Creation of the Cocos and Nazca plates by fission of the Farallon plate
Creation of the Cocos and Nazca plates by fission of the Farallon plate
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DOI：
10.1016/j.tecto.2005.05.011
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发表时间：
2005-08-01
期刊：
影响因子：
2.9
通讯作者：
Lonsdale, P
中科院分区：
文献类型：
--
作者：
Lonsdale, P
在整个第三纪早期，法拉隆海洋板块的面积因北方大小板块的分离而逐渐缩小，形成了独立运动的板块和微板块。法拉隆板块破碎的性质和历史主要是从东太平洋隆起的西太平洋板块侧翼的构造模式推断出来的，因为破碎的东太平洋板块侧翼已经俯冲。板块碎裂的最后一幕发生在中新世初期，当时科科斯板块被分离，留下了缩小了很多的法拉隆板块，改名为纳斯卡板块，并开始了科科斯-纳斯卡扩张。一些渐新世法拉隆板块的裂谷边缘，这是一个直接的记录，这个板块分裂事件已存活在东部热带太平洋，最广泛的北方秘鲁和厄瓜多尔。共轭北方裂谷边缘的小部分残留物暴露在哥斯达黎加外，可能还有巴拿马南部。海洋地球物理剖面图（测深、磁力和地震反射）和横跨这些断裂的海洋边缘的多波束声纳扫描带，加上对西部隆起侧翼30-20 Ma地壳的勘测，表明：㈠在形成新板块边界的局部岩石圈破裂之前，板块在一个几百公里宽的带中伸展和断裂。裂缝火山活动沿着其中一些裂缝建造了火山脊（例如，阿尔瓦拉多和萨米恩托脊），高1-2公里，平行于“绝对”法拉隆板块运动;它们非常类似于现在太平洋-纳斯卡隆起年轻西侧的裂缝脊。(ii)1-2百万年在法拉隆板块最后破裂之前，也许与岩石圈拉伸的时期相一致，整个板块改变方向向更东（“纳斯卡”）的路线;分裂后，北方（科科斯）部分恢复到东北绝对运动。(iii)板块分裂断裂成为最初的科科斯-纳斯卡扩张的地点，它是一个线性特征，至少在已知避免俯冲的680公里渐新世岩石圈破裂过程中，它没有遵循法拉隆板块上任何预先存在的特征，例如，转换断层的“断裂带”痕迹(iv)板块分裂断裂幸存部分的边缘有狭窄的肩部，由卸载下盘的隆起而隆起，部分被裂隙火山作用掩埋。(v)科科斯-纳斯卡扩张开始于23 Ma;关于巴拿马盆地东部更古老的科科斯-纳斯卡地壳的报告是基于错误识别的磁异常。越来越多的证据表明，23 Ma法拉隆板块裂变的驱动力是中美洲和南美洲俯冲带的板拉应力的分歧。分裂的时间和位置可能受到以下因素的影响：（i）中美洲俯冲带的东北板块拉力越来越大，由于北美和加勒比板块之间的运动，板块拉力变长并重新定向;（ii）进入加州俯冲带的板块北方部分的分离时间稍早，导致板块驱动应力的分歧较小;（iii）渐新世晚期，加拉帕戈斯热点使板块较老的部分弱化，该热点位于赤道区域的下面，在上升带和两个俯冲带之间。(c)2005 Elsevier B. V.保留所有权利。
Throughout the Early Tertiary the area of the Farallon oceanic plate was episodically diminished by detachment of large and small northern regions, which became independently moving plates and microplates. The nature and history of Farallon plate fragmentation has been inferred mainly from structural patterns on the western, Pacific-plate flank of the East Pacific Rise, because the fragmented eastern flank has been subducted. The final episode of plate fragmentation occurred at the beginning of the Miocene, when the Cocos plate was split off, leaving the much reduced Farallon plate to be renamed the Nazca plate, and initiating Cocos-Nazca spreading. Some Oligocene Farallon plate with rifted margins that are a direct record of this plate-splitting event has survived in the eastern tropical Pacific, most extensively off northern Peru and Ecuador. Small remnants of the conjugate northern rifted margin are exposed off Costa Rica, and perhaps south of Panama. Marine geophysical profiles (bathymetric, magnetic and seismic reflection) and multibeam sonar swaths across these rifted oceanic margins, combined with surveys of 30-20 Ma crust on the western rise-flank, indicate that (i) Localized lithospheric rupture to create a new plate boundary was preceded by plate stretching and fracturing in a belt several hundred kin wide. Fissural volcanism along some of these fractures built volcanic ridges (e.g., Alvarado and Sarmiento Ridges) that are 1-2 km high and parallel to "absolute" Farallon plate motion; they closely resemble fissural ridges described from the young western flank of the present Pacific-Nazca rise. (ii) For 1-2 m.y. prior to final rupture of the Farallon plate, perhaps coinciding with the period of lithospheric stretching, the entire plate changed direction to a more easterly ("Nazca-like") course; after the split the northern (Cocos) part reverted to a northeasterly absolute motion. (iii) The plate-splitting fracture that became the site of initial Cocos-Nazca spreading was a linear feature that at least through the 680 kin of ruptured Oligocene lithosphere known to have avoided subduction, did not follow any pre-existing feature on the Farallon plate, e.g., a "fracture zone' trail of a transform fault. (iv) The margins of surviving parts of the plate-splitting fracture have narrow shoulders raised by uplift of unloaded footwalls, and partially buried by fissural volcanism. (v) Cocos-Nazca spreading began at 23 Ma; reports of older Cocos-Nazca crust in the eastern Panama Basin were based on misidentified magnetic anomalies.There is increased evidence that the driving force for the 23 Ma fission of the Farallon plate was the divergence of slab-pull stresses at the Middle America and South America subduction zones. The timing and location of the split may have been influenced by (i) the increasingly divergent northeast slab pull at the Middle America subduction zone, which lengthened and reoriented because of motion between the North America and Caribbean plates; (ii) the slightly earlier detachment of a northern part of the plate that had been entering the California subduction zone, contributing a less divergent plate-driving stress; and (iii) weakening of older parts of the plate by the Galapagos hotspot, which had come to underlie the equatorial region, midway between the risecrest and the two subduction zones, by the Late Oligocene. (c) 2005 Elsevier B.V. All rights reserved.