Alexander Golynsky

Grenville‐Age versus Pan‐African Magnetic Anomaly Imprints in Western Dronning Maud Land, East Antarctica

In this article, we examine aeromagnetic data from a part of the western margin of the Pan‐African East Antarctic Orogen. The East Antarctic Orogen represents the southern continuation of the East African Orogen that together formed during the collision of East and West Gondwana during late Neoproterozoic/Early Paleozoic times (at ca. 580–515 Ma). The western margin of the East Antarctic Orogen is exposed in Heimefrontfjella, western Dronning Maud Land, where the western front of this orogen crops out as the Heimefront Shear Zone. Crust west of the Heimefront Shear Zone has typical Mesoproterozoic to early Neoproterozoic (Grenville‐age) K‐Ar and Ar‐Ar mineral cooling ages, and magnetic anomalies are broad, of high amplitude, elongate, and craton parallel with long wavelengths. East of the Heimefront Shear Zone, K‐Ar and Ar‐Ar mineral cooling ages range at between ca. 570 and 470 Ma, and the magnetic anomaly pattern is entirely different. Here, a large magnetic low persists, which is overprinted by small‐scale anomalies that are oriented parallel to the regional Pan‐African structural trends at a high angle to the Mesoproterozoic anomalies. Thus, the Pan‐African tectono‐thermal overprint has caused a fundamental redistribution of magnetic minerals. The data show that the combination of aeromagnetic mapping along with detailed fieldwork is a powerful method to delineate the extent of the East Antarctic Orogen in poorly exposed Antarctica.

Eocene to Miocene geometry of the West Antarctic Rift System

Tectonic models for the Late Cretaceous/Tertiary evolution of the West Antarctic Rift System range from hundreds of kilometres of extension to negligible strike-slip displacement and are based on a variety of observations, as well as kinematic and geodynamic models. Most data constraining these models originate from the Ross Sea/Adare Trough area and the Transantarctic Mountains. We use a new Antarctic continental crustal-thinning grid, combined with a revised plate-kinematic model based on East Antarctic – Australia – Pacific – West Antarctic plate circuit closure, to trace the geometry and extensional style of the Eocene – Oligocene West Antarctic Rift from the Ross Sea to the South Shetland Trench. The combined data suggest that from chron 21 (48 Ma) to chron 8 (26 Ma), the West Antarctic Rift System was characterised by extension in the west to dextral strike-slip in the east, where it was connected to the Pacific – Phoenix – East Antarctic triple junction via the Byrd Subglacial Basin and the Bentley Subglacial Trench, interpreted as pullapart basins. Seismic-reflection profiles crossing the De Gerlache Gravity Anomaly, a tectonic scar from a former spreading ridge jump in the Bellingshausen Sea, suggest Late Tertiary reactivation in a dextral strike-slip mode. This is supported by seismic-reflection profiles crossing the De Gerlache Gravity Anomaly in the Bellingshausen Sea, which show incised narrow sediment troughs and vertical faults indicating strike-slip movement along a north – south direction. Using pre-48 Ma plate circuit closure, we test the hypothesis that the Lord Howe Rise was attached to the Pacific Plate during the opening of the Tasman Sea. We show that this plate geometry may be plausible at least between 74 and 48 Ma, but further work especially on Australian – Antarctic relative plate motions is required to test this hypothesis.

The composite magnetic anomaly map of the East Antarctic

Abstract Airborne and marine magnetic observations in East Antarctica and adjacent seas of the Indian Ocean were compiled for a magnetic anomaly map of the Antarctic. For East Antarctica, over 260,000 line km of Russian reconnaissance magnetic data were used that had been collected since 1955 mainly at line spacings of about 5, 20 and 50 km. For the offshore areas, magnetic data from American, Australian, German, Japanese, and Russian marine expeditions were incorporated. Digitally recorded data and data digitized from published and unpublished maps and profiles were included in the compilation. Local grids of these data were developed and merged into a regional grid at an interval of 5 km. The prime product of this compilation is a shaded-relief map that shows the most complete and coherent perspective to date of the regions magnetic character. In combination with other types of data, the compilation provides new insight on the tectonic features and history of this largely inaccessible region of the world. It maps out approximately 4300 km of the Antarctic Continental Margin Magnetic Anomaly (ACMMA) related to Gondwana breakup, new cratons and mobile belts, and large submarine igneous provinces.

Crustal Provinces of the Prince Charles Mountains Region and Surrounding Areas in the Light of Aeromagnetic Data

The aeromagnetic data of the Lambert Glacier — Prince Charles Mountains area provide a rather complex but surprisingly coherent image for studying the geology and tectonic history of this region. Several distinct structural units can be differentiated in the magnetic anomaly data. The aeromagnetic data from the Prince Charles Mountains and surrounding areas reveal the spatial boundaries of the Archaean cratons at the Prince Charles Mountains and Vestfold-Rauer areas and suggest the existence of a previously unknown craton in Princess Elizabeth Land. The magnetic data differentiate the inner structure of the Beaver-Rayner Proterozoic mobile belt and the complex marginal belt of the Archaean cratons reworked by Mesoproterozoic to Neoproterozoic tectonism. The aeromagnetic data clearly indicate no obvious link of the Pan-African mobile belt in Prydz Bay with Lutzow-Holm Bay, and provide no evidence that it extends inland towards the Mawson Escarpment or Grove Mountains. Thus, East Gondwana probably was not divided into Indo-Antarctic and Australo-Antarctic sectors as suggested by a number of recent studies.

ADMAP — A Digital Magnetic Anomaly Map of the Antarctic

For a number of years the multi-national ADMAP working group has been compiling near surface and satellite magnetic data in the region south of 60° S. By the end of 2000, a 5 km grid of magnetic anomalies was produced for the entire region. The map readily portrays the first-order magnetic differences between oceanic and continental regions. The magnetic anomaly pattern over the continent reflects many phases of geological history whilst that over the abyssal plains of the surrounding oceans is dominated mostly by patterns of linear seafloor spreading anomalies and fracture zones. The Antarctic compilation reveals terranes of varying ages, including Proterozoic-Archaean cratons, Proterozoic-Palaeozoic mobile belts, Palaeozoic-Cenozoic magmatic arc systems and other important crustal features. The map delineates intra-continental rifts and major rifts along the Antarctic continental margin, the regional extent of plutons and volcanics, such as the Ferrar dolerites and Kirkpatrick basalts. The magnetic anomaly map of the Antarctic together with other geological and geophysical information provides new perspectives on the break-up of Gondwana and Rodinia evolution.

Application of satellite magnetic observations for estimating near-surface magnetic anomalies

Regional to continental scale magnetic anomaly maps are becoming increasingly available from airborne, shipborne, and terrestrial surveys. Satellite data are commonly considered to fill the coverage gaps in regional compilations of these near-surface surveys. For the near-surface Antarctic magnetic anomaly map being produced by the Antarctic Digital Magnetic Anomaly Project (ADMAP), we show that near-surface magnetic anomaly estimation is greatly enhanced by the joint inversion of the near-surface data with Ørsted satellite observations compared to Magsat data that have order-of-magnitude greater measurement errors, albeit collected at much lower orbital altitudes. The CHAMP satellite is observing the geomagnetic field with the same measurement accuracy as the Ørsted mission, but at the lower orbital altitudes covered by Magsat. Hence, additional significant improvement in predicting near-surface magnetic anomalies can result as lithospheric magnetic anomaly data from the CHAMP mission become available. Our analysis also suggests that a further order-of-magnitude improvement in the accuracy of the magnetometer measurements at minimum orbital altitude may reveal considerable new insight into the magnetic properties of the lithosphere.

A new magnetic map of the Weddell Sea and the Antarctic Peninsula

Abstract As part of the Antarctic Digital Magnetic Mapping Project (ADMAP) workers from VNIIOkeangeologia (Russia), the British Antarctic Survey (UK) and the Naval Research Laboratory (USA) have brought together almost all of the available magnetic data in the area 0–120°W, 60–90°S. The final map covers the whole Weddell Sea and adjacent land areas, the Antarctic Peninsula and the seas to the west, an area comparable in size with that of the USA. This paper describes the methods used during the compilation of the map and reviews briefly some of the main features shown on it. Distinct magnetic provinces are associated with Precambrian rocks of the East Antarctic craton, highly extended continental crust in the Weddell Sea embayment, the arc batholith of the Antarctic Peninsula, and oceanic crust of the northern Weddell Sea, which was created as a direct consequence of South America–Antarctica plate motion and oceanic crust generated at the Pacific–Antarctic ridge. The magnetic anomaly map thus provides an overview of the fragmentation of south-western Gondwana and the tectonic development of the Weddell Sea sector of Antarctica.

Heat flux distribution of Antarctica unveiled

Antarctica is the largest reservoir of ice on Earth. Understanding its ice sheet dynamics is crucial to unraveling past global climate change and making robust climatic and sea level predictions. Of the basic parameters that shape and control ice flow, the most poorly known is geothermal heat flux. Direct observations of heat flux are difficult to obtain in Antarctica, and until now continent-wide heat flux maps have only been derived from low-resolution satellite magnetic and seismological data. We present a high-resolution heat flux map and associated uncertainty derived from spectral analysis of the most advanced continental compilation of airborne magnetic data. Small-scale spatial variability and features consistent with known geology are better reproduced than in previous models, between 36% and 50%. Our high-resolution heat flux map and its uncertainty distribution provide an important new boundary condition to be used in studies on future subglacial hydrology, ice sheet dynamics, and sea level change.

Magnetic Anomalies of the Grove Mountains Region and Their Geological Significance

The geology of the Grove Mountains is poorly known. The magnetic anomalies of the Grove Mountains and surrounding areas are characterized by a prominent NE-SW to E-W fabric. Well defined magnetic anomalies along its periphery with the absence of intensive magnetic anomalies in the north are a distinctive feature of this region. The obliqueness of magnetic anomalies along the study area’s boundary with respect to its central part suggests that the northern Grove Mountains basement may be much older crust than the neighboring terranes of Meso- to early Neoproterozoic high-grade metamorphic rocks. The existence of two ancient cratonic blocks in the southern Prince Charles Mountains and Vestfold Hills suggests that this region may contain Archaean or Paleoproterozoic crust. The Grove Mountains crustal block is clearly discernible in the aeromagnetic data and can be considered as a region that underwent Grenvillian and/or Pan-African or both tectonism and reworking. The absence of any visible magnetic trends running towards the Prydz Bay coast or central part of the Mawson Escarpment precludes any direct tectonic correlation with these regions.

Crustal analysis of maud rise from combined satellite and near-surface magnetic survey data

We produced a crustal magnetization model for the Maud Rise in the southwest Indian Ocean off the coast of East Antarctica using magnetic observations from the Ørsted satellite and near-surface surveys complied by the Antarctic Digital Magnetic Anomaly Project (ADMAP). Joint inversion of the two anomaly fields suggests that the magnetic effects due to crustal thickness variations and remanence involving the normal polarity Cretaceous Quiet Zone (KQZ) dominate at satellite altitude (~700 km). The crustal thickness effects were modeled in the Ørsted data using crustal thickness variations derived from satellite altitude gravity data. Modeling of the residual Ørsted and near-surface magnetic anomalies supports extending the KQZ eastwards to the Astrid Ridge. The remaining near-surface anomalies involve crustal features with relatively high frequency effects that are strongly attenuated at satellite altitudes. The crustal modeling can be extended by the satellite magnetic anomalies across the Indian Ocean Ridge for insight on the crustal properties of the conjugate Agulhas Plateau. The modeling supports the Jurassic reconstruction of Gondwana when the African Limpopo-Zambezi and East Antarctic Princess Astrid coasts were connected as part of a relatively demagnetized crustal block.