Along‐strike variation of the sheeted dike complex in the Oman Ophiolite: Insights into subaxial ridge segment structures and the magma plumbing system
Along‐strike variation of the sheeted dike complex in the Oman Ophiolite: Insights into subaxial ridge segment structures and the magma plumbing system
复制标题
阿曼蛇绿岩片状岩脉复合体的沿走向变化：深入了解轴下脊段结构和岩浆管道系统
DOI：
--
复制
发表时间：
2003
期刊：
影响因子：
--
通讯作者：
Y. Adachi
中科院分区：
文献类型：
--
作者：
S. Umino;S. Miyashita;Fumiko Hotta;Y. Adachi
为了了解化石快速扩张脊下的浅层岩浆管道系统，研究了阿曼蛇绿岩北部60公里长片状脉杂岩的沿走向变化。大量岩脉侵入层状辉长岩的存在确定了Wadi Fizh古山脊段的北端。假设的片段中心位于Wadi Thuqbah，它比化石片段上的其他地方有更厚的Mono过渡带。片状岩脉以单质岩脉为主，99%为单质岩脉，多质岩脉和复合岩脉较少。1511条岩脉的厚度从<1 cm到bb1013 m不等，平均厚度为71.3 cm。在30 km长的岩脉复合体北半部，恢复后的岩脉走向表现为北向NS走向和南向NNE - NS走向，以Wadi Bani Umar al Gharbi南部为界。在区域边界，岩脉逐渐改变走向或相互侵入。堤坝向北加厚，古山脊段北端沿Wadi Fizh有最大的山峰，在Wadi Bani Umar al Gharbi有一个小山峰。大多数岩脉的体积mg#为55-66，与MORB的大部分重叠。较少见的、高度演化的岩脉Mg# 34-40是北域的特征。较厚的岩脉（bb0 ~ 3 m） Mg#含量较高，而较薄的岩脉（<2 m） Mg#含量变化较大。岩脉走向和整个岩石组成的区域变化可以用古脊段结构的长期变化来解释，古脊段的结构可与现今海洋中脊系统的三阶段相媲美，其跨度长达数万年。最初，段长熔体透镜沿古山脊轴线发育，形成了长而厚的高mg#岩脉。随着岩浆供应的减少，熔融透镜体分裂成南北两个较小的透镜体，由一个DEVAL包围，该DEVAL为较薄的岩脉侵入先前的厚岩脉。北部熔融透镜体与岩浆源的断裂改变了熔体成分，使其变成了高度演化的低Mg岩浆，这些岩浆随后以短演化岩脉的形式侵入。与此同时，段中心的主熔体透镜继续向高mg#岩脉供给岩浆，这是由较大的熔体透镜尺寸和深部岩浆房的间歇性岩浆供给维持的。
Along‐strike variations of the 60‐km‐long sheeted dike complex in the northern Oman Ophiolite were studied in order to understand the shallow magma plumbing system beneath the fossil fast spreading ridge. The presence of numerous dikes intruding into the layered gabbro defines the northern end of the paleoridge segment at Wadi Fizh. The postulated segment center is located at Wadi Thuqbah, which has a thicker Mono transition zone than elsewhere along the fossil segment. Aphyric dikes predominate in the sheeted dikes, of which 99% are simple, while multiple and composite dikes are few. The thickness of 1511 dikes ranges from <1 cm to >13 m, with an average thickness of 71.3 cm. Restored dike trends in the 30‐km‐long northern half of the dike complex display the NS trending north domain and NNE‐NS trending south domain bordered at the south of Wadi Bani Umar al Gharbi. In the domain boundary, dikes gradually change strikes or are mutually intrusive. Dike thickens northward with the largest peak along Wadi Fizh at the northern end of the paleoridge segment and a small peak at Wadi Bani Umar al Gharbi. Most dikes have a bulk Mg# of 55–66, which overlaps the majority of MORB. Less common, highly evolved dikes with Mg# 34–40 characterize the north domain. Thicker dikes (>3 m) tend to have high Mg#, while thinner dikes (<2 m) are highly variable in Mg#. The regional variations of the dike trends and the whole rock compositions can be explained by the secular variation in the structures of the paleoridge segment comparable to a third‐order segment of the present mid‐ocean ridge system spanning a few tens of thousands of years. Initially, the segment‐long melt lens developed along the paleoridge axis, which fed long and thick dikes with high Mg#. With decreasing supply of magma, the melt lens split up into the north and south smaller lenses bordered by a DEVAL that fed thinner dikes intruding into the former thick dikes. Cut‐off of the northern melt lens from the magma source changed the melt composition to highly evolved, low‐Mg# magmas, which subsequently intruded as short evolved dikes. Meanwhile, the main melt lens in the segment center continued feeding the high‐Mg# dikes which were maintained by the larger melt lens size and intermittent magma supply from deep magma chambers.