Spreading process of the northern Mariana Trough: Rifting‐spreading transition at 22°N
Spreading process of the northern Mariana Trough: Rifting‐spreading transition at 22°N
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DOI：
10.1029/2002gc000492
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发表时间：
2003-09
期刊：
影响因子：
3.7
通讯作者：
T. Yamazaki;N. Seama;K. Okino;K. Kitada;M. Joshima;H. Oda;J. Naka
中科院分区：
文献类型：
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作者：
T. Yamazaki;N. Seama;K. Okino;K. Kitada;M. Joshima;H. Oda;J. Naka
我们对马里亚纳海槽北方从19°N到24°N进行了地球物理调查。在该区域内，海槽从初始裂谷向南演化为海底扩张。本研究旨在阐明裂谷向扩张过渡的位置和时间，这是以前有争议的，以及过渡后海底扩张的过程。新的数据集包括带侧扫图像的条带测深和磁矢量异常。地幔布格重力异常（MBA）是使用卫星测高的自由空气重力异常计算的。裂谷向扩张的转变发生在约22°N处，这一点在水深测量中的海底扩张组构、清晰的磁线理和MBA中的靶心图案中得到了证明。在19°N ~ 22°N之间，有4个脊段，它们之间被3个非转换间断面分隔。最北段的岩浆供应相对丰富，与其他段相比，这是估计从一个较大的段长度，较浅的轴向深度，没有裂谷，和较低的MBA。另一方面，南部的下一个部分是一个岩浆匮乏的部分，有一个突出的裂谷。两个深地堑（称为中央地堑）是由岩浆伸展作用形成的。随着离火山弧距离的增加，富含岩浆、缺乏岩浆和正常段的连续性与Martinez和Taylor [2002]在Lau盆地的观察结果相同。磁异常揭示了扩张的详细历史。19°N ~ 20°N之间的海底扩张开始于5 Ma以前，20°N ~ 21°30′N之间的海底扩张开始于4 Ma左右。在2.58 Ma前，扩张中心西侧的扩张半速率在21° 30 ′N以南为2 ~ 3 cm/年，在21°30′N以北的松山纪为2 ~ 3 cm/年，而在布鲁赫纪为1 cm/年或更低。这些速率和方向的变化可能与菲律宾海板块运动的变化有关。在北方马里亚纳海槽，扩散是不对称的。一般来说，传播中心西侧的传播速率明显大于东侧。这种不对称性可能是火山前缘和弧后扩张中心下地幔上涌系统相互作用的结果，是弧后扩张的特征。
We have conducted a geophysical survey of the northern Mariana Trough from 19°N to 24°N. The trough evolves southward from incipient rifting to seafloor spreading within this region. This study aims to clarify the location and time of the rifting‐to‐spreading transition, which was controversial previously, and processes of seafloor spreading after the transition. The new data set includes swath bathymetry with side‐scan images and magnetic vector anomaly. The mantle Bouguer gravity anomaly (MBA) was calculated using the free‐air gravity anomaly from satellite altimetry. The rifting‐to‐spreading transition occurs at about 22°N, which is proved by seafloor‐spreading fabric in the bathymetry, clear magnetic lineations, and the bull's‐eye pattern in MBA. Four ridge segments separated by three nontransform discontinuities are recognized between 19°N and 22°N. The northernmost segment has relatively abundant magma supply compared with the other segments, which is estimated from a larger segment length, shallower axial depths with no rift valley, and lower MBA. The next segment to the south is, on the other hand, a magma‐starved segment with a prominent rift valley. Two anomalously deep grabens (called the Central Grabens) formed by amagmatic extension occur near the segment ends. The succession of magma‐rich, magma‐starved, and normal segments with increasing distance from the volcanic arc is the same as the observation in the Lau Basin reported by Martinez and Taylor [2002]. The magnetic anomaly revealed the detailed history of the spreading. The seafloor spreading between 19°N and 20°N began prior to 5 Ma, and that between 20°N and 21°30′N began at about 4 Ma. Spreading half‐rates in the western side of the spreading center were 2 to 3 cm/year before 2.58 Ma south of 21°30′N and during the Matuyama Chron north of 21°30′N, but an average during the Brunhes Chron is 1 cm/year or less. Orientations of the ridge axes, which range from −20° to 0° at present, have rotated about 20° clockwise since the start of the spreading. These changes in rate and direction might be associated with changes in the motion of the Philippine Sea plate. Spreading has been asymmetric in the northern Mariana Trough. The spreading rates of the western side of the spreading center have been significantly larger than the eastern counterpart in general. The asymmetry may have been caused by an interaction of mantle upwelling systems under the volcanic front and the backarc spreading center and would be a characteristic of backarc spreading.