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The diffuse deformation zone in the central Indian Ocean is the classical example of distributed deformation of the oceanic lithosphere, where shortening between the Indian and Capricorn plates is manifest as reverse faulting (5-10-km-spaced faults) and long-wavelength (100-300 km) folding. The onset of this deformation is commonly regarded as a key far-field indicator for the start of major uplift of the Himalayas and Tibet, some 4000 km further to the north, due to increased deviatoric stresses within the wider India-Asia area. There has been disagreement concerning the likely timing for the onset of deformation between plate-motion inversions and seismic reflection-based studies. In the present study, fault displacement data from seismic-reflection profiles within the central Indian Ocean demonstrate that compressional activity started much earlier than previously thought, at around 15.4-13.9 Ma. From reconstructions of fault activity histories, we shows that 12% of the total reverse fault population had been activated, and 14% of the total strain accumulated, prior to a sharp increase in the deformation rate at 8.0-7.5 Ma. There is no evidence for any regional unconformity before 8.0-7.5 Ma; early shortening was accommodated by activity on single isolated fault blocks. Total strain estimates derived are more variable and complex than those predicted from plate inversion, and they do not show simple west to east increase. [ABSTRACT FROM AUTHOR]

The Olympus Mons volcano on Mars is notable not only for its immense height and width, but also for substantial asymmetries in its structure. The gently sloped northwest flank extends to a much greater distance from the central caldera complex than the more steeply sloped southeast flank. Furthermore, the northwest flank exhibits lower-flank extensional faults, whereas the southeast shows upper-flank compressional terraces and lower-flank upthrust blocks. However, both the northwest and southeast flanks exhibit characteristic concave-upward profiles and steep bounding scarps, in contrast to other sectors. The NW-SE asymmetries are aligned with the regional slope from the Tharsis rise, but an understanding of the underlying causes has remained elusive. We use particle dynamics models of growing, spreading volcanoes to demonstrate that these flank structures could reflect the properties of the basement materials underlying Olympus Mons. We find that basal slopes alone are insufficient to produce the observed concave-upward slopes and asymmetries in flank extent and deformation style that are observed at Olympus Mons; instead, lateral variations in basal friction are required. These variations are most likely related to the presence of sediments, transported and preferentially accumulated downslope from the Tharsis rise. Such sediments likely correspond to ancient phyllosilicates (clays) recently discovered by the Mars Express mission. [ABSTRACT FROM AUTHOR]

The article presents the discussion on New zircon radiometric U-Pb ages and Lu-Hf isotopic data from the ultramafic-mafic sequences of Ranau and Telupid. Topics include marine red beds of the Oligocene Kulapis Formation showing mafic conglomerates and chloritic shales deriving from nearby ophiolitic sources; and ultramafic rocks normally devoiding of primary zircons but zircon crystallizing in ophiolitic rocks during hydrothermal alteration.

After 120 years of unsuccessful endeavor, a paradigm shift is required before earthquakes can be predicted. The most sensitive diagnostic of low-level changes of stress in in situ rock, variations in microcrack geometry, can be monitored by analyzing shear-wave splitting. The suggested paradigm shift is that, instead of investigating the source zone, we monitor stress accumulation before earthquakes at, possibly, substantial distances from the source. Characteristic temporal variations of shear-wave time delays have been observed in retrospect before 14 earthquakes worldwide. On one occasion, when changes were recognized early enough, the time, magnitude, and fault break of an M = 5 earthquake in southwest Iceland were successfully stress-forecast in a narrow time-magnitude window. Such stress accumulation can be theoretically modeled and is believed to be at least partially understood. When sufficient shear-wave source earthquakes are available, increasing time delays also show an abrupt decrease shortly before the impending earthquake occurs. This is not fully understood but is thought to be caused by stress relaxation as microcracks coalesce onto the eventual fault break. The new result confirming these ideas, and justifying the paradigm shift, is that logarithms of the durations of both increases and decreases in time delays are found to be proportional (self-similar) to the magnitudes of impending earthquakes. [ABSTRACT FROM AUTHOR]

Pseudotachylyte formed by frictional melting has been the only unequivocal evidence of past seismogenic fault slip. We report from high-velocity friction experiments on siderite-bearing gouge that mineral decomposition due to frictional heating also can leave evidence of paleoseismic events along shallow crustal faults other than pseudotachylyte. Experiments were conducted room dry on simulated gouge composed of siderite or mixture of siderite, calcite, and quartz, initially at room temperature, under normal stresses of 0.6-1.3 MPa and at seismic slip rates of 1.3-2.0 m/s. In all cases, gouge exhibited dramatic slip weakening and siderite was decomposed into nanocrystalline magnetite and CO2 gas, as confirmed by CO2 measurement, X-ray diffraction analyses, and transmission electron microscopy. The weakening was caused by the low frictional strength of ultrafine decomposition products at seismic slip rates. Magnetite formation during shearing changed gouge color to black and increased magnetic susceptibility by a few orders of magnitude. Those changes can be recognized in natural fault zones, and black gouge in the Chelungpu fault zone in Taiwan is perhaps such an example. Thus our results suggest that thermal decomposition in shallow crustal faults can be an important co-seismic process not only for dynamic fault weakening, but also for leaving seismic slip records. [ABSTRACT FROM AUTHOR]

The strengths of mountain belts and major faults have been notoriously difficult to constrain and there is ongoing debate over the controlling mechanisms and stress magnitudes. Here we show that the strengths of active thrust-belt wedges and their basal detachments can be directly determined from the covariation of surface slope a with detachment dip β, without strong assumptions about the specific strength-controlling mechanisms. Even a single taper measurement (α,β) can strongly constrain the set of possible wedge and detachment strengths. This theory is tested with dry sand wedges and then applied to the Niger delta thrust belt, the active Taiwan mountain belt, and the thrust that slipped in the M = 7.6 Chi-Chi earthquake. Their basal detachments are shown to be exceedingly weak, with effective coefficients of friction (0.04-0.1) that are an order of magnitude less than most laboratory friction coefficients (0.6-0.85). In contrast, these wedges are moderately strong internally, within the range of pressure-dependent strengths in deep boreholes. These results confirm the existence of exceedingly weak faults and strong crust, which raises important causal questions. [ABSTRACT FROM AUTHOR]

Exposures of gabbros and mantle-derived peridotites at slow-spreading oceanic ridges have been attributed to extension on long-lived, low-angle detachment faults, similar to those described in continental metamorphic core complexes. In continental settings, such detachments have been interpreted as having originated and remained active at shallow dips. Alternatively, currently shallow dipping fault surfaces may have originated at moderate to steep dips and been flattened by subsequent flexure and isostatic uplift. While the latter interpretation would be more consistent with Andersonian faulting theory, it predicts large footwall tilts that have not been observed in continental detachment faults. Here we use the magnetization of oceanic gabbro and peridotite samples exposed near the Fifteen-Twenty Fracture Zone on the Mid-Atlantic Ridge to demonstrate that substantial footwall rotations have occurred. Widespread rotations ranging from 50° to 80° indicate that original fault orientations dipped steeply toward the spreading axis. [ABSTRACT FROM AUTHOR]

Principal slip surfaces in fault zones accommodate most of the displacement during earthquakes. The topography of these surfaces is integral to earthquake and fault mechanics, but is practically unknown at the scale of earthquake slip. We use new laser-based methods to map exposed fault surfaces over scales of 10 pm to 120 m. These data provide the first quantitative evidence that fault-surface roughness evolves with increasing slip. Thousands of profiles ranging from 10 pm to >100 m in length show that small-slip faults (slip <1 m) are rougher than large-slip faults (slip 10-100 m or more) parallel to the slip direction. Surfaces of small-slip faults have asperities over the entire range of observed scales, while large-slip fault surfaces are polished, with RMS values of <3 mm on profiles as long as 1-2 m. The large-slip surfaces show smooth, elongate, quasi-elliptical bumps that are meters long and as high as -1 m. We infer that these bumps evolve during fault maturation. This difference in geometry implies that the nucleation, growth, and termination of earthquakes on evolved faults are fundamentally different than on new ones. [ABSTRACT FROM AUTHOR]

Dynamic topography provides a measure of stresses within the Earth's interior. Dense slabs induce an upper mantle flow that deflects the surface of the Earth downward above them. By combining a simple theoretical (Stokeslet) model of subduction, gravity modeling, and seismic tomography, I show that a significant fraction (as much as 2000 m) of the topographic variations observed above the Scotia, Mariana, and Hellenic subduction systems appears to be dynamically induced by stresses related to the underlying subduction. [ABSTRACT FROM AUTHOR]

Using a combination of GPS-measured horizontal velocities of 200 sites and 115,487 range-change rates determined with the permanent scatterer interferometric synthetic aperture radar (InSAR) method in the San Francisco Bay Area, we resolve vertical motions in the region at sub-mm/yr precision. The highest displacement rates are due to nontectonic processes, such as active landslides, subsidence and rebound over aquifers, and rapid settling of unconsolidated sediments along the bay margins. Residual displacement rates are determined by removing the contribution of the GPS-derived horizontal velocity field from the InSAR range-change rates. To isolate vertical tectonic rates, we use only those InSAR measurements made on material that was not Quaternary substrate, which is susceptible to nontectonic and seasonally varying ground motions. The InSAR residuals indicate significant uplift over the southern foothills of the active Mount Diablo anticlinorium, the Mission Hills stepover region of the Hayward and Calaveras faults, and the central and southern Santa Cruz Mountains located along a restraining bend of the San Andreas fault. [ABSTRACT FROM AUTHOR]

We present analytical results from four dredge locations across the eastern Zealandia continental margin and adjacent ocean crust. The 115 Ma dacites dredged from the West Wishbone Ridge (WWR) are isotopically primitive, weakly adakitic, slab-derived lavas. The 97 Ma A-type granites and a basalt from the easternmost Chatham Rise enlarge the known area of postsubduction Gondwana magmatism. Amphibolite-grade schists from a fault block south of the Chatham Rise provide a critical bridge between the Zealandia and West Antarctica belts of Jurassic- Cretaceous accretionary prism rocks. The new recognition of the WWR as a remnant of a 115 Ma intraoceanic subduction system means that previous hypotheses of the WWR as a fracture zone or spreading ridge require modification. The dacite ages constrain the start of Osbourn Trough spreading, which caused breakup of the Hikurangi-Manihiki igneous plateau, to before 115 Ma. We speculate that, after 115 Ma, the WWR was rifted by an intraoceanic spreading center that developed along its southeast side. Impingement of this spreading center against the Gondwana margin led to widespread 95-100 Ma postsubduction magmatism, variable lithospheric stretching, and ultimately continental splitting of Zealandia and West Antarctica across basement trends. [ABSTRACT FROM AUTHOR]

We report a magnetostratigraphic and rock magnetic study of the Yaha section, located on the southern flank of the central Tian Shan mountains, Asia. Our results show a two-fold increase in sedimentation rate as well as marked changes in rock magnetic characteristics ca. 11 Ma. After 11 Ma, sedimentation rate remained remarkably constant until at least 5.2 Ma. These findings are consistent with sedimentary records from other sections surrounding the Tian Shan. We conclude that uplift and erosion of the Tian Shan accelerated ca. 11 Ma, long after the onset of the collision between India and Asia, and that the range rapidly evolved toward a steady-state geometry via a balance between tectonic and erosion processes. [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]

In order to better understand mechanisms of active faults, we studied relationships between fault behavior and rock units along the Hayward fault using a three-dimensional geologic map. The three-dimensional map—constructed from hypocenters, potential field data, and surface map data—provided a geologic map of each fault surface, showing rock units on either side of the fault truncated by the fault. The two fault-surface maps were superimposed to create a rock-rock juxtaposition map. The three maps were compared with seismicity, including aseismic patches, surface creep, and fault dip along the fault, by using visualization software to explore three-dimensional relationships. Fault behavior appears to be correlated to the fault-surface maps, but not to the rock-rock juxtaposition map, suggesting that properties of individual wall-rock units, including rock strength, play an important role in fault behavior. Although preliminary, these results suggest that any attempt to understand the detailed distribution of earthquakes or creep along a fault should include consideration of the rock types that abut the fault surface, including the incorporation of observations of physical properties of the rock bodies that intersect the fault at depth. [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]

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]

We quantitatively investigate the relation between nappe stacking and subduction in the Aegean region. If nappe stacking is the result of the decoupling of upper-crustal parts (5–10 kin thick) from subducting lithosphere, then the amount of convergence estimated from balancing the nappe stack provides a lower limit to the amount of convergence accommodated by subduction. The balanced nappe stack combined with the estimated amount of completely subducted lithosphere indicates 700 km of Jurassic and 2400 km of post-Jurassic convergence. From seismic tomographic images of the underlying mantle, we estimate 2100–2500 km of post-Jurassic convergence. We conclude that (1) the imaged slab represents the subducted lithosphere that originally underlay the nappes, (2) since the Early Cretaceous, subduction in the Aegean has occurred in one single subduction zone, and (3) the composition of the original basement of the nappes indicates that at least 900 km of sub-upper-crust continental lithosphere subducted in the Aegean. [ABSTRACT FROM AUTHOR]

It is widely accepted that the thickened oceanic crust of the Caribbean plate, its basaltic accreted margins, and accreted mafic terranes in northwestern South America represent the remnants of a single ca. 90 Ma oceanic plateau. We review geologic, geochemical, and paleomagnetic evidence that suggests that the Caribbean-Colombian oceanic plateau in fact represents the remnants of two different oceanic plateaus, both dated as ca. 90 Ma. The first of these plateaus, the Caribbean Plateau, formed ca. 90 Ma in the vicinity of the present-day Galapagos hotspot. Northeastward movement of the Farallon plate meant that this plateau collided with the proto-Caribbean arc and northwestern South America <10 m.y. after the platcau's main phase of formation. Paleomagnetic evidence suggests that the second of these plateaus, the Gorgona Plateau, formed at 26°–30°S, possibly at the site of the present-day Sala y Gomez hotspot. Over the next ∼45 m.y., this plateau was carried progressively northeastward on the Farallon plate and collided in the middle Eocene with the proto-Andean subduction zone in northwestern South America. The recognition of a second ca. 90 Ma Pacific oceanic plateau strengthens the link between plateau formation and global oceanic anoxic events. [ABSTRACT FROM AUTHOR]

Oxygen, carbon, and strontium isotope variations in vein-filling calcite and quartz Cements and their host rocks are used to elucidate the origin, spatial and temporal evolution, and migration pathways of fluids in the detachment Nuncios fold complex, northeastern Mexico. The folded Mesozoic sedimentary sequence contains two regional paleohydrostratigraphic units separated by a unit of low permeability. Two main generations of cements are present in both paleohydrostratigraphic units. Distinct differences exist between δ18O, δ13C, 87Sr/86Sr, and fluid-inclusion temperatures of early vein-filling cements in the lower and the upper units. These differences, together with a strong correspondence between early cement and host-rock δ18O and δ13C values, suggest that early diagenetic fluids were compartmentalized between the two units. Late vein-filling cements have isotopic compositions and fluid-inclusion temperatures that converge to similar values, indicating a change to open fluid flow between the lower and upper units. We hypothesize that the fluid history of the Nuncios fold complex evolved in two main stages: (1) burial diagenesis and early folding, during which fluids were confined within individual units, and (2) late-stage folding, during which increased deformation associated with fold tightening caused the expulsion of fluid from the lower unit into the upper unit. [ABSTRACT FROM AUTHOR]

Diamond was synthesized at high temperature and pressure in a Walker-style multianvil apparatus from various supercritical C-O-H-rich fluid compositional systems. Depending on the type and amount of impurities added to the system, diamonds of varying morphology and bearing solid oxide inclusions were found within the run product. These characteristics bear a striking resemblance to metamorphic microdiamonds recovered from the Kokchetav massif, Kazakhstan; these natural diamonds share morphological traits with our synthesized diamonds, and both the natural and synthesized diamonds contain similar solid oxide inclusions. Our data favor formation of Kokchetav diamonds via crystallization from a supercritical C-O-H fluid, rather than from carbonate or carbonatite melt, as others have suggested. [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]

Exhumed high-pressure rocks from the Caledonian root zone in Norway provide analogues for processes occurring today under southern Tibet, allowing large-scale geophysical observations, from gravity and earthquakes, to be linked with the mechanical properties of metastable rocks under high mountains. Metastability is essential for the survival of thick mountain roots and, hence, of high mountains and is in turn controlled by water. If water is absent, dry granulite, formed from earlier melting episodes, is both stable and strong and likely to survive in the eclogite stability field of deep root zones for hundreds of million years. But if hydrous fluid is introduced, the transformation of granulite to eclogite is relatively rapid and accompanied by a dramatic loss of strength. In Norway, this transformation was initiated by water infiltration along fractures formed by earthquakes. The same process, as marked by deep earthquakes, may be occurring today beneath southern Tibet. [ABSTRACT FROM AUTHOR]

A new analysis of Deep Sea Drilling Project (DSDP) Leg 84 data demonstrates that the dominant process controlling the Guatemala margin tectonic evolution since ca. 25 Ma is subduction-erosion. Data from benthic foraminifera, assemblages from upper-slope DSDP Sites 568, 569, and 570 indicate long-term, progressive subsidence from upper to middle bathyal depths (600–1000 m) ca. 19 Ma to modern abyssal depths >2000 m). Rapid subsidence migrated landward starting at the Oligocene-Miocene boundary time under the current middle slope, where it increased sharply ca. 19 Ma, reached the current upper slope by ca. 15 Ma, and arrived at the uppermost slope ca. 2 Ma. Subsidence indicates crustal thinning by basal tectonic erosion of mass from the underside of the upper plate. Under the assumption that, in the Miocene, the morphology of the forearc was similar to that of today, landward migration of the trench was at a rate of 0.8–0.9 km/m.y. This linear rate corresponds to a tectonic erosion rate of the submerged forearc of 11.3–13.1 km³·m.y.-1.km-l. The evolution of arc magmatism and superfast spreading at the East Pacific Rise since early Miocene time may have caused slab shallowing and tectonic erosion that readjusted the forearc geometry. [ABSTRACT FROM AUTHOR]

In the deep crust, temperature, which is among the key parameters controlling lithospheric dynamics, is inferred by extrapolation from the surface using several assumptions that may fail in regions of active tectonics and fluid migration. In the rare case that temperatures of 700 °C or higher are exceeded in the upper and middle continental crust composed of quartz-rich felsic rocks, the α-β quartz transition (ABQT) will occur, generating a measurable seismic signature and offering the possibility for precisely estimating temperature from the known ABQT phase diagram. Here it is shown that all expected seismic features of the ABQT are met by the boundary between the upper and middle crust below the INDEPTH III profile in central Tibet. This finding implies that a temperature of 700 °C is achieved at a depth of 18 km under the southern Qiangtang block, which agrees with the depth to the top of a high electrical conductivity anomaly, likely representing partially melted crust. To the south in the northern Lhasa block, the ABQT is at 32 km depth, corresponding to a temperature of 800 °C. It thus appears that this seismic boundary representing the ABQT is the result of recent geologic processes rather than being a lithologic boundary. [ABSTRACT FROM AUTHOR]

Upper Ordovician-Lower Devonian strata of the Meguma terrane in the Canadian Appalachians contain zircon populations, including an important Mesoproterozoic zircon population (1.0–1.4 Ga), similar to those in coeval strata of Avalonia, and strongly suggest contiguous rather than discrete histories for these terranes throughout the Paleozoic. That these terranes were juxtaposed throughout the early Paleozoic is indicated by the absence of a Cambrian-Ordovician accretionary event, the lack of intervening suture-zone ophiolitic units, and the similarity of Avalonian and Meguma basement Nd isotope signatures in early Paleozoic igneous suites. As Avalonia had accreted to Laurentia-Baltica by the Early Silurian, these data suggest that the Meguma terrane, like Avalonia, resided along the same (northern) margin of the Rheic Ocean at that time. These conclusions have implications for reconstructions of the northern Gondwanan margin in the early Paleozoic and imply that the Silurian-Devonian Acadian orogeny in Maritime Canada occurred in an Andean-type setting and was not related to collision of the Meguma terrane with the Laurentian margin. [ABSTRACT FROM AUTHOR]

At depth, many fold-and-thrust belts are composed of a gently dipping, basal thrust fault and steeply dipping, shallower splay faults that terminate beneath folds at the surface. Movement on these buried faults is difficult to observe, but synthetic aperture radar (SAR) interferometry has imaged slip on at least 600 km² of the Shahdad basal-thrust and splay-fault network in southeast Iran. Approximately 70 mm of thrust motion on the 8°-dipping Shahdad basal thrust occurred 8–30 km to the east of the 14 March 1998 Fandoqa earthquake (Mw = 6.6) that involved 1.6 m of oblique (strike slip and normal slip) displacement on a steeply dipping fault. That earthquake transferred stress to the Shahdad basal thrust and associated splays, triggering slip either immediately or in the following six months. Modeling shows that, to produce the observed surface deformation, the Shahdad faults must have accommodated a nearly complete release of the shear stress increase. This could be due to either low friction on the faults or deformation throughout a wedge of material that is everywhere close to failure. The anomalously small magnitude of displacement on the Shahdad basal thrust and splay faults compared to the area of slip suggests a slip mechanism that is likely aseismic. [ABSTRACT FROM AUTHOR]

The notion that slip on faults is controlled by the balance between resolved shear stress and the magnitude of frictional resistance is examined in the light of the published orientations of ancient faults and slip lineations. By compiling data from more than 1500 faults used in 228 stress analyses, we observe that natural fault planes, as well as lineations formed by fault slip, display characteristic patterns of preferred orientation when rotated into the reference frame defined by the principal stress axes. These patterns vary systematically according to the relative magnitudes of principal stresses determined by fault-slip analysis. Furthermore, these patterns are strikingly similar to those predicted by a frictional model for fault reactivation in which the potential for slip is equated to the ratio of the components of shear stress and normal stress on the fault plane. Our findings therefore make a compelling case for the concept of frictional slip tendency for the prediction of fault reactivation and lend support to the validity of fault-slip methods for paleostress analysis. [ABSTRACT FROM AUTHOR]

Three-dimensional finite-element (FE) analysis of a fold-thrust belt wedge model provides graphical and quantitative information for the strain geometry, kinematics, and mechanics of salient formation in three-dimensional space. A nonlinear, elastic-plastic FE model, using the initial basin configuration of the restored Provo salient, Utah, develops realistic deformation features (e.g., salient) in the deformed sedimentary prism. The three-dimensional fold-thrust belt wedge model shows different deformation characteristics (based on S1, γmax, and σ1 orientations and material-displacement directions) in different parts of the salient, and its behavior is closely related to the preexisting template of the predeformational basin shape. The model results indicate plane-strain deformation with symmetric finite-strain geometry in the middle of the salient and nonplane-strain deformation with nonsymmetric finite-strain geometry at the lateral boundaries. Thus, conventional two-dimensional plane-strain assumptions in fold-thrust belt analysis (e.g., in balancing cross sections) are reasonable only in the middle of the salient; however, at the lateral boundaries, the results indicate fully three dimensional deformation and suggest that restorations need to be more carefully constrained in three dimensions on the basis of detailed geologic data. [ABSTRACT FROM AUTHOR]

We use multichannel seismic reflection (MCS) and gravity data from the southern IzuBonin convergent plate margin to test for tectonic erosion. The Hahajima Seamount is a serpentinite seamount on the Izu-Bonin forearc. This serpentinite body likely originated from the mantle wedge beneath the Izu-Bonin arc, but it subsequently detached. MCS data and gravity modeling demonstrate that the Ogasawara Plateau on the incoming Pacific plate has been partly subducted beneath the Hahajima Seamount. Our analysis indicates that the Hahajima Seamount is a "rootless" serpentinite seamount, and the "root" of the serpentinite body was eroded during subduction of the western edge of the Ogasawara Plateau. Structural features of the Hahajima Seamount, the Ogasawara Plateau, and the Philippine Sea plate suggest that tectonic erosion, particularly basal erosion, has been occurring throughout this area. [ABSTRACT FROM AUTHOR]

Cratonic uplift or subsidence, as recorded geologically by erosion or deposition, indicates the net change in lithospheric buoyancy. Density change is primarily controlled by temperature change, such that the geologic record reveals the net lithospheric heating or cooling. Our modeling shows that thermal stabilization of lithosphere can occur in <100 m.y., largely determined by the time for crustal radioactivity to warm the entire lithosphere. Longer-term thermal evolution (350-400 m.y.) is controlled by the feedback between isostatic and thermal responses. Crustal heat production is the dominant factor for evolution of crustal geotherms, whereas the detailed initial thermal structure is less important. The fact that many cratons are eroded to only modest depths indicates that they have a history of warming slightly since their formation, implying a rather cool 700-1000 °C for initial lithospheric mantle. This is consistent with the growth of cratonic lithosphere by progressive thickening during continental assembly and/or subduction stacking of oceanic lithosphere. Relatively warm early lithosphere due to elevated crustal heat production or higher initial lithospheric mantle temperatures may have had a lower preservation potential due to preferential deformation and destruction. Study of the Proterozoic orogen of the southwestern United States indicates that the distinct thermal and isostatic records of adjacent crustal blocks are compatible with observed differences in crustal heat production, but also with similar initial lithospheric mantle temperatures. [ABSTRACT FROM AUTHOR]

The Holocene climate of the Southern Ocean is not well understood, mainly because of the lack of high-resolution reconstructions of ocean surface properties. Here we present a 12,500-yr-long, decadal-scale record of Holocene sea-surface temperatures and seaice presence from the Polar Front of the East Atlantic Southern Ocean. The record shows gradual climate change, with no abrupt Neoglacial cooling, and an unprecedented late Holocene warming. The dominant forcing factor appears to be precessional insolation; Northern Hemisphere summer insolation correlates to at least the early to middle Holocene climate trend. Spectral analysis reveals centennial-scale cyclic climate changes with periods of 1220, 1070, 400, and 150 yr. The record shows good correlation to East Antarctic ice cores and to climate records from South Georgia and Bunger Oasis. However, the record shows out-of-phase behavior with regard to climate records from the western Antarctic Peninsula and the Peru-Chile Current; such behavior hints at a climatic divide through Patagonia, the Drake Passage, and between West and East Antarctica. [ABSTRACT FROM AUTHOR]

We investigate the Quaternary slip rate for the Blackwater fault, Eastern California shear zone, through mapping and geochronology of offset volcanic rocks. Basalt flows of the Black Mountains support the presence of faulting at 3.77 ± 0.11 Ma, 1.8 ± 0.1 km of subsequent slip, and a well-constrained long-term slip rate of 0.49 ± 0.04 mm/yr. Total slip diminishes northward, evidenced by a 0.3-1.8 km offset of a 7.23 ± 1.07 Ma dacite flow in the Black Hills and fault termination in the Lava Mountains, 5 km short of the Garlock fault. Slow long-term slip rate together with sparse evidence for Holocene rupture contradict predictions of rapid slip rate from tectonic geodesy. These results support the conclusion that as much as 95% of geodetic strain accumulation across the Blackwater fault, and thus from 1 to 6 mm/yr of geodetic strain measured across the Eastern California shear zone, is a transitory phenomenon. Discrepant geologic and geodetic results may indicate an increased near-term seismic hazard, but merit caution for interpretation of fault slip rates from geodesy alone. [ABSTRACT FROM AUTHOR]

Veins are common in Earth's crust, and are formed by a wide range of processes, which lead to crystal growth in dilation sites. The first-order processes in vein formation have been identified, but it is much less clear how these can be diagnosed from field studies. In order to better understand the microstructural evolution during vein growth, we grew veins of analogue material [alum, KAI(SO4)2·12H2O] in a transmitted-light cell from an advecting supersaturated fluid. Real-time observation shows the effects of flow rate and supersaturation on the evolving microstructure: (1) along-vein trends in growth rate caused by decreasing supersaturation, and (2) growth competition between clear crystals in the absence of nucleation and primary fluid inclusions. Although the overall trends in growth rate are in agreement with previous work, the local effects at the scale of individual grains reported here are less well understood; these new data form a basis for better interpretation of natural microstructures. To explore the possible effects of experimentally observed processes during vein growth, we simulate the growth kinetics of a quartz vein at various conditions of advective flow in Earth's crust. Results show that in general the along-vein changes in growth rate occur at length scales much larger than a typical outcrop. [ABSTRACT FROM AUTHOR]

Chagos Bank is a region of thick crust in the central Indian Ocean where a concentration of seismicity indicates that extension is ongoing. We have modeled bathymetry and gravity data to show that the crust-mantle boundary shallows near a seabed trough, consistent with a total extension of ∼15 km over a zone ∼50 km broad. This estimate is consistent with 5-10 m.y. of deformation at the present rate of relative India-Capricorn motion; the ∼15 km of extension is toward the lower limit of the total extension expected from magnetic anomaly reconstructions, but would be accumulated in 1-3 m.y. in a regime having the present-day seismicity. We attribute the localization of seismicity beneath Chagos Bank to a weak rheology caused by its thick crust. [ABSTRACT FROM AUTHOR]

The article focuses on new model for the growth of normal faults developed above pre-existing structures. Topics discussed include concerned that parts of the interpretation made by Bramham et al. are artifacts, and others are clouded by measurement error because they have not considered all the attributes and variables; and these affect both the position and path of a given fault on a L-D diagram and may account for much of the observed variance.

Studies foredeep tectonics and carbonate platform dynamics in the Huon Gulf, Papua New Guinea. Subsidence rate; Carbonate deposition; Comparison of the measured age with sea-level history.

The article discusses the role played by volcanic eruptions and tectonic movements in the formation of caldera-forming eruptions (CFEs). It explores the study conducted by G. R. Hughes and G. A. Manhood which focuses on evaluating the formation of calderas in relation to its tectonic environment, such as volcanic eruptions. It reveals that the flow of basaltic magma may control the formation of silicic magmatic systems that contributes to the development of CFEs. It states that the work carried out by Hughes and Manhood plays essential role in understanding the relation of arc magmatism and volcanic eruption with CFEs.