Interplay between faults and lava flows in construction of the upper oceanic crust:: The East Pacific Rise crest 9°25′-9°58′N
Interplay between faults and lava flows in construction of the upper oceanic crust:: The East Pacific Rise crest 9°25′-9°58′N
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DOI：
10.1029/2006gc001399
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发表时间：
2007-06-07
影响因子：
3.5
通讯作者：
Perfit, M. R.
中科院分区：
文献类型：
--
作者：
Escartin, J.;Soule, S. A.;Perfit, M. R.
[1]利用高分辨率侧扫声纳资料和近海底测深剖面，研究了东太平洋海隆(EPR)波峰在9°25‘~9°58’N之间的断层展布及其特征。由此产生的分析表明，年轻海底的变形特征和构造应变估计密度与相同扩张年龄的覆盖沉积物的较老海底相比存在重大差异。我们估计，由于最近熔岩流频繁的断层埋藏，“老”海底的构造形变和相关应变的表现类似于年轻海底的5倍。因此，看不见的、火山叠加的构造变形可能占到完全建立挤压桩(第2A层)所需的类似300米沉降量的30%到100%。许多更长的熔岩流动(大于类似于1公里)大坝反对向内面对的断层陡峭。这将它们的长度限制在1-2公里的距离内，这与挤压层获得其全部厚度的位置重合。在EPR，超过2%的板块分离是由脆性变形所调节的，脆性变形主要由向内的断层组成(类似于70%)。EPR峰顶的断层活动发生在狭窄的上地壳内，类似于4公里宽的上地壳，表现为覆盖在轴向岩浆室之上的脆性盖子。离轴线更远(40公里)的形变是由岩石圈由于热下沉引起的挠曲来调节的，导致类似50%的内向断层容纳类似50%的应变。根据熔岩流对断层的埋藏和断层崖对断层的拦流作用，我们发现，在山脊顶部及其上翼形成的低起伏生长断层强烈控制了2A层的发育。反过来，这些断层又对熔岩流沿山脊分布和跨越山脊的分布方式产生了深远的影响。
[1] The distribution of faults and fault characteristics along the East Pacific Rise (EPR) crest between 9 degrees 25'N and 9 degrees 58'N were studied using high-resolution side-scan sonar data and near-bottom bathymetric profiles. The resulting analysis shows important variations in the density of deformational features and tectonic strain estimates at young seafloor relative to older, sediment-covered seafloor of the same spreading age. We estimate that the expression of tectonic deformation and associated strain on "old'' seafloor is similar to 5 times greater than that on young'' seafloor, owing to the frequent fault burial by recent lava flows. Thus the unseen, volcanically overprinted tectonic deformation may contribute from 30% to 100% of the similar to 300 m of subsidence required to fully build up the extrusive pile ( Layer 2A). Many longer lava flows ( greater than similar to 1 km) dam against inward facing fault scarps. This limits their length at distances of 1 - 2 km, which are coincident with where the extrusive layer acquires its full thickness. More than 2% of plate separation at the EPR is accommodated by brittle deformation, which consists mainly of inward facing faults ( similar to 70%). Faulting at the EPR crest occurs within the narrow, similar to 4 km wide upper crust that behaves as a brittle lid overlying the axial magma chamber. Deformation at greater distances off axis ( up to 40 km) is accommodated by flexure of the lithosphere due to thermal subsidence, resulting in similar to 50% inward facing faults accommodating similar to 50% of the strain. On the basis of observed burial of faults by lava flows and damming of flows by fault scarps, we find that the development of Layer 2A is strongly controlled by low-relief growth faults that form at the ridge crest and its upper flanks. In turn, those faults have a profound impact on how lava flows are distributed along and across the ridge crest.