STRUCTURAL PATTERN OF THE GALAPAGOS MICROPLATE AND EVOLUTION OF THE GALAPAGOS TRIPLE JUNCTIONS
STRUCTURAL PATTERN OF THE GALAPAGOS MICROPLATE AND EVOLUTION OF THE GALAPAGOS TRIPLE JUNCTIONS
复制标题
DOI：
10.1029/jb093ib11p13551
复制
发表时间：
1988-11-10
期刊：
影响因子：
--
通讯作者：
LONSDALE, P
中科院分区：
文献类型：
--
作者：
LONSDALE, P
一个13,000平方公里的微板块介入，以防止纳斯卡、科科斯和太平洋板块在加拉帕戈斯群岛以西的赤道东太平洋交汇。微盘以6°/m.y的速度顺时针旋转。大约在其中心东南400公里处的一个“绝对”极，因此，尽管它的北缘与科科斯板块的邻近部分有类似的运动，但它的南缘慢了50%。加拉帕戈斯微板块的周长是由水深测量确定的，已经用海光仪进行了测量，并用深海拖船进行了检查。其边缘的三个三重结点中有两个是东太平洋隆起(EPR)顶端相距160公里的山脊-山脊-山脊(RRR)结点；最像典型的RRR结点是位于北纬1°10‘的太平洋-纳斯卡-加拉帕戈斯交汇处，在那里，东太平洋隆起的轴线由一条长70公里、高1公里的狭窄火山脊线连接。科科斯-纳斯卡扩张中心西端的科科斯-纳斯卡-加拉帕戈斯结合部被推测为RFF型，但“转换断层”分支表现为大的非转换偏移距。缺乏稳定的转换断层与结合部快速西移有关，这是由于Cocos-Nazca轴以60-70 mm/a的速度加长造成的。这一速率曾经是维持纳斯卡-科科斯-太平洋RRR连接稳定所必需的，甚至在微板诞生约1 Ma后仍保持不变。科科斯-纳斯卡地轴的持续传播，在喷发的传播体尖端之前，打开了EPR东部侧翼的赫斯深裂谷盆地。这个裂谷从其隆起的边缘到底部有超过3公里的起伏，在那里严重的衰减暴露了EPR地壳的基底层。类似的Dietz深裂谷盆地位于微板块东南部边缘，距离Hess Deep 70公里，是由加长的加拉帕戈斯-纳斯卡扩张轴穿过EPR侧翼的另一部分而形成的。
A 13,000‐km2microplate intervenes to prevent the junction of the Nazca, Cocos, and Pacific plates in the eastern equatorial Pacific Ocean west of the Galapagos Islands. The microplate is rotating clockwise at 6°/m.y. about an “absolute” pole 400 km southeast of its center, so that although its northern margin has a similar motion to adjacent parts of the Cocos plate, its southern margin is 50% slower. The perimeter of the Galapagos microplate is best defined by bathymetry, and has been surveyed with Sea Beam and examined by Deep Tow. Two of the three triple junctions on its margins are ridge‐ridge‐ridge (RRR) junctions 160 km apart on the crest of the East Pacific Rise (EPR); the most like a classic RRR junction is the Pacific‐Nazca‐Galapagos intersection at 1°10′N, where the EPR axis is joined by a narrow volcanic ridge 70 km long and 1 km high. The Cocos‐Nazca‐Galapagos junction at the west end of the Cocos‐Nazca spreading center is inferred to be of the RFF type, but the “transform fault” branches are represented by large nontransform offsets. Lack of stable transform faults is related to rapid westward migration of the junction, caused by lengthening of the Cocos‐Nazca axis at 60–70 mm/yr. This rate, which was once required to maintain a stable Nazca‐Cocos‐Pacific RRR junction, has persisted even after birth of the microplate about 1 Ma. Continuing propagation of the Cocos‐Nazca axis has opened up the Hess Deep rift basin in the eastern EPR flank in advance of the eruptive propagator tip. This rift valley has a relief of more than 3 km from its uplifted rims to the floor, where severe attenuation exposes basal layers of the EPR crust. The similar Dietz Deep rift basin, at the southeastern margin of the microplate 70 km from Hess Deep, was formed when a lengthening Galapagos‐Nazca spreading axis rifted through another part of the EPR flank.