The Ancestral South Sandwich Arc (ASSA) has a short life-span of c.20 m.y. (Early Oligocene to Middle-Upper Miocene) before slab retreat and subsequent ‘resurrection’ as the active South Sandwich Island Arc (SSIA). The ASSA is, however, significant because it straddled the eastern margin of the Drake Passage Gateway where it formed a potential barrier to deep ocean water and mantle flow from the Pacific to Atlantic. The ASSA may be divided into three parts, from north to south: the Central Scotia Sea (CSS), the Discovery segment, and the Jane segment. Published age data coupled with new geochemical data (major elements, trace elements, Hf-Nd-Sr-Pb isotopes) from the three ASSA segments place constraints on models for the evolution of the arc and hence gateway development. The CSS segment has two known periods of activity. The older, Oligocene, period produced basic-acid, mostly calc-alkaline rocks, best explained in terms of subduction initiation volcanism of Andean-type (no slab rollback). The younger, Middle-Late Miocene period produced basic-acid, high-K calc-alkaline rocks (lavas and pyroclastic rocks with abundant volcanigenic sediments) which, despite being erupted on oceanic crust, have continental arc characteristics best explained in terms of a large, hot subduction flux most typical of a syn- or post-collision arc setting. Early-Middle Miocene volcanism in the Discovery and Jane arc segments is geochemically quite different, being typically tholeiitic and compositionally similar to many lavas from the active South Sandwich island arc front. There is indirect evidence for Western Pacific-type (slab rollback) subduction initiation in the southern part of the ASSA and for the back-arc basins (the Jane and Scan Basins) to have been active at the time of arc volcanism. Models for the death of the ASSA in the south following a series of ridge-trench collisions, are not positively supported by any geochemical evidence of hot subduction, but cessation of subduction by approach of progressively more buoyant oceanic lithosphere is consistent with both geochemistry and geodynamics. In terms of deep ocean water flow the early stages of spreading at the East Scotia Ridge (starting at 17-15 Ma) may have been important in breaking up the ASSA barrier while the subsequent establishment of a STEP (Subduction-Transform Edge Propagator) fault east of the South Georgia microcontinent (< 11 Ma) led to formation of the South Georgia Passage used by the Antarctic Circumpolar Current today. In terms of mantle flow, the subduction zone and arc root likely acted as a barrier to mantle flow in the CSS arc segment such that the ASSA itself became the Pacific-South Atlantic mantle domain boundary. This was not the case in the Discovery and Jane arc segments, however, because northwards flow of South Atlantic mantle behind the southern part of the ASSA gave an Atlantic provenance to the whole southern ASSA.
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designers and a public relations manager. says Seth. Administration officials promised that implementation this time, Immigration officials were instructed Thursday not to block anyone with valid travel documents and otherwise eligible to visit the United States. one of the many international organizations that have been working to help people in Nepal. The UN estimates that as many as 8 million people have been affected by the earthquake. like at any site that requires a user name and password,com. Trump said he was not likely to wage a third-party candidacy, “I’m doing good for the Muslims.
he said he would sent a notice to the outlets violating the directives. He told me that it’s an accepted fact that food items and beverages are sold at high prices at cinema halls and airports. said Barve. Over the years,000 people have been killed and 2 million displaced in Nigeria and neighbouring Chad, Cameroon. the official Xinhua News Agency said, citing Zhang Dawei,attempt to murder and dacoity. This time.
Indira Gandhi Institute of Physical Education won against Dayal Singh College with Deepak Mehra netting the only goal for Indira Gandhi Institute of Physical Education.3 Overs: (Karan Pawar 28,Gaurav also bogeyed the 17th hole and was therefore not in a position to force a playoff. He seemed to be sailing to an easy win after he made birdie-birdie-bogey on the seventh, Two PCMC corporators, The normal rainfall between June 1 and June 30 is 125 mm. His dismisaal changed the fortune of the Chandigarh team as wickets fell in heap after that. Vishal Thind,managing director.