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.
C114 news June 11th morning news (Jiang Junmu) broadband mobile communication technology is advanced change, Chinese an annual increase of 100 million mobile users, the total is close to 1 billion 260 million, Deputy Minister of industry and information technology Liu Lihua said Wednesday.
at the 2014 World Mobile Forum held during the Asian mobile communications Expo (MAE), Liu Lihua will be one of the world’s most innovative broadband mobile communications, one of the fastest growing areas.
global mobile users reached 7 billion, penetration rate of up to 96%. The mobile Internet is swept with hitherto unknown speed, promote the change of people’s life in all aspects of cloud computing, big data; the upgrading of traditional industries, resulting in higher speed and stability requirements of the mobile communication network, to promote the evolution of mobile communication technology continues to upgrade.
new generation of mobile communication technology to accelerate the evolution, is showing two major trends. Liu Lihua said, on the one hand, large-scale development of terminal users, more than 80% Internet users through the Internet, mobile phone China the number of mobile phone users reached 500 million, in 2013 the national intelligent mobile phone shipments more than 900 million, more than the feature phone for the first time, 4G technology will further promote the popularization and development of a new business model and more new applications. On the other hand, the integration of mobile communication services and applications has a significant impact on people’s daily lives.
he pointed out that, in order to promote the popularization and application of a new generation of mobile communication technology, the Ministry will give support from industrial policy, regulatory policy, and actively promote the enterprise to accelerate investment; encourage and guide the industry to accelerate technology development, lay the foundation for the development of mobile Internet; carry out 5G research, promote broadband mobile communication technology continues to evolve.