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1.
New and published paleomagnetic measurements from Trans Altai and South Gobi zones in south Mongolia document large tectonic motions in between Late Carboniferous and Triassic. Magnetic inclinations confirm equatorial position of south Mongolian terranes in Late Carboniferous–Permian times. The evolution of magnetic declinations indicates 90° anticlockwise rotation in between latest Carboniferous and Early Triassic of all studied tectonic units around the Eulerian pole located close to axis of Mongolian orocline. The anticlockwise rotation continues in Triassic being accompanied by a major drift to the north. The structural and published geochronological data suggest Carboniferous E–W shortening of the whole region resulting in N–S trend of all continental and oceanic geological units followed by orthogonal N–S shortening during Late Permian to Early Jurassic. Both paleomagnetic and geological data converge in a tectonic model of oroclinal bending of Mongolian ribbon continent, westerly back arc oceanic domain and Mongol–Okhotsk subduction zone to the east. The oroclinal bending model is consistent with the coincidence of the Eulerian pole of rotation with the structural axis of Mongolian orocline. In addition, the Mesozoic collisional tectonics is reflected by late remagnetizations due to formation of wide deformation fronts and hydrothermal activity. 相似文献
2.
Paleomagnetism and the orocline hypothesis 总被引：3，自引：0，他引：3
Oroclines were originally defined by Carey as curved mountain belts which initially were straight, or at least straighter than they are today. In the last few years, the definition has been broadened to include any curved mountain belt, regardless of its original shape.Since the occurrence of oroclinal bending is best recorded in the change of declination as a function of tectonic setting, paleomagnetic and structural data from six potential oroclines have been compiled and analyzed to determine the amount of rotation displayed by the change of paleomagnetic declination relative to the change in strike of the fold belt.The arcuate belts investigated are: the Sicilian-Calabrian Arc and the Umbrian Arc of Italy, the Swiss portion of the Jura Mountains, the central portion of the Appalachian Mountains (from Pennsylvania to Virginia, U.S.A.), the Wyoming-Idaho overthrust belt of western North America and the Hercynides of Western and Central Europe.The Jura Mountains and the Pennsylvania-Virginia portion of the Appalachians fail to show significant oroclinal bending. The Wyoming-Idaho belt shows a combination of rotated (possibly oroclinal) and unrotated thrust sheets.In the Sicilian-Calabrian Arc significant oroclinal bending caused by the impingement of the Calabria-Peloritani nappes in the Late Tertiary can be demonstrated, while the Umbrian Arc of similar age, in the Northern Apennines, also shows oroclinal bending on a smaller scale.Hercynian Europe (the only belt included in which deformation of basement rocks can be demonstrated) shows oroclinal bending (at least 80°) as well as a marked original curvature (70°) in its western part.Common to all the oroclines studied in this paper is the probable impingement of a rigid block or continental margin during the orogeny, causing subsequent deformation and bending of the fold belt. 相似文献
3.
Arlo Brandon Weil Gabriel Gutiérrez-Alonso David Wicks 《International Journal of Earth Sciences》2013,102(1):43-60
The Esla tectonic unit lies along the southern boundary of the Cantabrian–Asturian Arc, a highly curved foreland fold-thrust belt that was deformed during the final amalgamation of the Pangea supercontinent. Previous structural and paleomagnetic analyses of the Cantabrian–Asturian Arc suggest a two-stage tectonic history in which an originally linear belt was bent into its present configuration, creating an orocline. The Esla tectonic unit is a particularly complex region due to the interaction of rotating thrust sheets from the southern limb of the arc and the southward-directed thrusts of the Picos de Europa tectonic domain during late-stage north–south shortening and oroclinal bending. These structural interactions resulted in intense modification of early-phase thin-skinned tectonic structures that were previously affected by a deeper out-of-sequence antiformal stack that passively deformed the early thrust stack. A total of 75 paleomagnetic sites were collected from the Portilla and Santa Lucia formations, two carbonate passive-margin reef platform units from the middle Devonian. Similar to other regions of the Cantabrian–Asturian Arc, Esla Unit samples carry a secondary remanent magnetization that was acquired after initial thrusting and folding of Variscan deformation in the late Carboniferous. Protracted deformation during late-stage oroclinal bending caused reactivation of existing thrust sheets that include the Esla and younger Corniero and Valbuena thrusts. When combined with existing structural data and interpretations, these data indicate that the present-day sinuosity of the Esla Unit is the consequence of both secondary rotation of originally linear features in the western Esla exposures (e.g., frontal thrusts), and secondary modification and tightening of originally curvilinear features in the eastern Esla exposures (e.g., hanging-wall lateral/oblique ramps). Differences in structural style between the Esla and other tectonic units of the arc highlight the complex kinematics of oroclinal bending, which at the orogen-scale buckled an originally linear, north–south (in present-day coordinates) trending Cantabrian–Asturian thrust belt during the final stages of Pangea amalgamation. 相似文献
4.
四川盆地南缘早三叠世古地磁研究表明,川东和川东南地区一系列北北东、北东向褶皱的形成,并非同造山期形成的弧形弯曲构造,它是受深部断裂控制形成的简单褶皱。这一结果再次表明,华北与扬子地块的拼合晚于早三叠世,可能于早/中侏罗世完成拼合过程。 相似文献
5.
Charles S. Hutchison 《International Journal of Earth Sciences》1994,83(2):388-405
The Triassic Indosinian Orogeny followed extinction of the Palaeotethys Ocean resulting in suturing of Gondwana affinity and Cathaysian blocks.The Gondwana affinity Sinoburmalaya block of Peninsular Malaysia, characterized by Carboniferous—Permian mudstones containing glacial dropstones and sparse fauna and flora, is traced extensively into Sumatra. This mudstone facies is flanked on the east by a sandstone-dominated facies and by carbonate localized in the Kinta Valley. The muddy and sandy facies both begin with a basal Carboniferous condensed red bed sequence, which unconformably overlies the older formations of Sinoburmalaya. Both facies also demonstrate a Late Permian conformable transition into overlying limestone. The Cathaysian block of East Malaya is characterized by Late Permian Gigantopteris flora and fusulinid limestones associated with andesitic volcanism. It is similar but not identical to the West Sumatra Carboniferous—Permian block, characterized by Early Permian volcanism, fusulinid limestones and early Cathaysian Jambi flora.The South to SSE trending central Peninsular Malaysian Triassic orogenic belt swings south-east from Singapore to Bangka, then east to Billiton. The Palaeotethys suture (Bentong—Raub Line) forms the western margin of this belt and is therefore unlikely to continue south along the Palaeogene Bengkalis Graben, which transects the north-west—south-east orogenic fabric of Sumatra.The oroclinal bending of the Indosinian Orogen, from a north-west—south-east grain in Sumatra to a northerly grain through Peninsular Malaysia, is attributed to the Palaeocene collision of India and its subsequent indentation into Eurasia. The bending was accomplished by clockwise rotation and right-lateral shear parallel to the orogenic grain. The Mesozoic Palaeotethyan sutures were transformed into Palaeocene and younger shear zones. The outer zones of the orocline experienced pull apart tectonics (Andaman Sea and Sumatra basins) while the inner part (East Malaya to Billiton), being compressional, lacks Cenozoic basins. 相似文献
6.
The Variscan mountain belt in Iberia defines a large “S” shape with the Cantabrian Orocline in the north and the Central Iberian curve, an alleged orocline belt of opposite curvature, to the south. The Cantabrian Orocline is kinematically well constrained, but the geometry and kinematics of the Central Iberian curve are still controversial. Here, we investigate the kinematics of the Central Iberian curve, which plays an important role in the amalgamation of Pangea since it may have accommodated much of the post-collisional deformation. We have performed a paleomagnetic study on Carboniferous granitoids and Cambrian limestones within the hinge of the curve. Our paleomagnetic and rock magnetic results show a primary magnetization in the granitoids and a widespread Carboniferous remagnetization of the limestones. Syn-kinematic granitoids show ca. 70° counter-clockwise rotations consistent with the southern limb of the Cantabrian Orocline. Post-kinematic granitoids and Cambrian limestones show consistent inclinations but very scattered declinations suggesting that they were magnetized coevally to and after the ~ 70° rotation. Our results show no differential rotations between northern, southern limb and the hinge zone. Therefore, we discard a late Carboniferous oroclinal origin for the Central Iberian curve. 相似文献
7.
柴达木盆地东缘早古生代弯山构造 总被引：1，自引：1，他引：0
位于中国中央造山带内部的柴达木盆地周缘出露有代表原特提斯洋盆的蛇绿岩带、指示大洋俯冲与大陆深俯冲的高压-超高压变质带以及不同性质的早古生代花岗岩带。根据这些构造单元的空间展布形态及其综合地质年龄分布,表现为一条环绕柴达木盆地东缘的连续而弯曲的加里东期造山带。造山带内发育一系列右行走滑断裂和韧性剪切带,与古地磁资料所揭示的柴达木地块在早古生代的相对逆时针旋转息息相关。本文提出,柴达木盆地周缘造山带为一弯山构造。它是在原特提斯洋向南斜向俯冲闭合过程中,诱发的大型走滑断裂和柴达木地块逆时针旋转牵引造山带发生弯曲所致。 相似文献
8.
Paleomagnetic data on Middle- and Late-Paleozoic rocks from the central part of the Ural-Mongolian Belt in Kazakhstan are considered. The primary remanences in the Permian rocks and secondary magnetization components of the same age in pre-Permian rocks of central and northern Kazakhstan are not rotated relative to the East European Platform. In southern Kazakhstan adjoining the Tien Shan almost all data point to large, up to 90°, counterclockwise rotation of blocks. These rotations, related to the regional wrench fault zone, must be subtracted from older paleomagnetic data to ensure their correct interpretation. The paleomagnetic declinations in Upper Carboniferous rocks coincide more or less over all of Kazakhstan, whereas the Silurian and Early Devonian declinations in the north and south of Kazakhstan differ approximately by 180°. It can be suggested that the Devonian volcanic belt, having a horseshoe outline, was initially an almost rectilinear NW-trending feature. Its oroclinal bending took place in the Devonian and Early Carboniferous and completed by the Late Carboniferous. We compared the model of the Kazakh Orocline based on paleomagnetic data with the geological events in this territory. It turned out that a slow bending of an initially rectilinear subduction zone is consistent with lateral migration of active volcanism and folding inside a developing loop, whereas extension outside the loop was accompanied by subsidence and rifting. In general, the proposed model connects the main tectonic events in Kazakhstan with the movements established from paleomagnetic data. 相似文献
9.
In this study, we report an extensive paleomagnetic study (76 sites) carried out in the Alborz Mts. (northern Iran), with the aim of reconstructing the rotation history and the origin of curvature of this orogenic chain. The analyzed deposits are the sedimentary successions of the Upper Red Formation (Miocene), Lower Red Formation (Oligocene) and Eocene clastic units. Paleomagnetic results indicate that the Alborz Mts. can be considered a secondary arc that originated as a linear mountain belt that progressively acquired its present day curvature through opposite vertical axis rotations along its strike. The curvature of the arc was entirely acquired after the middle-late Miocene, which is the age of the youngest investigated sediments (Upper Red Formation). Overall, our paleomagnetic data indicate that the Alborz Mts. can be considered an orocline.Our results define, for the first time, the rotational history of the entire Alborz curved mountain belt, and enable us to reconstruct the paleogeographic and tectonic evolution of northern Iran in the framework of Arabia-Eurasia continental deformation. The kinematics inferred by the pattern of paleomagnetic rotations is at odds with the present day kinematics of northern Iran, characterized by the westward extrusion of the South Caspian block, and by a left lateral shear between Central Iran and the central and western sectors of the Alborz Mts. By integrating paleomagnetic data with stratigraphic, thermochronological, structural and GPS information, we propose that the initiation of South Caspian subduction and the activation of westward extrusion of South Caspian block occurred diachronously and that the initiation of the present-day kinematics of northern Iran was quite recent (Lower Pleistocene, < 2 Ma). 相似文献
10.
Eocene paleomagnetism of the Caucasus (southwest Georgia): oroclinal bending in the Arabian syntaxis
The Caucasus is very important for our understanding of tectonic evolution of the Alpine belt, but only a few reliable paleomagnetic results were reported from this region so far. We studied a collection of more than 300 samples of middle Eocene volcanics and volcano-sedimentary rocks from 10 localities in the Adjaro–Trialet tectonic zone (ATZ) in the western part of the Caucasus. Stepwise thermal demagnetization isolates a characteristic remanent magnetization (ChRM) in 19 sites out of 31 studied. ChRM reversed directions prevail, and a few vectors of normal polarity are antipodal to the reversed ones after tilt correction. The fold test is positive too, and we consider the ChRM primary. Analysis of Tertiary declinations and strikes of Alpine folds in the Adjaro–Trialet zone and the Pontides in Northern Turkey shows a large data scatter; Late Cretaceous data from the same region, however, reveal good correlation between paleomagnetic and structural data. Combining Late Cretaceous and Tertiary data indicates oroclinal bending of the Alpine structures which are locally complicated with different deformation. The overall mean Tertiary inclination is slightly shallower than the reference Eurasian inclination recalculated from one apparent polar wander path (APWP), but agrees with other. This finding is in accord with geological evidence on moderate post-Eocene shortening across the Caucasus. We did not find any indication of long-lived paleomagnetic anomalies, such as to Cenozoic anomalously shallow inclinations further to the east in Central Asia. 相似文献
11.
In this study, an extensive paleomagnetic sampling (70 sites) was carried out in north-eastern Iran with the aim of reconstructing the rotation history of the outer margin of the Eurasia-Arabia collision area represented by the Ala-Dagh, Binalud and Kopeh-Dagh mountain belts. We sampled the red beds units from the Lower Cretaceous Shurijeh Fm. and from the Middle-Upper Miocene Upper Red Fm (URF). Paleomagnetic results from all the sampled areas show a homogeneous amount of CW rotations measured in the above-mentioned Formations. These paleomagnetic results suggest that the oroclinal bending process that caused the curvature of Alborz mountain belt in north Iran after the Middle-Late Miocene, also extended to the Ala-Dagh, Binalud and Kopeh-Dagh mountain belts, at the north-eastern border of the Arabia-Eurasia deforming zone.Based on our paleomagnetic results and on GPS, seismological, geomorphological and structural data available in the area, a hypothesis of tectonic evolution of the northern Iran-South Caspian Basin area, from Middle-Late Miocene to Present, is here proposed. In this model, the initiation of the oroclinal bending processes in northern Iran occurred about 6–4 myr ago, related to the impinging of North Iran between the South Caspian block and the southern margin of the Turan platform, driven by the northward subduction of the South Caspian basement under the Aspheron-Balkhan Sill. As paleomagnetic results from this study show a pattern of vertical axis rotations that is inconsistent with the present-day kinematics of the northern Iranian blocks as described by seismicity and GPS data, we suggest that the tectonic processes responsible for the bending of northern Iran mountain chains are no longer active and that the westward motion of the South Caspian basin, and therefore the initiation of opposite strike-slip motion along the Ashk-Abad and Shahrud faults, occurred very recently (∼2 My ago). We therefore propose that initiation of the northward subduction of the South Caspian basin below the Apsheron-Balkhan Sill and the westward extrusion of the South Caspian block did not occur at the same time, with the former occurring between the late Miocene and the Pliocene, and the latter during the Pleistocene. 相似文献
12.
Shinya Yoshioka Yu Yan Liu Ken Sato Hiroo Inokuchi Li Su Haider Zaman Yo-ichiro Otofuji 《Tectonophysics》2003,376(1-2):61-74
Paleomagnetic samples of Paleocene–Eocene red sandstones were collected at 36 sites from the Jiangdihe-4 and Zhaojiadian formations around the Yongren (26.1°N, 101.7°E) and Dayao areas (25.7°N, 101.3°E). These areas are located in the Chuxiong basin of the Chuan Dian Fragment, southwestern part of the Yangtze block. After stepwise thermal demagnetization, a high-temperature component with unblocking temperature of about 680 °C is isolated from 26 sites. The primary nature of this magnetization is ascertained through positive fold and reversal tests at 95% confidence level. The tilt-corrected mean paleomagnetic directions for the Yongren and Dayao areas are D=17.2°, I=26.6° with α95=5.8° and D=16.5°, I=31.1° with α95=4.8, respectively. Easterly deflected declinations from this study are consistent with those reported from other areas of the Chuxiong basin, indicating its wide presence in the Cretaceous–Eocene formations of the said basin. Comparison with declination values expected from the Cretaceous–Eocene APWP of Eurasia indicates that the magnitude of clockwise rotation systematically increases toward the southeast within the Chuxiong basin as well as in the Chuan Dian Fragment. This trend of the differential tectonic rotation in the Chuan Dian Fragment is consistent with curvature of the Xianshuihe–Xiojiang fault system. Deformation of the Chuxiong basin can fairly be associated with the formation of eastward bulge in the southern part of the Chuan Dian fragment. During southward displacement, the Chuan Dian Fragment was probably subjected to tectonic stresses as a result interaction with the Yangtze and Indochina blocks, which resulted into east–west extension and north–south shortening. 相似文献
13.
Yo-ichiro Otofuji Takaaki Matsuda Ryo Enami Koji Uno Katsuhiko Nishihama Li Su Ruslan G. Kulinich Petr S. Zimin Anatoly P. Matunin Vladimir G. Sakhno 《Tectonophysics》2002,350(3)
We present paleomagnetic results of Paleocene welded tuffs of the 53–50 Ma Bogopol Group from the northern region (46°N, 137°E) of the Sikhote Alin volcanic belt. Characteristic paleomagnetic directions with high unblocking temperature components above 560 °C were isolated from all the sites. A tilt-corrected mean paleomagnetic direction from the northern region is D=345.8°, I=49.9°, α95=14.6° (N=9). The reliability of the magnetization is ascertained through the presence of normal and reversed polarities. The mean paleomagnetic direction from the northern region of the Sikhote Alin volcanic belt reflects a counterclockwise rotation of 29° from the Paleocene mean paleomagnetic direction expected from its southern region. The counterclockwise rotation of 25° is suggested from the paleomagnetic data of the Kisin Group that underlies the Bogopol Group. These results establish that internal tectonic deformation occurred within the Sikhote Alin volcanic belt over the past 50 Ma. The northern region from 44.6° to 46.0°N in the Sikhote Alin volcanic belt was subjected to counterclockwise rotational motion through 29±17° with respect to the southern region. The tectonic rotation of the northern region is ascribable to relative motion between the Zhuravlevka terrane and the Olginsk–Taukhinsk terranes that compose the basements of the Sikhote Alin volcanic belt. 相似文献
14.
《International Geology Review》2012,54(10):1276-1294
The North Dabashan thrust belt, which is located in South Qinling, is bounded by the Ankang fault on the north and the Chengkou–Fangxian fault on the south. The North Dabashan thrust belt experienced multiple stages of structural deformation that were controlled by three palaeostress fields. The first structural event (Middle Triassic) involved NNW–SSE shortening and resulted in the formation of numerous dextral strike-slip structures along the entire Chengkou–Fangxian fault zone and within the North Dabashan thrust belt, which suggests that the South China Block moved to the NW and was obliquely subducted under the North China Block. The second structural event (Late Triassic–Early Jurassic) involved NE–SW shortening that formed NW–SE-trending structures in the North Dabashan thrust belt. The third structural event (Late Jurassic–Early Cretaceous) involved ENE–WSW or nearly E–W shortening and resulted in additional thrusting of the North Dabashan thrust belt to the WSW and formation of the WSW-convex Chengkou–Fangxian fault zone, which has an oroclinal shape. Owing to the pinning of the Hannan massif and Shennongjia massif culminations, numerous sinistral strike-slip structures developed along the eastern Chengkou–Fangxian fault zone and were superimposed over the early dextral strike-slip structures. 相似文献
15.
The processes of orocline formation are a topic of debate in geosciences. The Patagonian orocline has been a case in point for over a century. Large anomalous paleomagnetic pole rotations show that the orocline started to form at the same time as mid-Cretaceous closure of the Rocas Verdes Basin, today known from ophiolitic and basin fill remnants in the Patagonian and Fuegian Andes. Some studies therefore present bending of the Andes and closure of the basin as shared consequences of rotation of a small plate that was driven by subduction-related forces at the Pacific margin of Gondwana. An alternative view of the orocline is as a product of Cretaceous to Paleogene-aged sinistral oblique convergence at the plate-boundary scale. Geological data from Tierra del Fuego have been interpreted in support of both views. Here, I test these suggestions by comparing the Rocas Verdes Basin's tectonostratigraphy to predictions of a plate kinematic model for fragmentation of the western interior of Gondwana. The model is sufficient to explain the known history of basin opening to a width of ~ 100–300 km during the period 152–141 Ma and later closure in oblique plate convergence. As this convergence occurred by motion around a distant Euler pole, it could not have produced the Patagonian orocline by rotation of a lithospheric plate on its Pacific flank. The large anomalous paleomagnetic rotations of Tierra del Fuego, instead, are likely to have occurred within the crust by rotation and deformation of regional strike-slip faults and the intervening rocks to accommodate oblique convergence of the South American and Antarctic plates between Albian and Paleocene times. 相似文献
16.
《Journal of South American Earth Sciences》1999,12(2):221-235
The “Bolivian orocline” is the change in trend of the Andes from NW to N near 18°S. Paleomagnetic data have been used to infer that this bend was in part produced by wholesale opposed rotations (15–20° counterclockwise north of the bend and 15–20° clockwise south of it) of the two limbs of the orocline. Besides paleomagnetic data, shortening estimates from balanced cross-sections and variations in crustal cross-sectional area provide quantitative information on rotations and translations. The three sets of data do not agree closely, and therefore only loosely constrain the kinematics of the orocline. A map view kinematic model incorporating the major faults gives a more detailed picture. The resulting displacement field suggests that movement perpendicular to the orogen increases toward the bend, whereas the component of orogen-parallel movement increases away from it. Only weak rotations are indicated for the bend region. It is speculated that large-scale regional rotations of the limbs of the orocline are markedly lower than previously suggested, probably of the order of 5–10°. Stronger rotations are associated with strong lateral shortening gradients or may result from superimposed local phenomena. 相似文献
17.
The Aït Attab syncline, located in the Central High Atlas, displays a curved geometry in plan view, and is considered as one of the most spectacular fold shapes in the Central High Atlasic belt. We conducted a paleomagnetic study in Jurassic-Cretaceous red beds to investigate the origin of this geometry. The Natural Remanent Magnetization (NRM) is dominated by a secondary magnetization carried by haematite with unvarying normal polarity that has been dated at about 100 Ma. The regional fold test performed in both limbs of the syncline is positive and the paleomagnetic vectors (after tectonic correction) are parallel throughout the curvature, indicating a negative oroclinal bending test. These results are inconsistent with previous works that consider the bent geometry of this syncline to result from subsequent distortion of originally NE–SW trending structures by rotation about a vertical axis. We interpret the NRM data to demonstrate that the changing trend of the Aït Attab syncline is a primary feature, resulting from the influence of pre-existing, NE–SW and E-W-striking extensional faults that developed during a strike-slip regime. Paleomagnetic results also reveal that the tilting observed in the sampled red beds is post Albian, probably linked to the Cenozoic inversion of the High Atlasic belt. 相似文献
18.
本文根据塔里木地块及其以南的昆仑、羌塘和拉萨地块晚中生代特别是晚白垩世古地磁数据,提出青藏高原自晚白垩世后北向移动两千余公里,主要并不是通过它本身的大规模地壳缩短来完成,而是与塔里木地块一起作大规模整体北移的结果。一种可能的解释是,在欧亚大陆北部稳定区和塔里木地块之间广大的中亚构造带,自晚白垩世后发生了大规模的地壳缩短。 相似文献
19.
《International Geology Review》2012,54(15):1765-1775
Currently, two basic models describe the genesis of the Caribbean Plate: (i) a Pacific model that derives the Caribbean Plate off southern Mexico and (ii) an in situ model. The Pacific model requires the 1100–1400 km sinistral displacement recorded across the Cayman Trough to pass through the Gulf of Tehuantepec into the Middle America Trench, but no evidence of such a connection exists. The in situ model is inconsistent with the 1100–1400 km displacement across the Cayman Trough. A way through this impasse is indicated by the northwestward curvature of active oblique reverse to sinistral transcurrent faulting in southeast Mexico. Extending this potential solution back to ca. 80 Ma forms the basis of the new Pirate model, in which the Caribbean Plate and the Chortis and Chiapas blocks are derived from the northwest by anticlockwise rotation during the latest Cretaceous and Cenozoic. Following passage of the Chortis Block, the northern and southern parts of the Yucatan block collided along the intra-Yucatan suture, producing the 11–9 Ma Chiapas fold-and-thrust belt. The Pirate model accounts for the N-trending segment of the Laramide Sierra Madre Oriental–Zongolica foldbelts by anticlockwise drag, Palaeogene palaeocanyons, the second, 66–40 Ma phase of rifting in the western Gulf of Mexico, and post-10 Ma extension in the Chortis Block (Chortis–Sula rift province). Impingement of the East Pacific Rise on the Middle America Trench led to modification of the Pirate model involving subduction erosion of the ～200 km-wide, Eocene–Oligocene forearc at ca. 25 Ma, opening of the Gulf of California at ca. 6 Ma, and birth and ESE movement of the Southern Mexico block (<5 Ma) followed by its fragmentation. The Pirate mechanism indicates that the North American Plate is relatively weak and so tears and rotates into the trailing edge of the Caribbean Plate. 相似文献
20.
We provide the first comprehensive picture of the thermochronometric evolution of the Cimmerian Strandja metamorphic massif of SE Bulgaria and NW Turkey, concluding that the bulk of the massif has escaped significant Alpine-age deformation. Following Late Jurassic heating, the central part of the massif underwent a Kimmeridgian-Berriasian phase of relatively rapid cooling followed by very slow cooling in Cretaceous-to-Early Eocene times. These results are consistent with a Late Jurassic–Early Cretaceous Neocimmerian (palaeo-Alpine) phase of north-verging thrust imbrication and regional metamorphism, followed by slow cooling/exhumation driven by erosion. From a thermochronometric viewpoint, the bulk of the Cimmerian Strandja orogen was largely unaffected by the compressional stress related to the closure of the Vardar–?zmir–Ankara oceanic domain(s) to the south, contrary to the adjacent Rhodopes. Evidence of Alpine-age deformation is recorded only in the northern sector of the Strandja massif, where both basement and sedimentary rocks underwent cooling/exhumation associated with an important phase of shortening of the East Balkan fold-and-thrust belt starting in the Middle–Late Eocene. Such shortening focused in the former Srednogorie rift zone because this area had been rheologically weakened by Late Cretaceous extension. 相似文献