Rapid Surface Uplift Research Articles

Multiple sources of elevation change during and after the 2011–2012 Cordón Caulle, Chile eruption measured by satellite topographic time series

The 2011–2012 eruption at Cordón Caulle, Chile offers an exceptional opportunity to investigate topographic evolution of a laccolith, lava flows, and tephra during and after rhyolitic eruptions using satellite TanDEM-X and Plèiades data. We find distinct phases: rapid surface uplift from the laccolith and tephra (June–August 2011) and lava (June 2011–March 2012), followed by a reduction in the elevation of the laccolith and tephra (up to 19 m yr−1) until February 2013, and slower subsidence of all deposits until 2019 (the most recent data). The spatial distribution of subsidence-to-uplift ratios shows different volcanic and geomorphological processes occurring (degassing, cooling, crystallization, lateral movement, compaction, erosion). Pre-eruptive river channels showed elevation increases of up to 10–50 m due to tephra deposition, but this tephra was largely removed within three to four years. This research shows the potential of repeating high-resolution remote sensing elevation data to elucidate volcanic landscape evolution and yields insights into the co- and post-eruptive evolution of deposits.

Cenozoic crustal thickness variations and surface uplift in the southeastern Tibetan Plateau: Insights from detrital zircon trace elements in the Gongga Shan region

The timing and mechanism of uplift in the southeastern Tibet Plateau have long been subjects of debate. The Gongga Shan region, positioned at the convergence of the Songpan-Ganzi, Chuandian, and Yangtze blocks, serves as a crucial vantage point for unraveling the evolutionary history of the southeastern Tibet Plateau. Nevertheless, the uplift history of the Gongga Shan region remains shrouded in uncertainty. By employing multivariate trace element ratios and reconstructing crustal thickness using zircon Eu/Eu*, our research has unveiled distinct periods of crustal thickening and thinning events. Within the time span of ∼240–160 Ma, a discernible thickening trend emerged from ∼35 to ∼45 km between ∼240 and ∼ 215 Ma, followed by a relatively stable phase from ∼215 to ∼170 Ma, and subsequently a decline from ∼170 to ∼160 Ma, reducing the thickness from ∼45 to ∼30 km. In the period from ∼55 to ∼5 Ma, an initial increase in thickness occurred from ∼30 to ∼60 km between ∼55 and ∼ 30 Ma, succeeded by an overall thinning from ∼60 to ∼35 km between ∼30 and ∼ 10 Ma. Moreover, based on our reconstructed crustal thickness data, we have traced the paleo-elevation changes in the Gongga Shan region from the Cenozoic to the present, revealing a fluctuation from ∼0.5 to ∼4.5 km. We attribute the Triassic-Jurassic crustal thickening and subsequent thinning to the Triassic orogeny and post-collision extension following the closure of the Paleo-Tethys Ocean. Our findings further suggest that during the Eocene-Oligocene period, the Gongga Shan region experienced significant crustal thickening and surface uplift, indicative of intense compression. This phenomenon likely resulted from the northeast-directed compression of the Indian-Eurasian plate, causing substantial crustal shortening and thickening in specific areas of the southeastern Tibet Plateau, leading to rapid surface uplift. Subsequently, during the Oligocene-Miocene, the detachment and subsidence of the lithospheric mantle triggered rapid crustal thinning in the Gongga Shan region. This phase was accompanied by relatively stable and slight surface uplift, signifying a shift in the plateau uplift mode of the southeastern Tibet Plateau from compression to lateral extrusion.

Miocene surface uplift and orogenic evolution of the southern Andean Plateau (central Puna), northwestern Argentina

We present stable hydrogen-isotope analyses of volcanic glass ([Formula: see text]Dg) and radiometric ages (U-Pb zircon, U-Th calcite, AMS14C) from deformed sedimentary deposits in the vicinity of the intermontane Pocitos Basin in the central Puna of the Andean Plateau at about 24.5°S. Our results demonstrate 2-km surface uplift since the middle to late Miocene and protracted shortening that persists until the present day, while other sectors of the Puna show evidence for tectonically neutral and/or extensional settings. These findings are at odds with previous studies suggesting near-modern elevations (4 km) of the Puna Plateau since the late Eocene and formation of the intermontane Miocene Arizaro-Pocitos Basin associated with gravitational foundering of a dense lithosphere. Geophysical and geochemical data support the removal of continental lithosphere beneath the Puna, but the timing and mechanisms by which this removal occurs have remained controversial. We hypothesize that intermontane basin formation in the central Puna is the result of crustal shortening since about 20 Ma, followed by rapid surface uplift, likely related to lithospheric delamination.

Rapid topographic growth of the Taiwan orogen since ~1.3–1.5 Ma

We present the first paleotopographic reconstruction of Taiwan by measuring the hydrogen isotope composition of leaf waxes (δ 2 H n C29 ) preserved in 3-Ma and younger sediments of the southern Coastal Range. Plant leaf waxes record the δ 2 H of precipitation during formation, which is related to elevation. Leaf waxes produced across the orogen are transported and deposited in adjacent sedimentary basins, providing deep-time records of the source elevation of detrital organic matter. δ 2 H n C29 exported from the southern Taiwan orogen decreased by more than 40‰ since ~1.3–1.5 Ma, indicating an increase of >2 kilometers in the organic source elevation. The increase in organic source elevation is best explained by rapid surface uplift of the southern Central Range at around ~1.3–1.5 Ma and indicates that this part of the orogen was characterized by maximum elevations of at least 3 km at this time. Further increase in organic source elevation from ~0.85 to ~0.3 Ma indicates continued topographic growth to modern elevations.

Andean evolution, orogenic deformation and uplift of the Western Cordillera and Altiplano of southern Peru, northern Bolivia and Chile: Eocene-Oligocene lithospheric delamination

Reappraisal of Andean evolution in southern Peru, northern Bolivia and northern Chile provides support for models of orogenic cyclicity in which Andean crustal shortening in the Western Cordillera led to Eocene-Oligocene lithospheric delamination which triggered a renewed pulse of Andean uplift. The sedimentary fill of the Arequipa "rift" back-arc basin (Rhaetian-Neocomian) was controlled by two major graben-bounding fault systems: the Condoroma-Caylloma and Cincha-Lluta-Incapuquio; as well as the Cusco-Lagunillas fault system separating the back-arc region from the Cusco-Puno high. These thinned cortical inherited structures, were the most favourable places to undergo a positive tectonic inversion at the beginning of Andean compression (Albian), and then during Late Cretaceous-Paleocene shortening, they continued to develop as east-vergent crustal decollements which allowed crustal doubling and Western Cordillera thickening. The crustal thickening of >45 km took place along the Condoroma-Caylloma inverted graben where the lower crust, which was probably enriched in basalts, was subjected to high-pressure metamorphism leading to eclogitization, and became denser than the underlying mantle lithosphere and therefore delamination occurred. The subsequent asthenospheric upwelling led to lithospheric thinning, asthenospheric mantle magmatism of the first stage of Andahuaylas-Yauri batholith emplacement (∼48-43 Ma), which crystallized under temperatures of 1200–700 °C and pressures of 1.0–0.5 GPa (>40-30 km deep). This process was followed by the rapid surface uplift of the Western Cordillera that reached 3.1 km and fed the Kayra and Lower Moquegua basins, located on the Altiplano and in the forearc respectively. The delamination process was still active during 43–30 Ma, with second-stage magmatism of the Andahuaylas-Yauri batholith, emplaced continuously from deep mafic intrusions (40-30 km) to superficial porphyries (3 km). This indicates an important uplift of the Western Cordillera to 3.3 km, supported by mantle upwelling and the continuous flat-slab compression that prevented normal faults from developing, and rather produced the shortening of the delaminated crust. The Anta-Soncco foreland basins (43-30 Ma) of the Altiplano and Moquegua basin of the forearc, received the products of Cordilleran denudation at a rate of up to 700 m/My. The alkaline potassic magmatism (29–27 Ma) could represent episodes of post-delamination magmatism and the late stage of flat subduction.

Catastrophic craton destruction via wholesale lithosphere delamination

Abstract The nuclei of continents, manifested as cratons, are the most long-lived parts of Earth’s lithosphere. However, ancient cratons in some areas can be substantially destroyed through mechanisms that are not fully understood. We used experimentally calibrated geobarometers to calculate the equilibrium pressures of mafic magmas in the North China craton, which directly constrain the evolving depth of the lithosphere-asthenosphere boundary beneath the craton through time. We show that the lithospheric thickness of the eastern part of the craton decreased from ~200 km to ~35 km in the Early Cretaceous. This intense destruction took place within a short time interval of ~10 m.y., at least locally. Following this destruction, the lithosphere gradually rethickened and stabilized as the upwelling asthenosphere cooled and formed a juvenile lithosphere. We suggest that this catastrophic lithosphere thinning resulted from wholesale lithosphere delamination. As a consequence of this catastrophic loss of thick mantle roots, the eastern part of the North China craton may have undergone rapid crustal rebound and surface uplift, as recorded by the regional unconformities formed between 130 and 120 Ma in the destructed area.

Compositions and ages of Early Cretaceous volcanic and plutonic rocks in central Tibet: Insights into the magmatic and uplift response to slab breakoff

AbstractWe present new zircon U-Pb ages and Hf isotope compositions as well as whole-rock major- and trace-element geochemical and Sr-Nd isotopic data for silicic plutonic and volcanic rocks from the Duolong area of central Tibet. Combined with existing data, our new data indicate that these plutonic and volcanic rocks were formed in two stages ca. 120 Ma and ca. 110 Ma, respectively, in a postcollisional extensional setting that was triggered by slab breakoff. The similar geochemical compositions of granitoids and rhyolites, combined with their close spatial and temporal relationships, suggest that they were both derived from juvenile crustal material within a single magmatic system. We propose that the two inferred crustal melting events in the Duolong area were caused by two episodes of deep mantle activity triggered by the transition of the plate subduction angle from steep to shallow in response to the ascent of buoyant continental lithosphere during slab breakoff. Furthermore, rapid surface uplift during the late Early Cretaceous caused by slab breakoff made an important contribution to the formation of the proto–Tibetan Plateau. This study provides new insights into postcollisional tectonomagmatism and plateau uplift in central Tibet triggered by slab breakoff. We propose more generally that tectonic uplift during postcollisional processes (i.e., slab breakoff and lithospheric delamination) is a major contributor to plateau uplift in collision zones.

Method for Unloading Zonation Based on Strain per Unit Crack: Case Study of a Large-Scale Rocky Slope on the Qinghai–Tibet Plateau

Distribution of unloading zones determines stability of slopes, and the unloading of a large-scale rocky slope formed by rapid river erosion and surface uplift on the Qinghai–Tibet Plateau is particularly severe. Generally, unloading assessment relies on traditional methods, which are mainly related to phenomena. However, unloading is a process of deformation and failure regarding the rock mass. Based on deformation and failure, strain rate and crack rate established through theoretical analysis can measure the relationship between accumulative width of open cracks and unloading deformation and the relationship between accumulative number of cracks and unloading failure, respectively. Thus, a method that combines strain rate and crack rate, namely strain per unit crack (i.e., SPUC), is proposed. The SPUC was applied to assess the unloading zones of a large-scale rocky slope on the Qinghai–Tibet Plateau. The results show that the SPUC curve regularly varied and can be easily divided into three parts. Strong and weak unloading zones can be recognized from the SPUC curve. The reasonability of SPUC in the unloading zones assessment was confirmed by comparing and verifying with traditional methods. We found that SPUC has good universality and can compensate for the defect of using strain rate or crack rate to assess unloading zones.

Paleocene–Miocene topographic and tectonic evolution of the northern central Andean plateau, southern Peru

The Paleocene–Miocene sedimentary successions along the Western Cordillera – Altiplano Plateau margin in southern Peru record the growth history of the northern Altiplano Plateau and the development of the foreland basin system. We evaluate the paleoelevation history of the northern Altiplano Plateau for the period of primary upper crustal shortening (i.e., Paleocene–Miocene) to determine the amount of shortening-related surface uplift. We provide new apatite fission-track and tuff zircon U–Pb ages to add to the existing age models of the strata. We further calculate the first-order approximation of paleoelevations of these formations from paleo-meteoric water δ18Omw values reconstructed from authigenic carbonate δ18Oc. The calculations show that surface elevations increased by more than 1 km along with the basin development from backbulge and foredeep to wedge-top and hinterland basins. The calculated paleoelevation of 1.8–2.4 km at the end of contractional deformation during the late Miocene indicates that a rapid surface uplift of more than 1.5 km is required to attain the modern high elevations. It is further inferred that this post-late Miocene surface uplift was probably associated with the lower crustal flow and ensuing convective removal of lower lithosphere materials.

The Influence of Magma Storage and Ascent Conditions on Laguna del Maule Rhyolite Eruptions

AbstractThe scarcity of historical rhyolite eruptions means that volcanological and petrological studies of past eruptions are a key tool for assessing the potential for future hazardous activity and improving interpretations of unrest signals. For the last 18 ky, the Laguna del Maule (LdM) volcanic complex in Chile has erupted primarily rhyolites but with differing magma compositions, eruption styles and eruptive volumes. Rapid surface uplift and episodic seismic activity at LdM over the last two decades has emphasized the need to understand both the recent evolution of the magmatic system and the most likely future eruption scenarios. Using mineral composition, geothermobarometry and MELTS modeling, we assess the influence of the magma storage and ascent conditions on the magnitude and styles of three LdM rhyolites. Magmas of the first and largest Plinian-ignimbrite eruption (LdM: rdm; >17 km3 DRE) form a distinct mineral assemblage with An28–60 plagioclase, amphibole and quartz derived from a magma plumbing system over a large pressure range (90–350 MPa). We suggest that the rdm eruption was triggered by magma recharge and overpressure within a ~ 90 MPa magma chamber of high-silica (>76.5 wt.% SiO2) rhyolitic melt. The rdm eruption appears to have reset the LdM storage conditions, such that subsequent rhyolite eruptions have been smaller (<4 km3 DRE), involved less evolved melt (<75.8 wt.% SiO2) and produced (sub)Plinian-effusive eruption sequences. Of these, we have studied the earliest (Los Espejos: rle) and the most recent (Las Nieblas: rln). Both have mineral assemblages with An20–34 plagioclase and biotite formed in water-saturated crystal-poor rhyolite batches over limited pressure ranges (ΔP ~ 50 MPa) within a rhyodacitic mush reservoir. We suggest that rle and rln were triggered by injection of water-rich magma and volatile exsolution; the transition to effusive behavior occurred because of changes in magma temperature (rle) or magma decompression rate (rln). Similarities in the limited pressure range and high volatile content inferred for the current low-density magma body with the petrologically determined source conditions of magmas that fed past subplinian-effusive eruptions suggest that the next LdM eruption will be similar.

Changes in Plate Motions Caused by Increases in Gravitational Potential Energy of Mountain Belts

AbstractReconstructions of motions of the Nazca, South American, and Indian plates record short‐duration (≲10 Myr) variations in angular velocity, which enable a vector‐based test of the hypothesis that mountain uplift can cause changes in plate motion. Reductions in velocity of Nazca and South America between ∼12 and 6 Ma coincide with a phase of rapid surface uplift in the Central Andes. Decrease in the rate of India's convergence with Eurasia between ∼20 and 10 Ma corresponds to an increase in gravitational potential energy per unit area (GPE) within Tibet, marked by a transition from crustal thickening to thinning. The vectorial test shows that, in each case, the only change in driving force capable of balancing the change in basal drag is an increased resistance along the convergent boundary to the plate. Changes in GPE associated with mountain uplift provide a calibration for basal drags on plates. Basal tractions of ∼0.1–1 MPa provide resisting forces comparable in magnitude to driving forces from GPE variation in ocean lithosphere. The rapid change in motion of the Indian plate between about 48 and 41 Ma is explained by the juxtaposition of the Indian continent against the Andean‐type margin of the Transhimalaya and reduction in driving force due to loss of the slab. The net slab driving force lost was ∼2–4 TN m−1, in agreement with previous studies suggesting that forces resisting slabs' penetration into the mantle largely offset their negative buoyancy.

Three‐Dimensional Electrical Structure and Magma System of the Monogenetic Longgang Volcanic Field, Northeast China, Inferred From Broadband Magnetotelluric Data

AbstractThe Longgang volcanic field (LVF) is one of the largest intraplate monogenetic volcanic regions in China, and eruption lasted from the early Pleistocene to the Holocene. Previous research shows that the LVF is not only experiencing rapid surface uplift but also significant seismic activity. The magmatic system under the LVF poses a hazard of potential eruption. The three‐dimensional electrical resistivity model developed by magnetotelluric data shows that the upper crust of the LVF and the surrounding areas hosts a high‐resistivity body composed of volcanic rocks produced by massive eruptions during past volcanic episodes. There are two main high‐conductivity structures below the depth of 10 km in the southwest and northeast of the LVF. The two structures merge in the lower crust and extend to the mantle. We interpret these high‐conductivity structures to be magmatic channels (the resistivity of C1 is 20–50 and C2 is 5–20 Ωm). Magmatic channel upwelling along the C1 may have caused the eruption of the Jinlongdingzi volcano 1,700 years ago. The C2 magmatic channel in the northeast of the LVF is larger and lower resistivity than C1. The modern surface uplift and seismicity in the LVF is a result of upwelling and intrusion along C2 magmatic channel. The Hunjiang fault passing through the LVF may also influence the upwelling of material along the C2 magmatic channel, posing a hazard of future eruption in the LVF. The high‐conductivity structures in the LVF pass through the Moho and extend to the upper mantle and are connected from the top to bottom. Combined with geochemical data, we speculate that the magmatic system in the LVF may directly come from the upper mantle and the magma has experienced rapid ascent with limited crustal internal evolution.

Lateritic processes in Madagascar and the link with agricultural and socioeconomic conditions

Madagascar hosts a youthful landscape atop old bedrock geology. Observed rapid surface uplift – possibly a consequence of sub-plate mantle plume activity – does not fit the concept of “The Red Island”, i.e. thick piles of laterite, formed by slow chemical weathering that requires prolonged periods of tectonic quiescence. Here, we document the results of a three-year field campaign in which we sought to interrogate and decouple the climatic and tectonic drivers behind laterite formation, and establish a tentative link to agricultural productivity, which may reinforce local levels of poverty. We installed 45 rain gauges and merged their data with a satellite precipitation product to develop a new high-resolution climatology. We also collected 11 sediment samples from which we established 10Be-derived erosion rates; and measured laterite/saprolite thickness at 60 localities. The thickest lateritic profiles coincide with a narrow band of annual rainfall, suggesting that laterite evolution processes co-evolved with climate changes. Laterite thickness correlates negatively with erosion rate, and strongly positively with the headcount index of poverty. In the absence of agricultural technology, we propose a direct link between the local prevalence of lateritic soil and poor agricultural productivity. We also suggest that the spatial distribution of uplift/erosion and precipitation governs the distribution and thickness of laterite. Uplift and erosion rates vary dramatically over small distances, restricting the development of thick laterite to two small patches that straddle the central Hauts Plateaux.

Rapid surface uplift and crustal flow in\xa0the Central Andes (southern Peru) controlled by lithospheric drip dynamics

The high flux magmatism, crustal shortening/extension and plateau formation in Cordilleran orogenic systems have been explained by removal of lithosphere (lower crust and the sub-arc mantle lithosphere) that develops beneath the magmatic arc and hinterland regions. However, the primary role of this process driving surface uplift, and crustal deformation is not well understood. Here, reconciling geodynamic model predictions with lithospheric structure and paleoelevation estimates, we suggest that viscous drip-type lithospheric removal from beneath the Central (Peruvian) Andes can explain several tectonic features: (1) “double humped” shaped/axisymmetric topographic profile and rapid surface rise (up to 1.2 km in ~ 4.31 Myrs); (2) thicker crust associated with the lower surface elevation of the Altiplano plateau (Lake Titicaca region) (negative residual topography) and higher topography and thinner crust of Western and Eastern Cordilleras (positive residual topography); and (3) faster wave speed (colder)/sub-Moho anomaly underlying the Altiplano, surrounded by slower speed anomalies on both western arc-forearc areas and parts of the eastern Cordillera and Sub-Andes. Our results emphasize the important role of lithospheric drip and associated mantle dynamics in the transient evolution of Andean orogeny controlling surface uplift and crustal flow and thickening.

Rift Focusing and Magmatism During Late‐Stage Rifting in Afar

AbstractProcesses that facilitate the transition between continental rifting and sea‐floor spreading remain unclear. Variations in the spatial distribution of extension and magmatism through Afar and into the Red Sea are indicative of temporal evolution of the rifting process. We develop a time series of Sentinel‐1 interferometric synthetic aperture radar (InSAR) observations of ground deformation covering the whole Afar rift zone from 2014 to 2019, to study the distribution of extension. By incorporating Global Navigation Satellite System observations, we resolve 3D average velocities in the vertical, rift‐perpendicular, and rift‐parallel directions. Results show the spatial distribution of long‐wavelength deformation over the rift zone, as well as deformation at individual volcanic centers, including Dallol, Nabro, and Erta ’Ale. We find that in northern and central Afar, the majority of extension is accommodated close to the rift axis (15–30 km). In southern Afar, near the Nubia‐Arabia‐Somalia triple junction, amagmatic extension is distributed over 80–160 km, which may indicate an increase in rift focusing with rift maturity. We also observe rapid surface uplift and rift‐perpendicular extension at the Dabbahu‐Manda‐Hararo rift segment with velocities of 33 4 mm/yr and 37 4 mm/yr respectively. These are higher than the background extension rate of 18–20 mm/yr, but have decreased by 55%–70% since 2006–2010. The data suggests that this is due to an ongoing long‐lived response to the 2005–2010 rifting episode, with potential continued processes below the rift segment including a lower‐crustal viscous response and magma movement. Continued observations of surface deformation provide key constraints on tectono‐magmatic processes involved in rift development.

Thermal Constraints on the Longevity, Depth, and Vertical Extent of Magmatic Systems

AbstractMagmatic regions are typically viewed as vertical systems, with magma coming in the bottom and either freezing in the crust to form plutons or erupting to form volcanic rocks. Maintaining an upper‐crustal magmatic system for 105–106 Ma timescales requires establishing and maintaining a strong perturbation in the geotherm via continued input of magma from below. Thermal models indicate that establishing such a system requires the energy content of a vertical stack of magma tens of km thick, and maintaining the system requires continual supply of tens of km per million years. These rates of magma addition into the upper crust would require rapid crustal thickening and surface uplift, neither of which are observed at the required scale. Mass and energy balance issues are ameliorated if large magmatic systems are primarily lower‐crustal phenomena without long‐term upper‐crustal storage and if horizontal space‐making processes (extension), rather than vertical inflation, focus magmatism, and induce decompression melting.

The impact of earthquakes on orogen-scale exhumation

Abstract. Individual, large thrusting earthquakes can cause hundreds to thousands of years of exhumation in a geologically instantaneous moment through landslide generation. The bedrock landslides generated are important weathering agents through the conversion of bedrock into mobile regolith. Despite this, orogen-scale records of surface uplift and exhumation, whether sedimentary or geochemical, contain little to no evidence of individual large earthquakes. We examine how earthquakes and landslides influence exhumation and surface uplift rates with a zero-dimensional numerical model, supported by observations from the 2008 Mw 7.9 Wenchuan earthquake. We also simulate the concentration of cosmogenic radionuclides within the model domain, so we can examine the timescales over which earthquake-driven changes in exhumation can be measured. Our model uses empirically constrained relationships between seismic energy release, weathering, and landsliding volumes to show that large earthquakes generate the most surface uplift, despite causing lowering of the bedrock surface. Our model suggests that when earthquakes are the dominant rock uplift process in an orogen, rapid surface uplift can occur when regolith, which limits bedrock weathering, is preserved on the mountain range. After a large earthquake, there is a lowering in concentrations of 10Be in regolith leaving the orogen, but the concentrations return to the long-term average within 103 years. The timescale of the seismically induced cosmogenic nuclide concentration signal is shorter than the averaging time of most thermochronometers (>103 years). However, our model suggests that the short-term stochastic feedbacks between weathering and exhumation produce measurable increases in cosmogenically measured exhumation rates which can be linked to earthquakes.

Integrating Reservoir Dynamics, Crustal Stress, and Geophysical Observations of the Laguna del Maule Magmatic System by FEM Models and Data Assimilation

AbstractThe Laguna del Maule volcanic field is a large rhyolitic magmatic system in the Chilean Andes, which has exhibited frequent eruptions during the past 20 ka. Rapid surface uplift (>20 cm/year) has been observed since 2007 accompanied by localized earthquake swarms and microgravity changes, indicating the inflating magma reservoir may interact with a preexisting weak zone (i.e., Troncoso fault). In this investigation, we model the magma reservoir by data assimilation with Interferometric Synthetic Aperture Radar data. The reservoir geometry is comparable to the magma body inferred by seismic tomography, magnetotelluric, and gravity studies. The models also suggest that a weak zone, which has little effect on surface displacement, is important as a fluid transport channel to promote earthquakes and microgravity changes. In particular, concentrated dilatancy within the weak zone facilitates the microfracture formation during reservoir inflation. High‐pressure fluid can inject into the weak zone from the magma reservoir to trigger earthquakes and further migrate upward to create positive gravity changes by occupying unsaturated storages. The pore pressure will then decrease, halting the seismicity swarm until the next cycle. This “hydrofracturing” process may release some accumulated stress along the magma reservoir delaying an eventual eruption in turn. Besides, the resultant models are propagated forward in time to evaluate potential stress trajectories for future unrest.

Provenance and Drainage Evolution of the Red River Revealed by Pb Isotopic Analysis of Detrital K‐Feldspar

AbstractThe development of the Red River is closely related to the topographic changes in East Asia, but the evolution of this drainage system remains unclear. We determined Pb isotopic compositions of detrital K‐feldspars from the Yinggehai‐Song Hong Basin to understand the sedimentary provenance and to test models of drainage patterns in East Asia. The Pb isotopic data show that detritus in the northern basin was mainly derived from the Red River system since the late Oligocene, and that the Red River achieved its present state in the late Miocene (~10.5 Ma). The variable provenance over time suggests that the Red River was probably connected to the Middle Yangtze and Mekong Rivers before the Miocene, and lost these headwater areas in the middle and late Miocene, respectively. The drainage reorganization probably occurred in response to rapid surface uplift of eastern Tibetan Plateau.

Dating and morpho-stratigraphy of uplifted marine terraces in the Makran subduction zone (Iran)

Abstract. The western part of the Makran subduction zone (Iran) is currently experiencing active surface uplift, as attested by the presence of emerged marine terraces along the coast. To better understand the uplift recorded by these terraces, we investigated seven localities along the Iranian Makran and we performed radiocarbon, 230Th∕U and optically stimulated luminescence (OSL) dating of the layers of marine sediments deposited on top of the terraces. This enabled us to correlate the terraces regionally and to assign them to different Quaternary sea-level highstands. Our results show east–west variations in surface uplift rates mostly between 0.05 and 1.2 mm yr−1. We detected a region of anomalously high uplift rate, where two MIS 3 terraces are emerged, but we are uncertain how to interpret these results in a geologically coherent context. Although it is presently not clear whether the uplift of the terraces is linked to the occurrence of large megathrust earthquakes, our results highlight rapid surface uplift for a subduction zone context and heterogeneous accumulation of deformation in the overriding plate.