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The Longmen Shan thrust belt in the eastern margin of the Tibetan Plateau underwent deformation of D1 associated with the Late Triassic collision between the North and South China Blocks, followed by deformation of D2 and D3 related to the eastward growth of the Tibetan Plateau. The D1 is marked by moderately tight folds (f1), spaced cleavage (S1), mineral lineation (L1), multistage reactivated faults, and top-to-the south thrusting. This deformation initiated before 237 Ma and ended at 208 Ma. The 193-159 Ma D2 deformation is top-to-the-southeast directed and normal ductile in nature and was associated with the formation of half-graben basins. The Mesozoic deformation of the Longmen Shan belt was related to the subduction of the Paleo-Tethys oceanic lithosphere, followed by the South China Block underneath the Songpan-Ganze Terrane. The D1 was produced in the pro-side of the overriding Songpan-Ganze plate, most probably driven by slab corner flow above the retreating South China Block. The D2 and extensional Songpan-Ganze turbidite basin were produced by roll-back and migration of the overriding plate above the retreating subduction zone. This model for the deformation from D1 to D2 is similar to a Mediterranean-style model. The D3 is characterized by SE-ward thrusting with stepwise migration of rapid denudation and dextral strike-slip faulting during the Late Cretaceous to present. Therefore, the Longmen Shan thrust belt involved Mesozoic compressional and extensional events that were overprinted by the Late Cretaceous to Cenozoic compressional event. [ABSTRACT FROM AUTHOR]

Multimethod chronology was applied on intrusives bordering the Kyrgyz South Tien Shan suture (STSs) to decipher the timing of (1) formation and amalgamation of the suturing units and (2) intracontinental deformation that built the bordering mountain ranges. Zircon U/Pb data indicate similarities between the Tien Shan and Tarim Precambrian crust. Caledonian (∼440-410 Ma) and Hercynian (∼310-280 Ma) zircon U/Pb ages were found at the edge of the STSs, related to subduction and closure of the Turkestan Ocean and the formation of the suture itself. Permian-Triassic (∼280-210 Ma) titanite fission track and zircon (U-Th)/He data record the first signs of exhumation when the STSs evolved into a shear zone and the adjacent Tarim basin started to subside. Low-temperature thermochronological (apatite fission track, zircon and apatite (U-Th)/He) analyses reveal three distinct cooling phases, becoming younger toward the STSs center: (1) Jurassic-Cretaceous cooling ages provide evidence that a Mesozoic South Tien Shan orogen formed as a response to the Cimmerian orogeny; (2) Early Paleogene (∼60-45 Ma) data indicate a renewed pulse of STSs reactivation during the Early Cenozoic; (3) Neogene ages constrain the onset of the modern Tien Shan mountain building to the Late Oligocene (∼30-25 Ma), which intensified during the Miocene (∼10-8 Ma) and Pliocene (∼3-2 Ma). The Cenozoic signals may reflect renewed responses to collisions at the southern Eurasian border (i.e., the Kohistan-Dras and India-Eurasia collisions). This progressive rejuvenation of the STSs demonstrates that deformation has not migrated steadily into the forelands, but was focused on pre-existing basement structures. [ABSTRACT FROM AUTHOR]

The topographically prominent Sierra Nevada de Santa Marta forms part of a faulted block of continental crust located along the northern boundary of the South American Plate, hosts the highest elevation in the world (∼5.75 km) whose local base is at sea level, and juxtaposes oceanic plateau rocks of the Caribbean Plate. Quantification of the amount and timing of exhumation constrains interpretations of the history of the plate boundary, and the driving forces of rock uplift along the active margin. The Sierra Nevada Province of the southernmost Sierra Nevada de Santa Marta exhumed at elevated rates (≥0.2 Km/My) during 65-58 Ma in response to the collision of the Caribbean Plateau with northwestern South America. A second pulse of exhumation (≥0.32 Km/My) during 50-40 Ma was driven by underthrusting of the Caribbean Plate beneath northern South America. Subsequent exhumation at 40-25 Ma (≥0.15 Km/My) is recorded proximal to the Santa Marta-Bucaramanga Fault. More northerly regions of the Sierra Nevada Province exhumed rapidly during 26-29 Ma (∼0.7 Km/My). Further northward, the Santa Marta Province exhumed at elevated rates during 30-25 Ma and 25-16 Ma. The highest exhumation rates within the Sierra Nevada de Santa Marta progressed toward the northwest via the propagation of NW verging thrusts. Exhumation is not recorded after ∼16 Ma, which is unexpected given the high elevation and high erosive power of the climate, implying that rock and surface uplift that gave rise to the current topography was very recent (i.e., ≤1 Ma?), and there has been insufficient time to expose the fossil apatite partial annealing zone. [ABSTRACT FROM AUTHOR]

The contemporary presence of the Puli Topographic Embayment within the Taiwanese thrust belt provides insight into processes that initiate and maintain a subcritical state in a thin-skinned compressive wedge. Orogen-scale analyses of Taiwan have succeeded in describing the processes and interactions that affect overall development of the thrust belt; however, relatively little is known about which processes or boundary conditions control first-order organization of strain at intermediate scales within the orogenic wedge. We investigate spatial and temporal scales of variation in the overall topographic and structural architecture of a critical wedge and explore the boundary conditions that affect very rapid shortening and erosion at intermediate scales on the order of 101 kilometers and 104-105 years. Causal links between the structural and synorogenic stratigraphic architecture of the foreland basin and coincidence of the Puli Topographic Embayment provide a valuable case study of the effects of changing boundary conditions (e.g., variable erodibility or strength of rocks along strike) controlling the evolution of critically tapered thin-skinned orogens. Deeper incision of river networks into a thicker sequence of unconsolidated synorogenic sediments in the central western foreland may affect the onset of a topographically subcritical state. [ABSTRACT FROM AUTHOR]

The Eastern Cordillera (EC) and related ranges of Bolivia and Argentina exhibit a wide variety of structural features, both thick and thin skinned, that make this region a prime area to study the evolution of these two contrasting styles. Using a combination of structural, geochronological, and thermochronological techniques, this study investigates how and in what order the various structures of the Argentinean EC from 25 to 26°S have developed during the Cenozoic. New mapping in the Angastaco area preserves one of the thickest Cenozoic stratigraphic sections and records a complex structural evolution during the Neogene, characterized by inversion of Cretaceous Salta Rift structures. Detrital zircon U-Pb geochronology combined with stratigraphic and structural features typical of synsedimentary deformation constrains the age of orgenic growth in the area to ∼14 Ma. Detrital apatite (U-Th)/He thermochronology on samples collected across the width of the southernmost EC at this latitude document an eastward younging of ages interpreted as the result of sequential eastward propagation of exhumation (and inferred deformation) from ∼14 to 3 Ma at a rate of ∼8.3 mm/a. Our data, when compared with existing data, show that the Puna Plateau of NW Argentina was exhuming and deforming at the same time as the EC and inter-Andean regions of Bolivia, suggesting that the deformation front connects along strike despite of the differences in structural style. Whereas the deformation front reached the sub-Andes of Bolivia by ∼10 Ma, deformation localized in the EC of NW Argentina until ∼4 Ma. Rates of propagation through the whole region seem to be quasi-uniform regardless of different structural styles. [ABSTRACT FROM AUTHOR]

Constraining the timing of onset and rates of deformation within the Greater Caucasus mountains is key to understanding their role in accommodating deformation across the Arabia-Eurasia orogen. We present new low-temperature thermochronometric constraints on the Cenozoic thermal evolution of the central Greater Caucasus that elucidate a three-phase cooling history. Between 50 and 30 Ma, cooling within the range was negligible. In Oligocene time, cooling rates throughout the range increased to ∼4°C/Myr. These rates remained constant until the early Pliocene time, when they increased again, reaching ∼25°C/Myr along the axial part of the range. Rates and timing of Oligocene exhumation are consistent with previous results from the western Greater Caucasus and are proposed to result from onset of subduction of the Greater Caucasus back-arc basin. Rapid exhumation of the Greater Caucasus, beginning in Pliocene time, contrasts with previously reported thermal histories for other portions of the range. Pliocene exhumation of the central Greater Caucasus appears to be tectonically driven and coincides with widespread evidence for a major reorganization of the Arabia-Eurasia plate boundary. We hypothesize that this exhumation, and regionally observed plate reorganization, results from the collision of the Lesser Caucasus with Eurasia, completing the subduction of oceanic lithosphere across this segment of the Arabia-Eurasia plate boundary. [ABSTRACT FROM AUTHOR]

In seismically and tectonically active regions, the present-day strain field tends to bias interpretation of the geological record. This is usually reasonable, but in areas such as triple junctions, the orientation of stress and the locus of strain can evolve abruptly in space and time. We present deformation measurements using satellite radar interferometry (InSAR) and seismicity that together capture the intrusion of a ∼6 km long, ∼1.5 m wide dike into the upper crust of the Ethiopian rift in southern Afar during May 2000. Dike-induced volcano-tectonic seismicity suggests that the intrusion was injected laterally during a period of ∼4 days. Seismic moment release accounts for only 5% of the total 1.6 × 1018 Nm geodetic moment, showing that diking accommodates the majority of strain. The intrusion intriguingly strikes at N122°E, perpendicular to the trend of the present-day East African rift. The geometry and age constraints on faulting and volcanic activity in southern Afar, combined with plate reconstructions, suggest that the dike likely intrudes an ∼ESE-SE striking magmatic system that localized strain during Oligo-Miocene rifting in the Red Sea and Gulf of Aden. We also identify the southerly extent of the Arabian Plate in Afar during the Oligocene in mantle seismic tomographic images: an abrupt increase in seismic velocity in southern Afar is coincident with a stepped increase of ∼20 Myr in the time elapsed since the onset of plate stretching. The anomalous orientation of the May 2000 intrusion implies that African-Arabian tectonics still influences the stress field in southern Afar and is at least partly accommodated by magma intrusion. [ABSTRACT FROM AUTHOR]

This study presents the first results of the seismic character of the underthrusting Indian crust in the Sikkim Himalaya deduced through an analysis of ∼3600 receiver functions (RFs) abstracted from waveforms registered at 11 broadband stations spanning a 110 km long N-S profile from the foothills to the higher Himalaya. Common conversion point stacks of receiver functions prominently trace the northward dipping geometry of the Indian Moho beneath the Himalaya. Monte Carlo inversion of the azimuthal variations of the RFs at individual stations adopting the nearest neighborhood algorithm approach reveals that the crustal thickness varies from ∼40 km to 61 km from south to north, with a dip varying between 4° and 10° among stations. A Moho doublet prominently seen at a depth of ∼40 km in the higher Himalaya to the north of Main Boundary Thrust has been interpreted in terms of possible (partial) eclogitization of a granulitic Indian lower crust, akin to the finding just north of the study region beneath southern Tibet. A strong layer of anisotropy (∼17%) localized within a low-velocity layer between 20 and 30 km has a NW-SE oriented fast polarization direction counterintuitive to the convergence-parallel and range-perpendicular alignment expected in a convergent setting due to shear processes. Midcrustal transcurrent deformation in Sikkim and Bhutan, evidenced by a conjugate system of strike-slip faulting with NW to NE trending P axis orientations is the most feasible mechanism for causing a near strike parallel oriented fast axis of anisotropy in this segment of Himalaya. [ABSTRACT FROM AUTHOR]

The utility of multivariate foliar physiognomy, specifically the Climate Leaf Analysis Multivariate Program (CLAMP), to yield reliable estimates of enthalpy and, hence, paleoelevation has been demonstrated by comparison with other proxies, yet concerns have arisen regarding uncertainties arising from (1) apparent ambiguities in the scoring regime and (2) the way leaf size is scored. Regarding the first concern, scoring ambiguities are examined by reporting on scoring tests with novice users and interlaboratory comparisons. The uncertainties were found to be less than those arising from the statistical methodology underpinning CLAMP. In respect to the second concern, the effect of removing all size data both from modern test sites and fossil data was tested. Specifically, the effect of removing leaf size data from the 15 Ma Namling data set from south central Tibet was investigated. Removal of all size data from modern sites demonstrated that size data contributes little to estimates of mean annual temperature and enthalpy. Similarly, the removal of leaf size information from the Namling data set alone, but with calibration unchanged, and from both the Namling site and calibration sites, this time with recalibration, still yield paleoelevation estimates that have been independently matched by oxygen isotope techniques. Moreover, the removal of all leaf size information results in only small increases in uncertainty (±52 m). [ABSTRACT FROM AUTHOR]

The present-day topography of the Tian Shan range is considered to result from crustal shortening related to the ongoing India-Asia collision that started in the early Tertiary. In this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event. Apatite fission track analysis and (U-Th)/He dating on apatite and zircon indicate that inherited Paleozoic structures were reactivated in the late Paleozoic-early Mesozoic during a Cimmerian orogenic episode and also in the Late Cretaceous-Paleogene (around 65-60 Ma). These reactivations could have resulted from the accretion of the Kohistan-Dras arc or lithospheric extension in the Siberia-Mongolia zone. Activity resumed in the late Mesozoic prior to the major Tertiary orogenic phase. Finally, the ongoing deformation, which again reactivates inherited tectonic structures, tends to propagate inside the endoreic basins that were preserved in the range, leading to their progressive closure. This study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas. [ABSTRACT FROM AUTHOR]

Sedimentologic, provenance, oxygen isotope, and 40Ar/39Ar results provide insights into late Cenozoic evolution of an extensional hinterland basin in the Peruvian Andes. The 5-6.5 km Cordillera Blanca composes the glaciated footwall of a low-angle normal fault parallel to active contractional structures in the Andean fold-thrust belt. The ∼200 km long, WSW dipping (19°-36°) Cordillera Blanca detachment fault accommodated >12-15 km of dip-slip displacement, inducing subsidence of the hanging-wall supradetachment basin, which is filled by ∼1300 m of conglomerate, sandstone, siltstone, and limited carbonate of the upper Miocene-Pliocene Lloclla Formation. Lithofacies associations are attributed to lacustrine fan-delta to proximal, stream-dominated alluvial fan sedimentation. Provenance data record footwall unroofing of Jurassic through Miocene volcanic and sedimentary rocks during NW directed, axial dispersal of sediment. Provenance data record the appearance of footwall-derived granite clasts from the upper Miocene Cordillera Blanca batholith and a change to transverse, WSW directed transport. Variations in the character and preservation of basin fill suggest along-strike propagation of the fault through time. Initial extension and subsidence is constrained to the latest Miocene by an 40Ar/39Ar biotite age of 5.4 ± 0.1 Ma for a basal tuff in the Lloclla Formation. Estimation of paleolake water composition shows very negative δ18O(VSMOW) values (−13.6‰ to−18.2‰), indicating that high elevations comparable to modern were already attained in the Cordillera Blanca during earliest normal faulting and basin evolution. These results lend support to models suggesting that substantial shortening, crustal thickening, and surface uplift were necessary precursor conditions for the generation of the Cordillera Blanca detachment fault. [ABSTRACT FROM AUTHOR]

We can regard the occurrence of earthquakes as the partial release of tectonic stress by sudden brittle rupture. In the framework of linear elasticity, any indigenous source including earthquake rupture is represented by a moment tensor. The moment tensor is mathematically equivalent to the volume integral of stress release over the whole elastic region surrounding the source, and so we can quantitatively relate the centroid moment tensor (CMT) of seismic events with an unknown tectonic stress field. On the basis of such an idea and Bayesian statistical inference theory, we developed an inversion method to estimate the 3-D pattern of tectonic stress from CMT data. Applying the CMT data inversion method to 12,500 seismic events in and around Japan, we obtained precise 3-D tectonic stress patterns that illuminate the present-day (Quaternary) complex tectonic motion of Japanese islands. The stress pattern of the Kuril-Japan-Nankai arc is basically E-W compression, but the direction of intermediate principal stress changes from N-S (reverse faulting type) in northeast Japan to vertical (strike-slip faulting type) in southwest Japan. On the other hand, the stress pattern of the Ryukyu and Izu-Bonin back-arc regions is basically trench perpendicular tension (normal faulting type). In addition to these basic stress patterns governed by mechanical interaction between the Eurasian, North American, Pacific, and Philippine Sea plates, we can recognize several characteristic local stress patterns corresponding to the horizontal motion of the Kuril fore-arc sliver, the collision of the Izu Peninsula with the mainland of Japan, and the opening of the Beppu-Shimabara rift zone. [ABSTRACT FROM AUTHOR]

Measurements at ∼400 campaign-style GPS points and another 14 continuously recording stations in central Asia define variations in their velocities both along and across the Kyrgyz and neighboring parts of Tien Shan. They show that at the longitude of Kyrgyzstan the Tarim Basin converges with Eurasia at 20 ± 2 mm/yr, nearly two thirds of the total convergence rate between India and Eurasia at this longitude. This high rate suggests that the Tien Shan has grown into a major mountain range only late in the evolution of the India-Eurasia collision. Most of the convergence between Tarim and Eurasia within the upper crust of the Tien Shan presumably occurs by slip on faults on the edges of and within the belt, but 1-3 mm/yr of convergence is absorbed farther north, at the Dzungarian Alatau and at a lower rate with the Kazakh platform to the west. The Tarim Basin is thrust beneath the Tien Shan at ∼4-7 mm/yr. With respect to Eurasia, the Ferghana Valley rotates counterclockwise at ∼0.7° Myr−1 about an axis at the southwest end of the valley. Thus, GPS data place a bound of ∼4 mm/yr on the rate of crustal shortening across the Chatkal and neighboring ranges on the northwest margin of the Ferghana Valley, and they limit the present-day slip rate on the right-lateral Talas-Ferghana fault to less than ∼2 mm/yr. GPS measurements corroborate geologic evidence indicating that the northern margin of the Pamir overthrusts the Alay Valley and require a rate of at least 10 and possibly 15 mm/yr. [ABSTRACT FROM AUTHOR]

The distribution of oceanic domains and continental blocks in Central Anatolia remains a challenge in understanding the Alpine geodynamic evolution of the Tethys realm. The consumption of a Neotethys oceanic branch at the Mesozoic-Cenozoic boundary welded the Central Anatolian Crystalline Complex in central Turkey and the Anatolide-Tauride Block in western Turkey, with the northerly Eurasian margin. Whether those two regions constituted a single or two distinct continental masses is still matter of debate. High-pressure metamorphism has been locally evidenced in the Afyon Zone, which was, however, defined as a greenschist-facies metamorphic zone of the Anatolide-Tauride Block. Since the Afyon Zone composes a metamorphic equivalent of a continental margin exposed far south of the Izmir-Ankara suture zone, this encouraged us to reevaluate its metamorphic evolution in order to better understand the relation between western and central Turkey. Our investigations reveal that the high-pressure minerals Fe-Mg-carpholite and glaucophane are present in the entire Afyon Zone, which we reconsider as a blueschist-facies zone. We additionally present a tectonic reconstruction, stripping off the postcollisional tectonics. It reveals that today's bending of the high-pressure belt is consistent with an Eocene collision of the Anatolide-Tauride Block around the southern edge of the Central Anatolian Crystalline Complex. We argue that the Central Anatolian Crystalline Complex and the Anatolide-Tauride Block were two distinct continental masses separated by a Neotethyan oceanic stripe, the closure of which engendered subduction-related metamorphism in the latter and arc volcanism and high-grade metamorphism in the former by late Cretaceous to early Cenozoic. [ABSTRACT FROM AUTHOR]

The Rand and Sierra de Salinas schists of southern California were underplated beneath the southern Sierra Nevada batholith and adjacent Mojave-Salinia region along a shallow segment of the subducting Farallon plate in Late Cretaceous time. Various mechanisms, including return flow, isostatically driven uplift, upper plate normal faulting, erosion, or some combination thereof, have been proposed for the exhumation of the schist. We supplement existing kinematic data with new vorticity and strain analysis to characterize deformation in the Rand and Sierra de Salinas schists. These data indicate that the schist was transported to the SSW from deep to shallow crustal levels along a mylonitic contact (the Rand fault and Salinas shear zone) with upper plate assemblages. Crystallographic preferred orientation patterns in deformed quartzites reveal a decreasing simple shear component with increasing structural depth, suggesting a pure shear dominated westward flow within the subduction channel and localized simple shear along the upper channel boundary. The resulting flow type within the channel is that of general shear extrusion. Integration of these observations with published geochronologic, thermochronometric, thermobarometric, and paleomagnetic studies reveals a temporal relationship between schist unroofing and upper crustal extension and rotation. We present a model whereby trench-directed channelized extrusion of the underplated schist triggered gravitational collapse and clockwise rotation of the upper plate. [ABSTRACT FROM AUTHOR]

Subsidence in foreland basins is modulated by the size of the flexural load, the elastic thickness of the foreland lithosphere, the nature of the sedimentary fill, and the rate of convergence. Basal 'forebulge unconformities' are well known from these basins, but here we focus on a major unconformity in the Himalayan foreland, which removed much of the Oligocene-lower Miocene. This is a critical time in the Himalaya because it spans the period of initial rapid exhumation of high-grade metamorphic rocks and the start of motion on the Main Central Thrust. We show that the synchronous timing of unconformity and rapid Greater Himalayan exhumation may be explained by the same trigger, enhanced erosion. We estimate that accelerating erosion between 24 and 20 Ma would have removed ∼1.5 km more rock from the Greater Himalaya than would have been the case had erosion remained at the slower Paleogene rates. During this time erosion must have temporarily exceeded rock uplift rates. By transferring rock from the Himalaya to the Indian Ocean the load is reduced and the Indian Plate is flexed less, so that the depth of the foreland basin shallows to a new equilibrium state. We use a flexural model to estimate that erosional unloading could have caused uplift of 400-500 m of the basin at the range front, extending 70-150 km into the basin. Intensification of the Asian summer monsoon around the Oligo-Miocene boundary (∼24 Ma) is the most likely trigger of the stronger erosion. Similar unconformities are seen at 15-16 Ma and in the Pleistocene also, linked to faster erosion at these times. [ABSTRACT FROM AUTHOR]

The western flank of the Central Andean Plateau is a crustal-scale monoclinal fold, expressed in the geomorphology and in the westward tilt of fore-arc basin strata. Data from three fore-arc basins quantify the magnitude and time of displacement of the plateau system relative to the fore arc. From 18°30′S to 22°S there is a single monocline strand. There, other authors documented ∼2000 m (±500 m) of early and middle Miocene structural relief growth across small-scale monoclines, and our data reveal 810 m (±640 m) of ∼11-5 Ma relief growth and 400 m (±170 m) relief growth since ∼5 Ma across a long-wavelength monoclinal fold limb. This structural relief growth since ∼11 Ma approximates the topographic relief growth between the fore arc and the Altiplano plateau. From 22°S to 24°S there are two subparallel long-wavelength monoclines. Structural relief on the east side of the fore arc increased by 2840 m (±2510 m) during ∼17-10 Ma and by 2320 m (±1050 m) since ∼10 Ma. Some part of this monoclinal limb rotation led to topographic uplift of the adjacent Puna plateau. Rotation across the western monocline could have increased the altitude of the fore-arc basins by <900 m since ∼6 Ma and may result from intense heating of the eastern margin of the cold and strong Atacama lithosphere block. Although the wavelengths of the monoclines vary along strike and through time, the monoclinal style of deformation dominated the uplift history of the eastern fore arc of the central Andes throughout the Neogene. [ABSTRACT FROM AUTHOR]

The Pamir plateau forms a prominent tectonic salient along the western end of the Tibet-Tarim margin. Despite its tectonic significance, relatively little is known about the timing of major Cenozoic tectonic events in the Pamir. Here we present new apatite and zircon (U/Th)-He ages, bulk rock geochemistry, and Al-in-hornblende barometry results from the Karakul graben, a prominent north-south oriented rift basin located ∼50 km south of the Main Pamir Thrust. Although cooling ages do not record the onset of extension, graben-bounding normal faults provide exposures of otherwise slowly eroding rocks which record two Cenozoic thermal events. Existing geochronology and new results suggest that granitic rocks in the Karakul region were shallowly emplaced, cooled very quickly through ∼300°C, and have experienced less than 10 km of exhumation since the late Triassic. A long period of relatively slow exhumation throughout much of the late Mesozoic and Cenozoic was punctuated by two periods of accelerated exhumation during the middle Eocene (∼50-40 Ma) and early Miocene (∼25-16 Ma). We interpret the first period of accelerated exhumation as a result of tectonic uplift and subsequent erosion due to the northward propagation of the India-Asia collision. We attribute the second period of rapid exhumation to a renewed phase of tectonism and plateau uplift in the Pamir, perhaps related to a break off event along the down-going Indian plate at ∼25 Ma or to the onset of slip along the nascent Karakoram fault. [ABSTRACT FROM AUTHOR]

Rarely are geologic records available to constrain the spatial and temporal evolution of thrust-fault growth as slip accumulates during repeated earthquake events. Here, we utilize multiple generations of dated and deformed fluvial terraces to explore two key aspects of the along-strike kinematic development of the Ostler fault zone in southern New Zealand over the past ∼100 k.y.: accumulation of fault slip through space and time and fixed-length thrust growth that results in patterns of drainage diversion suggestive of laterally propagating faults. Along the Ostler fault, surface deformation patterns revealed by topographic surveying of terrace profiles in nine transverse drainages define systematic variations in fault geometry and suggest deformation over both listric and planar thrust ramps. Kinematic modeling of folded terrace profiles and >100 fault-scarp surveys along major fault sections reveals remarkably similar slip distributions for multiple successions of geomorphic surfaces spanning ∼100 k.y. Spatially abrupt and temporally sustained displacement gradients across zones of fault section overlap suggest that either persistent barriers to fault propagation or interference between overlapping faults dominate the interactions of fault tips from the scale of individual scarps to the entire fault zone. Deformed terrace surfaces dated using optically stimulated luminescence and cosmogenic radionuclides indicate steady, maximum rates of fault slip of ∼1.9 mm/yr during the Late Quaternary. Slip data synthesized along the central Ostler fault zone imply that displacement accumulated at approximately constant fault lengths over the past ∼100 k.y. A northward temporal progression of abandoned wind gaps along this section thus reflects lateral tilting in response to amplification of displacement, rather than simple fault lengthening or lateral propagation. Oscillations of climate at ∼104-yr time scales modulate the formation and incision of geomorphic surfaces during successive glacial stages. Superimposed on apparently steadier rates of fault slip, such climate-dependent surfaces contribute to a pattern of progressive drainage deflection along the central Ostler fault zone that is largely independent of fault propagation. [ABSTRACT FROM AUTHOR]

New structural, paleomagnetic, and apatite (U-Th)/He results from the continental margin inboard of the Queen Charlotte fault (∼54°N) delineate patterns of brittle faulting linked to transform development since ∼50 Ma. In the core of the orogen, ∼250 km from the transform, north striking, dip-slip brittle faults and vertical axis rotation of large crustal domains occurred after ∼50 Ma and before intrusion of mafic dikes at 20 Ma. By 20 Ma, dextral faulting was active in the core of the orogen, but extension had migrated toward the transform, continuing there until <9 Ma. Local tilting in the core of the orogen is associated with glacially driven, post-4 Ma exhumation. Integration with previous results shows that post-50 Ma dextral and normal faulting affected a region ∼250 km inboard of the transform and ∼300 km along strike. Initially widespread, the zone of active extension narrowed and migrated toward the transform ∼25 Ma after initiation of the transform, while dextral faulting continued throughout the region. Differential amounts of post-50 Ma extension created oroclines at the southern and northern boundaries of the deformed region. This region approximately corresponds to continental crust that was highly extended just prior to transform initiation. Variation in Neogene crustal tilts weakens interpretations relying on uniform tilting to explain anomalous paleomagnetic inclinations of mid-Cretaceous plutons. Similarities to the Gulf of California suggest that development of a transform in continental crust is aided by previous crustal extension and that initially widespread extension narrows and moves toward the transform as the margin develops. [ABSTRACT FROM AUTHOR]

We document a crustal-scale structural model for the central Chile Andes based on seismicity and surface geology, which consists in a major east verging ramp-detachment structure connecting the subduction zone with the cordillera. The ramp rises from the subducting slab at ∼60 km depth to 15-20 km below the western edge of the cordillera, extending eastward as a 10 km depth flat detachment. This structure plays a fundamental role in the Andean orogenesis because most of the shortening has been accommodated by structures rooted in it and allows the distribution of crustal thickening in a 'simple shear deformation mode.' Indeed, despite shortening distribution being very asymmetric (∼16 km versus ∼70 km in the western and eastern side, respectively), the western side is higher and thicker than what is expected. Yield strength envelopes show strong rheological control on this structure. V p and V p/ V s variations in the upper mantle and in the deepest limit of the seismogenic interplate contact mark the intersection of the ramp with the slab, which coincides with the blueschist-eclogite transition. Therefore, subduction processes would control the depth where the major east verging structure may merge with the slab. Such a ramp-flat structure is observed in other parts of the Chilean margin; hence, it seems to be a first-order feature in the Andean subduction zone. This structure delimitates upward the rocks, transmitting part of the plate convergence stress from the plate interface, and controls mountain-building tectonics, thus playing a key role in the Andean orogeny. [ABSTRACT FROM AUTHOR]

The NW-SE trending, ∼800 km long, dextral Karakoram Shear Zone bounds southwest Tibet. We investigate an area immediately NW of the Pangong Lake where midcrustal rocks sections of the shear zone are exposed. Here, the dominant shear zone is characterized by dextral mylonitic rocks sheared at amphibolite facies and partly retrogressed to greenschist facies. These rocks define a kilometric, SE plunging inclined-to-recumbent fold in the footwall of a north directed, oblique dextral thrust that exhumed anatectic rocks of the Pangong Range. Argon cooling ages reveal that the Pangong Range cooled from ∼700°C to 300°C between ∼18-15 and ∼10 Ma, contemporaneously with overthrusting. Toward the SE, closer to the Pangong Lake, this kilometric fold is rotated from its NW-SE trend to an E-W trend, and the sense of shear changes to sinistral, with a broadly north directed thrusting component. The documented structures contradict predictions of normal movement in this area derived from considerations of rigid block behavior of the crust and support the interpretation that the system records dextral transpression. Thrusting and exhumation of the deeper and hot rocks exposed in the Pangong Range, folding of the thrust footwall, and the development of a sinistral E-W trending shear zone are all compatible with transpression caused by a northward push by a rigid indenter such as the Ladakh Batholith. [ABSTRACT FROM AUTHOR]

The elevation history of Earth's surface is key to understanding the geodynamic processes responsible for the rise of plateaus. We investigate the timing of Colorado Plateau uplift by estimating depositional temperatures of Tertiary lake sediments that blanket the plateau interior and adjacent lowlands using carbonate clumped isotope paleothermometry (a measure of the temperature-dependent enrichment of 13C-18O bonds in carbonates). Comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate and therefore assess the contribution of changes in elevation to the variations of surface temperature on the plateau. Analysis of modern lake calcite from 350 to 3300 m elevation in the southwestern United States reveals a lake water carbonate temperature (LCT) lapse rate of 4.2 ± 0.6°C/km. Analysis of Miocene deposits from 88 to 1900 m elevation in the Colorado River drainage suggests that the ancient LCT lapse rate was 4.1 ± 0.7°C/km, and temperatures were 7.7 ± 2.0°C warmer at any one elevation than predicted by the modern trend. The inferred cooling is plausible in light of Pliocene temperature estimates off the coast of California, and the consistency of lapse rates through time supports the interpretation that there has been little or no elevation change for any of the samples since 6 Ma. Together with previous paleorelief estimates from apatite (U-Th)/He data from the Grand Canyon, our results suggest most or all of the plateau's lithospheric buoyancy was acquired ∼80-60 Ma and do not support explanations that ascribe most plateau uplift to Oligocene or younger disposal of either the Farallon or North American mantle lithosphere. [ABSTRACT FROM AUTHOR]

The orogen-scale morphology of the central Andes, which are longitudinally symmetric at ∼19°S, correlates with the modern geometry of the subducting Nazca slab but is largely independent of local bedrock geology or precipitation. Crustal thickness, as measured by the cross-strike width of the orogen above 3000 m and the cross-sectional area of the crust, is not well correlated with observed magnitudes of upper crustal shortening. In our interpretation, the large-scale morphology is instead correlated with and controlled by lithospheric-scale processes and subduction dynamics. Using a semianalytic, three-dimensional Newtonian viscous flow model, we produce Andean-like topography and distribution of upper crustal shortening during subduction of an oceanic lithosphere eastward beneath the Andes provided that (1) the more steeply dipping slab segment beneath the central Andes is overlain by the weak lower or middle crust, (2) the flat slab subduction segments to the north and south of this zone are overlain by the strong middle and lower crust, and (3) the steeply dipping central slab segment is overlain by a narrow, centrally localized zone of increased crustal shortening. The resulting model orogen displays substantial orogen-parallel flow in the weak lower crust above the steep slab zone. Orogen-parallel flow does not penetrate into the regions of stronger lower crust above the flat slab segments, resulting in a broad, plateau-topped orogen above the central slab segment and narrow but high orogenic segments above the flat slab region. Redistribution of material through lower crust flow can account for the observed mismatch between crustal volume and upper crustal shortening in the central Andes and may explain young (<10 Ma) crustal thickening and surface uplift that has been argued for in some regions. [ABSTRACT FROM AUTHOR]

Estimates of paleoelevation potentially constrain geodynamic models of continental deformation and inform interpretations of landscape and climate evolution. One widely used, paleobotanical approach reconstructs paleoelevation from the difference in estimated atmospheric enthalpy between a known sea level and a targeted, coeval, elevated fossil floral site. Enthalpy is estimated using Climate-Leaf Analysis Multivariate Program (CLAMP) on 31 leaf size and shape variables that have been calibrated in living forests. Errors related to CLAMP are significantly greater than often reported, and there are many sources of large potential error related to this method that are either difficult to quantify or unquantifiable and are thus not documented. Here, we quantify one significant bias, toward underestimation of leaf area in the CLAMP data set (∼50%), that affects all CLAMP climate estimates, including enthalpy. Crucially, errors in paleoelevation when the leaf size bias is included are in the range of ±2 km or more, at least 2 times the previous estimates, and exceeding the plausible paleoelevations of many fossil sites. Previously published paleoelevations derived from this technique are unlikely to be accurate either in magnitude or in estimated error. [ABSTRACT FROM AUTHOR]

Five years of continuously recording GPS observations in the Kingdom of Saudi Arabia together with new continuous and survey-mode GPS observations broadly distributed across the Arabian Peninsula provide the basis for substantially improved estimates of present-day motion and internal deformation of the Arabian plate. We derive the following relative, geodetic Euler vectors (latitude (°N), longitude (°E), rate (°/Myr, counterclockwise)) for Arabia-Nubia (31.7 ± 0.2, 24.6 ± 0.3, 0.37 ± 0.01), Arabia-Somalia (22.0 ± 0.5, 26.2 ± 0.5, 0.40 ± 0.01), Arabia-India (18.0 ± 3.8, 87.6 ± 3.3, 0.07 ± 0.01), Arabia-Sinai (35.7 ± 0.8, 17.1 ± 5.0, 0.15 ± 0.04), and Arabia-Eurasia (27.5 ± 0.1, 17.6 ± 0.3, 0.404 ± 0.004). We use these Euler vectors to estimate present-day stability of the Arabian plate, the rate and direction of extension across the Red Sea and Gulf of Aden, and slip rates along the southern Dead Sea fault south of the Lebanon restraining bend (4.5-4.7 ± 0.2 mm/yr, left lateral; 0.8-1.1 ± 0.3 mm/yr extension) and the Owens fracture zone (3.2-2.5 ± 0.5 mm/yr, right lateral, increasing from north to south; 1-2 mm/yr extension). On a broad scale, the Arabian plate has no resolvable internal deformation (weighted root mean square of residual motions for Arabia equals 0.6 mm/yr), although there is marginally significant evidence for N-S shortening in the Palmyride Mountains, Syria at ≤ 1.5 mm/yr. We show that present-day Arabia plate motion with respect to Eurasia is consistent within uncertainties (i.e., ±10%) with plate tectonic estimates since the early Miocene when Arabia separated from Nubia. We estimate the time of Red Sea and Gulf of Aden rifting from present-day Arabia motion, plate tectonic evidence for a 70% increase in Arabia-Nubia relative motion at 13 Ma, and the width of the Red Sea and Gulf of Aden and find that rifting initiated roughly simultaneously (±2.2 Myr) along the strike of the Red Sea from the Gulf of Suez to the Afar Triple Junction, as well as along the West Gulf of Aden at 24 ± 2.2 Ma. Based on the present kinematics, we hypothesize that the negative buoyancy of the subducted ocean lithosphere beneath the Makran and the Zagros fold-thrust belt is the principle driver of Arabia-Eurasia convergence and that resisting forces associated with Arabia-Eurasia continental collision have had little impact on plate motion. [ABSTRACT FROM AUTHOR]

We use digital elevation models and satellite imagery data completed with field observations to develop an integrated morphotectonic analysis of the anomalous topography of the Central Cordillera of Patagonia between 46°S and 48°S, in a region overlying subducted segments of the Chile Spreading Ridge. This region shows a number of peculiar features, not expected in a normal subduction-related belt located away from a buried spreading center. First, it is characterized by overall short-wavelength topography and highly contrasted reliefs, typical of deeply incised young mountain belts, but surprisingly, also by an average very low elevation of ∼900 m. Second, the Cordillera lacks central high reliefs; instead, there is a central, depressed domain with average low slope gradients including the deepest point of the study area (300 m below sea level in the bottom of Lake General Carrera/Buenos Aires). This depressed area is flanked by western and eastern regions of higher elevation having opposite general slope dips. To the east, the central Patagonian Cordillera is now separated from the flat plains of the Pampean domain (representing its former piedmont) and several elevated basaltic plateaus (mesetas) by 160°N-180°N trending morphotectonic corridors and the western border scarps of the mesetas. These scarps correspond to neotectonic features controlled by recent vertical faults, mostly active after 3 Ma. Remnants of a former peneplain, the Avellanos surface, are widespread within the entire Cordilleran region. From geological evidence, this peneplain formed between 15 and 4 Ma and was connected originally with the mesetas domain and now is dissected by these corridors. It is shown that a negative inversion related to extensional and strike-slip faulting occurred in the frontal region of the Cordillera at 3 Ma synchronously with the emplacement of magmatic products. Timing of the extensional deformation in central Patagonia is concomitant with the migration at depth of different segments of the South Chile Ridge, which entered the trench at 6 and 3 Ma, respectively, and the consequent opening of a slab window allows asthenospheric hot mantle to reach lithospheric regions. Finally, migration of segments of the Chile Spreading Ridge since 6 Ma triggered regional uplift of the Cordillera followed by limited extension in relation with increased thermal weakening of the crust. [ABSTRACT FROM AUTHOR]

The >20,000 km2 Athabasca granulite terrane is one of Earth's largest exposures of continental lower crust. The terrane is underlain by heterogeneous isobarically cooled orthogneisses termed the Mary batholith. A transect across the batholith documents early, penetrative subhorizontal to gently dipping gneissic foliation (S1). Kilometer- to meter-scale domains of S1 contain lineations (L1) defined by ribbons of recrystallized K-feldspar + plagioclase + quartz + amphibole ± orthopyroxene. L1 coincides with garnet aggregates, elongate mafic enclaves, and core-and-mantle structure in feldspar porphyroclasts. Lineations are coaxial with hinges of isoclinally folded layering (F1). L1 is interpreted as a composite mineral lineation with intersection and stretching components. Kinematics are uniformly top-to-the-ESE. Thermobarometry derived from synkinematic phases is compatible with granulite-grade (∼800°C) ductile lower crustal flow during D1 at ∼0.9 GPa (∼30 km paleodepths). Results from electron probe microanalyzer (EPMA) Th-U-total Pb monazite geochronology support Neoarchean (circa 2.60-2.55 Ga) garnet growth and melt-enhanced flow. Metamorphic reactions accompanying D1 strain were synkinematic, with preferential nucleation of high-Ca garnet and amphibole in the Na-rich mantles of recrystallized plagioclase porphyroclasts. Relatively H2O-poor and/or CO2-rich conditions during D1 are required by the preservation of fine-grained microstructures. Subhorizontal tectonites in the Mary batholith may represent an important field-based analog for lower crustal flow during orogenesis or large magnitude extension. The results illustrate the evolving strength of continental lower crust. Neoarchean subhorizontal flow of weak lower crust was followed by near-isobaric cooling and strengthening. Paleoproterozoic deformation events produced steep fabrics (S2), steeply dipping shear zones, and reactivation of S1, a record of strain localization and strain hardening in an isobarically cooled anisotropic medium. [ABSTRACT FROM AUTHOR]

The Transantarctic Mountains (TAM) define the western flank of the West Antarctic rift system. Cape Surprise, near the Shackleton Glacier in the central TAM, is the only location along the range's >3500 km length where upper Paleozoic Beacon Supergroup strata are down-faulted to near sea level. Previous studies have inferred a range front master normal fault accommodates extension and rock uplift across the TAM front in this region. The history of rock uplift is debated, suggested as early as Mesozoic, typically Cenozoic, or even Pliocene or younger. Structural observations, apatite fission track (AFT) thermochronology, and geomorphologic mapping undertaken within the TAM front east of the Shackleton Glacier indicate extension, faulting, and denudation was mostly late Eocene-late Oligocene and likely into the early Miocene. An exhumed AFT partial annealing zone is found at the coast and traced >50 km inland. The base of that exhumed partial annealing zone indicates denudation accelerated at ∼40 Ma near the coast and at 30-35 Ma on the inland side of the TAM front. Vertically offset AFT isochrones across the TAM front reveal a step-faulted architecture rather than a single master fault. The cumulative vertical offset of the 55 Ma isochrone is 2.3-2.7 km, compared to 2.4-2.6 km offset of Beacon strata, indicating that all significant normal faulting is Cenozoic, and not related to Mesozoic extension within the West Antarctic rift system. Denudation from <26 Ma to ∼14 Ma produced a locally preserved erosion surface within the TAM front. Erosion surface remnants indicate the TAM front has undergone minimal internal deformation and only 290-790 m of surface uplift along offshore faults since the middle Miocene. [ABSTRACT FROM AUTHOR]

We present new results on the long-term throw rates of active normal faults in the North Baikal Rift (NBR), eastern Siberia, based on a statistical analysis of triangular faceted scarps. Fault-bounded ridges in the NBR display typical morphologies with several contiguous facets separated by fault-perpendicular catchments. Over a range of 20 fault segments analyzed, triangular facet heights vary from ∼200 to >900 m. As fault scarps have been developing under similar long-term climatic conditions, we infer that the scatter in mean facet height arises from long-term differences in fault throw rate. We compare the morphology of NBR facets with results obtained in a previously published numerical model of facet growth. Using facet height as an input, model results provide estimates of the long-term fault throw rate. NBR throw rates vary between 0.2 and 1.2 mm yr−1. The throw rates are then compared with the cumulated throw, which has been constrained by geophysical and stratigraphic data in the basins. This provides an estimate of the age of fault and basin initiation. We show that the modern stage of basin development started circa 3 Myr ago, except for the North Baikal basin (∼8 Ma). Our results also suggest that a proportion of the observed throw is inherited from an earlier tectonic stage. [ABSTRACT FROM AUTHOR]

In this paper, a combined approach of geomorphic analyses, detailed geological mapping on SPOT 5 satellite images and field surveys, complemented by radiometric dating (40Ar/39Ar) allows proposing a new and consistent tectonic configuration for the northeastern Arabia-Eurasia collision zone. It favors a simple strike-slip faulting mechanism in NE Iran accommodating the northward motion of central Iran with respect to Eurasia between the Binalud and Kopeh Dagh mountains. Our results demonstrate that ∼2 mm/a (∼25%) of this northward motion has been transferred from the Binalud to the Kopeh Dagh through the Meshkan Transfer Zone since ∼5 Ma. The modern state of stress deduced from fault kinematics analyses shows N30°E trending maximum stress axis and confirms a dominant strike-slip faulting mechanism. Combining our geological data with other available data, we conclude that kinematics of deformation can be appropriately described by rigid block faulting in NE Iran; instead, the continuous deformation as it has been thought during the last 3 decades. [ABSTRACT FROM AUTHOR]

Though orogen-parallel shortening and vertical extension have dominated the tectonic evolution of the central Andes, a significant kinematic shift from horizontal contraction to extension appears to have occurred within the high Puna-Altiplano Plateau, with the establishment of extension oblique to the orogen since late Miocene time. We present data from the southern margin of the Puna Plateau, NW Argentina, where new normal faults have been documented in the Fiambalá, Punta Negra, and La Quebrada areas. The unifying characteristics of these areas are that young normal faults reactivate or crosscut older thrust and reverse faults. The relationship between the faults and the late Miocene-Pliocene Punaschotter conglomerate suggests that the extensional faulting must be younger than 3.5 to 7 Ma. Existing data are incomplete but indicate that similar horizontal extension has occurred in many regions throughout the Puna-Altiplano Plateau, while shortening continues along the plateau margins. Given the spatial and temporal distribution of this late Miocene to Pliocene kinematic shift, both lithospheric loss in the Puna Plateau and plateau-wide gravitational extensional spreading enhanced by slowing of plate convergence rate could be responsible. The young, disorganized, horizontal extension in the Andes today may be the precursor to more pronounced extension such as observed on the Tibetan Plateau since mid-Miocene time. [ABSTRACT FROM AUTHOR]

Slip rates of major active strike-slip faults within and around the Tibetan Plateau provide constraints for understanding the dynamics of continental deformation in general because large slip rates can be taken to imply localized deformation between rigid blocks and low slip rates on faults are more consistent with distributed deformation. Several major strike-slip faults have been studied during the last 3 decades. As one of important active strike-slip faults in and around the Tibetan Plateau, the slip rate of the Haiyuan fault has been discrepantly estimated to be high by proponents of 'escape tectonics' or low by others and GPS observations. To better constrain its slip rate and then to better understand the mechanics of intracontinental deformation, we try to more carefully consider offset geomorphic features and age constraints along the Haiyuan fault. In this paper, we select three sites where both upper and lower bounds of slip rate can be obtained. We find that slip rates are 4.2 ± 0.8 mm/yr at the Shaomayin, 4.5 ± 0.7 mm/yr at Gaowanzi, and 5.0 ± 2.5 mm/yr at Huangliangtan site. Combinations of these rates with those published previously yield an average slip rate of 4.5 ± 1.0 mm/yr on the Haiyuan fault. This rate agrees with the present-day slip rate of 4.3 ± 1.5 mm/yr measured by GPS, 4.2-8 mm/yr by interferometric synthetic aperture radar, and ∼5 mm/yr through paleoseismological studies. The temporal consistency suggests a steady state process of strain accumulation and release along the Haiyuan fault. The low slip rate suggests that the Haiyuan fault, similar to the Altyn Tagh fault, does not transfer a significant portion of the convergence between India and Asia out of India's path into Eurasia but merely redistributes crustal thickening. [ABSTRACT FROM AUTHOR]

We use field investigations, topographic profiles, and 10Be exposure dating to constrain the growth rate of the Yumu Shan, a thrust-bounded mountain range at the northeastern margin of Tibet. Wind gaps, fault scarps at the mountain front, and hanging paleocatchments indicate that the Yumu Shan is growing both laterally and vertically. Scarp profiles and 10Be ages yield rock uplift rates of ∼500 and ∼800 mm ka−1 for the eastern and central parts of the range, respectively. The fact that the rock uplift rate in the high center of the Yumu Shan exceeds catchment-wide 10Be denudation rates, which range from ∼180 to ∼280 mm ka−1, indicates that the mountain range continues to rise and has not yet reached a topographic steady state. Combining the total structural relief of the range with the rates of rock uplift and denudation suggests that the growth of the Yumu Shan started 3.7 ± 0.9 Ma ago. [ABSTRACT FROM AUTHOR]

Structural and thermochronologic studies of the western margin of the central Andean Plateau show changing styles of deformation through time that give insights into tectonic evolution. In southwest Peru, uplift of the plateau proceeded in several distinct phases. First, NW striking, NE dipping reverse faults accommodated uplift prior to ∼14-16 Ma. Subsequent uplift of the plateau relative to the piedmont (between the plateau and the Pacific Ocean) occurred between ∼14 and 2.2 Ma and was accommodated by NW striking, SW dipping normal faults and subparallel monoclinal folds. The youngest phase of uplift affected the piedmont region and the plateau margin as a coherent block. Although the uplift magnitude associated with phase 1 is unknown, phases 2 and 3 resulted in at least 2.4-3.0 km of uplift. Up to 1 km of this may have occurred during phase 3. Geodynamic processes occurring in both the continental interior and the subduction zone likely contributed to uplift. [ABSTRACT FROM AUTHOR]

Following the diachronous Cretaceous-Neogene onset of seafloor spreading in the northern Atlantic and Arctic oceans, the European passive margin and continental Europe underwent a generalized uplift. This long-wavelength Cenozoic uplift has been attributed either to mantle plumes and/or to the far-field compression in the Alps. We suggest an alternative mechanism or concause, where the asthenosphere depleted at the Mid-Atlantic Ridge was shifted relatively eastward beneath the continent because of the net rotation of the lithosphere. The partial melting at the oceanic ridge leaves the asthenosphere lighter. When migrating beneath the European continental lithosphere, the substitution of the older, denser mantle with the depleted, lighter asthenosphere should have generated an isostatic rebound and associated uplift of about 300-600 m. Dynamic topography exerted by the mantle flowing eastward could have enhanced the uplift process. [ABSTRACT FROM AUTHOR]

New thermochronometric data from the Eastern Cordillera of the Colombian Andes reveal diachronous exhumation associated with Cenozoic contractional deformation in this sector of the northern Andes. We present a comprehensive account of exhumation patterns along a 150-km-long, across-strike transect between ∼4° and 6°N by integrating 29 new apatite fission track (AFT) ages and 17 new zircon fission track (ZFT) ages with sparse published thermochronological data from this area. Our data reveal episodic eastward migration of the orogenic front at an average rate of 2.5-2.7 mm/a during the Late Cretaceous-Cenozoic. We identify three major stages of orogen propagation: (1) slow propagation (0.5-3.1 mm/a) until early Eocene; (2) rapid orogenic advance (4.0-18.0 mm/a) during middle-late Eocene, which accounts for ∼86% of the orogen's present width; and (3) slow orogen propagation (1.2-2.1 mm/a) from Oligocene to Holocene times. Our data demonstrate that in the course of changes in plate kinematics, the presence of inherited crustal anisotropies, such as the former rift-bounding faults of the Eastern Cordillera, favor a nonsystematic progression of foreland basin deformation through time by preferentially concentrating accommodation of slip and thrust loading along these zones of weakness. [ABSTRACT FROM AUTHOR]

This work analyzes the postmetamorphic evolution of the northwestern Alps thanks to a multiscale field geology study integrated by fission track analysis. It illustrates how the fission track method, constraining throws along major faults and age of mesoscale deformation, provides interpretation keys to detangle complex structural data sets. Results are discussed within the framework of the Alps-Apennines knot and give new insights on strain partitioning within transpressional orogenic belts. The axial NW Alps acted since the late Oligocene as an orogen-scale shear zone accommodating, in the Aosta Valley, dextral strike slip coeval with forward propagation of external thrusts. Within this transcurrent belt, right-lateral deformation was partitioned between the fast exhuming Western Block and the already unroofed Eastern Block. These blocks show contrasting structural characters. The former is cut by first-order longitudinal structures bounding major tectonostratigraphic units. The latter is fragmented by complex patterns of lower-order faults interpreted as subsidiary shears. The onset of mesoscale extension, widespread in the Eastern Block, is diachronous across the belt and migrated through time toward the European foreland. Transition from syncollisional shortening to orogen-scale transcurrence observed in the NW Alps corresponds to a regional strain field variation, documented in the mid-Oligocene all around the Alps-Apennines knot, which is possibly related to a change of the Adria trajectory relative to Europe. Since the late Oligocene, deformation associated with oblique plate convergence was partitioned between strike slip in the axial belt and thrusting in external areas. Most of the shortening was accommodated in the Helvetic chains (102 km). Deformation was limited elsewhere to an order of 101 km. [ABSTRACT FROM AUTHOR]

Reconstructions of the relative positions of the India and Eurasia plates, using recently revised histories of movement between India and Somalia and between North America and Eurasia and of the opening of the East African Rift, show that India's convergence rate with Eurasia slowed by more than 40% between 20 and 10 Ma. Much evidence suggests that beginning in that interval, the Tibetan Plateau grew outward rapidly and that radially oriented compressive strain in the area surrounding Tibet increased. An abrupt increase in the mean elevation of the plateau provides a simple explanation for all of these changes. Elementary calculations show that removal of mantle lithosphere from beneath Tibet, or from just part of it, would lead to both a modest increase in the mean elevation of the plateau of ∼1 km and a substantial change in the balance of forces per unit length applied to the India and Eurasia plates. [ABSTRACT FROM AUTHOR]

A marked contrast in strength (or viscosity) within a continuously deforming zone can lead to concentration of shear strain in the weaker material adjacent to the boundary between them, but localization comparable to the width of the Altyn Tagh shear zone requires an additional weakening process. During numerical experiments on a thin viscous sheet indented by a rigid object, a shear zone develops adjacent to a strong region mimicking the Tarim Basin, when the boundary between the weak and strong regions is oblique to the orientation of convergence. The width of this shear zone narrows with increased strain, and for comparable penetration by the indenter, the strain is more concentrated for larger values of n, the exponent that relates strain rate to a power of stress, and for smaller values of the Argand number Ar, a measure of buoyancy-induced stress relative to viscous stress. Increasing concentration of shear occurs as the indentation develops without weakening because of a change in material properties. Additional localization develops with the inclusion of strain-dependent weakening associated with, for instance, a temperature increase due to shear heating. For such localization to scale to the width of the Altyn Tagh fault zone of Tibet, the initial temperature near the Moho must be relatively low (∼600°C), and a large value of n (∼10) is required. This suggests that deformation there is described by a high-strength flow law, such as that proposed by Evans and Goetze (1979), in which the lithosphere would deform approximately plastically. [ABSTRACT FROM AUTHOR]

Apatite fission track analysis (AFTA) data are used to bring new light on the long-term and recent history of the Baikal rift region (Siberia). We describe the evolution of the topography along a NW-SE profile from the Siberian platform to the Barguzin range across the Baikal-southern Patom range and the northern termination of Lake Baikal. Our results show that the Baikal-Patom range started to form in the Early Carboniferous and was reactivated in Middle Jurassic-Lower Cretaceous times during the orogenic collapse of the Mongol-Okhotsk belt. Samples located in the Siberian platform recorded a continuous sedimentation up to the early Carboniferous but remain unaffected by later tectonic episodes. The Barguzin basin probably started to form as early as Late Cretaceous, suggesting a continuum of deformation between the postorogenic collapse and the opening of the Baikal Rift System (BRS). The initial driving mechanism for the opening of the BRS is thus independent from the India-Asia collision. AFTA show a late Miocene-early Pliocene increase in tectonic extension in the BRS that confirms previous thoughts and might reflect the first significant effect of the stress field generated by the India-Asia collision. [ABSTRACT FROM AUTHOR]

Long- and short-term strain variations along the Australian-Pacific plate boundary through the South Island of New Zealand, including a 300% increase in orogen width, coexistence of oblique thrusting on orthogonal structures, and variability in the locus of orogenic gold deposits, coincide with rheologically relevant geological variation. Our model investigates the consequences of thin, strong lower crust in the north and thick, weak lower crust in the south. Solution of the full 3-D mechanical equations reproduces the larger wavelength strain patterns of the orogen. A 3-D perturbation-based analytical solution leads to the identification of the sensitivity of displacement type to minor stress changes. Transition from boundary-normal thrusting to boundary-parallel thrusting occurs at the transition from strong to weak lower crust and is related to an increase in either τ yz (shear stress in the yz plane) or the ratio of the coordinate normal stresses, ( σ yy/ σ xx), where x and y are in the horizontal and z is vertical. Both mechanisms are compatible with the geologically dependent rheological variation employed in our model. [ABSTRACT FROM AUTHOR]

The Tian Shan Mountains constitute central Asia's longest and highest mountain range. Understanding their Cenozoic uplift history thus bears on mountain building processes in general, and on how deformation has occurred under the influence of the India-Asia collision in particular. In order to help decipher the uplift history of the Tian Shan, we collected 970 samples for magnetostratigraphic analysis along a 4571-m-thick section at the Jingou River (Xinjiang Province, China). Stepwise alternating field and thermal demagnetization isolate a linear magnetization component that is interpreted as primary. From this component, a magnetostratigraphic column composed of 67 polarity chrons are correlated with the reference geomagnetic polarity timescale between ∼1 Ma and ∼23.6 Ma, with some uncertainty below ∼21 Ma. This correlation places precise temporal control on the Neogene stratigraphy of the southern Junggar Basin and provides evidence for two significant stepwise increases in sediment accumulation rate at ∼16-15 Ma and ∼11-10 Ma. Rock magnetic parameters also undergo important changes at ∼16-15 Ma and ∼11-10 Ma that correlate with changes in sedimentary depositional environments. Together with previous work, we conclude that growth history of the modern Tian Shan Mountains includes two pulses of uplift and erosion at ∼16-15 Ma and ∼11-10 Ma. Middle to upper Tertiary rocks around the Tian Shan record very young (<∼5 Ma) counterclockwise paleomagnetic rotations, on the order of 15° to 20°, which are interpreted as because of strain partitioning with a component of sinistral shear that localized rotations in the piedmont. [ABSTRACT FROM AUTHOR]

The northern Sunda subduction zone, offshore Burma, and the associated Indo-Burmese Wedge mark the active eastern boundary of the Burma Platelet jammed between the India Plate and the Sunda Plate. The aim of this paper is to provide a structural and kinematics analysis of the Indo-Burmese Wedge based on seismic reflection, geodetic, and geological field data. We found out that the Indo-Burmese Wedge is the place of diffuse strain partitioning: right-lateral shearing in the innermost part and E-W shortening in the outermost part. In the outer wedge, thick-skinned deformation overprints thin-skinned deformation. It can be explained by the required preservation of the critical taper after the fast westward propagation of the outer wedge above a very efficient clayey décollement layer. The thick-skinned deformation is here characterized by major right-lateral strike-slip faults (the Kaladan Fault and the Chittagong Coastal Fault) and yet a typical internal deformation of the Indo-Burmese Wedge. We suggest that the westward migration of internal right-lateral shear deformation allows preservation of the strain-partitioning ratios between internal N-S trending right-lateral shearing and external E-W shortening. Some seismic lines show that the outer wedge deformation is not older than 2 Ma. Its propagation could have been enhanced by the large amount of sediments filling up the Sylhet flexural basin formed after the Pliocene tectonic uplift of the Shillong Plateau. [ABSTRACT FROM AUTHOR]

The Chile Triple Junction (CTJ) episodically migrated northward during the past 14 Ma from 54°S to its present-day position at 46°30′S, as different almost trench-parallel spreading segments entered in subduction. This migration resulted in the opening of an asthenospheric window below Patagonia, inducing a disturbance in the regional mantle convection. On the overriding plate, the middle Miocene time corresponds to a major change in the central Patagonian basin dynamics, with a transition from subsidence to generalized uplift. The detailed mapping and the morphological study of post-middle Miocene terraces evidence regional-scale trench-parallel tilt histories that differ depending on latitude. South of 46°30′S, the slopes of the fluvial terraces indicate a change from northward to southward tilt during late Miocene. Terraces younger than the early Pliocene do not show any trench-parallel tilt. North of 46°30′S, in contrast, only northward tilt, active until the Pleistocene, is recorded. We use a semianalytical model of dynamic topography which suggests that the northward migration of the Chile Triple Junction should be accompanied by a dynamic uplift of the central Patagonian basin. Uplift would cause both north directed and south directed tilt, north and south of the triple junction, respectively, with values of ∼0.1-0.2% 500 km east of the trench. Tilt measured in the southeastern part of the central Patagonian basin (∼0.1%) is comparable to values predicted using the semianalytical model. The dynamic topography associated to the Chile ridge subduction may have exerted a major control on the Neogene dynamics of Patagonia. [ABSTRACT FROM AUTHOR]

The pre-Mesozoic geodynamic evolution of SW Iberia has been investigated on the basis of detailed structural analysis, isotope dating, and petrologic study of high-pressure (HP) rocks, revealing the superposition of several tectonometamorphic events: (1) An HP event older than circa 358 Ma is recorded in basic rocks preserved inside marbles, which suggests subduction of a continental margin. The deformation associated with this stage is recorded by a refractory graphite fabric and noncoaxial mesoscopic structures found within the host metasediments. The sense of shear is top to south, revealing thrusting synthetic with subduction (underthrusting) to the north. (2) Recrystallization before circa 358 Ma is due to a regional-scale thermal episode and magmatism. (3) Noncoaxial deformation with top to north sense of shear in northward dipping large-scale shear zones is associated with pervasive hydration and metamorphic retrogression under mostly greenschist facies. This indicates exhumation by normal faulting in a detachment zone confined to the top to north and north dipping shear zones during postorogenic collapse soon after 358 Ma ago (inversion of earlier top to south thrusts). (4) Static recrystallization at circa 318 Ma is due to regional-scale granitic intrusions. [ABSTRACT FROM AUTHOR]

We examine the hypothesis that Pliocene exhumation of the external massifs in the central Alps is controlled by climatic change. New thermochronological data from the western Gastern-Aar massif are used to investigate the timing, extent, and reasons for Neogene exhumation. Our data reveal that exhumation was constant with 0.5 km/Ma over the last 10 Ma in the north. In the southern part, exhumation was of the same order until ∼3.5 Ma but then increased gradually toward the south to values of up to 1.2 km/Ma, resulting in overall northward tilting of the western Aar massif. We explain this accelerated exhumation in the south after ∼3.5 Ma mainly by tectonic denudation in the footwall of the Rhône-Simplon fault and discuss changes in deep crustal configuration, which may have triggered south directed normal faulting. We propose that the Rhône river was structurally trapped by the Rhône-Simplon normal fault zone, which additionally enhanced erosion in the southern section of the Aar massif. Climatic forcing may have an impact in the very late stage of exhumation due to Alpine glaciation in the late Pliocene. [ABSTRACT FROM AUTHOR]

We present results of a new model in which we couple a mechanical model to describe continental indentation in plan view with a landscape evolution model to describe drainage development. We apply the model to investigate aspects of the development of drainage systems, erosion, and exhumation in the India-Asia collision zone. It is shown that the orogen-scale distribution of erosion and exhumation can be well matched by the model. However, the elevation of the Tibetan Plateau and the steep topographic gradients at its margins are difficult to reproduce. They appear to require an additional cause of uplift. We show that some of the major observed river capture events can be reproduced by invoking such a late uplift in much of the orogen, except the region of the Sichuan Basin. This includes the inferred capture of the Yarlong-Tsangpo by the Brahmaputra and that of the Upper Yangtze by the Lower Yangtze (thereby deserting the Red River). [ABSTRACT FROM AUTHOR]

Using available information on the magnitude and age of tectonic shortening, as well as paleomagnetically determined tectonic rotations, we have run a series of 2-D map view restorations of the central Andes. Neogene shortening in the foreland belt induced only slight orogenic curvature of the central Andes. The constraints on the ages of the large observed fore-arc rotations (average of 37° counterclockwise in southern Peru and 29° clockwise in northern Chile) indicate that the Bolivian Orocline formed during the Eocene-Oligocene as a consequence of differential shortening focused in the Eastern Cordillera. To minimize local block rotations along the fore arc, the restoration that best fits the central Andean rotation pattern requires about 400 km of total (Paleogene plus Neogene) shortening near the Arica bend. This value corresponds to the upper bound of estimates of maximum horizontal shortening for the central Andes. Along-strike variations in horizontal shortening in the back arc induced bending of the continental margin, block rotations with fore-arc along-strike extension, and/or orogen-parallel transport of upper crustal material toward the symmetry axis of the orocline. [ABSTRACT FROM AUTHOR]

The southern Alborz mountains of northern Iran are an integral part of the Arabia/Eurasia collision zone. A magnetostratigraphic and rock magnetic investigation of the Eyvanekey stratigraphic section in the southern Alborz mountains reveals the spatiotemporal character of sedimentary facies migration in the Alborz foreland basin. The section constitutes three coarsening upward units (units 1, 2, and 3), comprising the Upper Red and Hezardarreh formations. Our data reveal that the Upper Red Formation was deposited between 17.5 and 7.5 Ma, while the depositional age of the top of the Hezardarreh Formation can be extrapolated to ∼6.2 Ma. Slow sediment accumulation rates correlate with sedimentary facies comprising prograding, coarsening-upward units. This is likely the result of intraforeland uplift (units 1 and 2) and basin inversion, probably associated with a growth syncline located in the proximal foreland (unit 3). In contrast, fine-grained strata at the bottom of each cycle are associated with faster sediment accumulation rates, testifying to enhanced flexural basin subsidence in the course of thrust loading. Progradation of coarse-grained facies also occurred during relatively fast sediment accumulation (top of unit 2), suggesting that the influx of coarse-grained sediment outpaced the storage capacity of the proximal foreland. Thus, despite an overall southward propagation of deformation into the southern Alborz foreland, the locus of active deformation must have migrated back and forth on a time scale of circa 0.7 to 2 Ma. [ABSTRACT FROM AUTHOR]