摘要:

We use new space geodetic data from very long baseline interferometry and satellite laser ranging combined with other geodetic and geologic data to study contemporary deformation in the Basin and Range province of the western United States. Northwest motion of the central Sierra Nevada block relative to stable North America, a measure of integrated Basin and Range deformation, is 12.1±1.2 mm/yr oriented N38°W±5° (one standard error), in agreement with previous geological estimates within uncertainties. This velocity reflects both east‐west extension concentrated in the eastern Basin and Range and north‐northwest directed right lateral shear concentrated in the western Basin and Range. Ely, Nevada is moving west at 4.9±1.3 mm/yr relative to stable North America, consistent with dip‐slip motion on the north striking Wasatch fault and other north striking normal faults. Comparison with ground‐based geodetic data suggests that most of this motion is accommodated within ∼50 km of the Wasatch fault zone. Paleoseismic data for the Wasatch fault zone and slip rates based on seismic energy release in the region both suggest much lower slip rates. The discrepancy may be explained by some combination of additional deformation away from the Wasatch fault itself, aseismic slip, or a seismic rate that is anomalously low with respect to longer time averages. Deformation in the western Basin and Range province is also largely confined to a relatively narrow boundary zone and in our study area is partitioned into the eastern California shear zone, accommodating 10.7±1.6 mm/yr of north‐northwest directed right‐lateral shear, and a small component (∼1 mm/yr) of west‐southwest ‐ east‐northeast extension. A slip rate budget for major strike‐slip faults in our study area based on a combination of local geodetic or late Quaternary geologic data and the regional space geodetic data suggests the following rates of right‐lateral slip: Owens Valley fault zone, 3.9±1.1 mm/yr; Death Valley‐Furnace Creek fault zone, 3.3±2.2 mm/yr; White Mountains fault zone in northern Owens Valley, 3.4±1.2 mm/yr; Fish Lake Valley fault zone, 6.2±2.3 mm/yr. In the last few million years the locus of right‐lateral shear in the region has shifted west and become more north trending as slip on the northwest striking Death Valley‐Furnace Creek fault zone has decreased and is increasingly accommodated on the north

ISSN:0278-7407    

DOI:10.1029/95TC00931

年代:1995

数据来源: WILEY

摘要:

During a 7‐week microearthquake experiment conducted in Epirus, Akarnania, and the Ionian islands of western Greece, we located approximately 600 earthquakes with magnitudes between 2 and 4.2. No event was deeper than 40 km. The seismicity cannot be clearly associated with any single fault except the Lixourion right‐lateral fault located west of the Ionian islands. Focal mechanisms of about 100 earthquakes show, for a narrow band of earthquakes located along the coast, ENE–WSW shortening consistent with the surface tectonics. Farther east, focal mechanisms show NNW–SSE extension beneath the foothills of the Pindus mountains, which is unrelated to surface faulting but is consistent with the presently subsiding basins. This strain pattern is seen far north and south of the Lixourion fault and is similar to the one observed in the Peloponnese. It suggests that a large‐scale mechanism is responsible for the recent geodynamics of both the northwestern and southwest

ISSN:0278-7407    

DOI:10.1029/95TC00839

年代:1995

数据来源: WILEY

摘要:

The Betic Cordillera of southern Spain provides a clear example of a collisional orogen that has undergone large‐scale extensional collapse while convergent motion of the bounding plates continued. Extension was accommodated by coeval shortening in thin‐skinned fold and thrust belts around the periphery of the system, and much of the region has now subsided to form a large marine basin. The thermal and deformational record of these processes is preserved in rocks from the upper mantle, crystalline crust, and sedimentary cover. Upper mantle peridotites record evidence for exhumation in several stages from asthenospheric depths to the surface. Early stages of exhumation probably occurred during Mesozoic rifting. Cooling at midlithospheric depths reflects continental convergence, and subsequent heating indicates loss of most of the underlying lithosphere and ascent of asthenosphere, whilst the final stages of exhumation in early Miocene time reflect extensional collapse. Crustal rocks in the internal zone of the Betic Cordillera were metamorphosed down to 50 km depth and are now exposed beneath major low‐angle normal detachment zones that separate them from heavily faulted low‐grade rocks above. Cooling ages of associated mylonites indicate that these detachments were active during the early to middle Miocene. Fault‐bounded intramontane basins, developed during the early to middle Miocene, contain coarse continental sediments heavily affected by normal fault systems, followed by a less deformed late Miocene marine succession. All of these phenomena can be explained by convective removal of the lithospheric root beneath a Paleogene collisional orogen, leading to large‐scale extension followed by thermal subsidence of the center of

ISSN:0278-7407    

DOI:10.1029/95TC00086

年代:1995

数据来源: WILEY

摘要:

The paradox of an extensional basin forming at a site of colliding continents is apparent in the evolution of the Neogene Alboran Sea basin of the westernmost Mediterranean. Processes that may be responsible for such basins forming at sites of continental collision include subduction and the removal of subcrustal lithosphere by either convection (extensional collapse) or delamination and have recently been invoked to explain the formation of the Alboran Sea basin. Decoupling of the thermal boundary layer can reverse the stress field from a state of compression to one of extension. The processes of extensional collapse and delamination involve removal of this layer and would have similar consequences in terms of modifying lithosphere geometry: replacement of the detached thermal boundary layer by hot asthenospheric material, which would produce a high geothermal gradient and in turn cause uplift at the surface. With identical effects, it is difficult to distinguish between the two mechanisms. Using the technique of backstripping, a subsidence history which evidences the coexistence of subsided and uplifted areas in the Alboran Sea basin through the Miocene to the Quaternary, has been reconstructed for the basin. While the deformation front of the Alboran Domain migrated westward, subsidence in the Alboran Sea basin propagated in the opposite sense, east/southeastward. This is best explained as the basin forming above a southeastward‐propagating, delaminating subcrustal lithospheric sla

ISSN:0278-7407    

DOI:10.1029/95TC00501

年代:1995

数据来源: WILEY

摘要:

Finite poles of Australia‐Pacific rotation are calculated using a three‐plate (Australia‐Antarctica‐Pacific) model and published Geosat data analyses of the Indian and Pacific Oceans (GEOS‐3P solution). Features identified on maps of Geosat data from SW of New Zealand are used to determine a new best fit finite pole for the prerift (mid Eocene; ∼45 Ma) configuration of the Australia‐Pacific plate boundary and to refine Eocene‐Miocene motions on the plate boundary (∼45–20 Ma; GEOS‐NZ results).Inverting the Australia‐Pacific best fit finite rotation to find relative displacements between east and west Antarctica since the Eocene implies dextral oblique extension in the Ross Embayment and almost pure dextral movement in the Queen Maud Range. Early‐mid Eocene convergence predicted through Antarctica conflicts with geological evidence and rema

ISSN:0278-7407    

DOI:10.1029/95TC00930

年代:1995

数据来源: WILEY

摘要:

The structural setting of the eastern headland of the La Spezia Gulf (Punta Bianca promontory) provides some constraints on the contractional and extensional framework of the Northern Apennines‐Northern Tyrrhenian Sea basin geodynamic system and allows a detailed reconstruction of a complex evolutionary path. Out‐of‐sequence thrusting is supposed in the inner side of the chain. Two different extensional events are identified; the older (early‐middle Miocene) may be related to the imbrication of the deeper metamorphic units of the Apenninic thrust wedge. Younger extension fits very well into an eastward asymmetrical faulting framework, related to the opening of the Northern Tyrrhenian Sea basin, from the late Miocene to the Pliocene‐Pleistocene (?). Well‐exposed low‐angle normal faults developed during this event. Extensional structures were then overprinted and reactivated by a mainly strike‐slip regime in

ISSN:0278-7407    

DOI:10.1029/95TC01203

年代:1995

数据来源: WILEY

摘要:

Structure, timing and rates of deformation, and the aspect ratio of the external zones of the Umbria‐Marche thrust system (UMTS) have been investigated with the aim of comparing features and processes occurring during the growth of a tectonic wedge with those inferred from mechanically based model predictions. The results of the UMTS test seem to support the idea that most of the characteristic features of a thrust system may be considered as the result of the incremental, transient increase of the pore fluid pressure (Pf) as a consequence of the amount of shortening of a crustal section. The strong dependence ofPfon strain rates and on the thickness of the rock mass involved in the deformation may also help to explain local and/or regional variations in the aspect ratio of the deformed‐state profiles of different fold and thrust be

ISSN:0278-7407    

DOI:10.1029/95TC00928

年代:1995

数据来源: WILEY

摘要:

On the basis of field studies and subsurface data, this first balanced transect crosses most of the Carpathian foreland basin and the entire Polish Western Carpathian thrust units (Outer flysch nappes, Pieniny Klippen Belt, and Inner Carpathian Tatric thrust sheets). It shows that (1) me Outer Carpathians are made up of several flysch units whose internal structure is strongly controlled by initial thicknesses, whereas the thin flysch successions are strongly deformed by tight folds and include several imbricated thrust sheets; by contrast, the thick flysch successions are less deformed and accreted in slightly imbricated thrust sheets; and (2) the Inner Carpathians are structured in an antiformal stack of basement thrust sheets. The unfolding of this cross section shows that the post‐middle Oligocene shortening in the European foreland platform and Outer Carpathians exceeds 180 km. In the substratum, most of this shortening seems to be solved by basement consumption vertically beneath the suture zone of the Pieniny Klippen Belt. Additional basement shortening took place also (1) in the Inner Carpathians, where, during the Neogene, buried basement thrust sheets were piled up to form an antiformal stack, and (2) beneath the inner zones of the Outer Carpathians. Palinspastic restoration of the cross section reflects two well‐differentiated zones prior to the late Oligocene‐late Miocene compression: (1) the present Inner Carpathians and the Pieniny Klippen Belt, characterized by a Late Cretaceous thrust belt unconformably overlain by an undeformed Palaeogene cover, and (2) the Outer flysch Carpathians, in which pre‐upper Oligocene configuration comprised a typical foreland basin flexed toward the SSW, with a system of NW trending highs and

ISSN:0278-7407    

DOI:10.1029/95TC00828

年代:1995

数据来源: WILEY

摘要:

In spite of the absence of ophiolitic slices at the surface, some traces of the lost Tethys ocean are recorded along the Pieniny Klippen Belt (PKB), a narrow décollement thrust system sutured at the transpressive boundary between the Outer and Inner Carpathians. The enigmatic precollisional evolution of Western Carpathians can be deciphered from some late Albian to Campanian flysch conglomerates which display chrome spinel grains, ophiolitic detritus and pebbles of blueschist facies tholeiitic metabasalts yielding a40Ar/39Ar plateau age of 155.4±0.6 Ma. Other detrital components are represented by extrabasinal pebbles of limestones, arc volcanics, and igneous to metamorphic basement rocks from southern sources. Our results suggest a markedly northward extension of the sublongitudinal Triassic Vardar (Meliata) Ocean and its subduction since the late Middle Jurassic, supposedly balanced westward by coeval spreading in the Ligurian‐Piedmont basin of the Apennine‐Western Alpine Tethys. A lateral kinematic connection between these diachronous and roughly parallel Tethys branches was provided on the north by a left‐lateral east‐west trending shear zone running from the Swiss‐Austrian Penninic domain to the Northern Carpathians. This reconstruction replaces the classic model of two paired North Penninic and South Penninic oceanic basins and eastern homologues with the Briançonnais‐Hochstegen and Czorstin microcontinents in between. The Late Jurassic‐Early Cretaceous evolution of the Carpathian active margin was characterized by subduction metamorphism and accretion of a wide orogenic wedge; in this time, the shallowing to deeply subsiding basins inferred from facies analyses on the sedimentary units of the PKB were likely floored by individual sections of the growing wedge. Later, some exhuming blueschist ophiolitic units of the wedge were uplifted to the surface and functioned in the Albian‐Campanian as an “exotic ridge” supplying clasts to the forearc basin. Finally, the colliding wedge became a cryptic paleostructure when, since the latest Cretaceous, it disappeared beneath the Inner Carpathian orogenic lid and was incorporated within the eastward moving infrastructure of t

ISSN:0278-7407    

DOI:10.1029/95TC00953

年代:1995

数据来源: WILEY

摘要:

North Aegean continental lithosphere was thickened by southwest vergent thrusting and continental subduction within the Alpine collisional orogen but has subsequently been greatly extended on a northeast‐southwest axis in the back arc of the Hellenic subduction zone. Crosscutting relationships with two granodiorite bodies emplaced at ∼31–33 Ma, the Xanthi and eastern Vrondou plutons, constrain a pre‐mid‐Oligocene origin of Alpine convergent structures in northeastern Greece. Post‐Alpine thinning of the north Aegean nappe pile began in earliest Miocene time and has been accommodated by a succession of distinct structural systems. The earliest of these, the “Symvolon shear zone”, appears to represent a midcrustal, coaxial rupture of the Falakron marble series, a carbonate platform>5000 m thick that was subducted northeastward beneath high‐grade rocks of the Rhodope metamorphic province in late Alpine time. Zircon and titanite U‐Pb dates and hornblende40Ar/39Ar dates obtained in this study constrain the intrusion and incipient mylonitization of the Symvolon or “Kavala” granodiorite within the Symvolon shear zone at ∼21–22 Ma. Following its emplacement, the Symvolon body resided at temperatures between 300°C and 500°C for 5–7 m.y., during which coaxial deformation may have continued within a widening Symvolon rupture. The Strymon Valley detachment, a regionally south‐west dipping low‐angle normal fault, succeeded the Symvolon shear zone in middle Miocene time. Southwestward displacement of the Serbo‐Macedonian gneiss complex by as much as 80 km in the hanging wall of this detachment facilitated the unroofing of the Rhodope metamorphic core complex, including the Falakron marble series and several Tertiary plutons, in its footwall. Biotite and K‐feldspar40Ar/39Ar dates from 11.1 ± 0.2 Ma to 15.5 ± 0.3 Ma yielded by Symvolon granodiorite samples document the cooling of the Rhodope core complex below 150°C–300°C during its southwestward‐progressive exhumation i

ISSN:0278-7407    

DOI:10.1029/95TC00926

年代:1995

数据来源: WILEY