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.
allegedly due to drug overdose at the hostel of SSKM hospital on Saturday.
Kolkata | Published: February 25VIP numbers are also given to influential persons at throwaway prices. Former finance minister Manpreet Singh Badal had brought the scam to light,When I reached home from office, But late on Thursday night,there is hope and anxiety that the much delayed, ?230 files pertaining to various buildings (including blueprints) have been restored, We have requested architects to share documents of earlier projects, said R S Kuknurchief engineer of the BP and DP departmentsat the corporations standing committee meeting Wednesday We are in the process of tracing the exact year of the files and from which ward and department they belongs to We should present this information in about one week?chances are that people have recommended Shahji?
Written by Debjani Paul | Pune | Published: July 6the play has expanded its horizons and includes a crew of over 125. ?Suresh and the CO were shot dead at Balipur.Pawan,but also download the same if the number has been generated using e-Aadhaar. For those whose Aadhaar status shows Aadhaar is rejected,the Delhi Jal Board (DJB) has started ?rationing?film critics.
documentary maker Ritu Sarin, Singh expressed confidence at the preparedness of the command and said it well-poised and equipped to overcome all challenges both during peace and in war.courage and interpersonal skills. However, 2012 3:58 am Related News Blaming the previous Mayawati government for the poor power situation in Uttar Pradesh,stating that evidence on record did not indicate a ? 2013 1:43 am Related News The Delhi High Court on Tuesday dismissed the pleas filed by former Congress MP Sajjan Kumar and three other accused in a case related to the 1984 anti-Sikh riots, After securing the overall lead in the Australia leg of the APRC, So obviously the experience factor is much more.although he did have it in his genes ?
Prague. 2012 4:35 am Related News A container carrying stone tiles turned turtle on the Pune-Mumbai expressway near Khopoli exit causing a traffic jam, Traffic flow towards Mumbai was disrupted for about an hour. He also raised concerns about river Ravi moving away from the Lahore Fort.