Advent Of Plate Tectonics Research Articles

The Paraná-Etendeka Continental Flood Basalt Province: A historical perspective of current knowledge and future research trends

The development of ideas concerning Continental Flood Basalt Provinces is not new, and many studies were completed on specific provinces before the advent of plate tectonics. The Paraná-Etendeka Province is not an exception, and actually is an example of a province that has been thoroughly studied for >100years. In this work, I present a brief summary of various aspects of this province from a rather general point of view, including many references of difficult access to a reader not versed on the Portuguese language. Key features include the presence of alkaline volcanism along the edges of the main basin, before and after a markedly tholeiitic event, the uneven spatial distribution of eruptive products relative to the location of continental rupture, the apparent lack of a pattern of temporal activity across the whole province and the close relationship between the structure of the underlying sedimentary basin and the distribution of volcanic rocks. By bringing together information relevant to all of those key features, an evolutionary model emphasizing the role played by the changing local structure is outlined. This model is an example of how key observations (many of which were overlooked for >50years) provide the required impetus for the completion of future research that has the potential to substantially change the form in which this province has been visualized for at least the past 30years.

Origins of the supercontinent cycle

The supercontinent cycle, by which Earth history is seen as having been punctuated by the episodic assembly and breakup of supercontinents, has influenced the rock record more than any other geologic phenomena, and its recognition is arguably the most important advance in Earth Science since plate tectonics. It documents fundamental aspects of the planet's interior dynamics and has charted the course of Earth's tectonic, climatic and biogeochemical evolution for billions of years. But while the widespread realization of the importance of supercontinents in Earth history is a relatively recent development, the supercontinent cycle was first proposed thirty years ago and episodicity in tectonic processes was recognized long before plate tectonics provided a potential explanation for its occurrence. With interest in the supercontinent cycle gaining momentum and the literature expanding rapidly, it is instructive to recall the historical context from which the concept developed. Here we examine the supercontinent cycle from this perspective by tracing its development from the early recognition of long-term episodicity in tectonic processes, through the identification of tectonic cycles following the advent of plate tectonics, to the first realization that these phenomena were the manifestation of episodic supercontinent assembly and breakup.

Developments in the geological exploration of Nepal

Prior to 1950, only sporadic geological observations by a few visitors were made in Nepal. With the opening of the country to foreigners in 1950, Nepal soon came into the focus of interest in Himalayan geology. It was the time of the classical "descriptive geology" with mapping as the primary objective. Several excellent monographs and the first geological maps of different parts of the Nepal Himalaya were produced. The best results were obtained in the richly fossiliferous "Tibetan" sedimentary zone in the north, whereas descriptions of the Central Crystalline zone and of the thick, unfossiliferous metasediments of the Lesser Himalaya reflected mainly the widely differing interpretations and conflicting views of the investigators; nappe structure vs. block tectonics was the main issue. ..
 With the advent of plate tectonics in the late 1960s, the Himalaya became the "collided range". Microstructural, mineralogical and geochemical studies in the search for stress and heat effects of subduction and collision on structure, metamorphism and magmatism became dominant and in Nepal concentrated on the Main Central Thrust, which was treated in terms of post­ collisional continental subduction. With it went a shift of emphasis from field to laboratory work, from observation to interpretation, from mapping to modelling, from fact to theory.
 The last thirty years were characterised by the strengthening and diversification of geological institutions in Nepal with the creation of a National Seismological Centre, the beginning of petroleum exploration in the southern foreland of the Himalaya, an intensification and modernisation of classical geological surveying and a strong engagement in the application of geology for engineering and natural hazard assessment purposes.

Plate acceleration: The obduction trigger?

Obduction processes, though spectacular (dense oceanic ophiolites are emplaced on top of light, continental rocks along thousands of km), have been little elucidated since the advent of plate tectonics. Based on convergence velocities and blueschist formation, we show that the two recent large-scale, Upper Jurassic and Upper Cretaceous obductions coincided with periods during which velocities increased abruptly and more than doubled. The latter obduction also modified the interplate coupling across adjacent subduction zones. We critically propose a mechanism in which large-scale obductions are triggered by intraplate instabilities resulting from sharp plate accelerations, possibly in response to superplume events.

Nineteenth-century observations of the Dun Mountain Ophiolite Belt, Nelson, New Zealand and trans-Tasman correlations

Abstract The Nelson Mineral Belt, part of the Dun Mountain Ophiolite Belt of Permian age, in the north of the South Island of New Zealand, was the subject of intense interest soon after the European settlement of New Zealand owing to the discovery of copper and chromite mineralization. The first geologist to survey the Mineral Belt in east Nelson was Thomas Ridge Hacket ( c . 1830–1884), who arrived from Britain in 1857, although he was primarily interested in the mineralization. The first scientific description of the belt followed the visit in 1859 of the geologist Ferdinand von Hochstetter (1829–1884) of the Austrian Geological Survey who regarded the belt as a sill. He recognized that Dun Mountain was not serpentinite, like the rest of the belt, but an olivine-rich rock that he named dunite. von Hochstetter tentatively considered that thick mafic rocks of the Brook Street Volcanics, that were then considered to be intrusives rather than sedimentary, may have been a correlative of the Mineral Belt. Between the belt and the Brook Street rocks he mapped the Wooded Peak Limestone and Maitai Slates. von Hochstetter tentatively assigned a Mesozoic age to all of the above rocks and for nearly 100 years Mesozoic sedimentary rocks in many parts of New Zealand were regarded as a correlative of the Maitai Slates. Both Hacket and von Hochstetter confirmed an abundance of chromite in the Mineral Belt, a finding that resulted in the building of New Zealand's first railway. Mining was short-lived but hopes were raised that gold might be found following Hacket's move to Queensland in the late 1860s. He recognized that the Gympie gold-fields had many similarities with Dun Mountain and reasoned that east Nelson might also be auriferous. This was taken up by men in Nelson such as Sir David Monro (1813–1877) and William Wells (1810–1893) who were keen geological observers, and by Monro's son in law Dr, later Sir James, Hector (1834–1907) who was director of the New Zealand Geological Survey. In 1870, Hector arranged for Edward Heydelbach Davis (1845–1871) to undertake a detailed examination of the Permo-Triassic rocks of east Nelson. Davis, like Hacket, regarded the Mineral Belt as metamorphosed Maitai rocks. As well as demonstrating that the east Nelson rocks did not contain economic concentrations of gold, copper or chromite, Davis showed that they were distinct from what had been thought to be similar rocks in the Coromandel gold-fields in North Island of New Zealand. This was the first, if not fully appreciated, step to limit the Maitai rocks. Hacket's correlation of the Gympie and Dun Mountain rocks was forgotten until the advent of plate tectonics. The various major rock units in Nelson are now recognized as terranes that accumulated as a result of convergent plate tectonics along the Mesozoic margin of Gondwanaland.

On the uncertainties in hot spot reconstructions and the significance of moving hot spot reference frames

It is widely accepted that substantial relative motion has occurred between the Indo‐Atlantic and Pacific hot spots since the Late Cretaceous. At the same time, a fixed Indo‐Atlantic hot spot reference frame has been argued for and used since the advent of plate tectonics, implying relatively little motion between the hot spots in this domain since about 130 Ma. Most plumes purported to have caused these hot spots, while being advected in the global‐scale mantle flow field, are assumed to move an order of magnitude more slowly than plates. However, the lifetime of a plume may be over ∼100 Myr, and the integrated motion of a plume is expected to be significant over these times. The uncertainties inherent in hot spot reconstructions are of a magnitude similar to the expected plume motion, and so any differences between a fixed and moving frame of reference must be discernible beyond the level of these uncertainties. We present a method for constraining hot spot reconstruction uncertainties, similar to that in use for relative plate motion. We use a modified Hellinger criterion of fit for the hot spot problem, using track geometries and radiometric dating, and derive covariance matrices for our Indo‐Atlantic rotations for the last 120 Myr. However, any given mantle convection model introduces additional uncertainties into such models, based on its model parameters and starting conditions (e.g., choice of global tomography model, viscosity profile, nature of mantle phase transitions). We use an interactive evolutionary approach, where we constrain the hot spot motion resulting from convection models to fit paleomagnetic constraints, and converge on an acceptable motion solution by varying unknowns over several generations of simulations. Our hot spot motion model shows large motion (5–10°) of the Indo‐Atlantic hot spots for times >80 Ma, consistent with available paleomagnetic constraints. The differences between the fixed and moving hot spot reference frames are not discernible over the level of uncertainty in such rotations for times <80 Ma.

W. Q. Kennedy, the Great Glen Fault and strike-slip motion

Abstract At the time it was written, Kennedy’s paper on the Great Glen Fault had clear evidence for a known lateral displacement, and the evidence was so well presented that it convinced a sceptical geological world that such movements were possible. The acceptance of large scaled lateral movements led to the concept of great fundamental fractures and, with the advent of plate tectonics and a climate of mobilistic thinking, many of these great fractures were later recognized as plate or terrane boundaries. Along with this thinking, new criteria evolved for recognizing those fractures that had been involved in major displacements—in fact the concept of throw became replaced by the concept of role. Role was identified from the history of the blocks on either side of the fracture, and where that history was incompatible with them being together, then a large role was possible for the fault itself. Taking a new look at the Great Glen Fault in these terms, it becomes clear that there are insufficient data on the rocks on either side to allow any conclusions about the nature and timing of its role to be deduced. If the later, displacements, which are at present the main concern of researchers, are the sum of the movements on the fracture then it is ironically the least significant of the four NE-SW fractures in Scotland.

Speculations on Basement Mobility in Gulf of Mexico: ABSTRACT

Since the advent of plate tectonics, we have been faced with explaining the genesis of the Gulf of Mexico. The Gulf basin is the most heavily explored basin in the world, yet concrete evidence relative to its origin has not yet surfaced. Like pieces of a puzzle, major clues in bathymetry, paleobasin margins, and shifting depocenters are coming together to form a picture of the evolution of the gulf. It is reasonable to propose that the Yucatan Peninsula was once in Texas waters. Verification of this hypothesis may vastly expand the hydrocarbon potential of the United States Gulf Coast area. As more geophysical and geologic data are collected, extrapolation of sedimentary facies and the basin axis into the Yucatan shelf and interior may move these speculations into the rea m of fact. End_of_Article - Last_Page 498------------

Plate Tectonics and Foreland Basement Deformation

The extent and complexity of Laramide foreland basement deformation in the Wyoming province adjacent to the Idaho-Wyoming thrust-fold belt have led to numerous tectonic hypotheses, including tangential crustal compression (manifest as thrusting), vertical uplift, and strike slip; actually, all three types of deformation have occurred. With the advent of plate tectonics, tangential compression related to subduction has been mentioned most frequently as the ultimate cause of foreland deformation. Tangential compression is presumably operative in all subduction-related orogenic belts, but because most orogenic belts do not have foreland basement deformation comparable with that of the Wyoming province, compression alone does not seem sufficient to account for foreland basement structuring. Apparently a more specific condition is necessary. It is here proposed that in addition to tangential compression and strike slip, a lithospheric slab subducted well beneath the foreland is a fundamental requisite for deformation there, providing the buoyancy necessary for uplift of basement blocks. Recent work based on K2O/SiO2 ratios of Cenozoic andesites suggests that paleosubduction did occur far east within the Wyoming province (Lipman and others, 1971).