Back Arc Extension in the Okinawa Trough
Back Arc Extension in the Okinawa Trough
复制标题
DOI：
10.1029/jb092ib13p14041
复制
发表时间：
1987-12
影响因子：
--
通讯作者：
J. Sibuet;J. Letouzey;Fl Barbier;J. Charvet;J. Foucher;T. Hilde;M. Kimura;L. Chiao;B. Marsset-B.
中科院分区：
文献类型：
--
作者：
J. Sibuet;J. Letouzey;Fl Barbier;J. Charvet;J. Foucher;T. Hilde;M. Kimura;L. Chiao;B. Marsset-B.
冲绳海槽位于中国东部，是琉球海沟-弧系后方大陆岩石圈内伸展形成的弧后盆地。中新世晚期的隆起，与最初相邻的琉球非火山弧和台湾-新子褶皱带的正常断层有关，对应于第一裂谷阶段。在冲绳海槽北部钻探的相应年龄的海洋沉积物支持了裂谷的时间。裂谷发生在中新世早期菲律宾板块相对于欧亚大陆的运动发生重大变化之后，并在上新世期间停止。第二次裂谷阶段大约在 2 年前开始。以前，在上里奥-更新世边界，一直持续到现在。在冲绳海槽中部和南部，它已经进入了比更北部更高级的阶段。 R/V Jean Charcot 的 POP 1 巡航期间收集的详细测深（海波束）、地震反射和磁学数据揭示了伸展过程的主要特征。弧后扩张阶段最近在冲绳海槽的南部和中部开始，例如几个呈梯队状，在某些情况下，重叠的活跃的中央地堑，方向为 N70°E–N80°E。其中一些凹陷被新鲜后弧玄武岩火山脊侵入，并伴有大的磁异常。这些呈阶梯状的活动裂谷之间的转换断层并不明显。我们认为，冲绳海槽南部的主要部分位于较薄的大陆地壳之下，除了冲绳海槽南部的梯形裂谷系统外，弧后盆地海洋域的宽度仅限于海槽轴向部分的数十公里或更小。裂谷中出现的轴向后弧火山脊系统终止于冲绳岛的纬度，而琉球弧中的活火山仅出现在冲绳岛北部。我们将这种活动弧和弧后火山活动之间的转变称为火山弧裂谷迁移现象（VAMP）。在全球范围内，弧后火山活动从冲绳海槽南部传播到冲绳VAMP地区。冲绳海槽北部继续发生裂谷，但尚未伴随相关的火山活动。冲绳 VAMP 区域的特点是一系列平行的玄武岩山脊，方向为 N75°E，并伴有岩脉侵入的线性磁异常特征。我们认为，弧后海洋域的形成是沿着北纬75°E的轴向弧后伸展带形成的，并且该区域目前终止于活动火山链的南端。弧后盆地洋壳形成初期为非稳态，其特点是缺乏发育的断裂带格局。 VAMP 区域在弧的火山带方向上的终止与 Molnar 和 Atwater 的建议一致，即火山弧是基本的薄弱线，决定了最初的后弧扩展发生的位置。显然，弧后伸展最初发生在位于琉球岛弧以西的大陆岩石圈内，沿其整个长度，但随后的弧后火山活动在该地区的最南端开始，然后向北移动。这种迁移伴随着弧线废弃部分火山活动的停止。我们将这种火山作用转移称为 VAMP 过程。因此，弧和弧后盆地火山活动似乎以这样一种方式相关联，即沿着弧的火山活动停止时，火山活动往往会同时迁移。弧和弧背活动的相互作用可能与板块收敛参数的变化有关。由于菲律宾海的板块运动至少在冲绳海槽的南部部分是倾斜于海沟的，因此我们认为施加在上覆板块边缘的倾斜阻力导致了弧内和弧后呈梯形伸展特征的发展。因此，琉球板块相对于欧亚大陆的运动是一种伸展走滑运动，其趋势大致平行于冲绳海槽。
The Okinawa Trough, lying to the east of China, is a back arc basin formed by extension within continental lithosphere behind the Ryukyu trench-arc system. Middle to late Miocene uplift, associated with normal faulting of the initially adjacent Ryukyu nonvolcanic arc and the Taiwan-Sinzi folded belt, corresponds to the first rifting phase. The timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern Okinawa Trough. The rifting occurred after a major early Miocene change in the motion of the Philippine plate with respect to Eurasia and ceased during the Pliocene. A second rifting phase started about 2 m.y. ago, at the Plio-Pleistocene boundary and has continued until the present time. It has proceeded to a more advanced stage in the middle and southern Okinawa Trough than it has farther north. Detailed bathymetric (Sea Beam), seismic reflection, and magnetics data collected during the POP 1 cruise of the R/V Jean Charcot reveal the principal features of the extensional processes. The back arc spreading phase started very recently in the southern and middle Okinawa Trough, as exemplified by several en echelon and, in some cases, overlapping active, central graben oriented N70°E–N80°E. Some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies. Transform faults between these en echelon active rifts are not obvious. We suggest that the major part of the southern Okinawa Trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern Okinawa Trough, the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough. The system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of Okinawa Island whereas active volcanoes in the Ryukyu arc occur only north of Okinawa Island. We refer to this transition between active arc and back arc volcanism as the volcanic arc-rift migration phenomenon (VAMP). Globally, back arc volcanism propagated from the southern Okinawa Trough to the Okinawa VAMP area. Rifting continues to occur in the northern Okinawa Trough but is not yet accompanied by associated volcanism. The Okinawa VAMP area is characterized by a series of parallel basaltic ridges oriented N75°E with associated linear magnetic anomalies characteristic of dyke intrusions. We suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending N75°E and that this zone presently ends at the southern extremity of the active volcanic chain. The initial phase of formation of back arc basin oceanic crust is non-steady state and is characterized by the lack of a developed fracture zone pattern. The termination of the VAMP area in the direction of the volcanic zone of the arc is consistent with the suggestion of Molnar and Atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs. Apparently, back arc extension initially occurred within the continental lithosphere located westward of the Ryukyu arc, along its whole length, but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward. This migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc. It is this transfer of volcanism that we call the VAMP process. Thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc. This interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence. Since the plate motion in the Phillippine sea is oblique to the trench at least in the southern part of the Okinawa Trough, we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc. The motion of the Ryukyu platelet with respect to Eurasia is consequently an extensional strike-slip motion trending roughly parallel to the Okinawa Trough.