Continental Deformation Research Articles

Block Tectonics Across Western Tibet and Multi‐Millennial Recurrence of Great Earthquakes on the Karakax Fault

AbstractFault slip rates are critical to quantify continental deformation. Those along the Karakax fault (northwestern Altyn Tagh Fault: ATF) have been debated, even though it is one of Tibet's most outstanding active faults. At Taersa, using LiDAR measurements of terrace and fan riser offsets (∼6 to ∼500 m) and10Be/26Al dating of alluvial surfaces (<210 ka), we obtain a late Quaternary slip rate of ∼2.5 ± 0.5 mm/yr. This doubles the ∼2.6 ± 0.5 mm/yr rate time span found to the east and west. We interpret the ∼150 km‐long, free‐faced rupture along the fault to be that of theM∼ 7.6 event felt in Hotan in 1882. Characteristic slip (∼6 m) during four large earthquakes since ∼10 ka implies a ∼2500 ± 500 years return time. A ∼3 mm/yr rate is consistent with the ∼80 km offset of the Karakax river since uplift of the West Kunlun range and sediment deposition in the Tarim foreland accelerated, ∼24 Ma ago. The faster slip rate (∼10.5 mm/yr) on the central ATF matches the sum of those along the reactivated West Tibetan terrane boundaries (Karakax and Longmu‐Gozha Co faults) at the Uzatagh triple junction (∼36°N, 83°E). The abrupt termination and altitude drop of the Karakorum range where the Longmu Co and Karakorum faults meet (Angmong junction), also reflect triple junction kinematics. Such localized changes account for the rise of the Karakorum and West Kunlun ranges and support lithospheric block tectonics rather than diffusely distributed deformation.

Nature and structural heterogeneities of the lithosphere control the continental deformation in the northeastern and eastern Iranian plateau as revealed by shear-wave splitting observations

To investigate the intracontinental deformation during the early stage of Arabia-Eurasia collision, we studied the seismic anisotropy of the northeastern and eastern Iranian plateau via teleseismic shear-wave splitting analysis using a dense array of 65 stations. While the average delay times of ∼0.75 s for most stations suggest a moderate magnitude of anisotropy, small-scale variations in fast polarization directions (FPDs) indicate complex anisotropic features that may be related to the nature and structural heterogeneities of the lithosphere. The variations in FPDs are correlated with tectonic boundaries, including the northeastern plateau around the Paleo-Tethys suture and large-scale strike-slip faults bounding the Lut block in the eastern plateau. This suggests that the weak boundary zones may have significantly impacted the lithospheric deformation and anisotropy in response to the ongoing continental collision. Within the Lut block, the insignificant surface deformation suggests that the upper crust might not be noticeably affected by collision, and the fault-induced deformation mainly occurs at depth. The regional northeastward asthenospheric flow driven by the lithospheric thickness contrast across the collisional front could contribute but to different extents among areas. The asthenosphere-induced anisotropy has a magnitude (delay time) comparable to that from lithospheric deformation in central Lut, consistent with the two-layer model observed there. It dominates the seismic anisotropy in northern Lut where the thin lithosphere may contribute less but probably facilitates melt concentration on the top of the asthenosphere and thus enhances anisotropy through aligned melt-filled pores. The complex deformation pattern of the study region suggests that the intracontinental deformation may be controlled by not only the collisional processes at the plate boundary but also the nature and structural heterogeneities of the continental lithosphere itself, and the Arabia-Eurasia convergence may be more preferentially accommodated along tectonic boundaries and at depth.

Links between foreland rheology and the growth and evolution of a young mountain belt in New Guinea

SUMMARYWe have studied the active and recent tectonics of New Guinea, using earthquake source modelling, analysis of gravity anomalies, seismic reflection profiles, and thermal and mechanical models. Our aim is to investigate the behaviour and evolution of a young continental deformation belt, and to explore the effects of lateral variations in foreland rheology on the deformation. We find that along-strike gradients in the lithosphere thickness of the southern foreland have resulted in correlated changes in seismogenic thickness, likely due to the effects on the temperature structure of the crust. The resulting variation in the strength of the foreland means that in the east, the foreland is broken through on thrust faults, whereas in the west it is relatively intact. The lack of correlation between the elevation of the mountain belt and the seismogenic thickness of the foreland is likely to be due to the time taken to thicken the crust in the mountains following changes in the rheology of the underthrusting foreland, as the thinned passive margin of northern Australia is consumed. The along-strike variation in whether the force exerted between the mountains and the lowlands is able to break the foreland crust enables us to estimate the effective coefficient of friction on foreland faults to be in the range of 0.01–0.28. We use force-balance calculations to show that the recent tectonic re-organization in western New Guinea is likely to be due to the development of increasing curvature in the Banda Arc, and that the impingement of continental material on the subduction zone may explain the unusually low force it exerts on western New Guinea.

Origin of Three‐Dimensional Crustal Stress Over the Conterminous United States

AbstractThe crustal stress field determines continental deformation, including intraplate seismicity and topographic undulations. However, the sources of observed crustal stress patterns remain debated, with proposed mechanisms including lateral variations in gravitational potential energy and mantle flow, the latter of which comprises plate boundary interactions and basal tractions. Here, we present a series of geodynamic models that simultaneously consider lithospheric and mantle dynamics in the same physical framework, based on which we investigate the sources of crustal stress over the conterminous U.S. The data‐oriented nature of these models allows us to systematically explore the relative contributions of different dynamic sources to the three‐dimensional crustal stress field. These models reveal that forces from the plate boundaries play a dominant role in generating the directional pattern of long‐wavelength horizontal crustal stress across the conterminous U.S. In the central U.S., especially regions of high‐topography, lithospheric density heterogeneities locally modify the crustal stress field. Similarly, mantle flow beneath the North American plate modulates crustal stress orientation in the eastern U.S., particularly in regions with thin lithosphere. Furthermore, we find that a denser‐than‐ambient lithospheric mantle beneath the central and eastern U.S. is required to match the observed continental‐scale E‐W topographic contrast.

Late Cretaceous to Early Cenozoic extension in the Lower Yangtze region (East China) driven by Izanagi-Pacific plate subduction

The intracontinental response to plate-boundary and mantle processes, such as subduction or continental collisions, is an important topic in the Earth Sciences. Cretaceous to Cenozoic extension across East China is related to the interaction between the Asian continental lithosphere and western Pacific oceanic subduction system, and the associated intra-plate structures and basins provide robust temporal and spatial records of regional continental deformation. Although extension may primarily be driven by slab rollback and/or back-arc opening, mid-ocean-ridge subduction may have played a significant role in this process. To explore how the western Pacific subduction system impacts intracontinental deformation across East China, we use onshore-offshore geological records, geophysical survey observations, and time-dependent Pacific plate models to document the temporal and spatial variation of continental deformation in the Lower Yangtze region adjacent to the Yellow Sea. Based on our compilation, we argue that mantle-wedge convection, with coupled subduction of the trench-parallel Izanagi (Paleo-Pacific)-Pacific mid-ocean ridge, exerts a first-order control on extensional deformation in East China. Beneath eastern China, the mantle wedge history consists of two phases: (1) initial development of the mantle wedge as the Cretaceous Izanagi slab transitioned from flat-slab to steep subduction; and (2) mature mantle wedge convection during Cenozoic subduction of the Pacific plate. Relatively steep subduction of the progressively younging Izanagi plate during the Late Cretaceous-Paleocene resulted in strong mantle convection and coupled upper plate extension in eastern China. The collision of the Izanagi-Pacific plate ridge system with the trench resulted in a magmatic gap and short-lived uplift of eastern China. Following this, subduction of the rapidly aging Pacific plate resulted in a larger, but relatively weaker, mantle convection cell that drove weaker upper plate extension. The vigor of wedge mantle convection was modulated by the age of the Pacific subducting slab, which directly influenced the formation and evolution of intracontinental extension and sedimentary basins across eastern China. The pre-existing Triassic Tan-Lu fault zone has reactivated since the Late Eocene (ca. 40 Ma) due to westward subduction of the Pacific slab to partition strain between extensional dextral faulting in the Bohai Bay and Lower Yangtze basins, thereby diversifying Cenozoic lithospheric extensional deformation in eastern China. Several major Cenozoic extensional basins spatially correlate with the Triassic Sulu orogenic belt, which we interpret to suggest that these basins are underlain by the older and fragmented orogenic basement that acted as mechanically weak zones for localized high-magnitude extension. We present a comprehensive tectonic model that relates intracontinental deformation to subduction zone dynamics, particularly emphasizing the importance of the age of the subducting slab, thus providing a coherent geologic process to explain the deformation kinematics in eastern China and the diversity of observed Mesozoic-Cenozoic basin formation.

Structure of the northwestern North Anatolian Fault Zone imaged via teleseismic scattering tomography

SUMMARYInformation on fault zone structure is essential for our understanding of earthquake mechanics, continental deformation and seismic hazard. We use the scattered seismic wavefield to study the subsurface structure of the North Anatolian Fault Zone (NAFZ) in the region of the 1999 İzmit and Düzce ruptures using data from an 18-month dense deployment of seismometers with a nominal station spacing of 7 km. Using the forward- and back-scattered energy that follows the direct P-wave arrival from teleseismic earthquakes, we apply a scattered wave inversion approach and are able to resolve changes in lithospheric structure on a scale of 10 km or less in an area of about 130 km by 100 km across the NAFZ. We find several crustal interfaces that are laterally incoherent beneath the surface strands of the NAFZ and evidence for contrasting crustal structures either side of the NAFZ, consistent with the presence of juxtaposed crustal blocks and ancient suture zones. Although the two strands of the NAFZ in the study region strike roughly east–west, we detect strong variations in structure both north–south, across boundaries of the major blocks, and east–west, parallel to the strike of the NAFZ. The surface expression of the two strands of the NAFZ is coincident with changes on main interfaces and interface terminations throughout the crust and into the upper mantle in the tomographic sections. We show that a dense passive network of seismometers is able to capture information from the scattered seismic wavefield and, using a tomographic approach, to resolve the fine scale structure of crust and lithospheric mantle even in geologically complex regions. Our results show that major shear zones exist beneath the NAFZ throughout the crust and into the lithospheric mantle, suggesting a strong coupling of strain at these depths.

On the relationship between strain rate and seismicity in the India–Asia collision zone: implications for probabilistic seismic hazard

SUMMARYThe increasing density of geodetic measurements makes it possible to map surface strain rate in many zones of active tectonics with unprecedented spatial resolution. Here we show that the strain tensor rate calculated from GPS in the India–Asia collision zone represents well the strain released in earthquakes. This means that geodetic data in the India–Asia collision zone region can be extrapolated back in time to estimate strain buildup on active faults, or the kinematics of continental deformation. We infer that the geodetic strain rates can be assumed stationary through time on the timescale needed to build up the elastic strain released by larger earthquakes, and that they can be used to estimate the probability of triggering earthquakes. We show that the background seismicity rate correlates with the geodetic strain rate. A good fit is obtained assuming a linear relationship ($\dot{N} = \lambda \ \cdot \dot{\epsilon }$, where $\dot{N}$ is the density of the rate of Mw ≥ 4 earthquakes, $\dot{\epsilon }$ is strain rate and λ = 2.5 ± 0.1 × 10−3 m−2), as would be expected from a standard Coulomb failure model. However, the fit is significantly better for a non-linear relationship ($\dot{N} = \gamma _1 \cdot \dot{\epsilon }^{\gamma _2}$ with γ1 = 2.5 ± 0.6 m−2 and γ2 = 1.42 ± 0.15). The b-value of the Gutenberg–Richter law, which characterize the magnitude–frequency distribution, is found to be insensitive to the strain rate. In the case of a linear correlation between seismicity and strain rate, the maximum magnitude earthquake, derived from the moment conservation principle, is expected to be independent of the strain rate. By contrast, the non-linear case implies that the maximum magnitude earthquake would be larger in zones of low strain rate. We show that within areas of constant strain rate, earthquakes above Mw 4 follow a Poisson distribution in time and and are uniformly distributed in space. These findings provide a framework to estimate the probability of occurrence and magnitude of earthquakes as a function of the geodetic strain rate. We describe how the seismicity models derived from this approach can be used as an input for probabilistic seismic hazard analysis. This method is easy to automatically update, and can be applied in a consistent manner to any continental zone of active tectonics with sufficient geodetic coverage.

A comprehensive database of active and potentially-active continental faults in Chile at 1:25,000 scale

In seismically-active regions, mapping active and potentially-active faults is the first step to assess seismic hazards and site selection for paleoseismic studies that will estimate recurrence rates. Here, we present a comprehensive database of active and potentially-active continental faults in Chile based on existing studies and new mapping at 1:25,000 scale using geologic and geomorphic criteria and digital elevation models derived from TanDEM-X and LiDAR data. The database includes 958 fault strands grouped into 17 fault systems and classified based on activity (81 proved, 589 probable, 288 possible). The database is a contribution to the world compilation of active faults with applications among others in seismic hazard assessments, territorial planning, paleoseismology, geodynamics, landscape evolution processes, geothermal exploration, and in the study of feedbacks between continental deformation and the plate-boundary seismic cycle along subduction zones.

Source Mechanism and Rupture Process of the 24 January 2020 Mw 6.7 Doğanyol–Sivrice Earthquake obtained from Seismological Waveform Analysis and Space Geodetic Observations on the East Anatolian Fault Zone (Turkey)

Here, we present the source mechanism and rupture process for the destructive 24 January 2020 Mw 6.7 Doğanyol–Sivrice earthquake at the East Anatolian Fault Zone (EAFZ, Turkey), obtained from seismological waveform analysis and space geodetic observations. Multi-data analyses and modelling in the present study provide fundamental data and strong constraints for retrieving complex source mechanism of an earthquake and its spatiotemporal slip characteristics along the ruptured segment of fault. The acquired slip model of this earthquake reveals heterogeneous slip distribution along strike N244°E of the fault plane dipping NW (68°) with duration of the source time function (STF) and low stress drop value (Δσ) of ~25 s and ~6 bars, respectively. Back-projection analysis validates fault length (L) stretching along strike for a distance of ~75 km and supports predominant south-westerly bilateral rupture propagation with a variable rupture velocity (Vr) of ~2.3–3.4 km/s along with two main patches, presumably a sequence of two asperities being ruptured following the surface trace of the EAFZ. The distribution of aftershocks based on the analysis of two months long data consistently confirms spreading of seismicity along the ruptured fault. The evaluation of Interferometric Synthetic Aperture Radar (InSAR) data reveals that left-lateral co-seismic slip and significant deformation extends for ~20 km on either side of the fault with evident post-seismic displacement. Yet, no significant vertical offsets were observed as GNSS stations detected only horizontal motions. Coda-wave analysis as an independent tool also confirms moment magnitude of Mw 6.7. Our results highlight a case of a damaging earthquake and enhance our understanding of earthquake mechanics, continental deformation and augmented earthquake risk on the EAFZ.

Tectonics and Landscape of the Central African Plateau and their Implications for a Propagating Southwestern Rift in Africa

AbstractThe Central African Plateau (CAP) covers a million square kilometers of African lithosphere absent of recent volcanism and intense seismicity. Treating the CAP erosion surface as a reference frame for measuring continental deformation reveals an active landscape of normal fault systems and crustal flexures. Free‐air gravity anomalies over the CAP reveal both a short‐wavelength (100–200 km) flexural and a longer‐wavelength (>500 km) mantle convective signature. Apatite fission track thermochronometry records the onset of regional cooling of the erosion surface below 60 °C between 38 and 22 Ma. The erosion surface was formed by the Latest Miocene and elevated to its present altitude (1,200 ± 50 m) in the Latest Miocene/Pliocene. High‐resolution Shuttle Radar Topography Mission‐ and LIDAR‐based digital elevation models of the erosion surface show active fault terraces and alluvial fan deformation associated with pre‐existing rift border faults. Flexural modeling of the footwall uplift of the Luangwa Rift border fault yields an effective elastic thickness of the CAP lithosphere of ~35 km. The rifting initiated in the Pliocene with, or soon after, elevation of the CAP. Subsequent Plio‐Pleistocene deformation of the CAP surface controls the Congo and Zambezi drainage systems and wetland locations. The CAP rifts link southwestward through the Zambezi, Kafue and Muchili Rifts to the Pleistocene aged Okavango and Eiseb Rifts of Botswana and Namibia, defining a propagating Southwestern Rift cutting the Nubian Plate. This active rift system developed along relatively thin (~150 km) lithosphere between the Congo and Kalahari cratons within crust inherited from Neoproterozoic collisional tectonics.

Thermo-rheological structure of the northern margin of the South China Sea: Structural and geodynamic implications

Rheological properties of continental lithosphere are key controls on the behavior of continental deformation. Using thermal structure, constrained by surface heat flow data and measured thermal properties of rocks, the present study calculates different thermo-rheological structure scenarios for the ocean–continent transition (OCT) at the northern margin of the South China Sea, using two different models: a conventional model, taking into account frictional sliding and power-law creep, and a model that additionally includes a high-pressure brittle-fracture mechanism. Two compositions of the lower part of the lithosphere are considered: a soft case with felsic granulite lower crust and wet peridotite lithospheric mantle, and a hard case with mafic granulite lower crust and dry peridotite lithospheric mantle. The former scenario shows a major rheological change from a “jelly sandwich” to a “Christmas tree” type of rheology from north to south along the margin. This complex rheological structure explains lateral changes in earthquake distribution and geometries of extensional faults of the OCT at the northern margin of the South China Sea. Further, our analyses indicate that the initial lithospheric rheology profile probably has only one ductile layer in the lower part of upper crust. Such an initial lithospheric rheology model predicts focused extension to form asymmetric margins, which is the case for the SCS.

Diachronous uplift in intra-continental orogeny: 2D thermo-mechanical modeling of the India-Asia collision

The Cenozoic India-Asia collision reactivated several ancient thrust belts in the interior of the Asian continent, including the West and East Kunlun ranges in central Tibet, and the Tian Shan and Qilian Shan further north. Both basin sedimentary records and thermochronological data show that the uplift of the South Tian Shan and Qilian Shan at the north occurred earlier than that of the West and East Kunlun ranges at the south. Diachronous continental deformation and initiation of uplift during orogeny are contrary to the general notion that the stress transfer in response to the India-Asia collision should propagate sequentially from south to north. Here we systematically conducted 2D thermo-mechanical simulations to investigate possible factors for this diachronous deformation pattern. The results show that a hotter Tian Shan lithosphere, with Moho temperature >100 °C hotter than that of the proto-southern Asia, leads to an earlier and higher uplift of the Tian Shan. Additionally, a faster convergence rate of the India-Asia collision results in a more efficient transfer of boundary force into the upper plate's interior, giving rise to a larger amount of uplift in the Tian Shan. We conclude that intra-continental ranges with weaker lithosphere, such as the Tian Shan or Qilian Shan, uplift earlier than stronger regions, such as the West and East Kunlun ranges. Faster convergence rates amplify this situation. Our results imply that the unique diachronous growth of the Tibetan plateau arises from its complex pre-collisional history, which includes collided arc-continent terranes with hotter and weaker lithosphere that respond to the effects of far-field stress transfer.

Foundered lithospheric segments dropped into the mantle transition zone beneath southern California, USA

AbstractThe diverse range of active tectonics occurring in southern California, USA, offers an opportunity to explore processes of continental deformation and modification in response to the instability of the Pacific and Farallon plates. Here, we present a high-resolution receiver-function image of the mantle transition zone (MTZ). Our result reveals significant lateral heterogeneities in the deep mantle beneath southern California. Both seismic tomography and MTZ discontinuity deflections reveal foundered lithospheric segments that have dropped into the MTZ beneath the western Transverse Ranges, the Peninsular Ranges, and part of the southern Sierra Nevada. Water dehydrated from these foundered materials may contribute to the observed MTZ thickening. Our observations, combined with previous tomography and geochemical results, indicate that lithospheric foundering of fossil arc roots provides a way for geochemical heterogeneities to be recycled into the underlying mantle, and suggest that the foundered materials can play a significant role in inducing lateral variations of MTZ structure.

Ali Mehmet Celâl Şengör: A geologist who unravels the histories of continents and oceans

This special issue is dedicated to Ali Mehmet Celâl Şengör for his outstanding contributions to plate tectonics and history of geology. His studies have unraveled several mysteries on the origin and deformation of continents and formation of orogenic belts in many parts of the world. We received 22 articles for the special issue, 11 of which are published in this issue. The rest of the articles will be published in the next issue. The articles in this issue mainly focus on geological processes in the Alpine–Himalayan orogenic belt and on the history of the theory of plate tectonics.

Surface Motions and Continental Deformation in the Indian Plate and the India‐Eurasia Collision Zone

AbstractThe collision of the Indian plate with Eurasia has played a major role in controlling the dynamics of central Asia leading to the world's largest continental deformation zone. In order to study the deformation within the Indian plate as well as the India‐Eurasia collision zone, we model the lithospheric stress field by calculating the two primary sources of stress, one arising due to topography and shallow lithospheric structure estimated by gravitational potential energy differences and the other arising from basal tractions derived from density‐driven mantle convection. We use several tomography models to calculate horizontal tractions using the convection code HC for two radially varying viscosity structures. We also take into account lateral viscosity variations in the lithosphere model arising from stiff cratons, weak plate boundaries, and strength variations due to old and young oceanic lithosphere. We do a quantitative comparison of our predicted deviatoric stresses, strain rates, and plate velocities with surface observables and find that the regional tomography model of Singh et al. (2014) embedded in the global S wave model S40RTS does a remarkable job of fitting the observations of GPS velocities and strain rates as well as intraplate stress field from the World Stress Map.

Pacific subduction control on Asian continental deformation including Tibetan extension and eastward extrusion tectonics

The India-Asia collision has formed the highest mountains on Earth and is thought to account for extensive intraplate deformation in Asia. The prevailing explanation considers the role of the Pacific and Sunda subduction zones as passive during deformation. Here we test the hypothesis that subduction played an active role and present geodynamic experiments of continental deformation that model Indian indentation and active subduction rollback. We show that the synchronous activity and interaction of the collision zone and subduction zones explain Asian deformation, and demonstrate that east-west extension in Tibet, eastward continental extrusion and Asian backarc basin formation are controlled by large-scale Pacific and Sunda slab rollback. The models require 1740 ± 300 km of Indian indentation such that backarc basins form and central East Asian extension conforms estimates. Indentation and rollback produce ~260–360 km of eastward extrusion and large-scale clockwise upper mantle circulation from Tibet towards East Asia and back to India.

Strain Rate Distribution in South‐Central Tibet From Two Decades of InSAR and GPS

AbstractThe degree to which deformation and seismicity is focused on major mapped structures remains a key unknown in assessing seismic hazards and testing continental deformation models. Here we combine 208 Global Positioning System (GPS) velocities with 12‐track Interferometric Synthetic Aperture Radar (InSAR) rate maps to form high‐resolution velocity and strain rate fields for south‐central Tibet. Our results show that deformation is not evenly distributed across the region. We find a few zones with high strain rates, most notably the Yutian‐Zhongba strain rate zone. However, the average of the strain rates is similar within and outside the mapped fault zones. In addition, the slip rates are low on all the conjugate strike‐slip faults widespread in central Tibet. The observations are difficult to reconcile with time‐invariant block models or with continuum models that lack mechanisms for strain localization. Our results support arguments that the most robust estimates of seismic hazard should integrate seismicity catalogues, active fault maps, and geodetic strain rate models.

Tectonothermal Evolution of the Cameros Basin: Implications for Tectonics of North Iberia

AbstractConstraining the way in which continental deformation is accommodated in time and space is essential to reconcile past plate movements with geological observations. Kinematic reconstructions of the Iberia‐Europe plate boundary are still debated. Here we focus on an inverted Mesozoic rift basin, the Cameros basin, which is part of the Iberian chain. We use a combination of detrital low‐temperature thermochronological techniques to define the time‐temperature evolution of the basin from Mesozoic rifting to Cenozoic collision. Zircon fission‐track analyses of Oligocene–Miocene sedimentary rocks yield two main age populations at ~170 ± 10 and ~100 ± 10 Ma, reflecting (i) an Early Jurassic thermal event related to the Atlantic‐Alpine Tethys opening and (ii) an Albo‐Cenomanian thermal event related to the Bay of Biscay opening. Thermal modeling of combined zircon fission‐track, apatite fission‐track, and apatite (U‐Th‐Sm)/He data reveals that collision‐related cooling of the Cameros basin started during the Paleocene (~60 Ma). A second cooling/exhumation phase of the basin is recorded from 35 to 25 Ma. Initial cooling occurred after a protracted postrift period characterized by persistence of high geothermal gradients, a feature also recognized in the Pyrenees. Our results show that the Iberian chain shared the same Early to Late Jurassic tectonothermal evolution with the Atlantic‐Alpine Tethyan rifted margins. From the Albian onward, the thermal evolution of the Cameros basin was very similar to that of the Pyrenees. This study shows that the preservation in mountain ranges of a succession of rifting events provide important clues for plate reconstructions.

New Paleomagnetic results from the Beiya porphyry-skarn gold–polymetallic deposit at the Western Dali faulted-block: Implications for the Cenozoic tectonic rotation of the Chuan-Dian Fragment, Southeastern Tibetan Plateau

The Chuan-Dian Fragment (CDF), in the southeastern Tibetan Plateau, is crucially important for understanding the intra–continental deformation behavior of the blocks between the stable Yangtze craton and the Indian Plate after the Indian-Asian collision. The Beiya porphyry-skarn gold–polymetallic deposit at the northwestern part of the fragment may provide an important paleomagnetic result for understanding the deformation behavior of the CDF. The paleomagnetic study of mineralized and intrusive rocks from the ~35 Ma Beiya deposit reveals a high temperature component with site–mean direction of D = 337.6°, I = 32.6°, k = 74.8, with α95 = 4.4°. Our results show that the Beiya deposit experienced 21.5° ± 3.1° of anticlockwise rotation relative to the stable part of the South China Block since ~35 Ma. The stable part of the Dali faulted-block is deduced to have experienced ~20° clockwise rotation based on a comparison of the fold-axis strike of Triassic strata between the Beiya deposit and surrounding stable area. A best-fit linear regression of the fold-axis strike direction and the tectonic rotation at each sampling site reveals that differential tectonic rotation occurred, accompanied by the horizontal deflection of strata within the CDF.

Research Highlights of the Indian Contributions to Geomagnetism and Aeronomy in the 21st Century

Gravimetry and Geodesy deal with the mass distribution and transport in the dynamic Earth system and determination of Earth’s shape and size. Since the 18th century, Indian scientists have been extensively contributing to the progress of Gravity and Geodetic studies. This article discusses the historical geodetic developments and summarizes the efforts that involve measurements and modelling of gravity and geodetic data in India over the past decade, using conventional land surveys to satellite observations. Historical obsevations, such as the Great Trigonometrical Survey during 1790-1850 for defining geodetic reference frame and gravity and geodetic observations in the Himalayan region (1830-1843) for hypothesising the concept of Isostasy, are phenomenal contributions made from studies in India. Recent studies are largely focused on understanding of subsurface mass distributions and mass variability due to different geophysical phenomenon, refining of geodectic datum, continental deformation and resource exploration.