Composition and evolution of the Ancestral South Sandwich Arc: Implications for the flow of deep ocean water and mantle through the Drake Passage Gateway
Composition and evolution of the Ancestral South Sandwich Arc: Implications for the flow of deep ocean water and mantle through the Drake Passage Gateway
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祖先南桑威奇弧的组成和演化：对通过德雷克海峡门户的深海水和地幔流动的影响
DOI：
10.1016/j.gloplacha.2014.08.017
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发表时间：
2014
影响因子：
3.9
通讯作者：
Pearce J
中科院分区：
文献类型：
--
作者：
Pearce J
祖先南三明治弧 (ASSA) 的寿命很短，大约为 c。 20 米（渐新世早期到中新世中晚期），然后板块退缩并随后“复活”为活跃的南桑威奇岛弧（SSIA）。然而，ASSA 意义重大，因为它横跨德雷克海峡门户的东缘，对深海水和从太平洋到大西洋的地幔流形成了潜在的屏障。 ASSA 从北到南可分为三个部分：中央斯科舍海 (CSS)、发现号段和简号段。已发布的年龄数据与来自三个 ASSA 段的新地球化学数据（主要元素、微量元素、Hf-Nd-Sr-Pb 同位素）相结合，对弧演化模型以及网关开发产生了限制。 CSS 部分有两个已知的活动周期。较古老的渐新世时期产生了碱性-酸性岩石，主要是钙碱性岩石，最好的解释是安第斯型俯冲起始火山作用（无板块回滚）。较年轻的中新世晚期产生了碱性酸性、高钾钙碱性岩石（具有丰富火山沉积物的熔岩和火山碎屑岩），尽管它们是在洋壳上喷发的，但其大陆弧特征最好用大的热俯冲通量来解释，这是最典型的同碰撞或后碰撞弧环境。发现弧段和简弧段的早中新世火山活动在地球化学上有很大不同，通常为拉斑岩，成分与活跃的南桑威奇岛弧前缘的许多熔岩相似。有间接证据表明，西太平洋型（板块回滚）俯冲起始于 ASSA 南部，并且弧后盆地（简和斯坎盆地）在弧火山活动时一直很活跃。一系列山脊-海沟碰撞后，南方ASSA死亡的模型并没有得到任何热俯冲地球化学证据的积极支持，但由于海洋岩石圈浮力逐渐增强而导致俯冲停止，这与地球化学和地球动力学是一致的。就深海水流而言，东斯科舍海脊（开始于 17-15Ma）的早期扩散阶段可能对于打破 ASSA 屏障非常重要，而随后在南乔治亚微大陆（<11Ma）以东建立的 STEP（俯冲变换边缘传播器）断层导致了今天南极绕极流所使用的南乔治亚航道的形成。就地幔流而言，俯冲带和弧根可能对CSS弧段的地幔流起到了屏障作用，使得ASSA本身成为太平洋-南大西洋地幔域边界。然而，发现号弧段和简弧段的情况并非如此，因为南大西洋地幔在阿萨萨南部后面向北流动，为整个阿萨萨南部提供了大西洋来源。
The Ancestral South Sandwich Arc (ASSA) has a short life-span of c. 20 m.y. (early Oligocene to middle–late 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–acidic, 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–acidic, 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 the northward flow of the South Atlantic mantle behind the southern part of the ASSA gave an Atlantic provenance to the whole southern ASSA.