首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Fission track ages have been measured for 12 sphenes, 18 zircons and 25 apatites separated largely from Lower Tertiary magmatic rocks of East Greenland, with a few examples from Caledonian rocks. The sphene and zircon ages of Caledonian rocks agree with other radiometric ages but apatite is strongly discordant indicating that these rocks cooled very slowly over a 200 m.y. period. It was not until the Permian/Lower Jurassic that they finally cooled below 100 ° C, possibly as a consequence of uplift and erosion at this time in connection with extensive rifting. No evidence of a Tertiary imprint has been found in these rocks.Layered gabbros, such as Skaergaard, were emplaced at about the same time (ca. 54 m.y.) as the latest plateau basalts. Some evidence of syenitic activity from this period occurs in the Angmagssalik area ca. 400 km to the south but the syenites of Kangerdlugssuaq cluster around 50 m.y. The Gardiner ultramafic alkaline complex and some of the offshore gabbros apparently also were emplaced at about 50 m.y. Late dykes in the Kangerdlugssuaq area were emplaced over a considerable time span (43-34 m.y.) in keeping with their variable petrographic character, and the Kialineq centre was formed at 36.2±0.4 m.y.Intrusions of the Masters Vig area differ in age. Kap Simpson and Kap Parry to the northeast were emplaced around 40 m.y. whereas the Werner Bjerge complex is the youngest igneous activity so far identified in Greenland with an age of 30.3±1.3 m.y.Many apatites give strongly discordant ages of about 36 m.y. and these are concentrated in the area of a major domal uplift centred on Kangerdlugssuaq. The uplift is older than these ages but on field evidence post-dates the basalts. It probably formed in conjunction with alkaline magmatism at ca. 50 m.y. Cooling below ca. 200 ° was slow for these intrusions and was probably controlled by a number of factors including erosion of the dome, high heat flow caused by continuing dyke injection and regional plateau uplift. The last is believed to have taken place about 35 m.y. ago at the time of emplacement of the Kialineq plutons and last dykes. Renewed rapid erosion and declining heat flow at this time led to rapid cooling of the rocks now at the surface to below 100 °.  相似文献   

2.
Eulerian rotations of continents induce changes of palaeomagnetic vector orientation that cannot easily be deduced from the parameters of the rotation. An algorithm for the calculation of the new palaeomagnetic declination is proposed and simple rules describing the phenomena are drawn. Applications of this algorithm to the relative rotations of Spain and Europe during the Mesozoic allow a comparison of the geological models with the available palaeomagnetic data, indicating: (1) Spain and Europe did not move with respect to one another between Lower Permian and Upper Triassic times; (2) the palaeomagnetic declination difference observed between these two blocks in the Triassic could be due to a multiphase history, the opening of the Bay of Biscay having occurred during the latest phase in Upper Cretaceous.  相似文献   

3.
《Geodinamica Acta》2001,14(5):307-320
In the Northern Apennines, the External Liguride (EL) units are interpreted as derived from the domain that joined the Ligure–Piemontese oceanic basin to the Adriatic plate continental margin. The EL units can be divided into two different groups according to the lithostratigraphic features of the basal complexes underlying the Upper Cretaceous–Lower Tertiary carbonate flysch (e.g. Helminthoid flysch). The first group includes the western successions characterized by Santonian–Campanian sedimentary melanges where slide blocks of lherzolitic mantle, gabbros, basalts, granulites, continental granitoids are represented. The second group is represented by the eastern successions where the Cenomanian–Campanian basal complexes mainly consist of sandstones and conglomerates where the mafic and ultramafic rocks are scarce or completely lacking. Their original substrate is represented by the Middle Triassic to Lower Cretaceous, mainly platform carbonate deposits, found as slices at the base of the eastern successions.The stratigraphic features shown by the basal complexes allow the reconstruction of their source area that is assumed to be also representative for the pre-Upper Cretaceous setting. The proposed reconstruction suggests the occurrence in the EL domain of two distinct domains. The eastern domain was characterized by a thinned and faulted continental crust belonging to the Adriatic continental margin. The western domain was instead floored by subcontinental mantle associated with lower and upper continental crust, representing the ocean–continent transition. This setting is interpreted as the result of the opening of the Ligure–Piemontese oceanic basin by passive rifting, mainly developed by simple shear, asymmetric extension of the continental crust.  相似文献   

4.
Abstract

In the Northern Apennines, the External Liguride (EL) units are interpreted as derived from the domain that joined the Ligure–Piemontese oceanic basin to the Adriatic plate continental margin. The EL units can be divided into two different groups according to the lithostratigraphic features of the basal complexes underlying the Upper Cretaceous–Lower Tertiary carbonate flysch (e.g. Helminthoid flysch). The first group includes the western successions characterized by Santonian–Campanian sedimentary melanges where slide blocks of lherzolitic mantle, gabbros, basalts, granulites, continental granitoids are represented. The second group is represented by the eastern successions where the Cenomanian–Campanian basal complexes mainly consist of sandstones and conglomerates where the mafic and ultramafic rocks are scarce or completely lacking. Their original substrate is represented by the Middle Triassic to Lower Cretaceous, mainly platform carbonate deposits, found as slices at the base of the eastern successions.

The stratigraphic features shown by the basal complexes allow the reconstruction of their source area that is assumed to be also representative for the pre-Upper Cretaceous setting. The proposed reconstruction suggests the occurrence in the EL domain of two distinct domains. The eastern domain was characterized by a thinned and faulted continental crust belonging to the Adriatic continental margin. The western domain was instead floored by subcontinental mantle associated with lower and upper continental crust, representing the ocean–continent transition. This setting is interpreted as the result of the opening of the Ligure–Piemontese oceanic basin by passive rifting, mainly developed by simple shear, asymmetric extension of the continental crust. © 2001 Éditions scientifiques et médicales Elsevier SAS  相似文献   

5.
A detailed palaeomagnetic study of Cretaceous age volcanic and sedimentary arc rocks from central Cuba has been carried out. Samples from 32 sites (12 localities) were subjected to detailed demagnetisation experiments. Nineteen sites from the Los Paso, Mataguá, Provincial and Cabaiguán Formations yielded high unblocking temperature, dual polarity directions of magnetisation which pass the fold tests with confidence levels of 95% or more and are considered to be primary in origin. The palaeomagnetic inclinations are equivalent to palaeolatitudes of 9°N for the Aptian, 18°N for the Albian. A synfolding remanence identified in 5 sites from the younger Hilario Formation indicates a late Cretaceous remagnetisation at a palaeolatitude of 16°N. Our results are in good agreement with previous palaeogeographic models and provide the first high quality palaeomagnetic data demonstrating the gradual northward movement of the Cretaceous Volcanic Arc throughout the Cretaceous. The declination values obtained all indicate significant and similar amounts of anticlockwise rotation from the oldest sequences studied through to the late Cretaceous remagnetisation. This rotation is most likely related to collision of the arc with the North American plate and transpressional strike slip movement along the northern margin of the Caribbean plate as it progressed eastwards into the large Proto-Caribbean basin.  相似文献   

6.
The results of radiometric dating of granitic rocks around Kotanopan near the west coast of Central Sumatra indicate an average age of 45 million years.Granites from the Lassi Mass in the Padang Highlands, Central Sumatra, and the Lampong Mass, South Sumatra, possess radiometric ages of ca. 112 and ca. 88 m.y., respectively. Granites and other rocks from the offshore areas north of Java indicate an average age of 100 m.y.Late Cretaceous granitic rocks are present in the islands of the Sunda Shelf namely Anambas (ca. 86 m.y.), Tembelan (ca. 85 m.y.) and Natuna (ca. 75 m.y.).Late Paleozoic granites possessing ages of ca. 276–298 m.y. are encountered in the basement rocks near Djambi, South Sumatra.The outcome of this radiometric age dating proves to be significant for it permits a fresh analysis of the geological evolution of Indonesia based on the plate-tectonics concept.The Tertiary volcano-plutonic arc exposed along the west coast of Sumatra can be traced to the south coast of Java. The corresponding subduction zone can be found in the islands west of Sumatra and the submarine ridge south of Java.The Late Cretaceous plutonic belt of Sumatra does not continue to Java but passes north of it, running however parallel to the subduction zone of Java. These two zones merge in the Meratus Mountains of Southeast Kalimantan.Sumatra was already a volcano-plutonic arc during Permian time, suggesting that since this Period the margins of at least four lithospheric plates have remained near the side of the active Sumatran arc.The presence of Permian volcanic and granitic rocks in the Malay Peninsula and West Kalimantan, and the results of the radiometric age determination of granitic rocks from the islands situated in the Sunda Shelf area, point to the existence of other Permian and Cretaceous volcano-plutonic arcs east and north of the arcs previously described in Sumatra and Java. Thus a double volcano-plutonic arc with opposing Benioff zones must have existed during Permian and Cretaceous time in this area.The Schwaner Mountains of West Kalimantan are considered to be the place where volcano-plutonic arcs of different ages have merged together. The correlative subduction zones have to be sought in the so-called Danau Formation of West Kalimantan and the northern part of the Kuching zone, the Sibu zone of Serawak situated north of the Schwaner Mountains.The evolution and complex geology of the western part of Indonesia can only be understood by the supposition of the existence of megaplates and sub-plates generated from spreading centers situated in the Indian Ocean and presumably in the area of the South China Sea, respectively.  相似文献   

7.
The paper considers Cretaceous magmatism at the continental margin of the Arctic Region. It is shown that Cretaceous igneous rocks of this region are rather heterogeneous in age, composition, and geodynamic formation setting. This differentiates them from rocks of typical large igneous provinces (LIPs). Local areas of magmatic activity, their substantial remoteness them from one another, and significant distinctions in age, composition of rocks, and formation conditions prevent us from unreservedly combining all occurrences of Cretaceous magmatism at the continental margin of the Arctic Region into a common igneous province. The stage of tholeiitic magmatism in the Svalbard Archipelago, Franz Josef Land, Arctic Canada, and the Alpha–Mendeleev Rise, which can be considered an LIP, began in the Early Cretaceous and continued for a long time, at least until the Campanian. The magmatism apparently had a plume source and was caused by extension during opening of the Canada Basin. Tholeiitic magmatism gave way to the alkaline magmatism stage from the Campanian to the onset of the Paleocene, related to continental rifting at the initial stage of formation of Eurasian Basin in the Arctic Region. No convincing evidence for a genetic link between Early Cretaceous tholeiitic and Late Cretaceous alkaline magmatism is known at present, nor for the alkaline magmatism belonging to a plume source.  相似文献   

8.
A total of 81 samples (244 specimens) from Upper Cretaceous Indus Molasse and Middle to Upper Cretaceous Dras Flyschoids of the Indus-Tsangpo suture zone in Ladakh (northwest Himalaya) has been studied by thermal demagnetization methods.Both formations showed a characteristic magnetization component indicative for equatorial to low northern palaeolatitudes of acquisition. Similar palaeolatitudes have been obtained before from secondary magnetization components of Early Tertiary age in the Ladakh Intrusives and in the Tibetan Sedimentary Series of central Nepal. The present characteristic components are interpreted likewise as secondary magnetizations which stabilized between 50 and 60 m.y. ago, during Greater India's collision with Asia's southern margin.The Dras Flyschoids show another magnetic component which, in case of primary origin, indicates acquisition at a low southern palaeolatitude. If correct, this interpretation supports recent suggestions for Late Cretaceous obduction of an island arc on Greater India's northern margin.  相似文献   

9.
《China Geology》2019,2(2):133-141
Source rocks are the material basis of oil and gas generation and determine the potential resources of exploration blocks and have important research value. This paper studies the lithology, thickness, and geochemistry of Mesozoic source rocks in the southeastern East China Sea continental shelf. The results show that the Mesozoic source rocks are mainly dark mudstone and coal-bearing strata. The total thickness of Lower–Middle Jurassic source rocks ranges from 100 m to 700 m, and that of Lower Cretaceous source rocks ranges from 50 m to 350 m. The overall thickness of Mesozoic source rocks is distributed in the NE direction and their thickness center is located in the Jilong Depression. The Lower–Middle Jurassic source rocks are mainly developed shallow marine dark mudstone and transitional coal measure strata. Those of the Lower Cretaceous are mainly mudstone of a fan delta front. Lower–Middle Jurassic and Lower Cretaceous hydrocarbon source rocks are dominated by type III kerogen, with Lower–Middle Jurassic hydrocarbon source rocks having high organic matter abundance and being medium–good hydrocarbon source rocks, while Lower Cretaceous hydrocarbon source rocks have relatively poor quality. From northwest to southeast, the vitrinite reflectance Ro of Mesozoic source rocks increases gradually. Source rocks in the study area are divided into three types. The first hydrocarbon-generating area is mainly located in the southeastern region of the study area, and the Jilong Depression is the hydrocarbon-generating center. The results of this study can provide a basis for exploration of Mesozoic oil and gas resources in the southeastern East China Sea continental shelf.© 2019 China Geology Editorial Office.  相似文献   

10.
Paleomagnetic data for the Cretaceous volcanic and sedimentary rocks in the Andean region of Peru are given. Reliable paleomagnetic field directions were obtained for three Cretaceous (Albian to Cenomanian) formations from calcareous sediments in northern Peru. Stable remanent magnetization directions were also derived from twelve Cretaceous lava flows and dikes in coastal Peru. Paleomagnetic data of the same age from the stable areas of South America such as Brazil demonstrate that the paleomagnetic poles are nearly coincident with the present pole, but Peruvian paleomagnetic directions studied here showed several tens of degrees of counterclockwise declination shifts. This suggests counterclockwise tectonic rotation of an extensive block which includes the whole of Andean Peru.  相似文献   

11.
Geologic mapping in the northern Sierra Los Ajos reveals new stratigraphic and structural data relevant to deciphering the Mesozoic–Cenozoic tectonic evolution of the range. The northern Sierra Los Ajos is cored by Proterozoic, Cambrian, Devonian, Mississippian, and Pennsylvanian strata, equivalent respectively to the Pinal Schist, Bolsa Quartzite and Abrigo Limestone, Martin Formation, Escabrosa Limestone, and Horquilla Limestone. The Proterozoic–Paleozoic sequence is mantled by Upper Cretaceous rocks partly equivalent to the Fort Crittenden and Salero Formations in Arizona, and the Cabullona Group in Sonora, Mexico.Absence of the Upper Jurassic–Lower Cretaceous Bisbee Group below the Upper Cretaceous rocks and above the Proterozoic–Paleozoic rocks indicates that the Sierra Los Ajos was part of the Cananea high, a topographic highland during the Late Jurassic and Early Cretaceous. Deposition of Upper Cretaceous rocks directly on Paleozoic and Proterozoic rocks indicates that the Sierra Los Ajos area had subsided as part of the Laramide Cabullona basin during Late Cretaceous time. Basal beds of the Upper Cretaceous sequence are clast-supported conglomerate composed locally of basement (Paleozoic) clasts. The conglomerate represents erosion of Paleozoic basement in the Sierra Los Ajos area coincident with development of the Cabullona basin.The present-day Sierra Los Ajos reaches elevations of greater than 2600 m, and was uplifted during Tertiary basin-and-range extension. Upper Cretaceous rocks are exposed at higher elevations in the northern Sierra Los Ajos and represent an uplifted part of the inverted Cabullona basin. Tertiary uplift of the Sierra Los Ajos was largely accommodated by vertical movement along the north-to-northwest-striking Sierra Los Ajos fault zone flanking the west side of the range. This fault zone structurally controls the configuration of the headwaters of the San Pedro River basin, an important bi-national water resource in the US-Mexico border region.  相似文献   

12.
A palaeomagnetic study of seven sites in redbeds of the Late Precambrian Bhander and Rewa Series of the Upper Vindhyan System confirms that their original magnetization was extensively overprinted during the Early Tertiary, possibly related to the extrusion of the Deccan Traps about 65 Ma ago. Careful thermal demagnetization at temperatures close to the Curie Temperature of hematite revealed the primary magnetization in 100 of 121 specimens investigated. The resulting palaeomagnetic pole for the Upper Vindhyan System lies at 51.0S 37.8E. A combination with all previous results gives an overall palaeomagnetic pole at 47.3S 32.7E (N = 18, K = 35.5, A95 = 5.8°). Twelve samples from the Gwalior Traps (1830 Ma) give a palaeomagnetic pole at 16N 160.5E after magnetic cleaning.Twelve flows collected from the Permo-Carboniferous Panjal Traps of Kashmir give mean direction D = 156.5, I = + 32.5 (κ = 19.8, α95 = 9.9°) with a positive fold test. The palaeomagnetic pole (32N 282E), however, lies close to that observed for Deccan Trap times in India. It appears that the magnetization of the Panjal Traps was acquired during the Early Tertiary Himalayan uplift following which they were tilted to their present attitudes.  相似文献   

13.
A.C. Ries 《Earth》1978,14(1):35-63
The anticlockwise rotation of the Iberian Peninsula away from south Brittany during the Mesozoic has been demonstrated from palaeomagnetic data. Marine magnetic, seismic and gravity surveys have indicated that there is oceanic crust in the Bay of Biscay. Initial rifting began in the Triassic but the major part of the rotation of the Iberian Peninsula occurred during the Late Cretaceous. Two mechanisms for the opening of the Bay of Biscay have been proposed, firstly a simple anticlockwise rotation of the Iberian plate and secondly, a 350 km sinistral displacement of the Iberian plate along transform faults about a pole of rotation near Paris. Geological data, partly new, favours the first mechanism but with a pole of rotation approximately 100 km east of the west end of the Pyrenees rather than in the southeast corner of the Bay of Biscay. Geophysical data indicates a further small rotation of the Iberian Peninsula during the Late Eocene which resulted in the formation of the Pyrenees.  相似文献   

14.
M. Manzoni 《Tectonophysics》1979,60(3-4):169-188
The magnetization of Lower Permian rocks from Sila has a mean direction D = 56.5°, I= +20.4° with 95 = 9.1° after correction for Upper Neogene tilting. A further correction for the attitude of the nappes after their Middle Miocene emplacement establishes paleolatitudes consistent with those from the Lower Permian Tethys. The remarkable internal consistency of the data has not supported the distinction of units with opposite vergences within the Sila crystalline nappes. The declination indicates that the Sila massif has rotated counter-clockwise by about 90° relative to the Apennines, Sardinia and the Southern Alps and therefore the well-known Apenninic rotation alone does not account for the total change of direction in tectonic transport. Accordingly, the structural trends of tectonic phases older than the emplacement time of the Calabrian nappes should no longer be referred to present-day geographic coordinates. The post-Late Cretaceous motion relative to the north Calabrian Apennines enhances the geotectonic role of the northern boundary of the Calabrian—Peloritan arc, since its sinistral-shear character permits both tectonic transport from the west and counter-clockwise motion during tectonic transport.  相似文献   

15.
The platform limestones of Apulia (Italy) outcropping in the Gargano peninsula have been restudied. Paleomagnetic research has been carried out on Upper Cretaceous, Lower Cretaceous and Jurassic rocks. Despite the low intensities of the NRM (10–100 μA/m), all samples (268) could be cleaned by stepwise A.F. and/or thermal demagnetization treatments. NRM directions could be determined accurately and reproducibly for 85% of the samples, using a ScT cryogenic magnetometer and double precision measuring procedures. NRM of the Jurassic limestone is carried by secondary haematite and the results are therefore rejected from further consideration. The Upper and Lower Cretaceous limestones have an NRM carried by magnetite. Minor bedding tilt corrections improve the grouping of the site-mean results. The Upper Cretaceous “Scaglia” limestone (Turonian-Senonian) reveals a characteristic mean direction of decl. = 327.7°, incl. = 38.2°, α95 = 4.3° (21 sites), while the Lower Cretaceous “Maiolica” limestone (Neocomian-Aptian/Albian) reveals a characteristic mean direction of decl. = 303.1°, incl. = 35.1°, α95 = 8.7° (8 sites). The Cretaceous results show a post-Aptian/Albian counterclockwise rotation of about 25°, which is expressed by the smeared distribution of the Late Cretaceous site-mean results and a post-Senonian (i.e. Tertiary) counterclockwise rotation of the same amount with respect to the pole. These results are in excellent agreement with contemporaneous paleomagnetic results from other peri-Adriatic regions. A Tertiary counterclockwise rotation of all the stable Adriatic block is strongly supported by the new results.  相似文献   

16.
Rock magnetic and palaeomagnetic studies were performed on Mesozoic redbeds collected from the central and southern Laos, the northeastern and the eastern parts of the Khorat Plateau on the Indochina Block. Totally 606 samples from 56 sites were sampled and standard palaeomagnetic experiments were made on them. Positive fold tests are demonstrated for redbeds of Lower and Upper Cretaceous, while insignificant fold test is resulted for Lower Jurassic redbeds. The remanence carrying minerals defined from thermomagnetic measurement, AF and Thermal demagnetizations and back-field IRM measurements are both magnetite and hematite. The positive fold test argues that the remanent magnetization of magnetite or titanomagnetite and hematite in the redbeds is the primary and occurred before folding. The mean palaeomagnetic poles for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous are defined at Plat./Plon. = 56.0°N/178.5°E (A95 = 2.6°), 63. 3°N/170.2°E (A95 = 6.9°), and 67.0°N/180.8°E (A95 = 4.9°), respectively. Our palaeomagnetic results indicate a latitudinal translations (clockwise rotations) of the Indochina Block with respect to the South China Block of −10.8 ± 8.8° (16.4 ± 9.0°); −11.1 ± 6.2° (17.8 ± 6.8°); and −5.3 ± 4.7° (13.3 ± 5.0°), for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous, respectively. These results indicate a latitudinal movement of the Indochina Block of about 5–11° (translation of about 750–1700 km in the southeastward direction along the Red River Fault) and clockwise rotation of 13–18° with respect to the South China Block. The estimated palaeoposition of the Khorat Plateau at ca. 21–26°N during Jurassic to Cretaceous argues for a close relation to the Sichuan Basin in the southwest of South China Block. These results confirm that the central part of the Indochina Block has acted like a rigid plate since Jurassic time and the results also support an earlier extrusion model for Indochina.  相似文献   

17.
1D (Petromod) hydrocarbon charge modeling and source rock characterization of the Lower Cretaceous and Upper Jurassic underlying the prolific Cretaceous and Tertiary reservoirs in the Basra oilfields in southern Iraq. The study is based on well data of the Majnoon, West Qurna, Nahr Umr, Zubair, and Rumaila oil fields. Burial histories indicate complete maturation of Upper Jurassic source rocks during the Late Cretaceous to Paleogene followed by very recent (Neogene) maturation of the Low/Mid Cretaceous succession from early to mid-oil window conditions, consistent with the regional Iraq study of Pitman et al. (Geo Arab 9(4):41–72, 2004). These two main phases of hydrocarbon generation are synchronous with the main tectonic events and trap formation associated with Late Cretaceous closure of the neo-Tethys; the onset of continent–continent collision associated with the Zagros orogeny and Neogene opening of the Gulf of Suez/Red Sea. Palynofacies of the Lower Cretaceous Sulaiy and Lower Yamama Formations and of the Upper Jurassic Najmah/Naokelekan confirm their source rock potential, supported by pyrolysis data. To what extent the Upper Jurassic source rocks contributed to charge of the overlying Cretaceous reservoirs remains uncertain because of the Upper Jurassic Gotnia evaporite seal in between. The younger Cretaceous rocks do not contain source rocks nor were they buried deep enough for significant hydrocarbon generation.  相似文献   

18.
张惠民  赵凤清 《地质论评》1994,40(4):312-321
本文从变质作用与岩石矿物获得剩磁的关系和剩磁获得时间与同位素记年的相关性，岩石的形变对磁化方向的影响等方面讨论了前寒武纪变质岩古地磁研究的可行性；并列举部分国外前寒武纪早期岩石的例证；同时重点以闽北地区前寒武纪变质岩的古地磁结果为例，讨论了获得磁性可信性及其在地质构造方面的意义。  相似文献   

19.
CRETACEOUS AND TERTIARY BOUNDARY IN THE TINGRI REGION OF SOUTHERN TIBETtheNNSFProject(49872 0 0 3)andtheNationalProject (G19980 40 80 0 )ofChina  相似文献   

20.
With the aim of obtaining Tertiary palaeomagnetic directions for the Adriatic Foreland of the Dinaric nappe system, we carried out a palaeomagnetic study on platform carbonates from stable Istria, from the northwestern and the Central Dalmatia segment of imbricated Adria. Despite the weak to very weak natural remanences of these rocks, we obtained tectonically useful palaeomagnetic directions for 25 sites from 20 localities. All exhibit westerly declinations, both before and after tilt correction. Concerning the age of the magnetizations, we conclude that five subhorizontal and magnetite bearing Eocene localities from stable Istria are likely to carry primary remanence, whereas three tilted and hematite-bearing ones were remagnetized. In the northwestern segment of imbricated Adria the cluster of the mean directions improved after tectonic correction indicating pre-tilting magnetization. In contrast, Maastrichtian–Eocene platform carbonates from Central Dalmatian were remagnetized in connection with the late Eocene–Oligocene deformation or Miocene hydrocarbon migration. Based on the appropriate site/locality means, we calculate mean palaeomagnetic directions for the above three areas and suggest an alternative interpretation of the data of Kissel et al. [J. Geophys. Res. 100 (1995) 14999] for the flysch of Central Dalmatia. The four area mean direction define a regional palaeomagnetic direction of Dec=336°, Inc=+52°, k=107, α95=9°. From these data we conclude that stable Istria, in close coordination with imbricated Adria, must have rotated by 30° counterclockwise in the Tertiary, relative to Africa and stable Europe. We suggest that the latest Miocene–early Pliocene counterclockwise rotations observed in northwestern Croatia and northeastern Slovenia were driven by that of the Adriatic Foreland, i.e. the rotation of the latter took place between 6 and 4 Ma.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号