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1.
The Taishu Group, a marine formation with a thickness of >5400 m, crops out on Tsushima Island, located in the southwestern Japan Sea. The group, which is generally regarded as early Eocene to early Miocene in age, provides important information about the tectonic setting of the Japan Sea. In this study, we present new SHRIMP U–Pb dates for igneous zircons from the Kunehama Tuff, which is in the basal part of the Taishu Group, and the Oobaura Tuff, which is in the uppermost part of the group. Results show that the Taishu Group was deposited rapidly, during the short interval of 17.9–15.9 Ma (early–middle Miocene), and is equivalent to other early–middle Miocene strata found in the Japan Sea region. Our results provide new constraints on the geological history of the Japan Sea and its islands.  相似文献   

2.
Ritsuo Nomura 《Island Arc》2021,30(1):e12421
The lower part of the Josoji Formation, Shimane Peninsula, contains clues for figuring out changes in deep-water characteristics during the opening of the Japan Sea. The foraminiferal assemblage includes early to middle Miocene biostratigraphic index taxa such as planktonic foraminiferal Globorotalia zealandica and Globorotaloides suteri. The occurrence of these two species, together with the absence of praeorbulinids, suggests that the lower part of the Josoji Formation is assigned to the top of planktonic foraminiferal Zone N7/M4 (16.39 Ma). The benthic foraminiferal assemblage, which is characterized by Cyclammina cancellata and Martinottiella communis, clearly suggests that the lower Josoji Formation was deposited at bathyal depths, and that it developed in association with the abrupt appearance of deep-sea calcareous forms. Such bathyal taxa are the main constituents of the Spirosigmoilinella compressa–Globobulimina auriculata Zone of the Josoji Formation and also of the Gyrodina–Gyroidinoides Zone at Ocean Drilling Program Site 797 in the Japan Sea. The base of these benthic foraminiferal zones can be correlated with the base of the nannofossil Sphenolithus heteromorphus Base Zone (= CNM6/CN3); thus, its estimated age is 17.65 Ma. This biostratigraphic information suggests that the lower Josoji Formation was deposited from shortly before 17.65–16.39 Ma in upper limit age. Evidence that fresh to brackish and shallow-water basins formed in the rifting interval of 20–18 Ma in the Japan Sea borderland suggests that the abrupt appearance of deep-sea calcareous foraminifera occurred about 1 my earlier in this area than in other sedimentary basins and suggests that a significant paleoceanographic change occurred in the proto-Japan Sea at 17.65 Ma.  相似文献   

3.
Hyesu  Yun  Songsuk  Yi  Jinyong  Oh  Hyunsook  Byun  Kooksun  Shin 《Island Arc》2007,16(2):262-275
Abstract   The Ulleung Basin is located in the southwestern part of the East Sea (Japan Sea) and contains thick Neogene sediment. Detailed examination of the stratigraphic distribution of dinoflagellates was carried out on samples from the onshore Pohang Basin (E well) and two wells (Gorae I and Dolgorae VII) in the southwestern Ulleung Basin, to investigate the early evolution of the basin. The results show that thick syn-rift sediments mainly consist of terrestrial deposits and are widespread over the basin. This supports an extensional tectonic origin for the basin. The initiation of the deposits dates back to 17–16.4 Ma. Furthermore, well-preserved Eocene to Oligocene dinoflagellate taxa found in Miocene deposits of wells implies that the age of initial rifting might be Oligocene or earlier. Our results provide constraints for understanding the opening process of the East Sea.  相似文献   

4.
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   

5.
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   

6.
Yo-Ichiro  Otofuji 《Island Arc》1996,5(3):229-249
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   

7.
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   

8.
Miocene igneous dikes older and younger than 15 Ma in Southwest Japan are thought to be oriented parallel and perpendicular to the arc, respectively. This difference of orientations was referred to as significant evidence for termination of the opening of the Japan Sea at 15 Ma. The tightest constraint comes from ~60 dikes in the Tajima–Myokensan area, northern Hyogo Prefecture. Here we present orientations of 716 planar intrusive bodies and the directions of 143 meso-scale faults, obtained using the latest stress inversion techniques from the lower to middle Miocene Hokutan Group in the Tajima–Myokensan area. The results contradict the 15 Ma hypothesis for the end of the opening of the Japan Sea. We find that intrusive bodies cannot be separated into two groups by their orientations as reported previously. Rather, the orientations of their poles comprise a horizontal girdle and a vertical cluster. The former indicates NE-SW extensional stress, and the latter NW-SE compression. However, the latter are interpreted as not representative of regional stress, based on common sill intrusions (the formation of which was not influenced by regional stress) in the well-stratified Muraoka Formation resulting in the vertical cluster of pole orientations from which compression was recognized. The results of fault-slip analysis are consistent with the extensional stress. Fission-track and U–Pb ages of zircons were obtained from seven intrusive bodies. These and previously published ages suggest that the area underwent NW-SE extension both before and after 15 Ma. In the main part of Southwest Japan, the weak extension was kept after 16 Ma when intra-arc rifting was terminated. This is consistent with the hypothesis that the Japan Sea continued to open until 13.5 Ma.  相似文献   

9.
The opening of the Japan Sea separated southwest Japan from the Eurasian continent during the Early to Middle Miocene. Since then, diverse igneous activities have occurred in relation to the subduction of the Philippine Sea Plate beneath southwest Japan. The Okinawa Trough formed in the back-arc region of the Ryukyu Arc since the Late Miocene. In the Koshikijima Islands, off the west coast of Kyushu and near the northern end of the Okinawa Trough, felsic to intermediate igneous rocks with Middle to Late Miocene radiometric ages occur as granitic intrusions and dikes. We obtained zircon U–Pb ages and whole-rock major- and trace-element compositions of Koshikijima granitic rocks to elucidate their magmagenesis. The U–Pb ages of granitic rocks in Kamikoshikijima and Shimokoshikijima and a dacite dike are about 10 Ma, suggesting that most magmatism on the Koshikijima Islands was coeval with early rifting in the Okinawa Trough. We infer that magmagenesis occurred via melting of lower crustal mafic rocks related to rifting in the Okinawa Trough based on the arc-like trace-element compositions of these I-type granites. Andesitic dikes preceded felsic igneous activity on the Koshikijima Islands, and their ages and petrochemistry will help elucidate the magmatism and tectonics in this area throughout the Miocene.  相似文献   

10.
Tadashi  Usuki  Hiroshi  Kaiden  Keiji  Misawa  Kazuyuki  Shiraishi 《Island Arc》2006,15(4):503-516
Abstract   In order to define the timing of granulite facies metamorphism, sensitive high-resolution ion microprobe (SHRIMP) U-Pb analyses were performed on zircons of three pelitic granulites from the lower metamorphic sequence of the Hidaka Metamorphic Belt, southern central Hokkaido, Japan. Both rounded and prismatic zircons were found in the granulite samples. The rounded zircons had thin (10–20 µm) concentric overgrowth rims on detrital cores, while the prismatic zircons did not have detrital cores. Both the overgrowth rims on the rounded zircons and the entire prismatic zircons were formed under granulite facies metamorphism and consistently yield Latest Oligocene–Early Miocene ages (23.7 ± 0.4 Ma to 17.2 ± 0.5 Ma; 206Pb/ 238U ages ( n  = 31) with low Th/U ratios, mostly <0.1). The internal structure of zircons and their SHRIMP U-Pb ages provide strong evidence in support of the granulite facies event occurring during the Latest Oligocene-Early Miocene. The detrital cores of rounded zircons show a huge variety of ages; Mesoarchean to Paleoproterozoic, Paleozoic to Mesozoic and Paleogene. The interior and marginal portions of the Eurasian continent including cratonic areas are suggested for their source provenances. These wide variations in age suggest that the protolith of the granulites of the lower metamorphic sequence were deposited near the trench of the Eurasian continental margin during Paleogene. The protolith of the lower metamorphic sequence of the Hidaka metamorphic belt was thrust under the upper metamorphic sequence, which had already been metamorphosed in early Paleogene. The Latest Oligocene-Early Miocene Hidaka high-temperature metamorphic event is presumed to have been caused by asthenospheric upwelling during back-arc rifting of the Kuril and Japan basins.  相似文献   

11.
The subduction of “hot” Shikoku Basin and the mantle upwelling related to the Japan Sea opening have induced extensive magmatism during the middle Miocene on both the back-arc and island-arc sides of southwest Japan. The Goto Islands are located on the back-arc side of northwestern Kyushu, and middle Miocene granitic rocks and associated volcanic, hypabyssal, and gabbroic rocks are exposed. The igneous rocks at Tannayama on Nakadori-jima in the Goto Islands consist of gabbronorite, granite, granite porphyry, diorite porphyry, andesite, and rhyolite. We performed detailed geological mapping at a 1:10 000 scale, as well as petrographical and geochemical analyses. We also determined the zircon U–Pb age dating of the igneous rocks from Tannayama together with a granitic rock in Yagatamesaki. The zircon U–Pb ages of the Tannayama igneous rocks show the crystallization ages of 14.7 Ma ± 0.3 Ma (gabbronorite), 15.9 Ma ± 0.5 Ma (granite), 15.4 Ma ± 0.9 Ma (granite porphyry), and 15.1 Ma ± 2.1 Ma (rhyolite). Zircons from the Yagatamesaki granitic rock yield 14.5 Ma ± 0.7 Ma. Considering field relationships, new zircon data indicate that the Tannayama granite formed at ~16–15 Ma, and the gabbronorite, granite porphyry, diorite porphyry, andesite, and subsequently rhyolite formed at 15–14 Ma, which overlaps a plutonic activity of the Yagatamesaki. The geochemical characteristics of the Tannayama igneous rocks are similar to those of the tholeiitic basalts and dacites of Hirado, and the granitic rocks of Tsushima in northwestern Kyushu. This suggests that the Tannayama igneous rocks can be correlated petrogenetically with the igneous rocks in those areas, with all of them generated by the upwelling of hot mantle diapirs during crustal thinning in an extensional environment during the middle Miocene.  相似文献   

12.
The Taebaeksan Basin is located in the mid‐eastern part of the southern Korean Peninsula and tectonically belonged to the Sino‐Korean Craton (SKC). It comprises largely the lower Paleozoic Joseon Supergroup and the upper Paleozoic Pyeongan Supergroup which are separated by a disconformity representing a 140 myr?long hiatus. This paper explores the early Paleozoic paleogeographical and tectonic evolution of the Taebaeksan Basin on the basis of updated stratigraphy, trilobite faunal assemblages, and detrital zircon U–Pb ages of the Joseon Supergroup. The Joseon Supergroup is a shallow marine siliciclastic‐carbonate succession ranging in age from the Cambrian Series 2 to Middle Ordovician. The Ongnyeobong Formation is the sole Upper Ordovician volcanic succession documented in the Taebaeksan Basin. It is suggested that in the early Paleozoic the Taebaeksan Basin was a part of an epeiric sea, the Joseon Sea, in east Gondwana. The Joseon Sea was the depositional site for lower Paleozoic successions of the SKC. Early Paleozoic sedimentation in the Joseon Sea commenced during the Cambrian Stage 3 (～ 520 Ma) and ceased by the end of the Darriwilian (～ 460 Ma). In the early Paleozoic, the SKC was located at the margin of east Gondwana and was separated from the South China Craton by an oceanic basin with incipient oceanic ridges, the Helan Trough. The spreading oceanic ridges and associated transform faults possibly promoted the uplift of the Joseon Sea, which resulted in cessation of sedimentation and break‐up of the SKC from core Gondwana by the end of the Ordovician.  相似文献   

13.
Significant advances were made in the last century in the investigations of the Neogene stress history of the NE Japan arc. However, previous studies have failed to fully resolve middle Miocene post‐rift stress conditions owing to their assumption of Andersonian faulting and an inability to determine maximum and intermediate stress axes from dike orientations. We applied the latest methods of paleostress analysis in this study to igneous dikes and mesoscale faults in the Kakunodate area of the NE Japan arc to elucidate post‐rift stress conditions. Stratigraphic constraints and U–Pb dating indicate that the doleritic and dacitic dikes were formed at 16–12 Ma and 15–12 Ma, respectively. Dolerite and dacite dikes yielded NW–SE extensional stresses with intermediate and low stress ratios, respectively. Mesoscale faults in the middle Miocene formations of the studied area indicated similar stresses. We suggest the sluggish deformations resulting in the dike intrusion and faulting in the normal‐faulting stress regime after the termination of intra‐arc rifting at ca. 15 Ma.  相似文献   

14.
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   

15.
Paleomagnetic measurements have been carried out on welded tuffs ranging in age between 58 Ma and 112 Ma from Yamaguchi and Go¯river areas in the central part of Southwest Japan. The new data, together with those of younger igneous rocks published previously, define the change of paleomagnetic field direction during the late Mesozoic/ Cenozoic period for Southwest Japan. The paleomagnetic direction from this area has pointed 56 ± 3° clockwise from the expected field direction estimated from APWP (apparent polar wandering path) of the whole of Eurasia during the period between 100 and 20 Ma. In comparison with the expected one from the eastern margin of Eurasia (Korea, China, Siberia), the Cretaceous field direction of Southwest Japan shows the clockwise deflection by 44–49°. These results establish that while the eastern margin of Eurasia, including Southwest Japan, was rotated more or less with respect to the main part of Eurasia during last 100 Ma, Southwest Japan was rotated clockwise through more than 40° with respect to the eastern margin of Eurasia since 20 Ma. The large amount of rotation for Southwest Japan implies that it is rotated by an opening of the southwestern part of the Japan Sea, which widens northeastward (fan shape opening). The tectonic feature of Southwest Japan and the Japan Sea is analogous to that of Corso-Sardinia and the Ligurian Sea in the Mediterranean, indicating that the fan shape opening is a specific feature of the rifting of the continental sliver at the continental rim.  相似文献   

16.
Volcanic history and tectonics of the Southwest Japan Arc   总被引：1，自引：0，他引：1  
Abstract Remarkable changes in volcanism and tectonism have occurred in a synchronous manner since 1.5–2 Ma at the junction of the Southwest Japan Arc and the Ryukyu Arc. Although extensive volcanism occurred in Kyushu before 2 Ma, the subduction-related volcanism started at ca 1.5 Ma, forming a NE–SW trend volcanic front, preceded by significant changes in whole-rock chemistry and mode of eruptions at ca 2 Ma. The Median Tectonic Line has intensified dextral motion since 2 Ma, with a northward shift of its active trace of as much as 10 km, accompanied by the formation of rhomboidal basins in Central Kyushu. Crustal rotation and incipient rifting has also occurred in South Kyushu and the northern Okinawa Trough over the past 2 million years. We emphasize that the commencement age of these events coincides with that of the transition to the westward convergence of the Philippine Sea plate, which we interpret as a primary cause of these synchronous episodes. We assume that the shift in subduction direction led to an increase of fluid component contamination from subducted oceanic slab, which then produced island-arc type volcanism along the volcanic front. Accelerated trench retreat along the Ryukyu Trench may have caused rifting and crustal rotation in the northern Ryukyu Arc.  相似文献   

17.
Hiroshi  Kitazato 《Island Arc》1997,6(2):144-157
Abstract The northern tip of the Izu-Ogasawara Arc on the Philippine Sea plate collided with the central part of the Honshu Arc in the early Quaternary. The collision history is recorded in late Cenozoic strata that are distributed widely in central Japan. To reconstruct paleotopography during the collision process, paleogeographic maps of central Japan were drawn at six time slices during the late Cenozoic. These maps were made from paleodepth data that were inferred from benthic foraminiferal fossil assemblages. Sedimentological information was also added to the maps. The paleogeographic maps show several distinctive geological features. The paleodepth of the area between the Izu-Ogasawara Arc and the Honshu Arc changed quickly from deep-sea to shallow marine during the Quaternary by means of rapid deposition of large amounts of coarse-grained detritus. The conglomerate was first deposited in a trough as deep-sea fan deposits, and filled the trough until an alluvial fan was formed. Forearc basins of the Honshu Arc facing the collision area subsided from 3 to 1 Ma. Vertical movement of the basin was inferred from a strata thickness/paleodepth correlation graph. It is thought that the tectonic inversion seen in sedimentary basins in the Kanto and Tokai regions might be closely related to the change of motion of the Philippine Sea plate. However, a basin of the Ashigara area sunk continuously without interruption until 0.7 Ma. The collision event affected strongly distribution of deep-sea benthic foraminifera. Paleogeographic maps show that a deep trough appeared in the Ashigara area between 3 and 1.5 Ma. This trough may have served as a passage for the migration of deep-sea benthic foraminifera between the Pacific and the Philippine Sea. Cold water benthic foraminiferal species occur west of the Izu-Ogasawara ridge deposited in strata during the existence of the passage.  相似文献   

18.
High-resolution reconstruction of Benioff zone depth–dip angle trajectory for Burma–Java subduction margin between 2° and 17°N Lat. reveals two major episodes of plate geometry change expressed as abrupt deviation in subduction angle. Estimation of effective rate of subduction in different time slices (and then length of subducted slab) allowed drawing of isochrones in Ma interval through these trajectories for the time period 5–12 Ma. With these isochrones, the deformation events on the subducting Indian plate are constrained in time as of 4–5 and 11 Ma old. This well-constrained time connotation offered scope for the correlation of slab deformation events with the well-established two-phase opening history of the Andaman Sea. While the 11 Ma event recorded from southern part of the study area is correlated with early stretching and rifting phase, the 4–5 Ma event is interpreted as major forcing behind the spreading phase of the Andaman Sea. Systematic spatio-temporal evaluation of Indian plate obliquity on the Andaman Sea evolution shows its definite control on the early rifting phase, initiated towards south near northwest Sumatra. The much young spreading phase recorded towards north of 7° Lat. is possibly the result of late Miocene–Pliocene trench retreat and follow-up transcurrent movement (along Sagaing and Sumatran fault system) with NW–SE pull-apart extension.Nonconformity between plate shape and subduction margin geometry is interpreted as the causative force behind Mid-Miocene intraplate extension and tearing. Enhanced stretching in the overriding plate consequently caused active forearc subsidence, recorded all along this plate margin. Initial phase of the Andaman Sea opening presumably remains concealed in this early–middle Miocene forearc subsidence history. The late Miocene–Pliocene pull-apart opening and spreading was possibly initiated near the western part of the Mergui–Sumatra region and propagated northward in subsequent period. A temporary halt in rifting at this pull-apart stage and northeastward veering of the Andaman Sea Ridge (ASR) are related with uplifting of oceanic crust in post-middle Miocene time in form of Alcock and Sewell seamounts, lying symmetrically north and south of this spreading ridge.  相似文献   

19.
Low‐temperature thermochronology provides information on the timing of rifting and denudation of passive margins, and the Red Sea with its well‐exposed, young rift margins is a suitable setting for its application. Here we present new apatite fission‐track (AFT) data from Sudan northern hinterland and Red Sea coastal areas. From the former region we obtained ages between 270 ± 2 Ma ad 253 ± 53 Ma, and from the coastal belt between 83 ± 8 Ma and 39 ± 7 Ma. These data prompted a review and comparison with low‐temperature thermochronological data from the whole Nubian Red Sea Margin, and a discussion on their implication in assessing the margin evolutionary style. AFT data are available for Egypt and Eritrea as well as apatite (U‐Th)/He (AHe) ages for two transects transversal to the margin in Eritrea. Both in Egypt and Eritrea AFT data record a cooling event at about 20–25 Ma (Early Miocene) and an earlier, more local, cooling event in Egypt at about 34 Ma (Early Oligocene). The thermal modeling of the Sudan samples provides an indication of a rapid cooling in Miocene times, but does not support nor rules out an Early Oligocene cooling phase. The re‐assessment of new and existing thermochronological data within the known geological framework of the Nubian and conjugate Arabian margins favours the hypothesis that early rifting stages were affecting the whole Gulf of Suez–Red Sea–Gulf of Aden system since the Oligocene. These precocious, more attenuated, phases were followed by major extension in Miocene times. As to the mode of margin evolution, AFT age patterns both in Egypt and Eritrea are incompatible with a downwarp model. The distribution of AHe ages across the Eritrean coastal plain suggests that there the escarpment was evolving predominantly by plateau degradation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

20.
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   

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