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1.
J. Golonka   《Tectonophysics》2004,381(1-4):235
Thirteen time interval maps were constructed, which depict the Triassic to Neogene plate tectonic configuration, paleogeography and general lithofacies of the southern margin of Eurasia. The aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework. The Hercynian Orogeny was completed by the collision of Gondwana and Laurussia, whereas the Tethys Ocean formed the embayment between the Eurasian and Gondwanian branches of Pangea. During Late Triassic–Early Jurassic times, several microplates were sutured to the Eurasian margin, closing the Paleotethys Ocean. A Jurassic–Cretaceous north-dipping subduction boundary was developed along this new continental margin south of the Pontides, Transcaucasus and Iranian plates. The subduction zone trench-pulling effect caused rifting, creating the back-arc basin of the Greater Caucasus–proto South Caspian Sea, which achieved its maximum width during the Late Cretaceous. In the western Tethys, separation of Eurasia from Gondwana resulted in the formation of the Ligurian–Penninic–Pieniny–Magura Ocean (Alpine Tethys) as an extension of Middle Atlantic system and a part of the Pangean breakup tectonic system. During Late Jurassic–Early Cretaceous times, the Outer Carpathian rift developed. The opening of the western Black Sea occurred by rifting and drifting of the western–central Pontides away from the Moesian and Scythian platforms of Eurasia during the Early Cretaceous–Cenomanian. The latest Cretaceous–Paleogene was the time of the closure of the Ligurian–Pieniny Ocean. Adria–Alcapa terranes continued their northward movement during Eocene–Early Miocene times. Their oblique collision with the North European plate led to the development of the accretionary wedge of the Outer Carpathians and its foreland basin. The formation of the West Carpathian thrusts was completed by the Miocene. The thrust front was still propagating eastwards in the eastern Carpathians.During the Late Cretaceous, the Lesser Caucasus, Sanandaj–Sirjan and Makran plates were sutured to the Iranian–Afghanistan plates in the Caucasus–Caspian Sea area. A north-dipping subduction zone jumped during Paleogene to the Scythian–Turan Platform. The Shatski terrane moved northward, closing the Greater Caucasus Basin and opening the eastern Black Sea. The South Caspian underwent reorganization during Oligocene–Neogene times. The southwestern part of the South Caspian Basin was reopened, while the northwestern part was gradually reduced in size. The collision of India and the Lut plate with Eurasia caused the deformation of Central Asia and created a system of NW–SE wrench faults. The remnants of Jurassic–Cretaceous back-arc systems, oceanic and attenuated crust, as well as Tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems.  相似文献   

2.
The results of our new paleomagnetic investigations on 21 sites in the Cévennes and Lure regions as well as previous studies demonstrate that all Mesozoic marly limestones of SE France exhibit similar paleomagnetic behavior with remagnetization disputed in age. The studied areas have the particularity to have been folded before (Late Eocene), the Alpine folding (Oligo–Miocene). Samples (201 marly limestones) dated from Lower Jurassic to Lower Cretaceous have been demagnetized by thermal treatment. They all present a well-defined component with a normal polarity which was mostly obtained between 200 and 350 °C. Numerous arguments lead from pretectonic to syntectonic widespread remagnetization related to orogenic fluid circulation affecting the whole basin. An Eocene age (between 35 and 40 Ma) is obtained for this remagnetization thanks both to the comparison of the average inclination of all regional paleomagnetic studies (+54.9°/−1.5°) with the expected paleomagnetic inclination and the syntectonic character of remagnetization.  相似文献   

3.
Paleomagnetic and plate tectonic constraints on the movement of Tibet   总被引：2，自引：0，他引：2  
The paleomagnetic results from Tibet, north of the Yarlung-Zang bo suture zone, show that Tibet was at about 15°–20°N in Middle Cretaceous time. It then moved south down to 7°–10°N in the Late Cretaceous-Paleogene. The oceanic crust of the Xigaze ophiolites was magnetized at 13°N but thereafter migrated further south. This movement is compared with the relative movement of India and Asia as deduced from magnetic anomalies and paleomagnetism. Experimental models on deformation help us to explain how Tibet moved during the Late Cretaceous under the constraint of the Africa-Arabia indenter and during the Upper Tertiary under the constraint of the Indian indenter.  相似文献   

4.
The Juiz de Fora Complex is mainly composed of granulites, and granodioritic-migmatite gneisses and is a cratonic basement of the Ribeira belt. Paleomagnetic analysis on samples from 64 sites widely distributed along the Além Paraíba dextral shear zone (SE Brazil, Rio de Janeiro State) yielded a northeastern, steep downward inclination direction (Dm=40.4°, Im=75.4, a95=6.0°, K=20.1) for 30 sites. The corresponding paleomagnetic pole (RB) is situated at 335.2°E; 0.6°S (a95=10.0°; K=7.9). Rock magnetism indicates that both (titano)magnetite and titanohematite are the main magnetic minerals responsible for this direction. Anisotropy of low-field magnetic susceptibility (AMS) measurements were used to correct the ChRM directions and consequently its corresponding paleomagnetic pole. This correction yielded a new mean ChRM (Dm = 2.9°, Im = 75.4°, a95 = 6.4°, K = 17.9) whose paleomagnetic pole RBc is located at 320.1°E, 4.2° N (a95=10.3°, K=7.5). Both mean ChRM and paleomagnetic pole obtained from uncorrected and corrected data are statistically different at the 95% confidence circle. Geological and geochronological data suggest that the age of the Juiz de Fora Complex pole is probably between 535–500 Ma, and paleomagnetic results permit further constraint on these ages to the interval 520–500 Ma by comparison with high quality paleomagnetic poles in the 560–500 Ma Gondwana APW path.  相似文献   

5.
This paper presents new paleomagnetic results on Cenozoic rocks from northern central Asia. Eighteen sites were sampled in Pliocene to Miocene clays and sandy clays of the Zaisan basin (southeastern Kazakhstan) and 12 sites in the upper Oligocene to Pleistocene clays and sandstones of the Chuya depression (Siberian Altai).Thermal demagnetization of isothermal remanent magnetization (IRM) showed that hematite and magnetite are the main ferromagnetic minerals in the deposits of the Zaisan basin. Stepwise thermal demagnetization up to 640–660 °C isolated a characteristic (ChRM) component of either normal or reverse polarity at nine sites. At two other sites, the great circles convergence method yielded a definite direction. Measurements of the anisotropy of magnetic susceptibility showed that the hematite-bearing sediments preserved their depositional fabric. These results suggest a primary origin of the ChRM and were substantiated by positive fold and reversal tests. The mean paleomagnetic direction for the Zaisan basin (D=9°, I=59°, k=19, α95=11°) is close to the expected direction derived from the APW path of Eurasia [J. Geophys. Res. 96 (1991) 4029] and shows that the basin did not rotated relative to stable Asia during the Tertiary.In the upper Pliocene–Pleistocene sandstones of the Chuya depression, a very stable ChRM carried by hematite was found. Its mean direction (D=9°, I=46°, k=25, α95=7°) is characterized by declination close to the one excepted for early Quaternary, whereas inclination is lower. In the middle Miocene to lower Pliocene clays and sandstones, a stable ChRM of both normal and reverse polarities carried by magnetite was isolated. Its mean direction (D=332°, I=63°, k=31, α95=4°) is deviated with respect to the reference direction and implies a Neogene, 39±8° counterclockwise rotation of the Chuya depression relative to stable Asia. These results and those from the literature suggest that the different amount of rotation found in the two basins is related to a sharp variation in their tectonic style, predominantly compressive in the Zaisan basin and transpressive in the Siberian Altai. At a larger scale, the pattern of vertical axis rotations deduced from paleomagnetic data in northern central Asia is consistent with the hypothesis of a large left-lateral shear zone running from the Pamirs to the Baikal. Heterogeneous rotations, however, indicate changes in style of faulting along the shear zone and local effect for the domains with the largest rotations.  相似文献   

6.
The main terrains involved in the Cretaceous–Tertiary tectonism in the South Carpathians segment of the European Alpine orogen are the Getic–Supragetic and Danubian continental crust fragments separated by the Severin oceanic crust-floored basin. During the Early–Middle Cretaceous times the Danubian microplate acted initially as a foreland unit strongly involved in the South Carpathians nappe stacking. Multistage folding/thrusting events, uplift/erosion and extensional stages and the development of associated sedimentary basins characterize the South Carpathians during Cretaceous to Tertiary convergence and collision events. The main Cretaceous tectogenetic events responsible for contraction and crustal thickening processes in the South Carpathians are Mid-Cretaceous (“Austrian phase”) and Latest Cretaceous (“Laramide” or “Getic phase”) in age. The architecture of the South Carpathians suggests polyphase tectonic evolution and mountain building and includes from top to bottom: the Getic–Supragetic basement/cover nappes, the Severin and Arjana cover nappes, and Danubian basement/cover nappes, all tectonically overriding the Moesian Platform. The Severin nappe complex (including Obarsia and Severin nappes) with Late Jurassic–Early Cretaceous ophiolites and turbidites is squeezed between the Danubian and Getic–Supragetic basement nappes as a result of successive thrusting of dismembered units during the inferred Mid- to Late Cretaceous subduction/collision followed by tectonic inversion processes.

Early Cretaceous thick-skinned tectonics was replaced by thin-skinned tectonics in Late Cretaceous. Thus, the former Middle Cretaceous “Austrian” nappe stack and its Albian–Lower Senonian cover got incorporated in the intra-Senonian “Laramide/Getic” stacking of the Getic–Supragetic/Severin/Arjana nappes onto the Danubian nappe duplex. The two contraction events are separated by an extensional tectonic phase in the upper plate recorded by the intrusion of the “Banatitic” magmas (84–73 Ma). The overthrusting of the entire South Carpathian Cretaceous nappe stack onto the fold/thrust foredeep units and to the Moesian Platform took place in the Late Miocene (intra-Sarmatian) times and was followed by extensional events and sedimentary basin formation.  相似文献   


7.
白垩纪以来中国西部地体运动的古地磁证据和问题   总被引：4，自引：0，他引：4  
地质证据表明中国西部各地体在白垩纪之前已经增生到欧亚大陆之上 ,但这些地体自白垩纪以来的古地磁极位置与稳定欧亚大陆的古地磁极位置存在较大差异 ,对其最可能的解释是发生在晚白垩世与古新世之交 (约 6 5Ma)印度板块和欧亚大陆之间的碰撞及其后印度板块的持续北向挤压 ,使得这些地体之间以及这些地体与稳定欧亚大陆之间发生了相对位移和地体内部的变形。文中利用现有的古地磁研究成果 ,计算了自白垩纪以来中国西部各地体与欧亚稳定大陆之间的南北向相对位移量。塔里木地块和柴达木地体的古地磁数据表明 ,阿尔金断裂至少经历了四期活动。在欧亚地区普遍存在的第三纪磁倾角偏缓现象 ,很可能反映了在该地区长期存在非偶极子场。  相似文献   

8.
We present a Late Cretaceous (81 Ma) pole position for the Pacific plate derived from paleomagnetic analyses of basalt samples from Detroit Seamount (of the Hawaiian–Emperor seamounts) that were oriented using Brunhes-age overprints. This pole is at much higher latitudes than the previously published Late Cretaceous pole positions based on the modeling of magnetic anomalies observed during marine surveys over seamounts. Our new pole suggests that the Pacific plate would have moved rapidly between 95 and 81 Ma at speeds as high as 19.8 (−10.8/+11.2) cm/year. The Pacific plate at this time was smaller than the present-day plate and had a substantial subducting boundary. The high-velocity estimates are comparable with those of other paleoplates having similar characteristics. Therefore, plate tectonic driving forces can explain the motion and there is no need to invoke true polar wander. Decreases in mantle drag associated with vigorous Late Cretaceous volcanism in the Pacific, however, may have contributed to the rapid plate speed. The new pole position, together with other reliable paleomagnetic indicators of Pacific apparent polar wander, further supports the notion of drift of the Hawaiian hotspot during the Late Cretaceous.  相似文献   

9.
The Hawaiian–Emperor Seamount chain records the motion of the Pacific Plate relative to the Hawaiian mantle hotspot for 80 m.y. A notable feature of the chain is the pronounced bend at its middle. This bend had been widely credited to a change in plate motion, but recent research suggests a change in hotspot motion as an alternative. Existing paleomagnetic data from the Emperor Chain suggest that the hotspot moved south during the Late Cretaceous and Early Tertiary, but reached its current latitude by the age of the bend. Thus, data from area of the bend are important for understanding changes in plume latitude. In this study, we analyze the magnetic anomalies of five seamounts (Annei, Daikakuji-W, Daikakuji- E, Abbott, and Colahan) in the region of the bend. These particular seamounts were chosen because they have been recently surveyed to collect multibeam bathymetry and magnetic data positioned with GPS navigation. Inversions of the magnetic and bathymetric data were performed to determine the mean magnetization of each seamount and from these results, paleomagnetic poles and paleolatitudes were calculated. Three of the five seamounts have reversed magnetic polarities (two are normal) and four contain a small volume of magnetic polarity opposite to the main body, consistent with formation during the Early Cenozoic, a time of geomagnetic field reversals. Although magnetization inhomogene ties can degrade the accuracy of paleomagnetic poles calculated from such models, the seamounts give results consistent with one another and with other Pacific paleomagnetic data of approximately the same age. Seamount paleolatitudes range from 13.7 to 23.7, with an average of 19.4 ± 7.4 (2σ). These values are indistinguishable from the present-day paleolatitude of the Hawaiian hotspot. Together with other paleomagnetic and geologic evidence, these data imply that the Hawaiian hotspot has moved little in latitude during the past 45 m.y.  相似文献   

10.
To study the relative and absolute timing of post-Variscan cooling and denudation processes in the Erzgebirge of the Mid-European Variscides, eight samples for apatite fission-track (AFT) analysis were collected from a ~1,300 m drill-core. The fission-track data reveal two stages of accelerated cooling through the apatite partial annealing zone (APAZ; i.e., 110±10–60 °C) in the Late Jurassic-Late Cretaceous and in the late Cenozoic, respectively. Late Jurassic-Late Cretaceous cooling corresponding to denudation of 1.5–5.9 km has been related to wrench tectonics along the Elbe Zone during Triassic-Jurassic Pangea breakup. Late Cenozoic exhumation of 2.1–5.6 km, and the increase of the geothermal gradient from 17±5 °C km–1 (Oligocene/Miocene) to 25–27 °C km–1 (recent) is likely connected to the formation of the Eger Graben starting from the Oligocene, as a result of the late Alpine orogenic phases.  相似文献   

11.
Paleomagnetic investigation in the Deseado Massif, southern Patagonia, suggests that Triassic sedimentary rocks carry a latest Triassic to Jurassic remagnetization and that earliest Jurassic plutonic complexes carry a reversed polarity magnetization of thermoremanent origin. Despite uncertainties in the timing of the observed remanence in the Triassic rocks and the lack of paleohorizontal control on the plutonic complexes, comparison of the derived pole positions with the most reliable Late Triassic–Jurassic apparent polar wander paths indicates that the study areas underwent significant clockwise vertical-axis rotation. In contrast, paleomagnetic results from mid-Cretaceous rocks in the region indicate no rotation. The observed crustal rotations in the Deseado Massif are thus bracketed to have occurred between Jurassic and Early Cretaceous times, documenting southern Patagonian deformation during the breakup of Western Gondwana and then enlarging the regional record of clockwise rotations associated with this event. These results suggest a more complex than previously supposed tectonic evolution of this part of South America.  相似文献   

12.
The study presents new paleomagnetic data on the Upper Cretaceous and Cretaceous-Paleogene boundary intervals of the southern Kulunda basin (Alei area), which were obtained from core samples collected from a 305-m-thick section penetrated in two wells. The paleomagnetic sections of each well were compiled and correlated based on the characteristic remanent magnetization (ChRM). Paleomagnetic, geological, stratigraphic, and paleontological data were used to compile the Upper Cretaceous and Cretaceous-Paleogene magnetostratigraphic section of the southern Kulunda basin. The magnetostratigraphic section consists of five magnetozones, one normal polarity zone, and four reversed polarity zones spanning the Upper Cretaceous and Lower Paleogene. The lower part of the Gan’kino Horizon, showing normal polarity, forms a single normal polarity magnetozone N. The upper part of the Gan’kino Horizon comprises two reversed polarity magnetozones (R1km and R2mt). The Talitsa and Lyulinvor Formations of Lower Paleogene age correspond to two reversed polarity magnetozones (R1zl and R2i). The compiled Upper Cretaceous and Lower Paleogene magnetostratigraphic section was correlated with the geomagnetic polarity time scale. Two options were considered for correlating the lower normal polarity part of the section with geomagnetic polarity time scale of Gradstein.  相似文献   

13.
Contractional structures (large anticlines and synclines, reverse faults and inverted centres of deposition) of assumed Late Cretaceous–Cenozoic age are common in Cretaceous–Tertiary basins of the northwestern European margin. The similarities in style, orientation and timing of these structures are striking. The present detailed analysis of one anticline (the Ormen Lange Dome) of the mid-Norwegian continental shelf indicates that the total contraction is moderate (less than 2–3%), and that the analysed anticline has been growing almost continuously since its initiation in Eocene till Present. Inversion in the Barents Sea started already in the Late Cretaceous. This episode is suggested to be related to far-field effects of active plate-margin processes, and transfer of stresses across the plate as a consequence of the sub Hercynian and Paleocene ‘Laramide' event of the Alpine Orogeny. The development of co-axial structures was facilitated by stress focusing along pre-existing, high-relief N–S- and NE–SW-trending fault complexes. Far-field plate tectonic stresses originating mainly from the Alpine Orogeny seem to have been the most important cause of contractional deformation on the NW European shelf. In addition, ridge push from the North Atlantic spreading may have contributed significantly, particularly during the Neogene.  相似文献   

14.
In order to better understand the tectonic environment of the Korean Peninsula since Cretaceous, a paleomagnetic study was carried out on the Jinan Basin located in southwestern Korea. From the demagnetization of 597 samples, we found that remanence is carried by pyrrhotite and/or magnetite (black siltstone) and hematite (red siltstone), which is a common magnetic mineral assemblage of the rocks remagnetized in Early Tertiary in Korea. All the rock units recorded identical ancient geomagnetic field directions. In particular, paleodirections were better clustered in geographic coordinates, indicating a secondary origin. The presence of abundant silicates as inclusions within Fe-oxides and Fe-sulfides confirms the authigenic origin of the magnetic carriers, precipitated by fluid mediated chemical processes. Compilation of the Korean Cretaceous and Tertiary poles indicates that the Jinan Basin was remagnetized in the Early Tertiary age. In addition, comparison of the Korean Cretaceous and Tertiary poles with those from adjacent major terrains including China and Siberia reveals that a dominant feature of tectonic motions in Korea was a vertical-axis rotation. Sense of vertical-axis rotation was time-dependent, with clear distinction between clockwise rotation in Cretaceous and counter-clockwise rotation in Early Tertiary. Such differences in the mode of vertical axis rotation might be caused by the activities of basin-bounding strike–slip faults in Korea, possibly driven by the changes of subduction regime of the Kula-Pacific plate in Early Tertiary.  相似文献   

15.
The thermal evolution of Corsica as recorded by zircon fission-tracks   总被引：1，自引：0，他引：1  
New zircon fission-track (ZFT) ages from Corsica record multiple thermal events that can be tied to the structural evolution of the western Mediterranean region. The Corsican zircons have a wide scatter of ZFT grain ages (243–14 Ma), which together define several age domains. Western Corsica consists largely of stable Hercynian basement characterized by ZFT ages in the range 161–114 Ma. We interpret these ages (Late Jurassic–Early Cretaceous) as the product of a long-lived Tethyan thermal event related to continental rifting and subsequent drifting during the separation of the European and African plates and the formation of the Liguro–Piemontese ocean basin. In contrast to Hercynian Corsica, Alpine Corsica (northeast Corsica) experienced widespread deformation and metamorphism in Late Cretaceous(?)–Tertiary time. Dated samples from Alpine Corsica range in age from 112 to 19 Ma and all are reset or partially reset by one or more Alpine thermal events. The youngest ZFT grain ages are from the northernmost Alpine Corsica and define an age population at  24 Ma that indicates cooling after Tertiary thermal events associated with the Alpine metamorphism and the opening of the Liguro–Provençal basin. A less well-defined ZFT age population at  72 Ma is present in both Alpine Corsica and Hercynian basement rocks. The thermal history of these rocks is not clear. One interpretation is that the ZFT population at  72 Ma reflects resetting during a Late Cretaceous event broadly synchronous with the early Alpine metamorphism. Another interpretation is that this peak is related to variable fission-track annealing and partial resetting during the Tertiary Alpine metamorphic event across central to north-eastern Corsica. This partial age resetting supports the presence of a fossil ZFT partial annealing zone and limits the peak temperature in this area below 300 °C, for both the affected pre-Alpine and Alpine units.  相似文献   

16.
Dolostones of the ∼1200 Ma Society Cliffs Formation within the hydrothermal zone surrounding the Nanisivik zinc deposits retain a stable characteristic remanent magnetization (ChRM) on alternating field and thermal step demagnetization. Based on the thermal data and saturation isothermal remanence analyses, the ChRM resides in pseudosingle domain magnetite and hematite. A paleomagnetic fold test favours a post-folding ChRM, and a paleomagnetic contact test, using a Franklin gabbro dike, indicates that the ChRM predates ∼720 Ma. The pole position calculated from the ChRM direction is at 168.2°E, 42.8°N (δp=4.9°, δm=6.8°), giving an age of 1095 ± 10 Ma on the well-defined “Logan Loop” portion of the North American apparent polar wander path. This age is considered to date recrystallization of the dolostone host rocks in the halo around the hydrothermal sulfide deposits. No evidence is found for a postulated Cretaceous remagnetization event in the region. Received: 9 January 1999 / Accepted: 3 March 2000  相似文献   

17.
The widely distributed Cenozoic paleomagnetic inclination anomaly in Asia is usually attributed to either a widespread error of magnetic field recording due to an inclination flattening mechanism in sediments, or to the persistence of an anomalous non-dipolar component of the geomagnetic field throughout the Tertiary. Based on an analysis of the Asian paleomagnetic database for Meso-Cenozoic times, we suggest that instead this puzzling anomaly results from an overlooked global plate tectonics cause where the wide so-called Eurasian plate would have suffered from previously undetected transpressive north–south relative movements between its western and eastern ends since the Cretaceous. These relative movements are most probably accommodated by a component of right-lateral shear movement distributed in the Tornquist–Tesseyre zone, and a localized left-lateral shear movement in the Ural Mountain chain during the Tertiary. Therefore, Eurasia was not the single rigid plate that Cenozoic plate reconstructions have accepted.  相似文献   

18.
In the area of Arosa?CDavos?CKlosters (Eastern Switzerland) the different tectonic elements of the Arosa zone mélange e.g. the Austroalpine fragments, the sedimentary cover of South Penninic ophiolite fragments, as well as the matrix (oceanic sediments and flysch rocks) show distinctively different metamorphic histories and also different climaxes (??peaks??) of Alpine metamorphism. This is shown by a wealth of Kübler-Index, vitrinite and bituminite reflectance measurements, and K-white mica b cell dimension data. At least six main metamorphic events can be recognized in the area of Arosa?CDavos?CKlosters: (1) A pre-orogenic event, typical for the Upper Austroalpine and for instance found in the sediments at the base of the Silvretta nappe but also in some tectonic fragments of the Arosa zone (Arosa zone mélange). (2) An epizonal oceanic metamorphism observed in the close vicinity of oceanic basement rocks units of the Arosa zone (South Penninic) is another pre-orogenic process. (3) A metamorphic overprint of the adjacent Lower Austroalpine nappes and structural fragments of the Lower Austroalpine in the Arosa zone. This metamorphic overprint is attributed to the orogenic metamorphic processes during the Late Cretaceous. (4) A thermal climax observed in the South Penninic sediments of the Arosa zone can be bracketed by the Austroalpine Late Cretaceous event (3) and the middle Tertiary event (5) in the Middle Penninic units and predates Oligocene extension of the ??Turba phase??. (6) North of Klosters, in the northern part of our study area, the entire tectonic pile from the North Penninic flysches to the Upper Austroalpine is strongly influenced by a late Tertiary high-grade diagenetic to low-anchizone event. In the Arosa zone mélange an individual orogenic metamorphic event is evidenced and gives a chance to resolve diagenetic?Cmetamorphic relations versus deformation. Six heating episodes in sedimentary rocks and seven deformation cycles can be distinguished. This is well explained by the propagation of the Alpine deformation front onto the foreland units. Flysches at the hanging wall of the mélange zone in the north of the study area (Walsertal zone) show data typical for low-grade diagenetic thermal conditions and are therefore sandwiched between higher metamorphic rock units and separated from theses units by a disconformity. The Arosa zone s.s., as defined in this paper, is characterised by metamorphic inversions in the hanging wall and at the footwall thrust, thus shows differences to the Walsertal zone in the north and to the Platta nappe in the south.  相似文献   

19.
The paper reviews paleomagnetic data from the Central West Carpathians (CWC) of Poland and Slovakia. The CWC constitute an orogen deformed by pre-Tertiary and Tertiary events, situated on the internal side of the Pieniny Klippen Belt and the Tertiary Outer West Carpathian accretionary wedge. The CWC are regarded as the eastern prolongation of the Austroalpine series. There are paleomagnetic evidences for a counterclockwise rotation of the CWC after Oligocene. Having subtracted the effect of this rotation, Middle Cretaceous paleomagnetic poles from the CWC are brought into agreement with preGosau paleopoles from the Upper Austroalpine units of the Northern Calcareous Alps (NCA). It is inferred that a common clockwise rotation of the CWC and NCA had taken place between 90-60 Ma (Middle — Late Cretaceous) during the oblique convergence of the Austroalpine/Central Carpathian realm with the Penninic continental basement.  相似文献   

20.
The exposed Cretaceous shelf succession of the Cauvery Basin, southeastern India, has provided a world-class record of mid and Late Cretaceous invertebrates, documented in a substantial literature. However, the lithostratigraphy of the succession has been little studied and previously subject to a range of nomenclature. It is revised here, on the basis of intensive regional mapping, to stabilize the definition and nomenclature of lithostratigraphic units. The Uttattur Group is restricted in outcrop to the Ariyalur district and divided into the Arogypapurum Formation (new; Albian), Dalmiapuram Formation (late Albian), and Karai Formation (late Albian–early Turonian) for which the Odiyam and Kunnam Members are recognized. The Trichinopoly Group follows unconformably and is also restricted in outcrop to the Ariyalur district. It is divided into the Kulakkalnattam Formation (Turonian) and Anaipadi Formation (late Turonian–Coniacian). The Ariyalur Group is more widely distributed. In the Ariyalur district, the Sillikkudi Formation (Santonian–Campanian) and its Kilpaluvari Member, the Kallakurichchi Formation (early Maastrichtian), the Kallamedu Formation (mid and Late Maastrichtian) and the Niniyur Formation (Danian) are recognized. The sequence in the Vriddhachalam area consists of the Parur and Patti formations (Campanian), Mattur Formation (late Campanian–earliest Maastrichtian) and Aladi Formation (Maastrichtian). For the Pondicherry district, the Valudavur and Mettuveli formations (Maastrichtian) and Kasur and Manaveli formations (Paleocene) comprise the succession. The interpreted depositional environments for the succession in the Ariyalur district indicate four eustatic cycles in the mid and Late Cretaceous and earliest Tertiary: late Albian–early Turonian, late Turonian–Santonian, Campanian, Maastrichtian, and Paleocene. Overall the Cauvery Basin sequence is arenaceous and relatively labile in terms of framework grain composition, and contrasts with the pelitic assemblage developed on the west Australian margin from which eastern India separated in the Early Cretaceous (Valanginian). The difference is ascribed to palaeoclimate as controlled by palaeolatitude. For the Late Cretaceous, the Cauvery Basin drifted north on the Indian plate from 40 to 30°S. This zone is inferred to constitute Southern Hemisphere horse latitudes for Late Cretaceous time, characterized by an arid climate, physical weathering and the production of labile sands. By contrast, the west Australian margin of matching tectonic history remained in a high palaeolatitude (>40°S) throughout the Late Cretaceous, experiencing a pluvial climate, the dominance of chemical weathering and the production of clays.  相似文献   

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