Identification Of Magnetic Anomalies Research Articles

Cretaceous–Paleocene extension at the southwestern continental margin of India and opening of the Laccadive basin: constraints from geophysical data

Abstract. Previous geophysical investigations of the western continental margin of India (WCMI) confirm the two-phase breakup history of the margin with the first breakup taking place between India and Madagascar that created the Mascarene Basin in the Late Cretaceous and the second breakup event in Early Paleocene with Seychelles separating from India. Despite numerous geoscientific studies along the WCMI, the opening of the Laccadive basin, situated along the southern part of the margin, remains poorly constrained. In this study, we evaluate the multi-channel seismic reflection and gravity anomalies at the margin to identify the early rift signatures in conjunction with the magnetic anomaly identifications in the Mascarene Basin. The analysis led to the identification of two trends of extensional structures, a NNW–SSE-oriented structure over the Laccadive Ridge north of Tellicherry Arch, interpreted to result from ENE–WSW extension, and a SSW–NNE-oriented structure in the Laccadive basin region towards the south, interpreted to result from NW–SE extension. Previous plate reconstruction models of the Mascarene Basin using marine magnetic lineations suggest that the ENE–WSW extension observed over the Laccadive Ridge could be related to the India–Madagascar separation. We associate the pattern of sediment deposition and the presence of a Paleocene trap volcanics, linked with the NW–SE grabens observed in the Laccadive basin region, to the extension between the Laccadive Ridge and the western coast of India after the separation of Madagascar from India. We further propose that the anticlockwise rotation of India and the passage of the Réunion plume have facilitated the opening of the Laccadive basin.

An automatic identification method of marine magnetic anomalies based on the sliding window correlation coefficient method

The identification of marine magnetic anomalies has fundamental importance to the study of plate tectonics and geodynamics. The traditional approach to identifying marine magnetic anomalies is by visual method and much depends on the experience of experts. Though the identification results are generally reasonable, they lack quantitative evaluation basis. Therefore, we proposed the sliding window correlation coefficient (SWCC) method to automatically identify marine magnetic anomalies and provide a quantitative and objective evaluation for the identification results. The Pearson correlation coefficient (PCC), Spearman rank correlation coefficient (SRCC) and Kendall rank correlation coefficient (KRCC) are compared in the SWCC method. The different skewness, spreading rates and random noises to the identification results are tested. The results show that the SWCC method is most optimal for identifying fast-spreading magnetic anomalies. The absolute values of the correlation coefficients at the same sliding steps are usually PCC > SRCC>KRCC, but the resolving abilities for different polarity chrons are usually KRCC>SRCC>PCC. Applications in the southwest Pacific verified the feasibility and effectiveness of the SWCC method, and suggest that short theoretical windows usually have limited feature information; therefore, combined neighbouring polarity chrons can improve the identification results of the SWCC method.

Detecting and mapping the ‘ephemeral’: magnetometric survey of a Pastoral Neolithic settlement at Luxmanda, Tanzania

Common assumptions about the ephemeral archaeological signature of pastoralist settlements have limited the application of geophysical techniques in the investigation of past herding societies. Here, the authors present a geophysical survey of Luxmanda, Tanzania, the largest-known settlement documented for the Pastoral Neolithic era in eastern Africa (c. 5000–1200 BP). The results demonstrate the value and potential of fluxgate gradiometry for the identification of magnetic anomalies relating to archaeological features, at a category of site where evidence for habitation was long thought to be undetectable. The study provides comparative data to enable archaeologists to identify loci for future investigations of mobile populations in eastern Africa and elsewhere.

Morphotectonic signatures and revised timing of opening of the Andaman Backarc Basin, Northeast Indian Ocean

The Andaman Backarc Basin is believed to have been formed by the present episode of seafloor spreading in the Andaman Sea, separating the Alcock Rise in the north (Burmese Plate) and the Sewell Rise in the south (Sunda Plate). The geophysical investigations carried out so far in this basin provided detailed information on the morphotectonic signatures of its central sector, however, such understanding of the eastern sector is still awaited. Those studies also inferred continual seafloor spreading in the Andaman Backarc Basin starting from 4.0 Ma, however, some of the subsequent studies, based on deep water sedimentation, postulated an episodic seafloor spreading responsible for the formation of the Andaman Backarc Basin. To address these problems, we revisited the morphotectonic signatures and evolution of the Andaman Backarc Basin using a new set of multibeam bathymetry and magnetic data from the central and eastern sectors of the Andaman Backarc Basin, complemented by the existing geophysical data from the central sector. Our updated bathymetry map of the newly surveyed northernmost segment (referred as Segment D), is characterized by the presence of a well-defined rift valley, with an along-axis gentle dip from the east to the west. The segment D is also characterized by the absence of significant magnetic anomalies, as in the case of segment C, corroborating the concept of replacement of layer 2A by a sill-sediment-metasedimentary layer, in a sedimented spreading centre. Further, our revisit to the magnetic anomaly identifications suggests that the magnetic anomalies over the segment B of the Andaman Backarc Basin can reasonably be explained in terms of continual seafloor spreading from chron C3An.1ny (5.894 Ma) till the present (0.0 Ma). Based on these identifications of magnetic anomalies and the plate tectonic reconstructions, we revise the age of opening of the Andaman Backarc Basin from 4.0 Ma to ~5.9 Ma.

A Global Data Set of Present‐Day Oceanic Crustal Age and Seafloor Spreading Parameters

AbstractWe present an updated oceanic crustal age grid and a set of complementary grids including spreading rate, asymmetry, direction, and obliquity. Our data set is based on a selected set of magnetic anomaly identifications and the plate tectonic model of Müller et al. (2019, 10.1029/2018TC005462). We find the mean age of oceanic crust is 64.2 Myr, slightly older than previous estimates, mainly due to the inclusion of pockets of Mesozoic aged crust in the Atlantic and Mediterranean and improvements to the Jurassic Pacific triangle. This older crust is partly compensated by additional Cenozoic‐aged back‐arc basin crust not included in previous models. The distribution of spreading modes based on area of preserved crust is relatively equal between slow (20–55 mm/yr) and fast (75–180 mm/yr) spreading systems at 33% and 39%, respectively. Crust transitional between fast and slow, or intermediate systems (55–75 mm/yr), cover 20% of the preserved ocean floor with much smaller proportions of crust formed at ultraslow (5%) and super‐fast (3%) spreading systems. Slow and intermediate spreading systems exhibit the most stable behavior in terms of spreading asymmetry and obliquity, with the widest distribution of obliquities occurring at ultraslow spreading systems, consistent with present‐day observations. Our confidence grid provides a complementary resource for nonexperts to identify those parts of the age grid that are least well constrained. Our grids in 6, 2, and 1 arc min resolution as well as our python workflow, isopolate, used to compute our data sets are freely available in online repositories and on the GPlates data portal.

Uncertainties in break-up markers along the Iberia–Newfoundland margins illustrated by new seismic data

Abstract. Plate tectonic modellers often rely on the identification of “break-up” markers to reconstruct the early stages of continental separation. Along the Iberian-Newfoundland margin, so-called break-up markers include interpretations of old magnetic anomalies from the M series, as well as the “J anomaly”. These have been used as the basis for plate tectonic reconstructions are based on the concept that these anomalies pinpoint the location of first oceanic lithosphere. However, uncertainties in the location and interpretation of break-up markers, as well as the difficulty in dating them precisely, has led to plate models that differ in both the timing and relative palaeo-positions of Iberia and Newfoundland during separation. We use newly available seismic data from the Southern Newfoundland Basin (SNB) to assess the suitability of commonly used break-up markers along the Newfoundland margin for plate kinematic reconstructions. Our data show that basement associated with the younger M-series magnetic anomalies is comprised of exhumed mantle and magmatic additions and most likely represents transitional domains and not true oceanic lithosphere. Because rifting propagated northward, we argue that M-series anomaly identifications further north, although in a region not imaged by our seismic, are also unlikely to be diagnostic of true oceanic crust beneath the SNB. Similarly, our data also allow us to show that the high amplitude of the J Anomaly is associated with a zone of exhumed mantle punctuated by significant volcanic additions and at times characterized by interbedded volcanics and sediments. Magmatic activity in the SNB at a time coinciding with M4 (128 Ma) and the presence of SDR packages onlapping onto a basement fault suggest that, at this time, plate divergence was still being accommodated by tectonic faulting. We illustrate the differences in the relative positions of Iberia and Newfoundland across published plate reconstructions and discuss how these are a direct consequence of the uncertainties introduced into the modelling procedure by the use of extended continental margin data (dubious magnetic anomaly identifications, break-up unconformity interpretations). We conclude that a different approach is needed for constraining plate kinematics of the Iberian plate pre-M0 times.

An object‐based approach to support the automatic delineation of magnetic anomalies

AbstractThe intensive use of geophysics in archaeological investigations demands new ways of fast and meaningful data interpretation. With the increasing size and complexity of magnetometer data, manual identification and delineation of magnetic anomalies becomes a time‐consuming activity. In this respect, our study introduces a new approach to automate this laborious procedure, implemented as a ready‐to‐use tool within the eCognition® software. The approach relies on a multiresolution segmentation (MRS) algorithm, which is applied on a single layer containing magnetic values. Magnetic anomalies are automatically identified and delineated at three levels of scale. Magnetic anomalies are thus classified as potential archaeological features. The degree of departure from a normal distribution is adjustable at 0.5 and 1 standard deviation (SD), respectively. The approach was tested on magnetometer images of a buried medieval village in the west of Romania. The data were acquired along parallel profiles covering six squares of 100 m × 100 m each. We have deliberately selected this magnetic map because it is not the top in terms of magnetic results and it provides staggers (due to data acquisition in 100 m grids) to show that if this algorithm works on this magnetic map, it will work defiantly on those where archaeological structures/anomalies are even more regulated. The tested scenes indicated accurate results, displaying positive‐ and negative‐valued magnetic anomalies with levels of detail almost similar to manually delineated anomalies. Our approach is simple to apply. Being implemented as a customized process for the eCognition® software, the tool attached to the article repository has a significant potential to support interpretation of any type of image obtained through geophysical measurements and we consider it an aid for large‐scale surveys.

Identification of magnetic anomalies of adjacent sourses using the wavelet transform modulus maxima and scale normalization

In the potential field inverse problems, accurate determination of the location for the anomaly sources and their properties played an important role. For geomagnetic anomalies of adjacent sources, they always superimpose upon each other not only in the spatial domain but also in the frequency domain, making the identification of these sources significantly problematic. In this paper, a new mother wavelet for effective analysis the properties of the close potential field sources was used. By theoretical modeling, using the wavelet transform modulus maxima (WTMM) method, we set up a correlative function between the scale parameter and geomagnetic source depth. Moreover, a scale normalization on the wavelet coefficients was introduced to enhancethe resolution for the separation of these sources in the scalograms, thereby determining their depth. After verifying the reliability of the proposed method on the modeling data, we have analysed the geomagnetic data in the Mekong delta. The results of this interpretation were consistency with previously published ones, furthermore, the level of resolution for this technique was quite coincidental with other methods using different geological data.

Identification of Magnetic Anomaly at Geothermal Subsurface Area PLTP Sarulla Unit I Pahae Jae, North Sumatera,Indonesia

This research was done entitled Identification of Magnetic Anomalies at Geothermal Subsurface Area at PLTP Sarulla Unit I Pahae Jae, North Tapanuli. This research was conducted to find out the dispersion pattern of earth magnetic anomaly based on its magnetism and to know the rock structure based on susceptibility value in the geothermal area. The measurements of Total magnetic field using Proton Precission Magnetometer (PPM) Elsec 770 type, Global Position System (GPS) for positioning and geological compass for north direction orientation. The data were collected randomly with the number of points obtained as much as 50 measuring point, then data analysis was done by using surfer 11 to get contour map and Mag2DCfor windows maps to get the magnetic anomaly cross section. The results showed that the magnetic anomaly value had the lowest value of 34,4358 nT and the highest value 144,789 nT moving from North toward East. While the results of quantitative interpretation of A’A model show sedimentary rock with k value (0.0035 x 103, 00059 x 103, 00061 x 103), and esite lava with k value (0.0277 x 103, 0.0241 x 103) and basalt with k value (0.2437 x 103).

No Evidence for Milankovitch Cycle Influence on Abyssal Hills at Intermediate, Fast, and Superfast Spreading Rates

AbstractA recent hypothesis contends that abyssal hill topography is linked to sea level periodicities expressed by Milankovitch cycles, predicting that abyssal hill elevation is correlated to crustal age. We test this prediction by stacking (averaging) bathymetry as a function of age to enhance age‐dependent signal while suppressing random (primarily faulted) components. Stacking is applied to bathymetry data flanking intermediate, fast, and superfast spreading ridges. Revised digital crustal age models were generated in these regions using a recent compilation of reliable magnetic anomaly identifications, with inferred temporal uncertainty of ~0.01 my. We utilize statistical properties of abyssal hills to predict the variability of the age‐stack under the null hypothesis that abyssal hills are random with respect to crustal age; the age‐stacked profile is significantly different from zero only if it exceeds this expected variability by a large margin. Our results do not support the presence of Milankovitch‐driven signals in abyssal hill topography.

Identification of magnetic anomalies in subsurface area of Sinabung mountain

This research was conducted by using geomagnetic methods. It aims to identify cross section anomalies and subsurface models. Measurements using a PPM (Proton Precession Magnetometers) Elsec 770 types data collection is done randomly with 27 measurement points. Data analysis was performed using 11 surfers to get a contour map and Mag2DC software to get the magnetic anomaly cross section. The results showed that the anomalous cross section with the geomagnetic method has the lowest value of 18.45 nT and the highest value reached 64.92 nT. From the anomaly, it was found that the value of vulnerability obtained is 0.0004, 0.00018, 0.0002 emu where subsurface layer model consists of dolomite and limestone.

Structure, mechanical properties and evolution of the lithosphere below the northwest continental margin of India

The continental breakup history at the northwest continental margin of India remained conjectural due to lack of clearly discernable magnetic anomaly identifications and the presence of several enigmatic structural/basement features whose structure was partly obscured by the Late Cretaceous Deccan magmatic event. In this study, a detailed analysis of the existing seismic and seismological data covering both onshore and offshore areas of the northwest Indian margin along with 3-D/2-D constrained potential field (gravity, magnetic and geoid) modeling has been carried out. The crustal structure and lithosphere–asthenosphere boundary (LAB) delineated across the margin provided valuable insights on the mechanism of continental extension. An analysis of the residual geoid anomaly (degree-10) map and the modeled LAB below Deccan volcanic province (DVP) revealed significant variation in upper mantle characteristics between the northwest (NW) and south central (SC) parts of DVP having thinner lithosphere in the NW part. The depth to LAB ranges 80–130 km at the margin with gradual thinning towards the western offshore having sharp gradient in the south (SC part of DVP) and gentle gradient in the north (NW part of DVP). The Moho configuration obtained from seismically constrained 3-D gravity inversion reveals that Moho depths vary 34–42 km below DVP and gradually thins to 16–20 km in the western offshore. The effective elastic thickness (Te) map computed through 3-D flexural modeling indicates that the Te values are in general lower in the region and range 12–25 km. Such lower Te values could be ascribed to the combined effect of the lithosphere stretching during Gondwana fragmentation in the Mesozoic and subsequent thermal influence of the Reunion plume. Based on the crustal stretching factors (β), Te estimates and the modeled lithosphere geometry at the margin in this study, we propose that the lithosphere below Laxmi–Gop basin region (β > 3.0) had undergone continuous stretching since India–Madagascar rifting (~ 88 Ma) /much prior to this event. However, this continuous stretching did not lead to breakup. Due to syn-rift cooling, the developed necking zone (brittle–ductile deformation) got ceased and led to the development of a new necking zone between Seychelles and Laxmi Ridge. Subsequent stretching between Seychelles and the Laxmi Ridge contemporaneous with the Deccan flood basalts eruption led to the seafloor spreading in the Western Basin (anomaly C28n). Thus, the Laxmi Ridge became a continental sliver.

Sequential patterns in Cenozoic marginal basins of the Northwest Pacific

AbstractBy using magnetic anomaly identifications, onshore and offshore exploratory wells, ODP drillings, isotopic dating and orthochronology results, this paper summarizes the tectonic event sequence (including extension, back‐arc spreading, subsidence, convergence/compressive deformation and thrusting) of the marginal basins of the NW Pacific and extracted sequence patterns of the marginal basins according to the tectonic event sequence from an array of oil company regional seismic lines and other geological data. Three important evolutionary stages of the Northwestern Pacific (NW Pacific) marginal sea basins are distinguished: from the Palaeocene to Eocene, from Oligocene to Middle Miocene and from the later Middle Miocene to the present day. Each stage corresponds to a rifting sequence (Palaeocene to Eocene), a drifting sequence (Oligocene to Middle Miocene) and a subsidence/convergence sequence (later Middle Miocene to the present day). The rifting sequence and drifting sequence developed sequentially in the South China Sea Basin, from Palaeocene to Eocene and from Oligocene to Middle Miocene, while in the Japan and Okhotsk Sea basins, an early stage rifting sequence was not developed in the Palaeocene to Eocene interval. However, the drifting and rifting sequence developed synchronously from the Oligocene to Middle Miocene. From the Later Miocene time, all the marginal basins of the Northwest Pacific basically stopped drifting and began to enter the subsidence (post‐drifting) stage. An arc‐continent collision from the south caused the formation of a convergence sequence in the southern margin of each marginal basin. The NW Pacific Plate collision with the Kuril–Kamchatka Arc led to the deformation of the subsidence sequence in the southern margin of the Kuril Sea Basin. The NW Pacific Plate convergence with the Japan Arc led to the formation of a convergence sequence in the southern margin of the Japan Sea Basin. The Borneo–Palawan Arc convergence with the Dangerous Grounds–Reed Bank Block in the South China Sea Basin from 15 Ma led to the formation of the convergence sequence in the southern margin of the South China Sea Basin. The degree of thrusting deformation of the convergent sequence increased gradually from north to south in the marginal basins of the Northwest Pacific. Copyright © 2016 John Wiley & Sons, Ltd.

The GPlates Portal: Cloud-Based Interactive 3D Visualization of Global Geophysical and Geological Data in a Web Browser.

The pace of scientific discovery is being transformed by the availability of ‘big data’ and open access, open source software tools. These innovations open up new avenues for how scientists communicate and share data and ideas with each other and with the general public. Here, we describe our efforts to bring to life our studies of the Earth system, both at present day and through deep geological time. The GPlates Portal (portal.gplates.org) is a gateway to a series of virtual globes based on the Cesium Javascript library. The portal allows fast interactive visualization of global geophysical and geological data sets, draped over digital terrain models. The globes use WebGL for hardware-accelerated graphics and are cross-platform and cross-browser compatible with complete camera control. The globes include a visualization of a high-resolution global digital elevation model and the vertical gradient of the global gravity field, highlighting small-scale seafloor fabric such as abyssal hills, fracture zones and seamounts in unprecedented detail. The portal also features globes portraying seafloor geology and a global data set of marine magnetic anomaly identifications. The portal is specifically designed to visualize models of the Earth through geological time. These space-time globes include tectonic reconstructions of the Earth’s gravity and magnetic fields, and several models of long-wavelength surface dynamic topography through time, including the interactive plotting of vertical motion histories at selected locations. The globes put the on-the-fly visualization of massive data sets at the fingertips of end-users to stimulate teaching and learning and novel avenues of inquiry.

Geodynamics of the South China Sea

The beginning of seafloor spreading in the South China Sea (SCS) is now established from IODP drilling Leg 349 at 33Ma. Chron 12 (32Ma) is the oldest chron identified in the SCS. The nature of the crust of the northeastern part of the SCS located north of chron C12, where chrons 15 to 17 were previously identified, is not oceanic but thinned continental crust intruded by volcanic elongated features emplaced 17–22Ma ago. Based on magnetic anomaly identifications, the end of the SCS spreading could be either 15.5, 20.5Ma (Briais et al., 1993; Barckhausen et al., 2014) or something else. However, as post-spreading magmatic activity (~13–3.5Ma) largely masks the spreading fabric in particular near the axis of the east sub-basin, published locations of the axial magnetic anomaly (extinct spreading axis) and spreading rates are not reliable. A contoured map of the extremely dense set of magnetic data shows that a few magnetic lineations belonging to the magnetic seafloor spreading fabric are still preserved and parallel to the N055° bathymetric seafloor spreading trends identified on swath-bathymetric maps in the central part of the SCS, suggesting that the extinct ridge axis is N055° trending with potential N145° transform faults. Based on published swath-bathymetric data, oceanic domains with different seafloor spreading lineaments have been delimited (N055°, N075° and N085°) and provide important constraints used to propose a kinematic sketch of the SCS opening. As a consequence, the Zhongnan faults zone, located between the east and southeast sub-basins, acted as a major fracture zone system during the SCS opening, with horizontal offsets varying from ~50km to ~140km.The flow-line pattern defined from the seafloor spreading lineaments and the few identified FZs have been used to highlight conjugate segments of continental margins. During the first phases of opening of the SCS, from the fit of continents to chron C10 (30Ma), the N175° extension observed in the Xisha trough and eventually south of the Macclesfield Bank extends to the Qui Nhon ridge, located along the eastern margin of Vietnam, in the southward prolongation of the Red River fault system. Normal faults curve toward the south with a horsetail geometry interpreted as evidence for a few tens of kilometers of dextral motion along the Qui Nhon ridge. Since chron 10 and until the end of SCS opening, the plate boundary located between the southern South China Sea (SSCS) and EU plates jumped westward several times from the location of the Ulugan fault near Palawan to the western limit of the southwest basin, explaining the progressive formation of the SCS from east to west and giving the characteristic V-shape of the SCS. The opening of the whole SCS is linked and occurred simultaneously with the northward subduction of the proto-SCS whose suture is located south of Palawan and extends westwards in north Borneo.

Magnetic signature of North-East Greenland, the Morris Jesup Rise, the Yermak Plateau, the central Fram Strait: Constraints for the rift/drift history between Greenland and Svalbard since the Eocene

A compilation of several aeromagnetic surveys across North Greenland and the Fram Strait area is presented. Across North Greenland, the data are related to the known onshore geology. The correlation between the geological structure and the large-scale magnetic anomalies is excellent. Along the North Greenland coast, the data indicate that the Late Mesozoic Kap Washington volcanics might have a larger areal extent than known from onshore geological mapping. The submarine Morris Jesup Rise is characterized by strong positive magnetic anomalies, and the anomalies across the plateau indicate the presence of distinct volcanic centers. This massive magmatism has occurred latest in conjunction with the Oligocene initial stages of plate divergence between Svalbard and North Greenland that led to the development of Fram Strait. Both plateaux, the Morris Jesup Rise and the Yermak Plateau, are interpreted to be of continental origin and, in the initial rift stage of the Eurasia Basin around 56Ma, to have been contiguous with the Lomonosov Ridge. More toward the east in the Fram Strait interpretations of seismic and bathymetric data indicate the presence of an active segment of mid-ocean ridge, the Lena Trough. This approximately 280-km-long segment terminates in the south at the NW–SE striking Spitsbergen Fracture Zone, while in the north it bends to connect with the Gakkel Ridge. A shallow water pathway along the line of the trough might have existed between those times and ~21Ma, above the propagating rift system in the north and, further south, over extending and subsiding continental crust of the Svalbard and North-East Greenland margins. Magnetic anomaly identifications indicate that the Lena Trough has remained an ultraslow spreading system, or possibly even all of the magnetic lineations may be signals of serpentinized exhumed mantle rocks rather than of basaltic crust.

Identification of magnetic anomalies based on ground magnetic data analysis using multifractal modelling: a case study in Qoja-Kandi, East Azerbaijan Province, Iran

Abstract. Ground magnetic anomaly separation using the reduction-to-the-pole (RTP) technique and the fractal concentration–area (C–A) method has been applied to the Qoja-Kandi prospecting area in northwestern Iran. The geophysical survey resulting in the ground magnetic data was conducted for magnetic element exploration. Firstly, the RTP technique was applied to recognize underground magnetic anomalies. RTP anomalies were classified into different populations based on the current method. For this reason, drilling point area determination by the RTP technique was complicated for magnetic anomalies, which are in the center and north of the studied area. Next, the C–A method was applied to the RTP magnetic anomalies (RTP-MA) to demonstrate magnetic susceptibility concentrations. This identification was appropriate for increasing the resolution of the drilling point area determination and decreasing the drilling risk issue, due to the economic costs of underground prospecting. In this study, the results of C–A modelling on the RTP-MA are compared with 8 borehole data. The results show that there is a good correlation between anomalies derived via the C–A method and the log report of boreholes. Two boreholes were drilled in magnetic susceptibility concentrations, based on multifractal modelling data analyses, between 63 533.1 and 66 296 nT. Drilling results showed appropriate magnetite thickness with grades greater than 20 % Fe. The total associated with anomalies containing andesite units hosts iron mineralization.

Semiautomatic fracture zone tracking

AbstractOceanic fracture zone traces are widely used in studies of seafloor morphology and plate kinematics. Satellite altimetry missions have resulted in high‐resolution gravity maps in which all major fracture zones and other tectonic fabric can be identified, and numerous scientists have digitized such lineaments. We have initiated a community effort to maintain low‐cost infrastructure that allows seafloor fabric lineaments to be stored, accessed, and updated. A key improvement over past efforts is our processing software (released as a GMT5 supplement) that allows for semiautomatic corrections to previously digitized fracture zone traces given improved gridded data sets. Here we report on our seafloor fabric processing tools, which complement our database of seafloor fabric lineations, magnetic anomaly identifications, and plate kinematic models.

Community infrastructure and repository for marine magnetic identifications

Magnetic anomaly identifications underpin plate tectonic reconstructions and form the primary data set from which the age of the oceanic lithosphere and seafloor spreading regimes in the ocean basins can be determined. Although these identifications are an invaluable resource, their usefulness to the wider scientific community has been limited due to the lack of a central community infrastructure to organize, host, and update these interpretations. We have developed an open-source, community-driven online infrastructure as a repository for quality-checked magnetic anomaly identifications from all ocean basins. We provide a global sample data set that comprises 96,733 individually picked magnetic anomaly identifications organized by ocean basin and publication reference, and provide accompanying Hellingerformat files, where available. Our infrastructure is designed to facilitate research in plate tectonic reconstructions or research that relies on an assessment of plate reconstructions, for both experts and nonexperts alike. To further enhance the existing repository and strengthen its value, we encourage others in the community to contribute to this effort.

The crustal structure of the Central Mozambique continental margin — Wide-angle seismic, gravity and magnetic study in the Mozambique Channel, Eastern Africa

Abstract The continental margin of Mozambique formed during the initial dispersal of Gondwana about 180 Ma. Due to the lack of deep seismic and dense potential field data, many details of the timing and geometry of the early breakup in this region remained unknown to date. To close this gap, a research project (MoBaMaSis (“Mozambique Basin Marine Seismic Survey”) with the French research vessel R/V Marion Dufresne II was conducted in 2007. This paper presents the results of P-wave, magnetic and 2D-gravity modelling along two parallel seismic refraction profiles between 37° and 41° E, crossing the Mozambique rifted margin. The crust shows the characteristics of normal to slightly thickened oceanic crust. A lower crustal high-velocity-body with P-wave-velocities of 7.0–7.5 km/s is observed along both profiles. Its origin is discussed in the context of upper mantle convection and thermal properties. The existing magnetic anomaly identifications have been extended to older ages. We postulate that the oldest oceanic crust near the Central Mozambique continental margin has been formed around M41n (166 Ma). Closer to the coast a pronounced negative magnetic anomaly exists that we interpret to coincide with the continent–ocean-transition. This implies that the position of the continent–ocean-transition is located significantly closer to the shoreline than proposed before.