Magnetic stripes of a transitional continental rift in Afar
Magnetic stripes of a transitional continental rift in Afar
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DOI：
10.1130/g32697.1
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发表时间：
2012-03-01
期刊：
影响因子：
5.8
通讯作者：
Alemu, Abera
中科院分区：
文献类型：
--
作者：
Bridges, David L.;Mickus, Kevin;Alemu, Abera
平行于洋中脊的磁条是海底扩张最重要的结果之一，在板块构造理论的建立和海底扩张速率的确定中发挥了重要作用。类似的磁异常模式还没有得到很好的记录在大陆裂谷过渡到海底扩张中心的地下。在这里，使用高分辨率的磁性数据，收集了整个Tendaho地堑在阿法尔凹陷，埃塞俄比亚，我们记录的第一个例子之一的陆上磁线理相似的模式和幅度的海底扩张中心的特点。类似于50公里宽的地堑是红海传播的陆地延续的最南端的结构和地貌表现，它被用来代表阿法尔境内的阿拉伯-努比亚板块边界。地堑以西北走向的边界断层为界，下盘主要为约。1.7 Ma玄武岩和下降的块体构成了逐渐向地堑中心的年轻玄武岩，达到约。35 ka。Tendaho磁场的特点是类似于10公里宽的线性负磁异常，对应于一个正常极性区，两侧是两个平行的，类似于20公里宽的线性正磁异常，极性相反。这项工作表明，在海洋扩张中心发展之前，过渡大陆裂谷中可以发育磁条。关于磁条可用于确定海底扩张开始日期的普遍假设，可能需要根据此处提供的证据重新评估。
Magnetic stripes parallel to mid-ocean ridges are one of the most significant consequences of seafloor spreading, and have played an essential role in the establishment of the plate tectonics theory and the determination of seafloor spreading rates. Similar magnetic anomaly patterns have not been well documented subaerially in continental rifts transitioning into seafloor spreading centers. Here, using high-resolution magnetic data that were collected across the Tendaho Graben in the Afar Depression, Ethiopia, we document one of the first examples of subaerial magnetic lineations similar in pattern and amplitude to those that characterize seafloor spreading centers. The similar to 50-km-wide graben is the southernmost structural and geomorphological expression of the on-land continuation of the Red Sea propagator, which is taken to represent the Arabian-Nubian plate boundary within Afar. The graben is bounded by northwest-trending border faults, with the footwalls dominated by ca. 1.7 Ma basalts and the downthrown blocks constituting progressively younger basalts toward the center of the graben, reaching ca. 35 ka. The Tendaho magnetic field is characterized by an similar to 10-km-wide linear negative magnetic anomaly that corresponds to a normal-polarity zone that is flanked by two parallel, similar to 20-km-wide linear positive magnetic anomalies of reversed polarity. This work shows that magnetic stripes can be developed in transitional continental rifts before the development of oceanic spreading centers. The common assumption that magnetic stripes can be used to date the onset of seafloor spreading may need to be re-evaluated in light of the evidence provided here.