Development of oceanic detachment and asymmetric spreading at the Australian‐Antarctic Discordance
Development of oceanic detachment and asymmetric spreading at the Australian‐Antarctic Discordance
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DOI：
10.1029/2004gc000793
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发表时间：
2004-12
期刊：
影响因子：
3.7
通讯作者：
K. Okino;K. Matsuda;D. Christie;Y. Nogi;K. Koizumi
中科院分区：
文献类型：
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作者：
K. Okino;K. Matsuda;D. Christie;Y. Nogi;K. Koizumi
已知最大的海洋拆离地形出现在澳大利亚-南极不一致（AAD）的B3段。使用新收集的测深，磁力和重力数据，我们表明B3段分为两个对比的二阶段。西部亚段B3 W的特征是有序的、脊平行的深海丘陵和低地幔布格重力异常。东部亚段，B3 E，显示粗糙，混乱的形态，并包括几个megamullions高地幔布格重力异常值的特点。据估计，B3 E南部的地壳最多薄3公里。混乱的形态与较薄的地壳相结合，支持了巨古龙是大洋大陆架暴露的下盘的观点。巨糜棱岩地体的特征是磁化强度比邻近地体高，这很可能是由于剥离面暴露的橄榄岩的蛇纹化作用。拆离面占总面积的70%以上的两个脊翼年轻于2 Ma在B3 E，表明海洋determinants发挥了重要作用，在其发展。在B3 E中的扩展是非常不对称的，与较大的分离表面相关的表观速率较高，其中发生了高达75%的总扩展。在B4段中也发现了类似的不对称扩张，这表明这是与AAD最深处的冷地幔和低岩浆供应相关的主要扩张模式，它仅限于AAD扩张轴的100 km长的部分。
The largest known oceanic detachment terrains occur in Segment B3 of the Australian‐Antarctic Discordance (AAD). Using newly collected bathymetry, magnetic, and gravity data, we show that Segment B3 is divided into two contrasting second‐order segments. The western subsegment, B3W, is characterized by well‐ordered, ridge parallel abyssal hills and low mantle Bouguer gravity anomalies. The eastern subsegment, B3E, displays rough, chaotic morphology and includes several megamullions characterized by high mantle Bouguer gravity anomaly values. The crust is estimated to be thinner by a maximum of 3 km in southern B3E. The combination of chaotic morphology with thinner crust supports the idea that the megamullions are exposed footwalls of oceanic detachments. Megamullion terrains are characterized by higher magnetization than adjacent terrains, most likely as a result of serpentinization of peridotite exposed at the detachment surfaces. Detachment surfaces constitute up to 70% of the total area of both ridge flanks younger than 2 Ma in B3E, indicating that oceanic detachments have played a major role in its development. Spreading in B3E has been extremely asymmetric, with higher apparent rates associated with the large detachment surfaces, where up to 75% of the total extension occurred. Similar asymmetric spreading on oceanic detachments is also recognized in Segment B4, suggesting that this is the dominant mode of extension associated with cold mantle and low magma supply in this deepest part of the AAD, where it is confined to a mere 100‐km‐long section of the AAD spreading axis.