Oceanic core complex development at the ultraslow spreading Mid-Cayman Spreading Center
Oceanic core complex development at the ultraslow spreading Mid-Cayman Spreading Center
复制标题
DOI：
10.1029/2010gc003240
复制
发表时间：
2011-03-15
影响因子：
3.5
通讯作者：
de Lepinay, Bernard Mercier
中科院分区：
文献类型：
--
作者：
Hayman, Nicholas W.;Grindlay, Nancy R.;de Lepinay, Bernard Mercier
大约三分之一的全球洋中脊系统以小于20毫米/年（全速）的速度扩展，预测地壳厚度较低，轴向深度较大，端元玄武岩成分和突出的轴向断层。这些预测在这里进一步研究沿着超低（15-17毫米/年）开曼群岛中部扩展中心（MCSC）通过汇编以前发表和未发表的数据。MCSC位于沿着加勒比-北美板块边界，是世界上最深（> 6公里）的扩张中心之一，并被认为是一些最薄（约3公里）的地壳的增生。MCSC产生端元洋中脊玄武岩成分，并容纳最近发现的热液喷口。多波束测深数据显示，轴向深度变化沿着MCSC与内脊裂谷壁所定义的更大规模的悬崖和冰碛。疏浚和近海底工作对主要来自最大轴向深度的玄武质熔岩进行了成像和取样，并与15%的橄榄岩相似，橄榄岩周围是来自突出的火山岩的辉长岩。辉长岩具有广泛的成分变化（troctolites铁辉长岩），并在许多地方包含高温（角闪岩麻粒岩相）剪切带。辉长岩组合物主要反映了近液相线阶段的积累，结晶范围内的玄武岩熔体，以及从与间隙熔体在一个亚轴糊状区的相互作用。从航磁数据反演的磁化变化与玄武质熔岩的不连续分布和结构上的不对称扩张是一致的。这些观测结果支持了MCSC海底扩张的海洋核复合体模型，可能使其成为超低速海底扩张通过淤泥带和拆离断层地壳过程的典型例子。
Roughly a third of the global mid-ocean ridge system spreads at < 20 mm/yr (full rate) with predicted low crustal thicknesses, great axial depths, end-member basalt compositions, and prominent axial faults. These predictions are here further investigated along the ultraslow (15-17 mm/yr) Mid-Cayman Spreading Center (MCSC) through a compilation of both previously published and unpublished data. The MCSC sits along the Caribbean-North American plate boundary and is one of the world's deepest (> 6 km) spreading centers, and thought to accrete some of the thinnest (similar to 3 km) crust. The MCSC generates end-member mid-ocean ridge basalt compositions and hosts recently discovered hydrothermal vents. Multibeam bathymetric data reveal that axial depth varies along the MCSC with intraridge rift walls defined by kilometer-scale escarpments and massifs. Dredging and near-bottom work has imaged and sampled predominantly basaltic lavas from the greatest axial depths and similar to 15% peridotite surrounded by gabbroic rocks from the prominent massifs. The gabbroic rocks exhibit wide compositional variation (troctolites to ferrogabbros) and in many places contain high-temperature (amphibolite to granulite facies) shear zones. Gabbroic compositions primarily reflect the accumulation of near-liquidus phases that crystallized from a range of basaltic melts, as well as from interactions with interstitial melts in a subaxial mush zone. Magnetization variations inverted from aeromagnetic data are consistent with a discontinuous distribution of basaltic lavas and structurally asymmetric spreading. These observations support an oceanic core complex model for MCSC seafloor spreading, potentially making it a type example of ultraslow seafloor spreading through mush zone and detachment fault crustal processes.