Tectonic Boundary Research Articles

Glacial Isostatic Adjustment, Intraplate Strain, and Relative Sea Level Changes in the Eastern United States

AbstractDetermining the motion of the North American plate is difficult due to horizontal intraplate deformation, caused mainly by glacial isostatic adjustment (GIA) in the parts of the plate that are not deforming tectonically. Determination of plate motions also depends on whether the geocenter of the geodetic reference frame coincides with the center of plate rotation. Any difference/error in the International Terrestrial Reference Frame geocenter will introduce an apparent deformation of the plate. We address the plate rotation and what correction models can best account for this internal deformation. We use continuous GPS sites located far from active tectonic boundaries to derive the velocity field in the eastern United States with uncertainties based on a colored noise model. We hypothesize that the velocities will be described by a rigid plate model once the deformation due to GIA and any geocenter/plate rotation center errors have been removed. We find the smallest intraplate residuals with both a geocenter correction and the ICE‐6G model applied. We further compare the coastal GPS vertical velocities with mean relative sea level change rate and find a ~1.9 mm/year difference, which matches the long‐term average global sea level change rate from tide gauges. The entire North American plate is deforming when analyzed at the ~1 mm/year level, and there is no instantaneously stable part due to the long‐wavelength GIA deformation. An accurate estimate of plate rotation cannot be determined from a geographic subset of the plate but only by removing the strain component via a GIA model or a simultaneous estimation of the spatially varying strain rate.

Late Cenozoic Clockwise Rotations in the Westernmost Part of the Arcuate Qiulitage Fold‐and‐Thrust Belt of Southern Tian Shan Foreland and Its Tectonic Implications

AbstractCurvature of fold‐and‐thrust belts (FTBs) is a rather common feature in foreland basins. The problem of how curves in FTBs originate is essential for understanding the propagation of deformation and tectonic history of orogens. In this study, we carried out systematic paleomagnetic studies in the westernmost part of the Qiulitage FTB, southern Tian Shan foreland, where thrusting, strike‐slip fault, and tectonic boundary coexist. Our new results suggest that the study area has been subjected to ~20° clockwise rotations after ~5 Ma. Oroclinal test of the paleomagnetic data across the FTB suggests that oroclinal bending caused by the formation of the curved Qiulitage FTB is the dominate reason for these tectonic rotations. The Kalayuergun dextral strike‐slip transfer fault delimiting the western boundary of the Qiulitage FTB is a thin‐skinned structure accommodating the discrepancy in horizontal displacement on both sides of it. These results also suggest that the formation of the curved Qiulitage FTB should not be older than ~5 Ma, indicating that the southern Tian Shan foreland has experienced significant tectonic shortening since the latest Miocene to early Pliocene. Our new results, together with previous studies on deformation history, estimates of crustal shortening, GPS observations and earthquake records, suggest that the southern Tian Shan foreland has been subjected to significant deformation during the past ~5 million years, and the crustal shortening is still ongoing.

Indentation tectonics of the Fanshi Block in the Trans-North China Orogen

The Trans-North China Orogen (TNCO) is a tectonic zone that records significant magmatic, metamorphic, and tectonic events during the Paleoproterozoic. The central part of the TNCO comprises several Precambrian blocks (the Hengshan Block, the Wutai Block, the Fuping Block, and the Fanshi Block) that are separated by three Paleoproterozoic ductile shear zones as tectonic boundaries. The Hengshan Block and the Fuping Block are represented by a group of large-scale gneissic domes, whereas the Wutai Block characterized by the ENE–WSW-trending synclinorium, and the framework of the Fanshi Block is dominated by strike-slip ductile shear zones superimposed on tight folds. We present detailed structural analysis of the Zhujiafang ductile shear zone in the central Hengshan, the Wangjiahui ductile shear zone at the northern margin of the Wutaishan, and the metamorphic complex between these two shear zones. The macro- and microstructures indicate that the ductile shear zones show different kinematics. The Zhujiafang ductile shear zone is E–W-trending and record sinistral strike-slip shearing, and the Wangjiahui ductile shear zone is WSW–ENE-trending and record dextral strike-slip shearing. Both of shear zones have similar deformation ages according to the 40Ar/39Ar dating results, and they cut through all the gneissosity and the fold developed in these metamorphic rocks. The kinematic difference between the Zhujiafang and the Wangjiahui ductile shear zones clearly define the Fanshi Block sandwiched between them, which is characterized by movement from west to east. The Fanshi block differs from the Hengshan Block and the Wutai Block in terms of deformation history, metamorphism, and magmatism. In addition, a series of NE-trending ductile–brittle thrust nappes inside the Wutai Block under the influence of the indention of the Fanshi Block inside. Therefore, we propose that the Fanshi Block was indented to the TNCO from west to east, accompanied by strong strike-slip ductile shearing and thrusting during the late Paleoproterozoic.

Spontaneous generation of ductile shear zones by thermal softening: Localization criterion, 1D to 3D modelling and application to the lithosphere

The generation of ductile shear zones is essential for the formation of tectonic plate boundaries, such as subduction or strike-slip zones. However, the primary mechanism of ductile strain localization is still contentious. We study here the spontaneous generation of ductile shear zones by thermal softening using thermo-mechanical numerical simulations for linear and power-law viscous flow in one-dimension (1D), 2D and 3D. All models are velocity-driven. The 1D model exhibits bulk simple shear whereas the 2D and 3D models exhibit bulk pure shear. The initial conditions include a small temperature perturbation in otherwise homogeneous material. We use a series of 1D simulations to determine a new analytical formula which predicts the temperature evolution inside the shear zone. This temperature prediction requires knowledge of only the boundary velocity, flow law and thermal parameters, but no a priori information about the shear zone itself, such as thickness, stress and strain rate. The prediction is valid for 1D, 2D and 3D shear zones in bulk pure and simple shear. The results show that shear heating dominates over conductive cooling if the relative temperature increase is >50°C. The temperature variation induced by the shear zone is nearly one order of magnitude wider than the corresponding finite strain variation so that no significant temperature variation occurs between shear zone and wall rock. Applying typical flow laws for lithospheric rocks shows that shear zone generation by thermal softening occurs for typical plate tectonic velocities of few cm.yr−1 or strain rates between 10−16 and 10−14 s−1. Shear stresses larger than 200 MPa can already cause strain localization. The results indicate that thermal softening is a feasible mechanism for spontaneous ductile shear zone generation in the lithosphere and may be one of the primary mechanisms of lithospheric strain localization.

Vertical motion of Phuket Island (1994–2018) due to the Sumatra-Andaman mega-thrust earthquake cycle: impact on sea-level and consequences for coral reefs

Macro-tidal coral reefs are particularly sensitive to medium to long-term changes in sea-level. Vertical motions of the seabed contribute to both lower or higher relative sea-level changes, particularly in tectonic plate boundary deformation zones along active subduction trenches. Phuket Island in Southern Thailand is subject to both horizontal and vertical land deformations during the seismic cycle of mega thrust earthquakes along the Sumatra and Andaman trenches. The relative sea-level changes in this region were historically monitored using the space geodetic techniques GPS and satellite altimetry alongside the traditional tide-gauge measurements over a period of almost 25 years. The GPS results show that the south of Thailand is still undergoing post-seismic deformations from the 2004 Mw 9.2 Sumatra-Andaman earthquake, after a significant change in the vertical motion of Phuket: from stable quasi-linear uplift at 2.5 ± 0.2 mm/yr, to (temporary) non-linear subsidence rates of 5–10 mm/yr in the past 14 quake aftermath years. The satellite altimetry data estimates the absolute sea-level rise in the Andaman Sea around the island at 3.9 ± 0.5 mm/yr. Therefore relative sea-level changes in Phuket appear to have been slightly positive until the end of 2004, followed by a significant increase averaging ~9 mm/yr that accumulated in 12 ± 1 cm by the end of 2018. Tide-gauge data gives a very similar result. The increased sea-level rise from 2005 onwards, due to tectonic land subsidence, correlates with the enhanced shallow coral reef growth and swift recoveries from bleaching events reported by long-term coral studies in this area.

Ross Ice Shelf response to climate driven by the tectonic imprint on seafloor bathymetry

Ocean melting has thinned Antarctica’s ice shelves at an increasing rate over the past two decades, leading to loss of grounded ice. The Ross Ice Shelf is currently close to steady state but geological records indicate that it can disintegrate rapidly, which would accelerate grounded ice loss from catchments equivalent to 11.6 m of global sea level rise. Here, we use data from the ROSETTA-Ice airborne survey and ocean simulations to identify the principal threats to Ross Ice Shelf stability. We locate the tectonic boundary between East and West Antarctica from magnetic anomalies and use gravity data to generate a new high-resolution map of sub-ice-shelf bathymetry. The tectonic imprint on the bathymetry constrains sub-ice-shelf ocean circulation, protecting the ice shelf grounding line from moderate changes in global ocean heat content. In contrast, local, seasonal production of warm upper-ocean water near the ice front drives rapid ice shelf melting east of Ross Island, where thinning would lead to faster grounded ice loss from both the East and West Antarctic ice sheets. We confirm high modelled melt rates in this region using ROSETTA-Ice radar data. Our findings highlight the significance of both the tectonic framework and local ocean–atmosphere exchange processes near the ice front in determining the future of the Antarctic Ice Sheet. The boundary between West and East Antarctica is a tectonic feature that bisects the Ross Ice Shelf. This boundary constrains ocean circulation under the ice, which affects ice stability, according to airborne survey data and ocean simulations.

Hierarchical Cluster Analysis of Dense GPS Data and Examination of the Nature of the Clusters Associated With Regional Tectonics in Taiwan

AbstractCollision of the Luzon Volcanic Arc is the primary causative factor behind the creation of Taiwan Island. Additionally, the indention of the Peikang basement highs in the Taiwan Strait and the back arc spreading of the Okinawa Trough are responsible for the characteristic tectonics in Taiwan. Identification of active tectonic boundaries is important for understanding neotectonics in Taiwan. We analyzed Global Positioning System (GPS) horizontal velocity data in Taiwan with a hierarchical cluster analysis method. We also developed a statistical scheme introducing information entropy to quantitatively assess the fuzziness of the obtained cluster boundaries, which enables us to distinguish a trustworthy discontinuity. The hierarchical representation, which is expressed by a dendrogram, suggests the relative importance of tectonic sources in this region. The major clusters, which appear at higher hierarchy, are likely to represent major tectonic features such as the Longitudinal Valley fault and lateral extrusion in southwest Taiwan. Those at lower hierarchy suggest velocity discontinuities associated with local geological structures such as active faults. For example, boundaries in east offshore Taiwan and southern Taiwan are identified without using geological information by this analysis. In addition to the identification of these clear tectonic boundaries, our statistical cluster assessment shows the existence of fuzzy cluster boundaries along the Coastal Plain and the Western Foothills, reflecting continuum deformation in west Taiwan.

Geo-Resilience By Soil Improvement: Contrasting the Performance of Two Embankments during a Megathrust Mw 7.8 Earthquake

The west coast of Ecuador forms the eastern side of the Pacific “ring of fire” along the Nazca tectonic plate boundary (Figure 1). The epicenter of the Ecuador earthquake on April 16, 2016 (Mw 7.8), was in the city of Pedernales in the province of Manabí. According to the United States Geological Survey (USGS), the main event was caused by shallow thrust faulting, at a hypocentral depth of 21 km, on or near the plate boundary between the Nazca and South America plates, where the Nazca subducts beneath the South America plate at a rate of 61 mm/yr. In the first 24 hours, over 135 aftershocks were recorded, with hundreds more in the weeks that followed. Overall, this megathrust earthquake and its aftershocks led to hundreds of fatalities and thousands of injuries, left tens of thousands homeless, and created an economic impact estimated at 3 percent of Ecuador’s gross domestic product.

Characterizing anatexis in the Greater Himalayan Sequence (Kumaun, NW India) in terms of pressure, temperature, time and deformation

We applied field observations combined with P-T pseudosection modelling, zircon U-Pb geochronology and bulk rock geochemistry along the Kali River Valley, Kumaun Himalaya to understand conditions of peak metamorphism and partial melting of the Greater Himalayan Sequence (GHS) along with spatiotemporal relationship between anatexis and fault activation. The southern tectonic boundary of GHS or the Main Central Thrust (MCT) is marked on the basis of structural, metamorphic and chronological evidences. Outcrop-scale observations suggest generation of partial melt at the base of the MCT. This partial melt migrated to higher structural levels and finally emplaced as tourmaline bearing leucogranite in the northern tectonic boundary of the GHS, which is marked by the South Tibetan Detachment Zone (STDZ). P-T pseudosection modelling shows that GHS have experienced muscovite dehydration melting at 9.2–9.8 kbar and 720°–725 °C, 8.4–8.7 kbar and 700°-710 °C, 7.8–8.4 kbar and 700–720 °C respectively at its lower, lower-middle and middle structural levels. Zircon U-Pb geochronology suggests that the GHS underwent suprasolidus peak metamorphism and post-peak anatexis during a time span of ~26–22 Ma at the base of the MCT and ~32–27 Ma at the middle structural level. The MCT is at least ~22 Ma old, being synkinematic to the partial melting event that took place at its base. Diachronous and brief episodes of partial melting and absence of sillimanite zone at the base of the GHS help us envisage a ‘critical taper wedge’ scenario, where partial melt weakened the overlying Himalayan wedge and triggered gravity collapse that formed the STDZ.

A new surface heat flow map of the Northern Apennines between latitudes 42.5 and 44.5 N

A revised surface heat flow map of a sector of the Northern Apennines is presented, constrained by recently available thermal and petrophysical logs from 174 wells drilled for geothermal and hydrocarbon exploration purposes. The borehole temperatures have been corrected for drilling, inclination, and palaeoclimate effects. The corrected temperature data, combined with petrophysical parameters for each individual formation, have been used to derive shallow geotherms (down to a maximum depth of 8 km), which have yielded site-specific heat flow values. These values, once corrected for palaeoclimatic topographic and erosion/sedimentation effects, have been contoured by a kriging procedure to obtain the heat flow map.The map shows a clear distinction between a western zone (the Tyrrhenian Domain) of high heat flow (>150 mW m−2), with closely spaced heat flow isolines, and an eastern zone (the Adriatic Domain) of relatively low (<70 mW m−2), spatially uniform heat flow. The boundary between the two zones is roughly parallel to the axis of the Apennines.Five crustal geotherms (extending to the Moho) and the corresponding rheological profiles confirm that the 70 mW m−2 isoline corresponds to a major tectonic boundary, across which the thermal, structural, and seismic properties of the lithosphere go through a significant change.

Shipboard Characterization of Tuvalu, Samoa, and Lau Dredge Samples Using Laser-Induced Breakdown Spectroscopy (LIBS)

Chemical analysis using laser-induced breakdown spectroscopy (LIBS) is well suited for field applications and was applied here for shipboard characterization of a large sample set during the RR1310 rock dredging expedition to the Tuvalu Seamounts. Although recently the most common data treatment for LIBS has consisted of a partial least squares approach to define sample groupings, we show that quantitative data of useful quality can be obtained with a univariate approach. Here, our analysis goal was a quantitative comparison of the total alkali (Na2O + K2O) versus silica (SiO2) contents of 586 representative dredge samples with known ranges in common rock types. Out of those samples, >400 form a single large group of alkalic basalts with minor basanites/tephrites (SiO2: 43-48 wt%, Na2O + K2O: 3-5 wt%), similar to known shield-stage compositions of the Rurutu and Samoa hotspots in the sampling area. In contrast, several dredge hauls contain samples with compositions that do not overlap with the majority of samples. This includes three dredges performed on the northern boundary of the Lau Basin that contain similar SiO2 compositions, but slightly higher total alkali (Na2O+K2O) content. Despite this difference, they classify as basanite/tephrite, similar to a subset of the main group. More importantly, similar compositions were previously reported from the same tectonic boundary, ascribed to hotspot mantle source material mixed into the Lau Basin back-arc. Although the quality of the compositional data suffices to enable sample selection for time-intensive analyses, higher precision is required for more in-depth petrogenetic interpretation. Error analysis based on repeat standard measurements suggests averaging 100 spectra per sample is optimal here, while use of a higher resolution spectrometer, together with better laser control, would improve results and interpretations.

Lithospheric structure of the Tien Shan region constrained by joint inversion of receiver function and Rayleigh wave dispersion

AbstractWe obtain a lithospheric shear‐wave velocity model across the Tien Shan orogenic belt by jointly inverting Rayleigh wave group velocities and teleseismic P‐wave receiver functions at 61 broadband seismic stations deployed in this region. Our new model reveals prominent lateral variations of shear‐wave velocity in both the crust and uppermost mantle. This model reveals different structures in the upper and middle crust across the Talas Fergana Fault, which may suggest the presence of a tectonic boundary between the western and central Tien Shan beneath the fault. According to the velocity images, the depth extent of the fault is ~40 km and this is confined to the crust. Pronounced low‐velocity anomalies are imaged in the middle crust and uppermost mantle beneath the southern and middle Tien Shan, implying that the upwelling of the materials from the upper mantle could have played an important role in the mountain building.

Deep lithospheric structure beneath the Polish part of the East European Craton as a result of magnetotelluric surveys

A fundamental tectonic boundary between the Precambrian East European Craton (EEC) and the younger Phanerozoic mountain belts of Europe runs through Poland. Whereas the transition zone between both tectonical units was intensely investigated by means of electromagnetic methods in the past, the image of electric conductivity of the EEC itself has not been detailed so far. In the present study the lithospheric structure beneath the northeast of Poland is investigated by means of three parallel magnetotelluric profiles. As a result the Polish part of the craton does not appear as homogeneously highresistive as repeatedly reported. Beneath a shallow (from 2 to 4 km) sedimentary layer a less resistive structure (several hundred Ωm) under all three profiles in mid-crustal to upper mantle depth becomes apparent in the high-resistive background. It spatially coincides with a magmatic body of the Upper Proterozoic age called Śniardwy lake gabbro intrusion.

Continental drift, plateau uplift, and the evolutions of monsoon and arid regions in Asia, Africa, and Australia during the Cenozoic

Monsoon and arid regions in the Asia-Africa-Australia (A-A-A) realm occupy more than 60% of the total area of these continents. Geological evidence showed that significant changes occurred to the A-A-A environments of the monsoon and arid regions, the land-ocean configuration in the Eastern Hemisphere, and the topography of the Tibetan Plateau (TP) in the Cenozoic. Motivated by this background, numerical experiments for 5 typical geological periods during the Cenozoic were conducted using a coupled ocean-atmosphere general circulation model to systemically explore the formations and evolutionary histories of the Cenozoic A-A-A monsoon and arid regions under the influences of continental drift and plateau uplift. Results of the numerical experiments indicate that the timings and causes of the formations of monsoon and arid regions in the A-A-A realm were very different. The northern and southern African monsoons existed during the mid-Paleocene, while the South Asian monsoon appeared in the Eocene after the Indian Subcontinent moved into the tropical Northern Hemisphere. In contrast, the East Asian monsoon and northern Australian monsoon were established much later in the Miocene. The establishment of the tropical monsoons in northern and southern Africa, South Asia, and Australia were determined by both the continental drift and seasonal migration of the Inter-Tropical Convergence Zone (ITCZ), while the position and height of the TP were the key factor for the establishment of the East Asian monsoon. The presence of the subtropical arid regions in northern and southern Africa, Asia, and Australia depended on the positions of the continents and the control of the planetary scale subtropical high pressure zones, while the arid regions in the Arabian Peninsula and West Asia were closely related to the retreat of the Paratethys Sea. The formation of the mid-latitude arid region in the Asian interior, on the other hand, was the consequence of the uplift of the TP. These results from this study provide insight to the important roles played by the earth’s tectonic boundary conditions in the formations and evolutions of regional climates during geological times.

Earthquake Education Through the Use of Documentary Movies

Unscientific, false, inaccurate and/or exaggerated reporting about anything in media or other platforms is a serious concern that needs a solution. This is particularly important when reporting about disasters (e.g. earthquakes). The lack of authentic scientific input into science news reporting may lead to news disasters, which may prove to be much more critical and dangerous than say -earthquake disasters. Therefore, this paper explores such a problem in a portion of NW Borneo and offers solution to improve the existing norms on the earthquake science, education and awareness programs in SE Asia. The explored field location is Sabah, Malaysia, which is targeted to map the level of earthquake science education and awareness of local people, and to examine the co-seismic deformation associated with the 5th June, 2015 earthquake. This event has surprised the local communities because the region is geographically located away from the active tectonic plate boundaries, and has traditionally been considered a low earthquake risk region. This is in contrast to the existence of high earthquake hazard and risk regions in the neighboring Indonesia and the Philippines. Therefore, not surprisingly, the residents of Borneo where puzzled, surprised and worried when a medium magnitude earthquake occurred and caused significant loss of life and property. The lack of scientific education on the causes, and remedies of earthquake hazards in most of the South and Southeast Asian regions is a reality, which needs a real solution. Therefore, through this work a small initiative has been started in Sabah, Malaysia where stories from the earthquake victims were recorded after the devastation caused by the June 2015 earthquake. Their real time experiences were blended with the updated scientific data on the occurrence of earthquakes in Borneo, which are mostly gathered from previously published works and the work presented here. The entire work is converted into a small documentary movie that highlights the causes of earthquake and how it impacts human life.

Cretaceous tectonic evolution of the Sava-Klepa Massif, Republic of North Macedonia – Results from calcite twin based automated paleostress analysis

The Sava-Klepa Massif represents an approximately 5 × 2 km sized fault-bounded block of dominantly basaltic rocks located within the Sava-Zone, an important suture zone between the Eurasian (Europe) and Gondwana (Adria) continental plates in the Balkans. Its nature and tectonic evolution is controversial: It is either interpreted as a remnant of the youngest Tethyan oceanic realm left behind after the main closure in the Late Jurassic or as the delimiter of a diffuse tectonic boundary between Adria and Europe, which had already collided in the Late Jurassic and was dominantly controlled by transtensional tectonics during Cretaceous times.In order to strengthen one or the other model, we concentrate on the Sava-Klepa Massif enclosing Paleozoic basement rocks, which mainly consist of a layered sequence of metamorphic marbles and mica schists. The metamorphic basement shows deformation structures clearly related to the Klepa event. Our results are based on paleostress and paleostrain analysis of twinned calcite from deformed marbles, and field observations, microstructural analysis, and 40Ar/39Ar dating of white mica. Paleostress and paleostrain analysis was enhanced by using an automated fabric analyser microscope, and developing the herein presented freeware standalone Windows® executable PACT software (Paleostress Analysis with Calcite Twins).Our results support the hypothesis that the Sava-Klepa Massif was formed during transtension as a pull-apart basin in the Late Cretaceous. This could have happened either after the collision of the European and Adriatic plates, or along a transtentional zone in the fore-arc region during subduction of the last Tethyan oceanic lithosphere.

Late Eocene – Early Miocene facies and stratigraphic development, Taranaki Basin, New Zealand: the transition to plate boundary tectonics during regional transgression

AbstractEight latest Eocene to earliest Miocene stratigraphic surfaces have been identified in petroleum well data from the Taranaki Basin, New Zealand. These surfaces define seven regional sedimentary packages, of variable thickness and lithofacies, forming a mixed siliciclastic–carbonate system. The evolving tectonic setting, particularly the initial development of the Australian–Pacific convergent margin, controlled geographic, stratigraphic and facies variability. This tectonic signal overprinted a regional transgressive trend that culminated in latest Oligocene times. The earliest influence of active compressional tectonics is reflected in the preservation of latest Eocene – Early Oligocene deepwater sediments in the northern Taranaki Basin. Thickness patterns for all mid Oligocene units onwards show a shift in sedimentation to the eastern Taranaki Basin, controlled by reverse movement on the Taranaki Fault System. This resulted in the deposition of a thick sedimentary wedge, initially of coarse clastic sediments, later carbonate dominated, in the foredeep close to the fault. In contrast, Oligocene active normal faulting in a small sub-basin in the south may represent the most northerly evidence for rifting in southern Zealandia, related to Emerald Basin formation. The Early Miocene period saw a return to clastic-dominated deposition, the onset of regional regression and the southward propagation of compressional tectonics.

Evidence of Major Structural Features over the Pan-African Domain in the Bertoua-Mbangue Area (East Cameroon) from a Multiscale Approach of Modeling and Interpretation of Aeromagnetic Data

The aim of this study is to investigate crustal structures from East Cameroon, using aeromagnetic data. The modeling of aeromagnetic data is conducted using the Oasis Montaj 8.0 software. The total magnetic intensity map reduced to the equator (RTE-TMI) shows important anomalies features, namely, the Northern East magnetic anomalies of high amplitude, the Southwest where very low values of the magnetic intensity were observed, and a corridor with negative values relatively high, separating the anomalies. The horizontal gradient map shows on the one hand brittle and folded structures carried out in the area of study and on the other hand various rectilinear, narrow, and short-wave anomalies that can be classified as a family of little faults. The maxima observed on the RTE-TMI maps are correlated to intrabasement contacts; and the map derived from Euler’s solutions permitted to evaluate the depth of the geological accidents observed from the other filters. This map also reveals new faults with a depth greater than 5000 m. The lineaments identified in the Southwestern part could be linked to the Pan-African orogeny and seem to correspond to deep-seated basement structures, which are referred to the tectonic boundary between Congo Craton and the Pan-African orogeny belt. A 23/4-D modeling confirmed the observations derived from the RTE-TMI and HGM maps analyses. It shows intrusive bodies composed of gneiss and porphyroid granite and some domes with their roof situated at various depths not exceeding 1800 m from the surface. The structural map of the study area shows the trending of the structural features observed, namely, NE-SW, NW-SE, ENE-WSW, and WNW-ESE, respectively, while the E-W and N-S are secondary orientation of the observed tectonic evidence. Moreover, circular anomalies observed over the area are assimilated to intrusions of high magnetic materials or to granitic domes.

Contrastive analysis of gravity and magnetic anomalies between North China Craton and Indian Shield

The evolution correlation between the North China Craton (NCC) and the Indian Shield (IND) is very important for plate reconstruction. Recently, more and more research results show that the NCC and IND had been pieced together in the Paleoproterozoic. In order to analyse the correlation between the NCC and IND, we use the latest gravity and magnetic data to study deep geophysical characteristics of the NCC and IND respectively, and we also use a two‐dimensional discrete wavelet transform method to discuss the division scheme of the basement tectonic unit in the Paleoproterozoic at the point of gravity and magnetic field. On the basis of gravity and magnetic anomalies, the NCC is divided into the Eastern Block, Western Block, and the Trans‐North China Orogen, which are further divided into the secondary tectonic zones and blocks. The IND is divided into the Southern Block, the Northern Block, and the Central Indian Tectonic Zone, and they also are further divided into secondary tectonic zones and ancient cratons. On the basis of that, according to the four Paleoproterozoic plate assemblage schemes proposed by predecessors, we compared the geophysical characteristics and the correlation through the regional gravity and magnetic anomalies between the two continents. The results show that the faults and tectonic boundaries in the Trans‐North China Orogen of the NCC correspond well to those in the Central Indian Tectonic Zone of IND. Moreover, the gravitational and magnetic anomalies in the Eastern Block of the NCC are quite similar to those in the Southern Block of IND, which shows that the NCC and IND might have been pieced together during the Paleoproterozoic. The geophysical result that verifies the correlation between the NCC and IND based on gravity and magnetic fields provides the evidence for Paleoproterozoic plate reconstruction and constrains the assembling patterns between the NCC and the IND.

Geological interpretation of the 2008 seismic reflection, refraction and magnetotelluric data from the northern Eyre Peninsula, Gawler Craton

A deep seismic reflection profile and coincident refraction and magnetotelluric data were acquired across the northern Eyre Peninsula, Gawler Craton in 2008 to enhance the prospectivity of this region for uranium and geothermal energy, by establishing the crustal architecture and regional geodynamic framework. The seismic line crossed several tectonic domain boundaries, including the Kalinjala Mylonite Zone, which is a key structure in the southern and central Gawler Craton. In the vicinity of the seismic section, this mylonite zone dips moderately to the east and appears to be a major crustal-scale fault which cuts through to the Moho; it separates middle to lower crust of differing seismic reflectivity. The changes in seismic character correspond with the boundary between the Olympic Fe-oxide Cu- Au-U Province (host of Olympic Dam and Prominent Hill deposits) in the east, and the Central Gawler Au Province in the west, and also are suggested to limit the extent of the South Australian Heat Flow Anomaly.