbia River basalts of the northwestern United States, formed by the Yellowstone hotspot. Currently three models for the origin of the Deccan basalt volcanism have been proposed: mantle plume theory, plate rift theory, and impact-induced theory. In mantle plume theory, Deccan flood basalts were the first manifestation of the Reunion hotspot that rose from the core-mantle boundary and subse- quently produced the hotspot trails underlying the Laccadive, Maldive, and Chagos islands; the Mascarene Plateau; and the youngest volcanic islands of Mauritius and Reunion (Morgan 1981). The age of the hotspot tracks decreases gradually from the Deccan traps to the Reunion hotspot, thus appearing to be consistent with the northward motion of the Indian plate over a fixed plume (Duncan and Pyle 1988). Although the hotspot model is very attractive, there are some geochemical problems with this model. Geochemical analysis indicates that the likely source for the Deccan volcanism is rift volcanism rather than Reunion hotspot (Mahoney 1988). Later, Mahoney et al. (2002) recognized several phases of non-MORB phases of Deccan volcanism. Further geochemical and geothermal evidence suggests that Deccan magmas were generated at relatively shallow (34-45 km) depth and rules out the possibility of its origin by a deep mantle plume (Sen 1988). To circumvent these criticisms, White and McKenzie (1989) proposed a model that combines both plume and rifting origins. They argued that the Deccan volcanism was associated with the breakup of the Seychelles microcontinent from India. The enormous Deccan flood basalts of India and the Seychelles-Saya de Malha volcanic province were created when the Seychelles split above the Reunion hotspot (Figs. 7, 10). However, there is some conflict of timing between these two events: the onset of Deccan volcanism and rifting of India and Seychelles. What triggered the rifting of the Seychelles from India? Was it the Reunion hotspot or the Shiva impact? The ...