Tectonic rotations during the Chile Ridge collision and obduction of the Taitao ophiolite (southern Chile)
Tectonic rotations during the Chile Ridge collision and obduction of the Taitao ophiolite (southern Chile)
复制标题
智利海岭碰撞期间的构造旋转和泰涛蛇绿岩（智利南部）的仰冲
DOI：
10.1111/j.1440-1738.2005.00487.x
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发表时间：
2005
期刊：
影响因子：
1.5
通讯作者：
T. Yamazaki
中科院分区：
文献类型：
--
作者：
E. Veloso;R. Anma;T. Yamazaki
< 6马幼太涛蛇绿岩，暴露于太涛半岛最西端，位于智利三联结东南约40 km处，由一完整的洋石圈层序组成。为了解蛇绿岩在南美板块前弧上复杂的逆冲过程，进行了系统的古地磁采样研究。观察了两种具有代表性的剩磁矢量退磁路径。一类具有稳定的单矢量退磁路径，在火山碎屑岩和岩脉杂岩中观察到。它们的剩余磁化矢量的方向表示不同程度的逆时针旋转。另一种以多向磁路为特征，在深部单元（辉长岩和超镁质岩）中观察到。由此分离出两个不同的稳定剩余磁化矢量；一种具有高矫顽力，另一种沿退磁路径具有低矫顽力，且粘性磁化影响较小。这表明，复杂的变形历史涉及至少两个旋转事件。从高矫顽力剩余磁化矢量推断出的顺时针旋转归因于脊碰撞事件，从低矫顽力剩余磁化矢量推断出的逆时针旋转归因于蛇绿岩在逆冲和最终就位期间进入南美前弧的调节阶段。褶皱在这一时期发展起来。古地磁恢复表明，深裂单元和岩脉复合体的内部构造可能起源于靠近转换断层的洋中脊环境。逆冲过程中，深成岩杂岩单元逆时针旋转，形成了与基底之间的构造间隙。火山碎屑岩一定是在它们现在的位置附近沉积的，填充了构造间隙，因为构造旋转对这些岩石的影响较小。
Abstract The < 6 Ma young Taitao ophiolite, exposed at the westernmost promontory of the Taitao Peninsula, is located approximately 40 km southeast of the Chile triple junction and consists of a complete sequence of oceanic lithosphere. Systematic sampling for paleomagnetic study was performed to understand the complex obduction processes of the ophiolite onto the forearc of the South American Plate. Two representative demagnetization paths of remanent magnetization vectors were observed. One is characterized by stable univectorial demagnetization paths and was observed in volcaniclastic rocks and dyke complexes. Orientations of their remanent magnetization vectors indicate various degrees of counterclockwise rotations. The other is characterized by multivectorial demagnetization paths and was observed in the plutonic units (gabbros and ultramafic rocks). From these, two distinct stable remanent magnetization vectors were isolated; one has high coercivity and the other has low coercivity along the demagnetization paths with little influence of viscous magnetizations. This suggests that the complex deformation history involved at least two rotational events. The clockwise rotation, inferred from high coercivity remanent magnetization vectors, was attributed to a ridge collision event and the counterclockwise rotation, inferred from the low coercivity remanent magnetization vectors, was attributed to an accommodation phase into the South American forearc during obduction and final emplacement of the ophiolite. Folds developed during this period. Paleomagnetic restorations of the internal structures of the plutonic units and dyke complexes suggest that they probably originated in a mid‐oceanic ridge environment near a transform fault. The counterclockwise rotation of the plutonic and dyke complex units during the obduction generated tectonic gaps between these and the basement. The volcaniclastic rocks must have been deposited at nearly their present location, filling the tectonic gaps, as less effect of tectonic rotation was identified on these rocks.