Deep Seismic Sounding Research Articles

Deep structural insights into the origin of the Heyuan ms 4.5 revealed by deep seismic sounding profiles in southeast China

This study presents an interpretation of a deep seismic sounding (DSS) profile that carried out along the Cathaysia Block in southeast china, aiming to explore the crustal velocity structure. Data used in the survey were obtained from three controlled-source explosions conducted along the 320 km long Lianping-Heyuan-Shanwei profile. The modeling was based on ray tracing, using the extrapolation of seismic wave arrival times with the help of travel times predicted from a one-dimensional velocity model. The average velocity structure of the middle crust is 6.0–6.4 km/s, while a low velocity anomaly of approximately 0.1–0.2 km/s in the vicinity of the Heyuan-Shaowu fault zone. The resulting 2D velocity model indicates that steeply dipping low-velocity zones that correlate with the projection of two major fault zones. These zones, together with a flat LVZ at a depth of 12 km, define a triangular region that correlates with numerous hypocenters. This tectonic setting is favorable for the accumulation and release of strain in high-velocity media within the triangular region. The unique triangular structure in the upper crust provides necessary shallow medium conditions for seismic activity. This indicates that increased seismicity within this area is partially attributed to heightened stress within higher-velocity material. The triangular annular low-velocity body, situated in the upper crust, is influenced by dynamic environmental factors caused by deep thermal disturbances. The deep-seated fault serves as a conduit for the historical migration of thermal material, likely contributing to the seismogenic conditions for earthquakes in Heyuan’s region through deep-seated thermal disturbances. These findings provide a novel geophysical reference model for the regional seismicity near the Xinfengjang reservoir and significantly contribute to understanding the causal relationship between tectonic setting and seismicity. In comparison with previous studies, our research is dedicated to investigating the causes of shallow earthquakes in the region and exploring the relationship between deep and shallow structures.

Глибинні геологічні моделі району надглибокої cвердловини Saatly DW-1 на основі комплексу геофізичних даних

The purpose of the article is to study the reasons for the failure to achieve the scientific and geological goals set for the ultra-deep well DW-1, drilled in the Saatli region of Azerbaijan. The analysis will focus on the existing deep models built for this region, which are deemed insufficient in reflecting the truth. The paper highlights the importance of adopting a new approach to the recently created deep model and its potential benefits to the scientific community.Methodology. The technique includes a detailed comprehensive analysis of the gravitational and magnetic fields in this region, the use of local magnetic anomalies to build a model of the deep geological structure utilizing data from deep seismic sounding (DSS) and the correlation method of refracted waves (CMRW). Results. The spatial position of effusive formations in the geological section was determined using the local anomaly of the geomagnetic field in the Saatly region. At the same time, the geometric dimensions of the volcanic body were chosen in such a way that the magnetic field created by it corresponded to the observed local magnetic field. Thus, a model of the geological section up to a depth of 15 km was developed, with the display of the spatial position of the volcanic formation. In this model, unlike the previous one, the spatial position of the volcanic formation in the vertical geological section is completely different. In the newly constructed model, it turns out that there is a separate volcanic formation in the area of the Saatly DW-1. And in the previous models, it was shown that the magma came here from the Muradhanly zone, located at a distance of 25-30 km. The boundaries of the crystalline foundation and the basalt layer in the area of the DW-1 in the zone of the volcanic body are not traced. The root of the volcano narrows and goes deep into the earth. At a depth of about 15 km, the magma-producing channel has a width of 1 km. Based on the established model, it was determined that the ultra-deep well DW-1 is located on the magma-producing channel of the volcano that existed here. From the analysis of the obtained model data, it turns out that the extension of the Saatly DW-1 to depth will not allow opening the consolidated crust (crystalline foundation) and basalt layer. Because, although these layers are closer to the earth's surface in the area of the DW-1, the active volcano here has destroyed these boundaries. Orginality. Seismic survey materials were used to study the deep structures of the region, gravimagnetic data on profiles with an observation step of 250 m, and a technique was applied to construct the spatial positions of effusive formations in the geological section. Scientific novelty. It has been established that the geomagnetic field of this region is formed from three main effects - the effect of the sedimentary complex, the effect of the thickness between the basement and Curie surfaces, and the effect of local manifestations of magmatism. The sum of the first two effects quite accurately corresponds to the regional background of the observed geomagnetic field. Local positive anomalies isolated from the observed field are associated with local heterogeneities - in this region with volcanogenic formations in the sedimentary complex. Practical significance. A new geological-geophysical model was created by determining the spatial position of effusive formations in the geological section near the Saatly DW-1 well using the local anomaly of the geomagnetic field. This model has real possibilities in the direction of installation of ultra-deep wells for the study of deep layers of the earth's crust.

New Ideas about the Structure and Nature of the Crust of the Western Bay of Bengal, Obtained Taking into Account Deep Seismic Sounding Data

New Ideas about the Structure and Nature of the Crust of the Western Bay of Bengal, Obtained Taking into Account Deep Seismic Sounding Data

TECTONICS AND GEOLOGICAL STRUCTURE OF THE MAYA-KYLLAKH ZONE (SOUTH VERKHOYANSK REGION) OBTAINED FROM BALANCED CROSS-SECTIONS

A technique for balancing cross-sections is used to construct geometrically consistent structural sections through fold-thrust belts. Unlike the predecessor studies, the balanced cross-sections in this study were obtained using the deep seismic sounding and well data and Move Software. Two detailed balanced cross-sections pass through the central part of the South Verkhoyansk region: the 80 km long Yudoma cross-section running along 59°45ʹ N, and the 122 km long Allakh-Yun cross-section within 60°40ʹ – 61°00ʹ N. Both sections are characterized by a thin-skinned structure, "mechanical stratigraphy", emergent leading imbricate fans in the foreland, thick Riphean strata, and eastward dip of the detachment surface. The surface shortening values are ~33 % for the Yudoma cross-section and ~26 % for the Allakh-Yun cross-section, showing an old-to-young-complex decrease from 39 % for the Yudoma cross-section to 19 % for the Allakh-Yun cross-section. On the Yudoma cross-section, the detachment occurs in the Middle Riphean deposits and dips down to 8 km; on the Allah-Yun cross-section, it occurs in the Lower Riphean deposits and dips down to 15 km. The difference in the detachment level may indicate the presence of a ramp between the cross-sections or an inaccurate localization of a ramp between the Central and Kyllakh-Eibeke-Khayata segments. The changes in the geological structure across and along the strike of the orogen are traced; the obtained cross-sections are compared with each other, with other cross-sections across the South and West Verkhoyansk regions, and with the cross-sections through the foreland fold and thrust belts of the Urals, Appalachians, and Cordillera of North America.

Anomalous geoobjects in the Lithosphere of Uzbekistan and their interrelations with ore deposits

One of the priority tasks of the Geological Service of the Republic of Uzbekistan is the study of the paleozoic foundation under the cover of Meso-Cenozoic sediments, mainly using deep seismic sounding profiles, in order to trace known ore fields and mineralized zones in the overlying part of the basement. In recent years, in the laboratory “Structure of the Lithosphere” of the Institute of Geology and Geophysics named after Kh.M. Abdullayev, new data have been obtained as a result of reinterpretation of a complex of geophysical data. In the present work examines the role of anomalous geoobjects with high and low seismic density parameters along deep seismic sounding (DSS) profiles in the Lithosphere of Uzbekistan from the point of view of their spatial correlation with explored deposits of ore minerals. New regional features of the interrelationships between the geological structure of the lithospheric deep structures of Uzbekistan and the spatial distribution of deposits have been identified.

СТРУКТУРНО-ПЛОТНОСТНАЯ МОДЕЛЬ ЗЕМНОЙ КОРЫ ЗАПАДНОГО ШЕЛЬФА О-ВА САХАЛИН И ЕЕ ГЕОЛОГИЧЕСКАЯ ИНТЕРПРЕТАЦИЯ

Structural and density modeling of the Earth's crust carried out using a deep seismic sounding profile previously tested along the western shelf of Sakhalin Island offered a clearer view of the layered block structure of the main tectonic faults and their newtwork within the crust of the region, where a large number of strong crustal earthquakes are concentrated. The density structures of the resulting model were compared with geological data on the adjacent territory of Sakhalin Island. Our structural and density model made it possible to separate volcanic blocks and blocks of sialic crust and to trace the submerged prolongation of the largest geological complexes of the western edge of Sakhalin Island on the shelf. There are signs of spatial correlation between seismic events and some tectonic faults.

STRUCTURE OF LOCAL ELEVATION DEMAL, KUMAK, ALAK LOCATED WITHIN THE ZHAZGURLIN DEPRESSION

In the article, the main purpose of the research is to study the deep structure of the territory, to identify and trace faults in the Zhazgurli depression of the South Mangyshlak. In tectonic terms, the study area is confined to the central part of the Southern Mangyshlak trough. The considered structures Demal, Kumak, Alak are located within the Zhazgurli depression. The authors present the current understanding of the geological structure of the sites under consideration, which is based on the materials of seismic surveys and well drilling data, as well as on the basis of previously performed work. The ideas about the structure of the foundation are based on the materials of geophysical research, first of all, gravity and magnetic exploration, as well as seismic exploration of the CMRV (correlation method of refracted waves) DSS (deep seismic sounding) MEWE (the method of exchange waves of earthquakes). The geological structure of the area was revised on the basis of volumetric seismic survey materials, which allowed us to obtain new data on the structure of the main structures.

Structure of the Earth’s Crust of the Persian Gulf According to Deep Seismic Sounding Results

Structure of the Earth’s Crust of the Persian Gulf According to Deep Seismic Sounding Results

The Earth’s Crust Structure of the Persian Gulf According the Results of Deep Seismic Sounding

The article presents the results of seismic work performed by the DSS method in the Persian Gulf. Bottom analog type seismographs and seismic airgun sources were used in the works. The bottom seismographs were placed and the shooting was carried out according to three regional profiles with a length from 100 to 250 km. The main result of these studies was to obtain velocity-depth model of the sedimentary cover and the Earth’s crust up to Moxo boundary, which was revealed at a depth of about 43 km in the water area. Given that the thickness of the upper crust is only 4–5 km, and the speed characteristics of the remaining layers, the crust type can be attributed to the subcontinental Archean type. This situation (complete absence or drowning of the upper layer of the Earth’s crust) is typical for the waters closest to the Persian Gulf: the Black Sea, the Caspian Sea, the Mediterranean and the Red Seas. A structure was found in the Earth’s crust of the studied area, which may be a brachianticline having an isometric dome-shaped shape, which corresponds to the folding of the platform type in the areas of salt-dome tectonics. No faults have been found in the Earth’s crust of the Persian Gulf water area adjacent to the Bushehr Peninsula.

Transcarpathian Depression: Study of Low-Velocity Zones in the Earth’s Crust Based on the Seismic Regional Profiles Data

Transcarpathian depression (TD) is located in the junction zone of the eastern margin of ALCAPA terrain and the northern part of Tisza-Dacia one, buried under thick Neogene molasses. The Earth’s crust structure of the TD is not clearly understood.
 The purpose of this work is to refine the TD crust structure and identify low-velocity zones by interpreting wave images obtained from WARR PANCAKE profile data using the finite-difference reflection/refraction migration method.
 The crustal domain beneath the TD is interpreted to be limited from southwest by a fault gently southwest dipping, traced from Pieniny Klippen Belt on the surface. Within domain two suture zones being the Alpine Tethys ocean remnants and cemented the European plate and ALCAPA microplate, were distinguished: Piemont-Liguria and PKB ones, as well as a rootless fragment of ALCAPA terrain. The Outer Carpathians thrust belt of 13 km depth borders the TD by subvertical Transcarpathian fault. The crust structure of the Pannonian segment is interpreted to be a pile of thick- and thin-skinned basement nappes of the Tisza terrain and cover nappes with superimposed younger extensional structures.
 High-reflectivity and low-velocity zone at depths of 10­—20 km is identified. The zone follows the pattern of isotherms in the temperature range of 300—500°. On the deep seismic sounding (DSS) Chop—Velykiy Bychkiv profile, running along TD and crossing the PANCAKE line, two low-velocity zones were also distinguished. Published data on numerical and physical modeling, the deep well cores, as well as fault zones in natural outcrops suggest that the low-velocity zones have increased porosity, fracturing, and fluid saturation. Our results suggest a high hydrocarbon potential of the TD, associated with the low-velocity zones.

2022 Joint Barringer Medal for Kai Wünnemann and Gareth S. Collins

2022 Joint Barringer Medal for Kai Wünnemann and Gareth S. Collins

Contrasting lithospheric geophysical structure of the Black Sea subbasins: Relevance to testing geotectonic models for this mega depression

We present an integrated analysis of the geophysical parameters of the lithosphere of Black Sea basin obtained as a result of the interpretation of magnetic, gravity, thermal, deep seismic sounding and seismic-tomographic data. It first demonstrates inherent significant differences in geophysical parameters of lithosphere in the Western and Eastern Black Sea subbasins existing from the prerift stage. The set of reviewed parameters responsible for formation of the present-day lithosphere includes types of crust, depths to acoustic basement, configuration of subbasins, depths to Moho, heat flow and relief of the thermal-asthenosphere boundary (LAB), trends of main deep faults of the crystalline crust, their kinematic types, occurring linear magnetic anomalies, velocity pattern of subcrustal mantle. The above-mentioned parameters of the lithosphere are indicators of the age, geodynamics and driving mechanisms for opening of a subbasins. Oblique trends of the subbasins and the topography of Moho discontinuity in the west and east domains, oblique striking of pre-rifting Istanbul zone and the Shatsky Ridge and different trends of deep faults in the crystalline crust suggest distinct lithospheric structure existing from pre-opening of the Black Sea subbasins and different geodynamical conditions of its formation. The Odesa-Sinop-Ordu deep fault zone as a direct continuation of the Golovanivskaya suture zone of the Ukrainian shield and its slope, probably is of the Precambrian age. So it could be the tectonic boundary between two segments of pre-rift continental crust and between future subbasins. The examples illustrate how indicated parameters of the lithosphere can geophysically confirm the basic ideas of available models for geodynamics of the Black Sea.

Lithosphere Density Model of the Middle Urals Segment

For the Middle and North Urals segments and adjacent territories of the East European Platform and West Siberian Plate (within the graticular trapezoid with geographic coordinates 53–65° N, 48–72° E), ten deep seismic sounding (DSS) profiles were reprocessed using two-dimensional (2D) seismic tomography method, and gradient sections of crustal velocities were constructed in the form of grid functions. In the same format, density sections were constructed. The coefficients of density–velocity empirical correlation were calculated using the solution algorithm of 2D inverse problem of gravimetry. The method and calculation technology of a three-dimensional (3D) density distribution with tying to 2D data from reference seismic sections are embedded in the procedure of quantitative interpretation of potential fields with construction of 3D geophysical models. A stable solution of the 3D inverse problem of gravimetry is sought on the correctness set of the family of horizontal layers with 2D density distribution.

Characterizing the shallow structure with the multimodal dispersion curves and the body wave refraction traveltimes from deep seismic sounding data

Deep seismic sounding (DSS) profiles are one of the most powerful tools for detecting crustal structures, and they have been deployed worldwide. Generally, the analysis of DSS data mainly focuses on body waves, while the surface waves are considered noise. We suggest that the surface waves in DSS data can be used to constrain subsurface structures. In this study, we use a DSS profile in the Piedmont and Atlantic Coastal Plain as an example to present the usage of the DSS surface wave. Multimodal dispersion curves were extracted from the DSS data with the Frequency-Bessel transform method, and were used in Monte Carlo joint inversions with body wave refraction traveltimes to constrain the shallow structures. Through the inversion, a horizontal stratum on the surface was identified in the Piedmont, and a two-layer sedimentary structure was identified in the Atlantic Coastal Plain. Comparisons with existing studies verified the accuracy of the shallow structures obtained in this study, demonstrating that the shallow velocity structure could be well constrained with the additional constraints provided by the multimodal dispersion curves. Thus, we believe that further research on the surface waves recorded in DSS surveys is warranted.

Implications on crustal structure from the South Finland Coastal (SOFIC) deep seismic sounding profile

We present results from a deep seismic sounding (DSS) experiment carried out along the southern coast of Finland in summer 2015. Data used in the survey derived from industrial blasts recorded by temporary project stations and permanent network stations. The western 220 km part of the 450 km long Southern Finland Coastal (SOFIC) profile runs along the Uusimaa belt (UB) in the 1.7–1.9 Ga Southern Finland subprovince (SFS) of the Svecofennian domain, while the 170 km part in the east crosses the 1.62–1.65 Ga Wiborg rapakivi batholith (WRB). The farthest 60 km cross a geologically diverse area consisting of supracrustal rocks and granitoids of the Saimaa area (SA), an eastern extension of the SFS. Our results show that the Moho boundary depth varies significantly, from ca. 52–54 km below UB to 40–45 km below WRB. All three crustal layers (upper, middle, and lower) have their maximum depth in the contact zone between UB and the WRB. Below WRB, a lower crust with Vp ~6.7–6.9 km/s is observed. High velocity lower crust was observed below UB (Vp ~7.2 km/s) and possibly below SA (Vp ~7.35 km/s). The modelling was based on ray tracing, using the extrapolation of seismic wave arrival times with the help of travel times predicted from a one-dimensional velocity model. The resulting two-dimensional velocity model partly relies on data from the intersecting DSS profiles and supports previous observations of the lithospheric structure of southeastern Fennoscandia.

Crustal Structure of the Chuan‐Dian Block Revealed by Deep Seismic Sounding and its Implications for the Outward Expansion of the East Tibetan Plateau

AbstractThe Chuan‐Dian Block (CDB) is located in the southeastern margin of the Tibetan Plateau, with a complex geological structure and active regional faults. The present tectonic condition with strong crustal deformation is closely related to the ongoing collision of the India and Eurasia plates since 65 Ma. The study of the crustal structure of this area is key to revealing the evolution and deep geodynamics of the lateral collision zone of the Tibetan Plateau. Deep seismic sounding is the most efficient method with which to unravel the velocity structure of the whole crust. Since the 1980s, 19 deep seismic sounding profiles have been captured within the CDB area. In this study, we systematically integrate the research results of the 19 profiles in this area, then image the 3D crustal velocity, by sampling with a 5 km spacing and 2D/3D Kriging interpolation. The results show the following. (1) The Moho depth in the study area deepens from 30 km in the south to 66 km in the north, whereas there is no apparent variation from west to east. The Pn wave velocity is higher in stable tectonic units, such as 7.95 km/s in the Lanping‐Simao block and 7.94 km/s in the western margin of the Yangtze block, than in active or mobile tectonic units, such as 7.81 km/s in the Baoshan block, 7.72 km/s in the Tengchong block and 7.82 km/s in the Zhongdian block. (2) The crustal nature of the Tengchong block, the northern Lanping‐Simao block and the Zhongdian block reflects a type of orogenic belt, having relatively strong tectonic activities, whereas the crustal nature of the central Lanping‐Simao block and the western margin of the Yangtze block represents a type of platform. The different features of the upper‐middle crust velocity, Moho depth and Pn wave velocity to both sides of the Red River fault zone and the Xianshuihe fault zone, reflect that they are clearly ultra‐crustal. (3) Based on the distribution of the low velocity zones in the crust, the crustal material of the Tibetan Plateau is flowing in a NW–SE direction to the north of 26°N and to the west of 101°E, then diverting to flowing eastwards to the east of 101°E.

Characteristics of Radiogenic Heat Production of Widely Distributed Granitoids in Western Sichuan, Southeast Tibetan Plateau

Abstract Investigating the genesis of geothermal resources requires a thorough understanding of the heat source mechanism, which is also a vital basis for the efficient exploration and utilization of geothermal resources. Situated in the eastern Himalayan syntax, western Sichuan is considered to be one of the main concentration regions of high-temperature geothermal resources in China. To date, various studies have been carried out to reveal the heat source and genesis of the abundant high-temperature resources in this area; however, studies on the contribution of the radioactive heat generated by the widely distributed granitoids to the high-temperature geothermal resources remain scarce. In order to resolve this knowledge gap, we attempted to obtain evidence from the geochemical data published in the literature in the past few decades. A total of 548 radiogenic heat production rate data were determined. The statistical data indicate that the average concentrations of the heat-producing elements U, Th, and K are 6.09±5.22 ppm, 26.74±16.78 ppm, and 3.51±0.82%, respectively. The calculated heat production values of the granitoids vary from 0.52 to 10.86 μW/m3, yielding an arithmetic average value of 3.74±2.15 μW/m3, which is higher than that of global Mesozoic–Cenozoic granites (3.09±1.62 μW/m3). Based on the heat production values, the capacity of the granitic batholiths to store heat was assessed, and the Dongcuo pluton was found to be the largest heat reservoir (382.88×1013 J/a). The distribution of the crustal heat flow was examined using the calculated heat production data and the stratigraphic structure obtained via deep seismic sounding in the study area. The results indicate that the crustal heat flow is 48.3–56.2 mW/m2, which is mainly contributed by the radioactive decay in the granitoids in the upper crust. The fact that it accounts for nearly half of the regional background heat flow indicates that the radiogenic heat from the granitoids is an important heat source for the formation of the thermal anomaly and the high-temperature geothermal resources in the study area. Thus, the results obtained in this study highlight the importance of the widely distributed granitoids to high-temperature geothermal resources in western Sichuan.

Collision‐Induced Subduction Polarity Reversal Explains the Crustal Structure of Northern Borneo: New Results From Virtual Deep Seismic Sounding (VDSS)

AbstractSubduction polarity reversal (SPR) is a key subduction initiation mechanism often associated with arc‐continent collision zones. Northern Borneo has long been recognized as a location where sequential but opposing subduction zones were present in the Miocene, but has not been examined in the context of SPR. Here, we exploit teleseismic data from northern Borneo to investigate crustal thickness variations using Virtual Deep Seismic Sounding (VDSS). Our results reveal a thick crustal root beneath the Crocker Range and an area of relatively thin crust in the southeast, which appears to extend northeast into the Sulu Sea, where back‐arc rifting behind the younger subduction zone developed. Overall, our findings are consistent with predictions from numerical models of SPR involving arc‐continent collision, but with several important differences—including a substantial mountain range and more limited back‐arc rifting that can be attributed to northern Borneo being an example of SPR involving continent‐continent collision.

Three-Dimensional Image of Crustal Density Model: A Case Study in South Kamchatka

Abstract —The methodology for building a 3D density model of the Earth’s crust and upper mantle for a crustal block in the South Kamchatka Peninsula is presented. The model is derived from the interpretation of the Bouguer anomaly values and data obtained by deep seismic soundings and electrical prospecting methods. 3D image creation can be viewed as a several phase procedure. At the first step, the area of interest is investigated through a network of intersecting profiles utilized for subsequent modeling depth density sections using the parameter scanning procedure. The a priori data include materials of geophysical surveys and geological, and petrophysical studies as well as results of depth estimation at singular points by the Euler deconvolution method. The next step involves formation of a 3D density matrix from the cross-section models. Coordinates in the cross-section planes are defined in the square grid nodes and converted to plane rectangular coordinates (the SK-42 reference system). A file of the cross-sectional database of density values is thus produced. For area shaving a sparse network of cross-sections, an additional database is derived from grid files of densities mapped horizon-wise. This ultimately results in the creation of the unified databases. A 3D network of cubic unit cells for three-dimensional (voxel) representation of density of the geologic medium is calculated. The model of density of unit cube with edge measuring 4 km was constructed for entire investigated block of the Earth’s crust. The model was detailed by decreasing successively the unit cube edges to 2.0, 1.0, and 0.5 km. The 3D modeling results are presented as block diagrams and density isosurface maps in horizontal slices at different depths. The block diagrams show isosurfaces with densities typical of deep subsurface boundaries and structures. The isosurfaces for densities of 2.75 and 2.90 g/cm3 reflect the morphology of the roof of the crystalline basement, and the lower–upper crust boundary, respectively, while the isosurfaces of 3.20 and 3.33 g/cm3 represent feasible shape of the crust–upper mantle contact. The lower-density zone ubiquitously observed in the investigated crustal block is caused by rock destruction along the deep fault. It is identified in the model with 1 km cubic unit cell side and encompasses the feeding systems of volcanoes, namely: Sopka Asacha (Asacha Volcano), Mutnovskaya Sopka (Mutnovsky Volcano), Gorelaya Sopka (Gorely Volcano), and Vilyuchinskaya Sopka (Vilyuchansky Volcano).The model with a 0.50 km cubic unit cell side shows a 2.85 g/cm3 isosurface, which delineates a column-shaped high-density region. A higher density revealed in the block is assumed to be associated with basite intrusions. 3D density models based on cross-section modeling provide additional information for geodynamic reconstructions, allowing a rough estimation of the geometry of concealed geologic features and their volumes, and can be utilized in 3D modeling to build initial models.

Seismic investigations around an aseismic Comorin ridge, Indian Ocean

Aseismic ridges and oceanic plateaux, typically buried under thick post-rift sediments, are isolated entities of enigmatic crustal character. Limited availability of deep seismic soundings hinders their precise characterization. Here, we present new crustal images from the Comorin ridge and adjoining basins in the Central Indian Ocean. Further, we seismically characterize the oldest oceanic crust south of Sri Lanka. We observe that the NW–SE-trending Comorin ridge, having distinct topography, is bounded by crustal blocks of contrasting ages and characters. Using seismic interpretation and potential field modelling, we propose its genesis as a transverse ridge with an anomalously thick ( c. 14 km) oceanic crust including considerable magmatic underplating. Additional constraints from plate reconstruction modelling suggest that a linear oceanic transform developed between India and Madagascar during their separation while the Marion hotspot remained in their close proximity. Based on several lines of evidence, we infer that shearing motion along the transform and coeval hotspot interactions are the likely emplacement mechanism for the ridge. The high-resolution seismic images demonstrate widespread crustal deformation in the form of high-angle faulting and long-wavelength folding. New findings have important implications for an improved understanding of the early Gondwana break-up, seafloor creation and subsequent compressional tectonics in the Indian Ocean. Supplementary material : Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.6073139