共查询到20条相似文献，搜索用时 31 毫秒
1.
Opening of the Japan Sea back arc basin was accompanied by extensional tectonics in the drifting southwest Japan arc. Various trends of Early Miocene grabens in the arc suggest multi-directional rifting, which necessarily involved strike-slip components of some of basin-margin faults. However, such components are not well understood. In this work we conducted a field survey in the Early Miocene Ichishi basin on the northern side of the Median Tectonic Line, central southwest Japan. We found that the basin was a compound of grabens that were formed along normal and sinistral strike-slip faults, the latter of which had northeast–southwest trends. The block faulting in this phase produced basement highs between sub-basins, which were filled with the lower part of the Ichishi Group. We found a low-angle angular unconformity at a middle horizon in the group, with which we define the upper and lower part of the group. The upper part onlapped both the basement highs and the lower part. It means that the transtensional basin formation ceased sometime between 18 and 17.5 Ma in the Ichishi area. The Ichishi basin turned subsequently into a sag basin subsided due to normal faulting probably along the Nunobiki-sanchi-toen fault zone. The transtension and the basin sag were driven by ENE–WSW extensional stress. This arc-parallel extension produced grabens various areas including Ichishi in the Early Miocene. The extensional deformation was eventually localized to the deep rift along the Fossa Magna to make the lithosphere under southwest Japan decoupled from that under northeast Japan. The decoupling allowed the rapid rotation of southwest Japan from ~17.5 Ma. The cluster of those grabens around the Ise bay probably determined the southeastern margin of the Kinki triangle. 相似文献
2.
Yasuto Itoh 《Physics of the Earth and Planetary Interiors》2005,153(4):220-226
Off the southern coast of Hokkaido the Hidaka-oki (offshore Hidaka) basin has developed on the western flank of a collision suture under the influence of long-standing compressional plate motion and provoked tectonic stresses around the northwestern Pacific rim throughout the late Cenozoic. The basin forming history of the Japan arc and Kuril arc collision zone is described on the basis of seismic reflection data interpretation. We identify two stages of basin formation: the older (late Oligocene-Miocene) faulted en echelon graben (pull-apart basin) and younger (Plio-Pleistocene) regional downwarping. Paleoenvironmental changes recorded within the fore-arc sediments indicate that the older basin filled up by the late Miocene. We inferred the volumes of the distinctive basins from the depth-conversion of seismic data, which suggest episodic uplifts and massive erosion of the Hidaka Mountains in the middle-late Miocene and the Plio-Pleistocene. Estimated sediment supply rates into the basins have a similar level for the both stages. Cause of an episodic uplift in the older stage is attributed to the delayed opening of the Japan Sea. The eastern Eurasian margin underwent N-S right-lateral faulting at 25 Ma as a result of rifting of the Kuril back-arc basin. Formation of the Japan Sea back-arc basin since the early Miocene (ca. 20 Ma) caused eastward motion of the western Hokkaido block and transpressive regime along the pre-existing N-S shear deformation zone. 相似文献
3.
Crustal shortening of Southwest Japan in the Late Miocene 总被引：5，自引：0，他引：5
Abstract Tectonic deformation of an island arc is interpreted on the basis of geophysical data. Extensive reflection seismic, gravity, geomagnetic data around the back-arc region of Southwest Japan delineate east-west to northeast-southwest folding, and imply conspicuous compression on the southern margin of the Sea of Japan. Because geological data of exploration boreholes indicate that the coinpressive regime was dominant in the late Miocene, the tectonic event seems to be linked with coeval resumption of subduction of the Philippine Sea Plate. Strong coupling of the young buoyant oceanic plate brought about north-south shortening of the overriding continental lithosphere, and left wrench deformation at the southwestern corner of the Sea of Japan. Amount of shortening for the back-arc shelf and mountainous ranges of Southwest Japan is estimated to be ca 10 km, adopting a uniform ratio of shortening (0.944) since the Miocene determined on the shelf from depth-converted seismic profiles. Along the western side of a bend of boundary between the Eurasian Plate and Philippine Sea Plate, the middle Miocene and younger sediments upon the back-arc shelf are much less deformed than the northern equivalents, and the fore-arc Miocene strata are deformed by left wrenching, facts which are indicative of northerly initial convergence of the Philippine Sea Plate at the end of Miocene and crustal decoupling on the west of Kyushu Island. 相似文献
4.
Japan Sea: a pull-apart basin? 总被引：1，自引：0，他引：1
Recent field work in the Hokkaido Central Belt and marine geology studies along the eastern margin of Japan Sea in addition to previously published data lead us to propose a new model of opening of the Japan Sea. The synthesis of both on-land and offshore structural data gives new constraints about the structural evolution of the system. The rhombohedral shape of the Japan Basin and the particular tectonic behaviour of the margins on both east and west sides can be explained by an early Eo-Oligocene rifting of a pull-apart basin accommodated along two large right-lateral shear zones, east of Korea and west of northeast Japan and Sakhalin. It is followed, during Upper Oligocene/Lower Miocene, by the main opening of the Japan Basin as a mega pull-apart. Then a back-arc spreading probably related to the subduction process, induced the creation of the Yamato and Tsushima Basins at the end of Lower Miocene and in Middle Miocene. Clockwise rotation of southwest Japan larger than 20° or major bending of Honshu mainland deduced from paleomagnetic studies is unlikely at this time. Since 1 or 2 My B.P. to Present, compression prevails along the eastern margin of the Japan Sea. The generation of marginal basins as pull-apart basins along intracontinental strike-slip faults is a mechanism which has been proposed by other authors concerning the South China Sea, the question then is whether the fragmentation of the Asiatic continent is an intracontinental deformation related process as proposed here or a subduction related one. 相似文献
5.
Abstract This paper provides untilted paleomagnetic data obtained from the early Miocene strata around the Kanazawa‐Iozen area, in the eastern part of south‐west Japan. A thick pile of volcaniclastics and marine transgressive sediments underlie the area; they were deposited in the early stage of the Japan Sea opening event. Progressive thermal demagnetization tests isolated stable primary magnetic vectors from eight sites in the upper part of the Iozen Formation. Overall, the tilt‐corrected mean direction of this unit is D = 36.4°, I = 51.6° and α95 = 12.1. Together with a published paleomagnetic and chronological database, the present results suggest that clockwise rotation of south‐west Japan, linked to the back‐arc opening, commenced in the early Miocene and accelerated at the same time as rapid subsidence along the Japan Sea coast. Post‐opening, differential rotation within the eastern part of south‐west Japan is assumed, based on selected paleomagnetic data from the latest Early Miocene. 相似文献
6.
Eiji Sasao 《Island Arc》2013,22(2):170-184
A petrographic study of sandstones from the Miocene Mizunami Group in Central Japan has been performed on core samples from a single borehole, in order to evaluate the provenance of the sedimentary rock. Evaluation of the provenance is based on bulk mineral, heavy mineral and plagioclase contents and on whole rock chemical compositions. The sandstones studied are divisible into three types; the first type is characterized by the occurrence of biotite and plagioclase ranging from albite to oligoclase, the second type is characterized by the dominance of amphibole and labradorite with pyroxene (clinopyroxene > orthopyroxene), and the third type is characterized by the dominance of pyroxene (orthopyroxene > clinopyroxene) and andesine with lesser labradorite, bytownite and anorthite. The first type is interpreted to be derived from the basement granite, whereas the others were derived mostly from volcanic ash, judging from their mineral compositions. The volcanic activity that supplied the volcanic ash to the Mizunami Basin occurred in two phases, distinguishable by variations in their mineralogical and geochemical compositions, an indication of change in character of the volcanic activity. This petrographic study of the sandstones in the Mizunami Group suggests that unrecognized volcanic activity occurred around the Mizunami Basin, even though potential provenance of the volcanic ash has not yet been identified. 相似文献
7.
Abstract Recent paleomagnetic studies are reviewed in an effort to clarify the relationship between the intra-arc deformation of central Japan and the collision tectonics of the Izu-Bonin Arc. The cusp structure of the pre-Neogene terranes of central Japan, called the Kanto Syntaxis, suggests a collisional origin with the Izu-Bonin Arc. The paleomagnetic results and newly obtained radiometric ages of the Kanto Mountains revealed the Miocene rotational history of the east wing of the Kanto Syntaxis. More than 90° clockwise rotation of the Kanto Mountains took place after deposition of the Miocene Chichibu Basin (planktonic foraminiferal zone of N.8: 16.6–15.2 Ma). After synthesizing the paleomagnetic data of the Japanese Islands and collision tectonics of central Japan, it appears that approximately a half rotation (40–50°) probably occurred at ca 15 Ma in association with the rapid rotation of Southwest Japan. The remainder (50-40°) continued until 6 Ma, resulting in the sharp bent structure of the pre-Neogene accretionary complexes (Kanto Syntaxis). The latter rotation seems to have been caused by the collision of the Izu-Bonin Arc on the northwestward migrating Philippine Sea Plate. 相似文献
8.
大别山北缘位于大别造山带与华北陆块会聚地带,其深部精细结构还存在一些争议问题.根据近年来在研究区域内采集的地球物理数据,通过OMEGA、OASIS和FUGRO-LCT等多个重磁电震软件处理,获得了深部信息丰富的多种地球物理属性图像.本文从中选取了2条平行的电法和地震剖面,辅以高精度重磁数据,揭示了大别山北缘深部地质结构总体呈现华北陆块南向俯冲、北淮阳构造带向北逆冲的特征,并可清楚地识别大别山北缘造山带、肥南山前坳陷带和肥北斜坡带.其特征分别如下:①大别山北缘造山带,地震反射杂乱,电性高阻大于2000Ωm,以磨子潭-晓天断裂为界分为北大别杂岩带和北淮阳构造带,主要由大别群、卢镇关杂岩和佛子岭群组成,沿舒城-信阳断裂逆冲于中、下侏罗统之上,浅部发育北倾的金寨-龙门冲滑覆断裂.②肥南山前坳陷带,上部为中、新生界,呈现中低阻特征,地震反射界面清楚,断面波明显;下部为华北型前中生界沉积岩(上部可能残存古生界),电性特征为低阻(5~50 Ωm),地震反射较连续,内部反射弱.以六安断裂为界分为舒城凹陷和肥中断裂带,其北侧边界为肥中断裂.③肥北斜坡带,上部主要为侏罗系,呈现中低阻、水平层状地震反射特征;下部主要为霍邱群,电性为高阻,地震反射杂乱;中间为华北型前中生界沉积岩,向北逐渐减薄、直至缺失.上述认识将为华北陆块南向俯冲、南北板块碰撞缝合线和油气资源勘查等研究提供深部地质约束. 相似文献
9.
Miocene intra‐arc rifting associated with the opening of the Japan Sea formed grabens in several areas in Southwest (SW) Japan, but the extensional tectonics of the arc are still not well understood. In this study, we first document the tectonostratigraphy of the Hokutan Group in the northwestern part of the Kinki district, and demonstrate the termination of extensional tectonics at ca 16.5 Ma, as inferred from grabens in the lower part of the group being unconformably overlain by sediments of the upper part. Second, we review early Miocene grabens in SW Japan to suggest that intra‐arc rifting was abandoned at ca 16 Ma, essentially simultaneously with the end of rotation of the SW Japan arc as evidenced by paleomagnetic studies. The lesser numbers of grabens and reduced thicknesses of graben fills suggest that extensional deformation of the SW Japan arc was significantly weaker than that of the Northeast (NE) Japan arc, which was broken into blocks, indicating various degrees of paleomagnetic rotation within NE Japan. The weak deformation has allowed paleomagnetic studies to infer the coherent rotation of the SW Japan arc. 相似文献
10.
A magnetic anomaly map of the northern part of the Philippine Sea plate shows two conspicuous north–south rows of long-wavelength anomalies over the Izu–Ogasawara (Bonin) arc, which are slightly oblique to the present volcanic front. These anomalies are enhanced on reduced-to-pole and upward-continued anomaly maps. The east row is associated with frontal arc highs (the Shinkurose Ridge), and the west row is accompanied by the Nishi-Shichito Ridge. Another belt of long-wavelength anomalies very similar to the former two occurs over the Kyushu–Palau Ridge. To explain the similarity of the magnetic anomalies, it is proposed that after the spreading of the Shikoku Basin separated the Izu–Ogasawara arc from the Kyushu–Palau Ridge, another rifting event occurred in the Miocene, which divided the Izu–Ogasawara arc into the Nishi-Shichito and Shinkurose ridges. The occurrence of Miocene rifting has also been suggested from the geology of the collision zone of the Izu–Ogasawara arc against the Southwest Japan arc: the Misaka terrain yields peculiar volcanic rocks suggesting back-arc rifting at ～ 15 Ma. The magnetic anomaly belts over the Izu–Ogasawara arc do not extend south beyond the Sofugan Tectonic Line, suggesting a difference in tectonic history between the northern and southern parts of the Izu–Ogasawara arc. It is estimated that the Miocene extension was directed northeast–southwest, utilizing normal faults originally formed during Oligocene rifting. The direction is close to the final stage of the Shikoku Basin spreading. On a gravity anomaly relief map, northeast–southwest lineaments can be recognized in the Shikoku Basin as well as over the Nishi-Shichito Ridge. We thus consider that lines of structural weakness connected transform faults of the Shikoku Basin spreading system and the transfer faults of the Miocene Izu–Ogasawara arc rifting. Volcanism on the Nishi-Shichito Ridge has continued along the lines of weakness, which could have caused the en echelon arrangement of the volcanoes. 相似文献
11.
Abstract The Nankai Trough, off southwest Japan, is one of the best sites for the study of geomorphic characteristics of a clastic accretionary prism. A recent multibeam survey over the central and eastern parts of the Nankai accretionary prism has revealed a large variation of the topography along the trough axis. Analysis of the bathymetric data suggests the existence of prism deformational features of different scales, such as depressions, embayment structures and cusps. These structures are the results of slope instability caused by basement relief of subducted oceanic plate. Unstable slopes recover by new accretion and development of a low angle thrust. Small-scale deformation due to the subduction of a small isolated seamount is then adjusted to the regional trend. By contrast, a 30 km indentation of the wedge observed in the eastern part of the Nankai Trough, the Tenryu Cusp, has seemed to retain its geometry. The subducted Philippine Sea plate has deformed greatly near the eastern end of the Nankai Trough, because of the collision between the Izu-Ogasawara (Bonin) arc and central Japan. Therefore, the indentation may be the result of the continuous subduction of a basement high, such as the Zenisu Ridge, which has been formed under north-south compression due to the arc-arc collision. 相似文献
12.
Abstract Meso- and microscale structural analyses were carried out in the Hatagawa shear zone, north-eastern Japan. The shear zone is a sinistral strike–slip ductile shear zone, and has a 1-km wide north-south trending region where quartz mean grain size of approximately 35 μm does not vary significantly. Two types of quartz microstructures, A and B, occur in the western and eastern part of the shear zone, respectively. The lattice preferred orientation (LPO) patterns are characterized by a type I crossed girdle in the samples with the quartz microstructure A, and a Y maximum in the samples with the quartz microstructure B. The microstructures under optical and transmission electron microscopes indicates that the quartz recrystallization occurred predominantly by progressive subgrain rotation in microstructure A, and by both progressive subgrain rotation and grain boundary migration in microstructure B. This suggests different deformation conditions in the western and eastern parts of the shear zone. Quartz LPO patterns, presence of myrmekite, feldspar compositions, and dislocation density also suggest difference in the deformation conditions. The syn-deformation temperature in the western part of the shear zone was lower than that of the eastern part of the shear zone. The stress in the western part of the shear zone was higher than that of the eastern part of the shear zone. The difference in the deformation conditions would affect not only the quartz microstructure, but also the quartz LPO patterns and the presence of myrmekite around K-feldspar porphyroclasts. 相似文献
13.
Over 500 oriented samples of felsic rocks of Cretaceous to Middle Miocene age were collected along the Go¯River in the central part of Southwest Japan, in an attempt to detect the process of tectonic rotation of Southwest Japan from the paleomagnetic view point. Thermal demagnetization was successful in isolating characteristic directions from the remanent magnetization of samples. Reliability of the paleomagnetic direction is ascertained through the agreement of directions from different kinds of rocks as well as the presence of both normal and reversed polarities. The paleomagnetic results establish that Southwest Japan began to rotate clockwise through58 ± 14° later than 28 Ma and ceased its motion by about 12 Ma. Southwest Japan has undergone no detectable north-south translation since 28 Ma. These results imply that southwest Japan was rotated about the pivot around 34°N, 129°E between 28 Ma and 12 Ma in association with the opening of the Japan Sea. 相似文献
14.
本文对"鲁科一井"(CCSD-LK-Ⅰ)768.9~1112.3m之间的上白垩统沉积岩样品进行了岩石磁学、磁化率各向异性(AMS)以及天然剩磁组分的研究.在此基础上,分析了利用特征剩磁(ChRM)和黏滞剩磁(VRM)方向恢复岩芯原始方位的可行性.三轴等温剩磁热退磁曲线、磁滞回线、反向场退磁曲线、一阶反转曲线等岩石磁学测量结果表明,沉积岩的主要载磁矿物为磁铁矿和赤铁矿.335块样品的AMS测量结果表明磁化率椭球主轴的最大轴K1和中间轴K2与水平面夹角较小,最小轴K3接近垂直于水平面分布,说明沉积岩保留了原始沉积磁组构特征.系统热退磁实验表明,多数样品在25~350℃和500~690℃温度段分别获得VRM和ChRM分量.利用ChRM偏角方向,并考虑构造旋转量校正,对VRM偏角方向进行恢复,Fisher统计得到DVRM=-1.3°,IVRM=59.6°,与当地现代地磁场方向(D=-6.7°,I=53.9°)基本一致.用ChRM偏角方向对磁化率主轴K1偏角方向进行校正,校正的结果为:D_(ch_K1)=349.2°,I_(ch_K1)=-0.7°.本文研究结果对于地质勘探中利用古地磁学方法恢复钻孔岩芯原始方位具有一定参考意义. 相似文献
15.
A seismic gap in the eastern margin of the Sea of Japan as inferred from the time-space distribution of past seismicity 总被引：3，自引：0，他引：3
Abstract Based on the spatial distribution of the focal areas from previous large earthquakes, a significant seismic gap was found off the coast of the Akita Prefecture at the eastern margin of the Sea of Japan. We forecast that the 75 km segment of plate boundary may be ruptured by a large thrust earthquake with a magnitude of 7.5 in the near future. The time of occurrence is uncertain, but the recurrence interval of large earthquakes in this region suggests that it will be no later than the end of next century. The time sequence of large earthquakes in the eastern margin of the Sea of Japan shows a systematic shortening of the earthquake interval for the past 250 years. This feature is simulated successfully by a simple mechanical model that represents a plate boundary by segmented blocks, each of which is composed of a spring friction slider system. We further propose to revise the conventionally accepted plate boundary between the Eurasian and Okhotsk plates in the eastern margin of the Sea of Japan; the observed data of seismic activity and recent crustal deformation indicate that the southern part of the plate boundary traverses the land region from Niigata to Otari along the Shinanogawa seismic belt. The fault geometries of previous large earthquakes show that the mode of plate convergence in the eastern margin of the Sea of Japan is a collision type rather than a simple eastward subduction as was postulated in early studies. 相似文献
16.
We present new Middle Miocene paleomagnetic data for the central Japan Arc, and discuss their implications for Miocene rotation. To obtain a refined paleodirection, we made magnetic measurements on basaltic to andesitic lavas and intrusive rocks from 12 sites in the Tsugu volcanic rocks (ca 15 Ma) in the northern part of the Shitara area, Japan. Significant secondary magnetizations in samples with strong magnetic intensities are interpreted as lightning‐induced components. Mean directions carried by magnetite and/or titanomagnetite were determined for all sites. An overall mean direction with a northerly declination was obtained from dual‐polarity site means for nine sites. This direction is indistinguishable from the mean direction for coeval parallel dikes in the northern part of the Shitara area, and also indistinguishable from the Miocene reference direction derived from the paleopole for the North China Block in the Asian continent. These comparisons suggest little or no rotation or latitudinal motion in the study area with respect to the North China Block since 15 Ma. We obtained a refined early Middle Miocene paleodirection (D = 9.7°, I = 52.5°, α95 = 4.8°; 30 sites) and paleopole (82.0°N, 230.8°E, A95 = 5.6°) for Shitara by combining data from the Tsugu volcanic rocks and a coeval dike swarm. An anomalous direction found at three sites could be a record of an extraordinary field during a geomagnetic polarity transition or excursion. Paleomagnetic data from Shitara suggest that: (i) the western wing of the Kanto Syntaxis, a prominent cuspate geologic structure in central Honshu, underwent a counterclockwise rotation with respect to the main part of the southwestern Japan Arc between ca 17.5 Ma and 15 Ma; (ii) collision between the Japan and Izu–Bonin (Ogasawara) Arcs began prior to 15 Ma; and (iii) clockwise rotation of the entire southwestern part of the Japan Arc had ceased by 15 Ma. 相似文献
17.
Em
Mrton Lszl Fodor Bogomir Jelen Pter Mrton Helena Rifelj Renata Kevri 《Journal of Geodynamics》2002,34(5)
Combined paleomagnetic and structural research was carried out in the Mura-Zala Basin including the western and southern surrounding hills in northeastern Slovenia. The Mura-Zala Basin was formed due to ENE–WSW trending crustal extension in the late Early Miocene (18.3–16.5 Ma). First, marine sedimentation took place in several more or less confined depressions, then in a unified basin. During thermal subsidence in the late Miocene deltaic to fluvial sediments were deposited. After sedimentation, the southernmost, deepest depression was inverted. Map-scale folds, reverse and strike-slip faults were originated by NNW–SSE compression. This deformation occurred in the latest Miocene–Pliocene and is reflected also in the magnetic fabric (low field susceptibility anisotropy). After this folding, the Karpatian sediments of the Haloze acquired magnetization, then suffered 30° counterclockwise rotation relative to the present north (40° counterclockwise with respect to stable Europe). This Pliocene (Quaternary?) rotation affected a wide area around the Mura-Zala Basin. The latest Miocene to Quaternary folding and subsequent rotation may be connected to the counterclockwise rotation of the Adriatic microplate. 相似文献
18.
Large tectonic movement of the Japan Arc in late Cenozoic times inferred from paleomagnetism: Review and synthesis 总被引：4，自引：0，他引：4
Abstract Paleomagnetic studies facilitate an understanding of the evolution of the Japan Arc in Cenozoic times from the perspective of tectonic movement. The Japan Arc rifted from the Asian continent in the middle Miocene, while East Asia, including the Japan Arc, moved northward at the same time. The rifting phenomenon of the Japan Arc is described by differential rotation of Southwest and Northeast Japan. Southwest Japan was rotated clockwise through about 45° and Northeast Japan was rotated counter-clockwise through about 40°. This differential rotation occurred concurrently at about 15 Ma. Eighty percent of the rotation was completed during a period of 1.8 million years. These factors lead us to propose a'double door'opening mode with a fast spreading rate of 21 cm/yr for the evolution of the Japan Sea, suggesting that the asthenosphere with a low viscosity was injected beneath the Japan Sea area. The large northward motion of East Asia in relation to Europe is expected from the apparent polar wander path constructed from the paleomagnetic data of the Japan Arc. East Asia may have moved northward by more than 1700 km between 20 Ma and 10 Ma accompanied by a slightly clockwise rotation of 10°. The eastern part of the Eurasian plate was subjected to extreme geodynamic conditions in late Cenozoic times. 相似文献
19.
Early Miocene sediments of the Morozaki Group in central Japan contain deep-sea fossils that have been dated using biostratigraphic and radiometric data. In this study, we utilize magnetostratigraphy to provide a more precise age for mudstones from just below the layer containing the fossils. Rock magnetic experiments suggest that both magnetic iron sulfide and Ti-poor titanomagnetite carry the remanent magnetization of the mudstones. Two different stratigraphic sites have normal polarity directions with a northeastern declination, which can be correlated with Chronozone C5Dn. Given their magnetostratigraphic position near the C5Dn/C5Dr chronozone boundary (17.466 Ma) and a high sedimentation rate, the estimated age for both the sites and the deep-sea fossils is ~17.4 Ma. The northeasterly-directed site-mean directions suggest clockwise tectonic rotation, most likely due to the Early Miocene clockwise rotation of Southwest Japan associated with the back-arc opening of the Japan Sea. The deep-sea fossils, dated at ~17.4 Ma, represent organisms deposited within a submarine structural depression formed by crustal extension during the back-arc opening stage. 相似文献
20.
Graciano P. Yumul JR Carla B. Dimalanta Rodolfo A. Tamayo JR Jenny Anne L. Barretto 《Island Arc》2000,9(4):627-637
Abstract The Palawan microcontinental block collided with the Philippine Mobile Belt in the Central Philippine region resulting in the counterclockwise rotation of Mindoro– Marinduque and clockwise rotation of Panay. The collision also brought about the clockwise rotation of north-east Negros, Cebu, north-west Masbate and Bohol (collectively called the Western Visayan block), resulting into their present-day northeast–southwest trend. This suggests a far more dramatic role of the collision than was previously recognized. Furthermore, the south-east Sulu Sea sub-basin is inferred to have also undergone collision-related clockwise rotation which can account for the observed east-west trending magnetic lineations in the basin. Aside from explaining the contrasting morphological trends of the different islands in Central Philippines, the rotation can also explain, albeit in a different way, how the belts of sedimentary basins, ophiolites and arcs in Panay and Negros can extend to Northern Luzon. Published paleomagnetic data suggest that the collision-related rotation commenced during the early to middle Miocene and had ceased by the late Miocene. 相似文献