Constraints on inner forearc deformation from balanced cross sections, Fila Costeña thrust belt, Costa Rica
Constraints on inner forearc deformation from balanced cross sections, Fila Costeña thrust belt, Costa Rica
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哥斯达黎加 Fila Costeña 冲断带平衡截面对内前弧变形的约束
DOI：
10.1029/2006tc001949
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发表时间：
2007
期刊：
影响因子：
4.2
通讯作者：
M. Protti
中科院分区：
文献类型：
--
作者：
J. Sitchler;D. Fisher;T. Gardner;M. Protti
哥斯达黎加前弧的Fila Costeña冲断带容纳了科科斯板块和巴拿马微板块汇聚的很大一部分。逆冲带的地质图描绘了一个由三匹马组成的复式构造，它们包括始新世石灰岩和渐新世至早中新世的碎屑岩，位于俯冲科科斯山脊轴线的内侧。通过在该位置沿一条垂直于逆冲带的NE-SW走向的断面构造横断面，我们限制了大约40 mm/a的缩短速率，并提出在内前弧处占据了整个板块会聚速率的50%。始新世逆冲板块底部的石灰岩由于断裂滑移减少和底部滑脱的侧向斜坡，在远离科科斯山脊轴的陆地投影的两个方向上向外尖灭。逆冲带终止于巴拿马边界附近，在俯冲巴拿马断裂带的陆地投影处。这些观察表明，随着巴拿马三重结点的迁移和科科斯板块加厚边缘的浅俯冲开始，缩短正在向东传播。尼加拉瓜弧前没有类似的特征，那里的俯冲地壳更古老，俯冲更陡峭，没有来水的海脊和海山，这表明哥斯达黎加弧前盆地的变形反映了科科斯海脊内侧会聚板块之间的更大耦合。
The Fila Costeña thrust belt in the forearc of Costa Rica is accommodating a significant portion of the convergence of the Cocos plate and Panama microplate. Geologic mapping of the thrust belt depicts a duplex with three horses that incorporate Eocene limestones and Oligocene to early Miocene clastics inboard of the subducting Cocos Ridge axis. By constructing a cross section at this location along a NE–SW trending transect perpendicular to the thrust belt, we constrain a shortening rate of approximately 40 mm/a and propose that as much as 50% of the total plate convergence rate is taken up in the inner forearc. The Eocene limestones at the base of the thrust sheets pinch out in both directions away from the onland projection of the Cocos Ridge axis owing to decrease in slip on faults and a lateral ramp in the basal décollement. The thrust belt terminates near the Panama border at the onland projection of the subducting Panama Fracture Zone. These observations suggest that shortening is propagating to the east with the migration of the Panama triple junction and the onset of shallow subduction of the thickened edge of the Cocos plate. The absence of similar features in the Nicaraguan forearc, where the subducting crust is older, subducts more steeply, and lacks incoming ridges and seamounts, indicates that deformation of the forearc basin in Costa Rica reflects greater coupling between the converging plates inboard of the Cocos Ridge.