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We examine three-dimensional seismic data from the Santos Basin, offshore Brazil, to determine how, where, and when radial faults grow near a salt diapir. We show roof stretching alone cannot account for the large heights and lengths of the kilometer-scale radial faults, suggesting stock widening ('stem push'), a mechanism implied in numerical models but not yet recognized in natural examples, played a pivotal role in fault formation. We suggest that, when a diapir is covered by a roof, radial faults form due to roof stretching, extending no further than the limit of the drape folding. The roof may then be shouldered aside and the faults buried along the stock flanks, exposing these strata to stem push-related stresses that may then re-activate preexisting, or form new, radial faults. We suggest the causal mechanism for radial fault formation will likely change as roof thickness varies during diapirism, with this reflecting the ratio between sedimentation rate and salt volumetric flux. [ABSTRACT FROM AUTHOR]

The south-central portion of the Columbia Basin in Washington State (USA), although not the primary eruptive center for the Columbia River Basalt (CRB), contains the thickest package of CRB lavas, at over 4 km. Prior to CRB deposition the region was a sediment-filled rift basin dating back to the early Eocene. Previous studies interpret a lower-crust, high-velocity body below the thick basalt deposits as a syn-extensional magmatic underplate. CRB layers thicken toward the center of the basin, revealing a pulse of subsidence during deposition that ceased coincident with cessation of CRB eruptions. We propose a subsidence mechanism based on metamorphic transition of the underplate from basalt to eclogite facies, driven by the increased pressure of CRB loading. We demonstrate the plausibility of our interpretation using numerical models of the mechanical and chemical components of the system. Further, we constrain the effective elastic thickness of the Miocene Columbia Basin lithosphere, finding it to be much thinner (5-10 km) than previous estimates. [ABSTRACT FROM AUTHOR]

Initiation of subduction is rarely encountered in modern tectonic environments due to its ephemeral and destructive nature. We report the geological and geophysical evidence indicating a transitional phase from buckling to embryonic subduction along the eastern Korean margin. The transition appears to be caused by compressional reactivation of the strike-slip boundary between the continental (Korean Peninsula) and oceanic (Ulleung Basin) crusts since the Early Pliocene. Evidence for compressional reactivation includes (1) a west-dipping major thrust and coincident crustal buckling of the Ulleung Basin; (2) an east-west structural asymmetry inferred from the gravity anomaly and P-wave tomography; and (3) ongoing crustal uplift and high-angle faults along the eastern Korean margin. The juxtaposition of underthrusting and buckling of the crust in the Ulleung Basin, and its associated ubiquitous reverse faulting on the eastern Korean margin, imply the potential development of a new subduction system along the western margin of the East Sea (Japan Sea). We propose that the East Sea comprises two incipient subduction margins (i.e., the Korean and Japanese sides), which are now competing to reach a self-sustaining subduction stage. [ABSTRACT FROM AUTHOR]

The tectonic origin of the Pennsylvanian-Permian Ancestral Rocky Mountain system is debated. Most models invoke stress from collision along the Ouachita-Marathon belt as the primary driver for Ancestral Rocky Mountain (ARM) (western USA) tectonism, but no existing model has convincingly explained the timing, northeastsouthwest contractional kinematics, and amagmatic nature of this system. We propose that stress generated by transpressional deformation along the southwestern (Sonora) margin of Laurentia combined with that from collision along the Ouachita-Marathon and Nevada margins drove uplift and basin development of the ARM. This model explains ARM timing, uplift kinematics, and lack of magmatism, and is supported by a new generation of late Paleozoic global plate reconstructions. [ABSTRACT FROM AUTHOR]

Tectonic forcing of stratigraphic architecture is likely in foreland basins. Tectonic driving forces are increasingly being invoked to explain stratigraphic patterns in the Cretaceous Western Interior Seaway Basin of North America, yet the evidence is largely circumstantial, and the details of driving forces remain elusive. In this paper I show direct stratigraphic evidence for syndepositional growth of a structural arch with at least 50 m of relief during accumulation of the upper Turonian Ferron Sandstone in south-central Utah, United States. Progressive growth of the arch was superimposed on several high-frequency stratal cycles that were driven by a more regionally extensive process (geodynamic or eustatic) and that produced laterally amalgamated sandstone bodies in a depositional strike-parallel orientation (north-south). All of this stratigraphy was then truncated by a more or less planar erosion surface (sequence boundary) that can be traced physically over at least 67 km north-south. This surface was later tilted northward, such that the upper member of the Ferron Sandstone thins progressively southward from 50 to 10 m over 67 km. The facies juxtapositions revealed by the Ferron Sandstone could, if seen in exposure of limited lateral extent, be wrongly interpreted as recording regionally extensive relative sea-level drops and potentially used in error as evidence for substantial eustatic sea-level falls during the Turonian. The folding and tilting documented in this study can be clearly attributed to geodynamic and/or tectonic driving forces, likely related to migration of a forebulge. [ABSTRACT FROM AUTHOR]

An unusual group of more than 100 earthquakes is located ~600 km beneath the North Fiji Basin in the southwest Pacific Ocean. These earthquakes are attributed to seismicity within detached segments of the subducted Australian plate. One of these detached slab segments has collided with, and now impinges on, the subducted Pacific plate at a depth of ~500 km. The region in the mantle where the two slab segments meet is also characterized by an unparalleled abundance of large-magnitude (Mw >7.0) earthquakes for this depth. The folded shape of the Pacific slab beneath Fiji, as well as the abundance of earthquakes, is interpreted to result from deformation and deformation-enhanced phase transformations as the two slabs collide and settle on the 660 km discontinuity. Detachment of the slab segments is interpreted to have occurred at ca. 5 Ma, but collision between the eastern segment and the west-dipping Pacific slab is interpreted to have occurred at ca. 4 Ma, coincident with initial opening of the overriding Lau Basin. [ABSTRACT FROM AUTHOR]

The southern highlands of the Moon comprise superposed ejecta layers, individually as thick as a few kilometers, from the major basins. Smaller (1-16-km-diameter) impact craters that penetrate this layered megaregolith and excavate material from depth have radar properties that provide insight into the variability of megaregolith thickness above a postulated basement of large crustal blocks. We observe a signifi cant difference in the population of radar-bright craters, 1-16 km and larger in diameter, between regions of the southeastern nearside highlands north and south of ∼lat 48°S. There are about one-third more radar-bright craters north of this line than to the south, broadly coincident with the mapped boundary between southern deposits mapped as pre-Nectarian age and those of Nectarian-Imbrian age to the north. The radar-bright crater population is consistent with a megaregolith thickness of ∼1.5 km in the north and ∼2.5 km in the south, a difference we attribute to South Pole-Aitken basin ejecta. [ABSTRACT FROM AUTHOR]

The Eocene deep-marine siliciclastic fill of the Ainsa basin, Spanish Pyrenees, gives unprecedented temporal resolution of the causes and timing of coarse elastic sediment supply to a deep-marine basin. Early Eocene tectonic subsidence linked to Pyrenean orogenesis created the Ainsa basin, with water depths of ∼400-800 m above a foundered shallow-marine mixed carbonate and clastic shelf. The ∼25 sandbodies or channelized submarine fans in the basin were controlled by the ∼400 k.y. Milankovitch frequency, with modes at ∼100 k.y. and ∼41 k.y. (possibly stacked ∼23 k.y.) influencing bottom-water conditions in the basin, causing periodic stratification in the water column across a submarine sill at the western basin margin (early Boltaña anticline). Intrabasinal tectonics defined and controlled the position of eight sandy systems and their constituent fans, in a process of seesaw tectonics, by (1) westward lateral offset stacking of sandy fans due to growth of the eastern side of the basin, represented today by the Mediano anticline, and (2) eastward (orogenward) back stepping of the depositional axis of each sandy system, due to phases of relative uplift of the Boltafla anticline. During basin infill, uplift of the Boltaña anticline led to increasing basin narrowing and depositional confinement. Unlike the earlier depositional systems, the youngest deep-marine system was fed from a more southern sediment source between the growth anticlines, as was the overlying deltaic system. All the older deep-marine sandy systems were fed from southeast point sources, from canyons and erosional lower-slope channels eroding the growing Mediano anticline. The depositional style outlined in this paper might be common to other active margins where siliciclastic basins evolve between active thrusts. [ABSTRACT FROM AUTHOR]

Far-field compressional stresses resulting from arc collisions with the northeast coast of Africa-Arabia propagated across the African plate in the Santonian (ca. 84 Ma), and later similar pulses occurred through much of the Cenozoic. Waves of inversion-related features including folds, thrusts, and igneous activity developed during the compressional events. Structures generated were uneven in intensity and distribution, and were commonly concentrated in existing rifts. Because of the irregular shapes of the North African continental margin and associated inboard basins, Cyrenaica underwent the most severe shortening, although deformation extended eastward from Libya to the Levant. Areas south and southeast of Cyrenaica (the Sirt Basin and the far Western Desert of Egypt) underwent very little shortening because they occupied a regional strain shadow. The eastern region of the Western Desert and Sinai, which were not sheltered by the stress-absorbing Cyrenaica inversion, recorded strong compressional deformation synchronous with that in Cyrenaica. As closure of the Mediterranean continues, Cyrenaica will become an indenter comparable to those of other orogenic belts. The detailed tectonic evolution of individual northeast African basins has depended on their positions in relation to the Cyrenaican strain shadow. No single subsidence and paleostress history reflects the complete regional development of the converging Mediterranean-North African margin. [ABSTRACT FROM AUTHOR]

The occurrence of strike-normal extension in mountain belts undergoing active contraction is not predicted by analytical solutions for the mechanics of purely frictional orogens. To test the idea that ductile rocks at depth might allow extensional deformation to occur in otherwise frictional and contractional orogens, we have conducted a series of analog experiments with purely frictional and layered frictional-ductile rheologies. By precisely measuring the horizontal deformation field, we have quantitatively confirmed the qualitative observation that analog frictional wedges do not extend. This is consistent with published numerical models, and is in contrast to purely viscous models that commonly display coeval extension with contraction. Our modeling also demonstrates that layered frictional-ductile models can, during active convergence, result in discrete extensional normal faulting even when only a relatively thin ductile layer is present. The resulting extension, though relatively small in magnitude compared to the active contraction, can greatly modify the final profile of a convergent orogen and can lead to the formation of a broad plateau between the pro-wedge and the retro-wedge. [ABSTRACT FROM AUTHOR]

We present new Earth-based radar observations of ejecta associated with the lunar Orientale impact basin. We can distinguish (1) a block-poor ejecta facies composing a concentric halo of mantling material 10 m or greater in thickness that extends more than 1000 km from the basin center, and (2) a melt-rich deposit that forms a discontinuous but a really extensive stratigraphic marker across the southern highlands. The melt-rich component likely extends well into the South Pole-Aitken basin, a key target for future landed and sample return missions. The observation of these two ejecta facies and their distribution across the southern nearside yields new insight into the types and distribution of material contributed by large basin-forming impacts to the highlands megaregolith. [ABSTRACT FROM AUTHOR]

Both Taconian (ca. 450 Ma) and Acadian (ca. 380 Ma) ages of high-grade deformation and metamorphism have been advocated for the Western Blue Ridge, southern Appalachians, United States. To resolve this debate, metamorphic monazite from the Great Smoky Mountains was dated via in situ microsampling plus isotope dilution-thermal ionization mass spectrometry (ID-TIMS). U-Pb ages are 450 ± 5 Ma (±2σ error), and mean 207Pb/206Pb ages are 453 ± 10 Ma. These data indicate that peak metamorphism and high-grade deformation occurred during the Taconian orogeny, although they do allow for a low-grade (subamphibolite-facies) Acadian overprint. Unresolved issues remain regarding the comparability of U-Pb TIMS ages with those obtained via other methods. [ABSTRACT FROM AUTHOR]

The displacement rate history of the Loreto fault, Gulf of California, is well documented; it is characterized by episodically accelerating displacement (10 k.y. frequency) superimposed upon a period of 200 k.y. of increasing fault displacement rate. A detailed conglomerate provenance analysis in the Loreto basin records the footwall unroofing history, which has been profoundly affected by increased fault displacement rate. Clast count data capture an immediate drainage response to a significant increase in slip rate, along with the occurrence and systematic increase in abundance of a new source rock type. Our data record an increase in the rate of incision and catchment expansion associated with this increase in displacement rate. A provenance signal from a shorter-term (100 k.y.) displacement rate increase has a 30–40 k.y. lag time. No change in provenance is recorded for high-frequency (10 k.y.) variations, which are filtered out by the system. [ABSTRACT FROM AUTHOR]

The long-standing difficulty of correlating Pennsylvanian strata among provincial faunal regions is resolved by effecting ‘digital’ correlation of major glacial-eustatic cyclothems that represent highstands when certain species achieved more global distribution than usual. In the late Moscovian-early Gzhelian (late Desmoinesian-early Virgilian) succession in the midcontinent United States, several major cyclothems are correlated, by both conodont species in common and cyclothem scale, with cyclothems in Russia (Moscow Basin) and Ukraine (Donets Basin), and the remaining cyclothems fit into the framework by position and scale. In this way the suggested event marker for the global Kasimovian-Gzhelian stage boundary (first appearance of Idiognathodus simulator) is supported, while possible event markers for the Moscovian-Kasimovian boundary await further evaluation. [ABSTRACT FROM AUTHOR]

Interpretation of industry seismic lines indicates that the eastern margin of the northern Gulf of California contains the inactive Adair-Tepoca and Upper Tiburón basins. The western margin is active and includes the Wagner, Consag, Upper Delfín, and Lower Delfín basins. These basin systems are separated by a wide basement high across which the upper strata in the inactive basins correspond to the middle and lower strata in the active basins, recording the westward migration of strain and subsidence during late Pliocene time. Our results illustrate the formation of an abandoned rift margin along the eastern Gulf of California. [ABSTRACT FROM AUTHOR]

It is widely believed that cyclic sedimentation in active tectonic basins is caused by external forcing such as sea-level cycles, episodic tectonic events, or variation in sediment supply due to climate change. Here we present a case of cyclic sedimentation in an experiment subject to constant fault slip rate and sediment discharge with no base-level fluctuation. The experiment was designed to study sedimentation in a simplified extensional relay ramp system. Reorganization of the fluvial channel network in a cyclic manner caused local variation in sediment supply to the hanging-wall basin, where subsidence was maximized, and resulted in autogenic appearance and disappearance of a lake associated with 90° rotation of paleocurrent direction and delta formation. Comparing an early phase of the experiment using no external forcing (i.e., no tectonic movement or base-level change) with the following main phase of the experiment (i.e., including subsidence in an extensional relay ramp pattern) shows that the characteristic time scale for channel mobility was five times longer during the phase with subsidence than during the previous phase without subsidence. Active fault slip imposed a new, longer time scale for autogenic dynamics by establishing a linked tectonic-sedimentation system. Scaling the experimental results to field length and time scales suggests that comparable autogenic cycles would produce 10–20-m-thick strata on time scales of 105 yr, comparable to observed cases attributed to allogenic effects. [ABSTRACT FROM AUTHOR]

The geometry of foreland basins is controlled by a dynamic balance between thrust-belt migration, flexural subsidence, and fluvial deposition. To improve our ability to quantify the relationships between tectonics, climate, and foreland basin geometry, I developed analytic solutions for basin topography and stratigraphy using a classic two-dimensional mathematical model of foreland basin evolution. Model predictions for basin topography are successfully tested against observed profiles along a humid-to-arid climatic gradient in the central Andes. Using published estimates for the thrust-belt migration rate, flexural parameter, and thrust-front basin depth in this region, I show that basin topographic profiles can be used to estimate the upstream erosion rate at any point along a foreland basin. Basin-averaged erosion rates estimated in this way vary from 0.025 to 0.045 mm/yr in the central Andes, increasing from semiarid to humid climates. [ABSTRACT FROM AUTHOR]

Several basins are developing near bends on strands of the North Anatolian transform fault in northwest Turkey. Oblique slip on these faults, rather than strain partitioning, accounts for trans-tension and subsidence. These basins are asymmetric, and tilt and subside most rapidly at their narrow ends near the bends. The turbidite surface marking the floor of the Cinarcik Basin (eastern Marmara Sea) was mostly abandoned at a sudden drop in sedimentation, which was likely coincident with the 14 ka lake-sea transition, and is now a warped reference surface from which we can measure strain and sedimentation. Subsidence and tilt are rapid, but do not require late Quaternary changes in regime. They are linked to transcurrent motion by slip parallel to an oblique bend on the North Anatolian fault and suggest tsunamogenic vertical motion in large Marmara Sea earthquakes. [ABSTRACT FROM AUTHOR]

Spectral analysis of both shipborne and airborne magnetic maps of the southern Tyrrhenian Sea reveals seven subparallel positive-negative magnetic anomaly stripes over the flat-lying deep floor of the Marsili oceanic basin. This represents the first evidence of oceanic magnetic anomalies in the Tyrrhenian Sea. The central positive stripe is along the Marsili seamount, a superinflated spreading ridge located at the basin axis. The stratigraphy of Ocean Drilling Program Site 650 and K/Ar ages from the Marsili seamount suggest that the Marsili Basin opened at the remarkable full-spreading rate of ∼19 cm/yr between ca. 1.6 and 2.1 Ma about the Olduvai subchron. This is the highest spreading rate ever documented, including that observed at the Cocos-Pacific plate boundary. Renewed but slow spreading during the Brunhes chron (after 0.78 Ma), coupled with huge magmatic inflation, gave rise to the Marsili volcano. Our new data and interpretation show that backarc spreading of the Tyrrhenian Sea was episodic, with sudden rapid pulses punctuating relatively long periods of tectonic quiescence. [ABSTRACT FROM AUTHOR]

This study examines the response of a forearc to the increase in sediment flux to the trench caused by the onset of glacial denudation in the Patagonian Andes. We investigated shelf-coastal basins in south-central Chile, which generally comprise Eocene-early Miocene nearshore facies overlain by late Miocene-early Pliocene deep-water siltstones and by late Pliocene-Quaternary nearshore deposits. Seismic profiles and coastal exposures reveal Eocene-early Pliocene extension followed by ongoing late Pliocene compression evidenced from growth strata adjacent to seismically active reverse faults. The onset of major global cooling ca. 6 Ma triggered glacial denudation in the uplifted high Andes. Exhumed material transported along the steep and humid Andean western slope increased trench sedimentation rates and caused continuous accretion and subduction of terrigenous material. We interpret forearc basin inversion as a response to a decrease in slope and basal friction of the wedge caused by frontal accretion and subduction of water-rich material, respectively, in order to reach a critical taper. This process lifted the shelf ∼1.5 km during the middle Pliocene. The Juan Fernández Ridge and Chile Rise confined >2 km trench fill between 45 and 34°S, limiting accretion and basin inversion. Glacial age trench fill and the steady decrease in plate convergence rate shifted this segment of the margin from erosive to accretionary during the Pliocene. [ABSTRACT FROM AUTHOR]

Recently collected multibeam bathymetry and hydroacoustic earthquake data are used to investigate the recent tectonics of the Explorer-Juan de Fuca Ridge systems, the boundaries between the Pacific and northern Juan de Fuca plates. The bathymetric and seismic evidence presented is consistent with a zone of shear extending well south of the Sovanco Fracture Zone to include the Heck and Heckle seamounts, and potentially as far south as the Springfield Seamounts and Cobb offset along the Juan de Fuca Ridge. This indicates that the triple junction between the Pacific-Juan de Fuca-North American plates may be reorganizing southward to establish at the Cobb offset. [ABSTRACT FROM AUTHOR]

Unusual compositions of some oceanic basalts have been attributed to their sources containing continental lithosphere detached during the breakup of Gondwana. However, the processes of how such continental lithospheric material is detached and transported into the ocean basin have not been constrained. Here we identify Walvis Ridge, where it has been argued that Deep Sea Drilling Project (DSDP) Site 525A contains continental material, as a unique location to constrain these processes. Absolute plate motion (relative to the Tristan mantle plume) and relative plate motion (between Africa and South America) of the African plate are oblique to one another, such that tectonic detachment versus hotspot-related thermal erosion should sample spatially separated continental units of different age. We present isotopic compositions of xenoliths representing the neo-Proterozoic lithosphere at the inferred site for tectonic detachment during continental breakup and show that this process does not explain the Walvis Ridge DSDP Site 525A mantle source. Rather, thermal erosion of ancient cratonic mantle by the Tristan mantle plume is indicated. A convective return flow is required to transport the eroded subcontinental lithospheric mantle to the site of plume activity some ∼50 m.y. later and provides constraints on the direction and velocity of mantle flow in the upper mantle. [ABSTRACT FROM AUTHOR]

We have determined the chemical composition of ∼350-m.y.-old solutions extracted from fluid inclusions, and strontium isotopic compositions of hydrothermal minerals from the Irish zinc-lead orefield. These data show that ore-forming fluids were derived from evaporated seawater and acquired metals by deep circulation within fractures in continental crust. Mineralization occurred in the near-seafloor environment when these solutions returned to the surface via thermohaline convection and mixed with brines rich in H2S produced by bacterial reduction of seawater sulfate. The results indicate that deep penetration of seawater or evaporated sea-water into the continental crust can occur in rift zones or extending passive margins and that this process can generate large volumes of base metal ore-forming solutions. Our results are inconsistent with topographic flow models for mineralization in the district, and support deep convection models for ore formation. The widespread development of evaporitic brines on the Laurussian continental margin under late Paleozoic greenhouse conditions is likely to have been critical for generating numerous accumulations of base metals in sedimentary basins at this time. [ABSTRACT FROM AUTHOR]

Proterozoic terranes in Australia record complex tectonic histories in the interval 1900-1400 Ma that have previously been interpreted by means of simple intracratonic or plate-tectonic models. However, these models do not fully account for (1) repeated tectonic reactivation (both orogenesis and rifting), (2) mainly high-temperature-low-pressure metamorphism, (3) rifting and sag creating thick sedimentary basins, (4) the nature and timing of voluminous felsic magmatism, (5) relatively large aspect ratio orogenic belts, and (6) a general paucity of diagnostic plate-boundary features. A key to understanding these histories is the observation that Australian Proterozoic terranes are characterized by an extraordinary, but heterogeneous, enrichment of the heat-producing elements. This enrichment must contribute to long-term lithospheric weakening, and thus we advocate a hybrid lithospheric evolution model with two tectonic switches: plate-boundary-derived stresses and heat-producing-element-related lithospheric weakening. The Australian Proterozoic crustal growth record is therefore a function of the magnitude of these stresses, the way in which the heat-producing elements are distributed, and how both of these change with time. [ABSTRACT FROM AUTHOR]

We use three large normal fault arrays in the northeastern Basin and Range Province, western United States, to document catchment development and relief production during fault growth. Fault slip and slip rates increase systematically along strike from zero at the fault tips. Catchment relief and across-strike range width both increase as slip accumulates but reach maximum values at a distance of ∼15 km from the fault tips and remain uniform along strike over much of the footwalls. Catchment outlet spacing also increases away from the fault tips but does not reach a uniform value and may vary by a factor of 5–6 along strike. We infer that catchments first elongate in the across-strike direction as slip accumulates and the range half-width increases. Once the half-width reaches its maximum value, continued catchment growth is possible only by along-strike capture, which increases outlet spacing but not relief. The close correspondence between catchment relief and range half-width suggests that geomorphically limited hillslope and channel gradients are achieved within the 15 km tip zone. Thus, the limiting factor in footwall development is the width of the range, which is controlled by two external agents: the geometry and spacing of the major faults, and the elevations of base level on both flanks. [ABSTRACT FROM AUTHOR]

Our results from seismic anisotropy analyses reveal for the first time the complex spatial variability of the characteristics of subsurface tectonic structures associated with ridge propagation. The significance lies in the fact that these variations are found at a locality with few lineaments or fissures at seafloor level. The over- lap region between mid-ocean ridge segments at 9°N on the East Pacific Rise is characterized by aligned cracks that are structurally more closely related to the propagating-ridge segment. These aligned cracks, which are approximately parallel to the ridge segments, provide conclusive observational evidence for establishing the nontransform nature of overlapping spreading centers, especially those with overlap basins covered by volcanic edifices. The aligned cracks of the 9°03′N overlapping spreading center are more similar to the ridge-parallel lineaments observed between overlapping axial-summit collapse troughs than those found at larger overlapping spreading centers. Our results therefore suggest that the lithospheric deformation between overlapping ridge segments depends on ridge offset and that this dependency may be thermally related. [ABSTRACT FROM AUTHOR]

An intriguing paradox in European tectonics is that present intracontinental seismicity seems to be broadly distributed, whereas past deformation was restricted to sedimentary basin areas. These basins were created by repeated Mesozoic rifting and later affected by pervasive Late Cretaceous—early Tertiary inversion. We propose that the change from localized deformation to distributed seismicity reflects changes in strength due to an interplay between Neogene thermal perturbations by mantle plumes and stress-induced intraplate deformation. As a result, inversion tectonics in the North Sea Basin area ceased and gave way to lithaspheric folding, which is most pronounced in onshore Paleozoic massif areas. Thermomechanical models demonstrate that this important transition in the mode and distribution of intraplate deformation can be explained by a strength reversal resulting from the combined effects of changes in Moho depth due to the transition from rifting to inversion and heating by mantle plumes. [ABSTRACT FROM AUTHOR]

Detrital white mica has been dated by the single-grain 40Ar/39Ar technique from three distinct stratigraphic levels and tectonic settings w)thin the Dinarides in order to monitor the geodynamic evolution of this segment of Alpine orogen, which is located near the transition of Variscan to Pan-African continental crust. Detrital micas of a Pennsylvanian foreland basin suggest erosion of medium to deep crustal levels of the Variscan orogen. The 40Ar/39Ar ages indicate almost no preservation of older, pre-Variscan crust, except for a low proportion of late Pan-African ages. These data are in accordance with previous findings from the Variscan belt that suggest that the whole upper level of Variscan crust had been nearly entirely eroded prior to molasse deposition. Variscan micas also dominate in graywackes of the Middle to Late Jurassic trench-filling deposits exposed within the Dinaric ophiolite belt, indicating a nearby Variscan continent. No mica from a Mesozoic metamorphic accretionary complex has been detected. By contrast, the Upper Cretaceous Vardar Flysch postdates the emplacement of the Dinaric ophiolite belt as part of the Dinaric-Carpathian metamorphic orogenic wedge, and likely represents a collapse basin postdating Early to early Late Cretaceous nappe stacking. The studied micas comprise a dominant Variscan group and a subordinate Early Cretaceous group from the eroding metamorphic orogenic wedge. [ABSTRACT FROM AUTHOR]

Newly released reflection seismic and borehole data, combined with sedimentological, provenance, and biostratigraphic data from Upper Cretaceous—Paleocene strata in the proximal part of the Cordilleran foreland-basin system in Utah, establish the nature of tectonic controls on stratigraphic sequences in the proximal to distal foreland basin. During Campanian time, coarse-grained sand and gravel were derived from the internally shortening Charleston-Nebo salient of the Sevier thrust belt. A rapid, regional Campanian progradational event in the distal foreland basin (>200 km from the thrust belt in >8 m.y.) can be tied directly to active thrust-generated growth structures and an influx of quartzose detritus derived from the Charleston-Nebo salient. Eustatic sea-level variation exerted a minimal role in sequence progradation. [ABSTRACT FROM AUTHOR]

Studies the crustal structure and tectonics from the Los Angeles basin to the Mojave Desert, southern California. Maximum depth of the Los Angeles basin; Formation of north dipping buttress by the Duarte branch of the Sierra Madre fault zone; Dip and depth extension of the San Andreas fault line.

Presents a synthesis of oceanographic, paleoenvironmental and tectonic factors that affect carbonate platform development in eastern ocean basins. Barred basins; Paleozoic tectonics; Cool-water intrusion due to open-ocean gyral circulation; Upwelling of cool, nutrient-rich and sometimes toxic water; Anoxic platform drowning during transgression; Deflection of cool eastern ocean basin currents.

The article focuses on the study of the internal structure and geochemistry of Phanerozoic ophiolites and Archean tectonics. The study shows a complex pattern of igneous accretion that involved multiple stages in suprasubduction zone (SSZ) environments. The subduction of the ocean floor in the older basins is discussed. Furthermore, the SSZ ophiolites generated during the arc-trench rollback cycles have structurally and geochemically heterogeneous crustal components that attests to the progressive evolution of their mantle melt sources.