Progressive deformation of an evaporite-bearing accretionary complex: SeaMARC I, SeaBeam and piston-core observations from the Mediterranean Ridge
Progressive deformation of an evaporite-bearing accretionary complex: SeaMARC I, SeaBeam and piston-core observations from the Mediterranean Ridge
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含蒸发岩的增生杂岩的渐进变形：来自地中海海脊的 SeaMARC I、SeaBeam 和活塞岩心观测
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发表时间：
1992
期刊：
影响因子：
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通讯作者：
M. Cita
中科院分区：
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作者：
K. Kastens;N. Breen;M. Cita
地中海海脊是非洲板块和爱琴海之间的板块边缘汇聚形成的一个弧形的变形沉积物脊。沿着苏尔特深海平原未变形浊积岩与地中海海脊褶皱和断层沉积物之间的接触面，进行了SeaMARC I和SeaBeam密集勘探，随后进行了活塞取芯。沿着洋脊外缘，表层沉积物变形为正弦形脊和槽（波长0.5-2公里，振幅20-150米），我们将其解释为褶皱。在平面图中，脊和槽组构平行于西北-东南走向的区域等高线，这表明褶皱是在垂直于地中海脊的挤压作用下形成的。最外面的海脊正在向深海平原上脱落碎片裙，这意味着隆起和变形正在进行中。我们表明，最外面的褶皱的几何形状可以通过弹性弯曲的一个包的5-10个相对较强的层，每层10-20米厚，较弱的层之间的夹层，我们等同于强层与石膏层在上墨西拿的上花岗岩。将海底从平坦层折叠成观察到的山脊和海槽地形将使该层缩短不到2%。2%的缩短（等于2%的增厚）是不足以创建所观察到的地中海海脊的救济，即使整个沉积物柱下降到基底参与，我们推断，额外的缩短/增厚是由逆冲断层上方的滑脱层在顶部的墨西拿盐层容纳。在距离变形前沿15公里以上和距离深海平原500米以上的地方，边缘锐利、粒度细的侧扫线理几乎没有垂直起伏，横穿大规模的海脊和海槽地形。这些细粒线理分为两组，走向为N/S至NNE/SSW和~ENE。我们将这些线性构造解释为共轭走滑断层的痕迹，这些断层形成于形成NW/SE向褶皱的同一挤压体制中。走滑断层的发生可能与最初盐控滑脱面之上叠瓦状逆冲扇停止发育相一致。地中海海脊的以下特征归因于在进入的沉积剖面中存在碳酸盐岩：（1）最初的变形是褶皱而不是逆冲断层;（2）狭窄的锥形;（3）快速向外生长;（4）岩溶作用。
The Mediterranean Ridge is an arcuate ridge of deformed sediment caught up in the convergent plate margin between the African plate and the Aegean. An intensive campaign of SeaMARC I and SeaBeam surveys followed by piston coring has been conducted along the contact between undeformed turbidites of the Sirte Abyssal Plain and folded and faulted sediments of the Mediterranean Ridge. Along the outer edge of the Ridge, surficial sediments have been deformed into sinusoidal ridges and troughs (wavelengths 0.5–2 km, amplitude 20–150 m), which we interpret as folds. In plan view, the ridge and the trough fabric parallels the NW-SE trending regional contours, suggesting that the folds formed in response to compression orthogonal to the Mediterranean Ridge. The outermost ridge is shedding a debris apron out onto the abyssal plain, implying that uplift and deformation are ongoing. We show that the geometry of the outermost folds can be produced by elastic bending of a packet of 5–10 relatively strong layers, each 10–20 m thick, interbedded between weaker layers; we equate the strong layers with gypsum beds in the Messinian upper evaporites. Folding the seafloor from a flat layer into the observed ridge and trough topography would shorten the layer by less than 2%. Two percent shortening (equals two percent thickening) is insufficient to create the observed relief of the Mediterranean Ridge even if the entire sediment column down to basement were involved; we infer that additional shortening/thickening is accommodated by thrust faulting above a decollement at the top of the Messinian salt layer. At distances > 15 km from the deformation front and more than 500 m from the abyssal plain, sharp-edged, fine-grained side-scan lineations with very little vertical relief cut across the kilometer-scale ridge and trough topography. These fine-grained lineations fall in two groups trending N/S to NNE/SSW and ~ENE. We interpret these lineaments as traces of conjugate strike-slip faults formed in the same compressional regime which formed the NW/SE trending folds. The onset of strike-slip faulting may coincide with the cessation of imbricate thrust fan development above the initial salt-controlled decollement surface. The following characteristics of the Mediterranean Ridge are attributed to the presence of evaporites in the incoming sedimentary section: (1) initial deformation by folding rather than thrust faulting; (2) narrow taper; (3) rapid rate of outward growth; (4) karstification.