Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift
Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift
复制标题
皮托深裂谷暴露的超快扩张洋壳变形的古地磁约束
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
J. Karson
中科院分区：
文献类型：
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作者：
A. J. Horst;R. Varga;J. Gee;J. Karson
[1] 高斯年代期间南东太平洋隆起 (EPR) 超快扩张（~142 km Ma−1，完全扩张速率）产生的最上层洋壳暴露在沿皮托深裂谷东北壁的构造窗口中。对来自两个相邻研究区域的完全定向岩脉 (62) 和辉长岩 (5) 样本进行古地磁分析，得出自举平均剩磁方向为 38.9° ± 8.1°、−16.7° ± 15.6°、n = 23（A 区）和 30.4° ± 8.0°、-25.1° ± 12.9°、n = 44（B 区），两者均显着与南纬 23° 处的地心轴偶极子预期方向不同。区域构造和露头规模结构数据与自举剩磁方向相结合，约束模型涉及一系列三个旋转，导致堤坝恢复到与 (1) 扩张过程中地壳块向内倾斜（区域 A = 11°，区域 B = 22°）相关的近垂直方向，(2) 复活节的顺时针垂直轴旋转微孔板（A = 46°，B = 44°），以及（3）Pito Deep Rift 处的块倾斜（A = 21°，B = 10°）。这些数据支持了EPR南部增生的结构模型，其中露头规模的断层和块体旋转适应了与扩张相关的轴下沉降，该沉降通常小于在赫斯深裂谷暴露的快速扩张速度下产生的地壳中观察到的沉降。这些数据也支持之前对复活节微板附近地壳顺时针旋转的估计。岩脉样本的自然剩磁 (NRM) 的算术平均值为 5.96 A/m ± 3.76，这表明它们对观测到的从快速到超快扩展地壳的磁异常有显着贡献。
[1] The uppermost oceanic crust produced at the superfast spreading (∼142 km Ma−1, full-spreading rate) southern East Pacific Rise (EPR) during the Gauss Chron is exposed in a tectonic window along the northeastern wall of the Pito Deep Rift. Paleomagnetic analysis of fully oriented dike (62) and gabbro (5) samples from two adjacent study areas yield bootstrapped mean remanence directions of 38.9° ± 8.1°, −16.7° ± 15.6°, n = 23 (Area A) and 30.4° ± 8.0°, −25.1° ± 12.9°, n = 44 (Area B), both are significantly distinct from the Geocentric Axial Dipole expected direction at 23° S. Regional tectonics and outcrop-scale structural data combined with bootstrapped remanence directions constrain models that involve a sequence of three rotations that result in dikes restored to subvertical orientations related to (1) inward-tilting of crustal blocks during spreading (Area A = 11°, Area B = 22°), (2) clockwise, vertical-axis rotation of the Easter Microplate (A = 46°, B = 44°), and (3) block tilting at Pito Deep Rift (A = 21°, B = 10°). These data support a structural model for accretion at the southern EPR in which outcrop-scale faulting and block rotation accommodates spreading-related subaxial subsidence that is generally less than that observed in crust generated at a fast spreading rate exposed at Hess Deep Rift. These data also support previous estimates for the clockwise rotation of crust adjacent to the Easter Microplate. Dike sample natural remanent magnetization (NRM) has an arithmetic mean of 5.96 A/m ± 3.76, which suggests that they significantly contribute to observed magnetic anomalies from fast- to superfast-spread crust.