摘要:

The Menderes Massif forms the western of the two large metamorphic culminations within the Turkish Alpide orogen. It has three major lithologic units, with a gneissic “core” at the base and a “schist” and a “marble” envelope overlying it successively, although relations between them have been largely obscured by the polymetamorphic and structurally complex history of the Massif. We present a review of the available stratigraphic evidence and combine it with new isotopic ages from the central and southern parts of the Massif to constrain the timing of major tectonic events that shaped the Massif since the late Proterozoic (Pt3). In the southern part of the Massif (sensu stricto) three episodes of deformation and metamorphism are distinguished, whereas in its northern part there are four. The first episode occurred at −500 ± 10 Ma with intense deformation and metamorphism at high grade amphibolite facies with local anatexis. In the central part of the Massif, the 470 ± 9 Ma‐old now highly deformed tonalitic and granitic intrusions mark the end of this episode. On a Cambrian reconstruction of continents around the eastern Mediterranean, the Menderes Massif forms the southern end of the Pan‐African orogenic collage of northeastern Africa and Arabia. The area of earliest Palaeozoic deformation in the Menderes may connect with the northwest African orogenic collage along the strike via the Bozburun and Saricicek diabases, arkoses, and schists in the center of the Karacahisar dome interpreted herein as fragments of a Pan‐African suture. The earliest Palaeozoic deformations to affect the rocks were probably related to the last Pan‐African collisions and associated postcollisional convergence. The southern part of the Massif was undeformed from early Ordovician to the early (? later) Eocene, whereas the northern part was deformed, metamorphosed and intruded possibly during the late Triassic, related to the closure of the Karakaya marginal basin of Palaeo‐Tethys. The next major event affecting the whole of the Massif was the intense deformation and widespread metamorphism that reached high amphibolite grade in the structurally lower parts, and only greenschist grade in the outermost envelope. This metamorphism, here called the “main Menderes metamorphism” (MMM), is biostratigraphically constrained between early Eocene and early Oligocene time. Rb/Sr isotopic data show a spread of ages between 60 Ma and 25 Ma, with the greatest number of determinations around 35 ± 5 Ma. This number is in excellent agreement with the stratigraphic evidence and shows that MMM took place during latest Eocene time or at the transition from Eocene to Oligocene time. Along the northern border of the Massif, deformation and metamorphism had already taken place during the late Cretaceous in a high pressure/low temperature (HP/LT) metamorphic belt (northernmost part of Menderes Massif sensu lato), which was then covered by Palaeocene molasse. The evolution of the HP/LT belt was probably related to the obduction of the Bozkir ophiolites from the Izmir‐Ankara branch of the Neo‐Tethys ocean and preceded terminal collision in the evolution of the Massif. The MMM was a product of the latest Palaeocene collision across Neo‐Tethys and the consequent internal imbrication of the Menderes‐Taurus block that resulted in the burial of the Menderes Massif area beneath the Lycian nappe complex. A low grade metamorphic event dated at 10 to 5 Ma is interpreted to be related to the extensional deformation in the Aegean and western Turkey, which has been dated stratigraphically to ha

ISSN:0278-7407    

DOI:10.1029/TC003i007p00693

年代:1984

数据来源: WILEY

摘要:

In a previous paper, we derived plate tectonic models for continental accretion from the early Archaean (3800 m.y. B.P.) until the present. The models are dependent upon the number of continental masses, the seafloor creation rate and the continental surface area. The models can be tested by examining their predictions for three key geological indicators: sea level changes, stable isotopic evolution (e.g., continental surface area), and oceanic heat loss. Models of paleo‐sea level changes produced by the accretion of the continents reproduce the following features of earth history: (1) greater continental emergence (lower sea level) during the Archaean than the Proterozoic; (2) maximum continental emergence about 3000 m.y. B.P.; and (3) maximum continental submergence (high sea level) from 30 to 125 m.y. B.P. The high sea level stand between 380–525 m.y. B.P. is only weakly reproduced, probably due to the simplified nature of the model. Changes in the number of continental masses can result in tectonic erosion or accretion of the continents, with resulting changes in sea level. The two major transgressions in the Phanerozoic, although still requiring some increase in the total terrestrial heat loss, can be sucessfully explained by a combination of increases in continental surface area and in seafloor creation rate. Changes in the total heat loss of the ocean basins predicted by our plate tectonic models closely parallel the changes in terrestrial heat production predicted by Wasserburg et al. (1964). This result is consistent with thermal history models which assume whole mantle convection. The history of changes in continental surface area predicted by our best continental accretion models lies within the ranges of estimated continental surface area derived from independent geochemical models of isotope evolut

ISSN:0278-7407    

DOI:10.1029/TC003i007p00709

年代:1984

数据来源: WILEY

摘要:

The subsidence history of the North Louisiana Salt Basin, determined from well data, indicates that the region underwent extension during rifting and has since passively subsided due to conductive cooling of the lithosphere. Timing of the rifting event is consistent with opening of the Gulf of Mexico during Late Triassic to Early Jurassic time. Crustal extension by a factor of 1.5 to 2 was computed from “tectonic” subsidence curves. However, data from the early subsidence history are insufficient to distinguish between uniform and nonuniform extension of the lithosphere. The magnitude of extension is in good agreement with total sediment and crustal thicknesses from seismic refraction data in the adjacent Central Mississippi Salt Basin. The temperature distribution within the sediments is calculated using a simple heat conduction model. Temperature and subsidence effects of thermal insulation by overlying sediments are included. The computed temperature distribution is in good agreement with bottom hole temperatures measured in deep wells. Temperature histories predicted for selected stratigraphic horizons within the North Louisiana Salt Basin suggest that thermal conditions have been favorable for hydrocarbon generation in the older stata. Results from a two‐dimensional heat conduction model suggest that a probable cause for the early formation of the adjacent uplifts is lateral heat conduction from the basin. Rapid extension of the lithosphere underneath areas with horizontal dimensions of 50–100 km produces extremely rapid early subsidence due to lateral heat conduction. The moderate subsidence rate observed in the North Louisiana Salt Basin during the Jurassic and Early Cretaceous suggests slow extension over a long period

ISSN:0278-7407    

DOI:10.1029/TC003i007p00723

年代:1984

数据来源: WILEY

摘要:

The Rocky Mountain foreland and Great Plains of the western United States were formerly part of a continental platform, adjusted by erosion and deposition in Cambrian through Jurassic time to near mean sea level, and therefore to a near‐uniform crustal thickness of approximately 33 km. Today the region stands at regional elevations up to 2 km, isostatically supported by a crust exceeding 50 km in thickness. Reasonable estimates of Tertiary sedimentation and Laramide strain do not account for more than 15% of the implied thickening. However, from approximately 70‐40 m.y. B.P., this region was underlain by a horizontally‐subducting slab of Farallon plate lithosphere moving northeast; this slab could have been the cause of the thickening. Finite‐difference thermal models with specified kinematics show only a temporary cooling of the base of the North American lithosphere by this slab. The excess weight of the slab would have depressed the region; plate‐bending calculations show a quantitative agreement of predicted depression with upper Cretaceous isopachs. Since depression by this slab lasted until the Eocene at least, the latest‐Cretaceous regression was probably caused by a Laramide crustal thickening event. The Farallon slab might have caused crustal thickening in two ways. Its excess weight would have drawn in ductile lower crust from surrounding regions. However, calculations show that this effect is too slow, too local, and too reversible to explain most of the crustal thickening. Therefore it seems likely that ductile lower crust was transported from SW to NE by shear stresses which the Farallon plate exerted on the base of the North American lithosphere. A preliminary finite‐element calculation based on this hypothesis shows the correct general pattern of crustal thickening. An unexpected but encouraging result is that predicted principal compression directions are orthogonal to many Laramide bas

ISSN:0278-7407    

DOI:10.1029/TC003i007p00741

年代:1984

数据来源: WILEY

摘要:

The geochronology, stratigraphy, and spatial relationships of Middle and Late Jurassic terranes of the Klamath Mountains strongly suggest that they were formed in a single west‐facing magmatic arc built upon older accreted terranes. A Middle Jurassic arc complex is represented by the volcanic rocks of the western Hayfork terrane and consanguineous dioritic to peridotitic plutons. New U/Pb zircon dates indicate that the Middle Jurassic plutonic belt was active from 159 to 174 Ma and is much more extensive than previously thought. This plutonic belt became inactive just as the 157 Ma Josephine ophiolite, which lies west and structurally below the Middle Jurassic arc, was generated. Late Jurassic volcanic and plutonic arc rocks (Rogue Formation and Chetco intrusive complex) lie outboard and structurally beneath the Josephine ophiolite; U/Pb and K/Ar age data indicate that this arc complex is coeval with the Josephine ophiolite. Both the Late Jurassic arc complex and the Josephine ophiolite are overlain by the “Galice Formation,” a Late Jurassic flysch sequence, and are intruded by 150 Ma dikes and sills. The following tectonic model is presented that accounts for the age and distribution of these terranes: a Middle Jurassic arc built on older accreted terranes undergoes rifting at 160 Ma, resulting in formation of a remnant arc/back‐arc basin/island arc triad. This system collapsed during the Late Jurassic Nevadan Orogeny (150 Ma) and was strongly deformed and stacked into a series of east‐dipping thrust sheets. Arc magmatism was active both before and after the Nevadan Orogeny, but virtually ceased

ISSN:0278-7407    

DOI:10.1029/TC003i007p00759

年代:1984

数据来源: WILEY

摘要:

Evolutionary models that have been proposed for the Pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central Axial Zone. It has been suggested by previous workers that uplift is a result of Alpine compression, or long lived strike slip movement on the North Pyrenean Fault. We critically assess these models and propose a new model based on the generation of a thin‐skinned, linked thrust system, due to Alpine collision of Iberia and Europe. Pyrenean Alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6° within Hercynian basement. Northerly directed thrusts of the North Pyrenean Zone and Northern Folded Foreland are backthrusts from this sole fault. A total orogenic shortening of 106 km in the central Pyrenees was achieved between the Palaeocene and Oligocene at a time‐averaged rate of 0.62 cm yr−1. A thin‐ skinned model requires that the North Pyrenean Fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surfa

ISSN:0278-7407    

DOI:10.1029/TC003i007p00773

年代:1984

数据来源: WILEY

摘要:

In recent years, most geotectonic syntheses of the North Atlantic Caledonides have adopted a two plate configuration, with a roughly E‐W closure direction between Laurentia and Baltica producing the N‐S striking Scandinavian and East Greenland Caledonides and inducing dextral strike‐slip along the NE‐SW oriented British sector of the Iapetus suture. The North German‐Polish Caledonides are a third arm to the Appalachian‐N. Atlantic Caledonide orogen. Recently, Ziegler has proposed that the mid‐Palaeozoic deformation belts of S. Britain ‐ N. Germany‐Poland and also of central Europe were produced by the northward impact of microcontinental fragments onto the southern margin of the already sutured continental mass of Laurentia‐Baltica. Some ascribe the whole Appalachian orogen to a sequence of terrane accretion events in mid‐Ordovician through mid‐Devonian time. A N‐S collision direction would induce sinistral shear across the British sector of the Iapetus suture. In this paper, we outline the evidence for sinistral displacements within the British Caledonides and for their age. We conclude that the “non‐metamorphic Caledonides” were produced by the northerly accretion of a Cadomian terrane in late Silurian‐early Devonian time, and that this event was entirely separate from the earlier Laurentia‐Baltica collision which produced the post‐Grampian thrust related

ISSN:0278-7407    

DOI:10.1029/TC003i007p00781

年代:1984

数据来源: WILEY