MEVTV study: Early tectonic evolution of Mars: Crustal dichotomy to Valles Marineris

Several fundamental problems were addressed in the early impact, tectonic, and volcanic evolution of the martian lithosphere: (1) origin and evolution of the fundamental crustal dichotomy, including development of the highland/lowland transition zone; (2) growth and evolution of the Valles Marineris; and (3) nature and role of major resurfacing events in early martian history. The results in these areas are briefly summarized

Role of tectonic stress in seepage evolution along the gas hydrate‐charged Vestnesa Ridge, Fram Strait

Methane expulsion from the world ocean floor is a broadly observed phenomenon known to be episodic. Yet the processes that modulate seepage remain elusive. In the Arctic offshore west Svalbard, for instance, seepage at 200–400 m water depth may be explained by ocean temperature‐controlled gas hydrate instabilities at the shelf break, but additional processes are required to explain seepage in permanently cold waters at depths \u3e1000 m. We discuss the influence of tectonic stress on seepage evolution along the ~100 km long hydrate‐bearing Vestnesa Ridge in Fram Strait. High‐resolution P‐Cable 3‐D seismic data revealed fine‐scale (\u3e10 m width) near‐vertical faults and fractures controlling seepage distribution. Gas chimneys record multiple seepage events coinciding with glacial intensification and active faulting. The faults document the influence of nearby tectonic stress fields in seepage evolution along this deepwater gas hydrate system for at least the last ~2.7 Ma

The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U-Th-Sm)/He thermochronology

Atlantic-type continental margins have long been considered “passive” tectonic settings throughout the entire postrift phase. Recent studies question the long-term stability of these margins and have shown that postrift uplift and reactivation of preexisting structures may be a common feature of a continental margin's evolution. The Namaqualand sector of the western continental margin of South Africa is characterized by a ubiquitously faulted basement but lacks preservation of younger geological strata to constrain postrift tectonic fault activity. Here we present the first systematic study using joint apatite fission track and apatite (U-Th-Sm)/He thermochronology to achieve a better understanding on the chronology and tectonic style of landscape evolution across this region. Apatite fission track ages range from 58.3 ± 2.6 to 132.2 ± 3.6 Ma, with mean track lengths between 10.9 ± 0.19 and 14.35 ± 0.22 µm, and mean (U-Th-Sm)/He sample ages range from 55.8 ± 31.3 to 120.6 ± 31.4 Ma. Joint inverse modeling of these data reveals two distinct episodes of cooling at approximately 150–130 Ma and 110–90 Ma with limited cooling during the Cenozoic. Estimates of denudation based on these thermal histories predict approximately 1–3 km of denudation coinciding with two major tectonic events. The first event, during the Early Cretaceous, was driven by continental rifting and the development and removal of synrift topography. The second event, during the Late Cretaceous, includes localized reactivation of basement structures as well as regional mantle-driven uplift. Relative tectonic stability prevailed during the Cenozoic, and regional denudation over this time is constrained to be less than 1 km

Tectonic evolution of the Archaean high-grade terrain of South India

The southern Indian shield consists of three major tectonic provinces viz., (1) Dharwar Craton, (2) Eastern Ghat Mobile Belt, and (3) Pandyan Mobile Belt. An understanding of their mutual relations is crucial for formulating crustal evolution models. The tectonic evolution of these provinces is summarized

Geological evolution of the Pietersburg greenstonebelt, South Africa and associated gold mineralization

The polyphase history of gold mineralization seen in the Pietersburg greenstone belt is integrated with the geochemical and tectonic evolution of greenstone belts as a whole. The four distinct regional geological settings of gold mineralization are described

Tectonics, volcanism, landscape structure and human evolution in the African Rift

Tectonic movements and volcanism in the African Rift have usually been considered of relevance to human evolution only at very large geographical and chronological scales, principally in relation to longterm topographic and climatic variation at the continental scale. At the more loca1 scale of catchment basins and individual sites, tectonic features are generally considered to be at worst disruptive and at best incidental features enhancing the preservation and exposure of early sites. We demonstrate that recent lava flows and fault scarps in a tectonically active region create a distinctive landscape structure with a complex and highly differentiated topography of enclosures, barriers and fertile basins. This landscape structure has an important potential impact on the co-evolution of prey-predator interactions and on interspecific relationships more generally. In particular, we suggest that it would have offered unique opportunities for the development of a hominid niche characterised by bipedalism, meat-eating and stone tool use. These landscape features are best appreciated by looking at areas which today have rapid rates of tectonic movement and frequent volcanic activity, as in eastern Afar and Djibouti. These provide a better analogy for the Plio-Pleistocene environments occupied by early hominids than the present-day landscapes where their fossil remains and artefacts have been discovered. The latter areas are now less active than was the case when the sites were formed. They have also been radically transfomed by ongoing geomorphological processes in the intervening millennia. Thus, previous attempts to reconstruct the local landscape setting adjacent to these early hominid sites necessarily rely on limited geological windows into the ancient land surface and thus tend to filter out small-scale topographic detail because it cannot be reliably identified. It is precisely this local detail that we consider to be of importance in understanding the environmental contribution to co-evolutionary developments

Neogene plate tectonic reconstructions and geodynamics of North Island sedimentary basins: Implications for the petroleum systems

Although the modern Australia-Pacific plate boundary through New Zealand is relatively straight, there have been significant changes in its geometry during the Neogene. Within the North Island sector there has been a fundamental transition from an Alpine Fault translation/transpression regime to a Hikurangi margin subduction regime. This transition has been accompanied by the southward encroachment of the edge of the Pacific plate oceanic slab into Australia lithosphere, shortened and thickened along its eastern margin as a consequence of the prior Alpine Fault transpression, the process now operating in South Island. The response of the Australia lithosphere at the surface to the emplacement of the subducted slab at depth, has differed in the East Coast forearc region versus the foreland in western North Island, where the depth to the slab is greater and there has been a characteristic southward migration of depocentres pinned to the leading edge of the slab. The recent publication of new rotation parameters for relative motion of the Australia, Antarctic and Pacific plates, have provided key new data from which to plot the successive emplacement history of the Pacific slab beneath North Island, thus enabling the comparisons to be made with basin stratigraphy and geohistory. These data also constrain the age of subduction initiation at various points along the present trend of the Hikurangi Trough, identifying a younging of subduction initiation to the southwest. An implication of this younging direction is that the modern accretion¬ary prism south of Cape Kidnappers can be no older than late Miocene (c. 11 Ma). The focus of this paper is on new ideas about the tectonic development of North Island and its basins, which have implications for hydrocarbon exploration

On the origin of the North Pacific arcs

We present a new hypothesis that relates global plate tectonics to the formation of marginal basins, island arcs, spreading ridges and arc-shaped mountain belts around the North Pacific Ocean. According to our model, the ellipsoidal-shaped Paleogene basins of the South China Sea, Parece-Vela Basin, Shikoku Basin, Sea of Japan and the Sea of Okhotsk in addition to those of the North American Cordillera can be attributed to the change in plate convergence direction at 42 Ma between the Indoaustralian and Eurasian plates. The new direction of convergence was parallel to the eastern continental margin of Asia and resulted in widespread extension perpendicular to this margin and to the western margin of North America. Both margins form part of a circle parallel to the Indoaustralian-Eurasian direction of convergence