Igneous Activity at the Birth of an Ocean Basin in Eastern Greece

1974 ◽  
Vol 11 (6) ◽  
pp. 842-853 ◽  
Author(s):  
Andrew Hynes
Keyword(s):  
Red Sea ◽  
Marine Sediments ◽  
Ocean Basin ◽  
Igneous Rocks ◽  
Continental Margins ◽  
Plate Boundaries ◽  
Plate Margin ◽  
Igneous Activity ◽  
Thrust Sheets ◽  
Ophiolitic Rock

A sequence of varied igneous rocks, of Triassic age, occurs in a complex stack of thrust sheets in the Othris Mountains of eastern Greece. The igneous rocks, which are picritic basalts, diabases, keratophyric tuffs, and pillow lavas, are conformably overlain by marine sediments typical of continental margins, and tectonically overlain by several thrust sheets of ophiolitic rock. The igneous rocks are undersaturated with silica. They are similar in chemistry to igneous rocks erupted on the margins of the Red Sea, which are located on a young, accreting plate margin. The igneous rocks of the Othris Mountains are interpreted as evidence of the development of an accreting plate margin in eastern Greece in Triassic time. The ophiolites overlying them probably came from an ocean basin created at that margin.In contrast to the rocks on the margins of the Red Sea, igneous rocks on many other modern oceanic margins are saturated with silica. This contrast is tentatively related to the speed with which an accreting plate margin develops. Silica-saturated igneous rocks are probably erupted at rapidly separating continental margins, whereas silica-undersaturated igneous rocks are probably erupted in the early stages of activity at plate boundaries which begin to spread only slowly.

Revisiting hotspots and continental breakup—Updating the classical three-arm model

2022 ◽  
Author(s):  
Carol A. Stein ◽  
Seth Stein ◽  
Molly M. Gallahue ◽  
Reece P. Elling
Keyword(s):  
Conceptual Model ◽  
Mantle Plume ◽  
Ocean Basin ◽  
The Other ◽  
Continental Margins ◽  
Plate Boundaries ◽  
Continental Rifting ◽  
Continental Breakup ◽  
Junction Points ◽  
Insight Into

ABSTRACT Classic models proposed that continental rifting begins at hotspots—domal uplifts with associated magmatism—from which three rift arms extend. Rift arms from different hotspots link up to form new plate boundaries, along which the continent breaks up, generating a new ocean basin and leaving failed arms, termed aulacogens, within the continent. In subsequent studies, hotspots became increasingly viewed as manifestations of deeper upwellings or plumes, which were the primary cause of continental rifting. We revisited this conceptual model and found that it remains useful, though some aspects require updates based on subsequent results. First, the rift arms are often parts of boundaries of transient microplates accommodating motion between the major plates. The microplates form as continents break up, and they are ultimately incorporated into one of the major plates, leaving identifiable fossil features on land and/or offshore. Second, much of the magmatism associated with rifting is preserved either at depth, in underplated layers, or offshore. Third, many structures formed during rifting survive at the resulting passive continental margins, so study of one can yield insight into the other. Fourth, hotspots play at most a secondary role in continental breakup, because most of the associated volcanism reflects plate divergence, so three-arm junction points may not reflect localized upwelling of a deep mantle plume.

Geochemistry of bimodal amphibolitic—felsic gneiss complexes from eastern Massif Central, France

1995 ◽  
Vol 132 (3) ◽  
pp. 321-337 ◽  
Author(s):  
Bernard Briand ◽  
Jean-Luc Bouchardon ◽  
Houssa Ouali ◽  
Michel Piboule ◽  
Paul Capiez
Keyword(s):  
Crustal Contamination ◽  
Igneous Rocks ◽  
Chemical Characteristics ◽  
Continental Margins ◽  
High Grade ◽  
Transitional Stage ◽  
Crust Formation ◽  
Massif Central ◽  
Mantle Sources ◽  
Two Populations

AbstractHigh-grade basic and acidic meta-igneous rocks are widespread in the bimodal amphibolitic—felsic gneiss complexes, which are characteristic formations of the ‘Middle Allochthonous Unit’ from eastern and southern French Massif Central. The metabasites from the Lyonnais and Doux complexes are chemically diverse and range from N-MORB type tholeiitic to transitional types. The two populations are not related by fractional crystallization or crustal contamination processes and their chemical characteristics reflect differences in their mantle sources. An ensialic setting is supported by the crustally-derived character of some of the associated felsic rocks, but the presence of N-MORB-type metabasites argues for an extensional environment. This bimodal association compares well with the magmatism of rifted continental margins and may reflect a transitional stage between continental rifting and oceanic crust formation during the Cambro-Ordovician spreading event.

scholarly journals GEODYNAMICS AND MAGMATISM OF THE PACIFIC-TYPE TRANSFORM MARGINS. ASPECTS AND DISCRIMINANT DIAGRAMS

2021 ◽  
pp. 3-24
Author(s):  
A.V. Grebennikov ◽  
◽  
A.I. Khanchuk ◽  
Keyword(s):  
Continental Margin ◽  
Tectonic Setting ◽  
Island Arc ◽  
Igneous Rocks ◽  
High Alumina ◽  
Plate Boundaries ◽  
Spreading Ridge ◽  
Convergent Margins ◽  
Oceanic Plate ◽  
Plate Movement

Transform margins represent lithospheric plate boundaries with horizontal sliding of oceanic plate, which in time and space replaced the subduction related convergent margins. This happened due to: spreading ridge–trench intersection (California; Queen Charlotte–Northern Cordilleran, West of the Antarctic Peninsula, and probably the Late Miocene–Pleistocene Southernmost South America) or ridge death along continental margin (Baja California); change in the direction of oceanic plate movement (Western Aleutian–Komandorsk; Southernmost tip of the Andes); and island arc-continent collision (New Guinea Island). Post-subduction magmatism is related to a slab window that resulted either from the spreading ridge collision (subduction) with a continental margin or slab tear formation, or slab break-off after subduction cessation due to other reasons. Igneous magmatic series formed in consequence of these events show diversity of tholeiitic (sub-alkaline), alkaline or calc-alkaline, high-alumina and adakitic rocks. The comprehensive geochemical dataset (more than 2400 analyses) on igneous rocks of the model transform and convergent geodynamic settings allowed to substantiate the most informative triple diagrams for the petrogenic oxides TiO2 × 10 – Fe2O3Tot – MgO and trace elements Nb – La– Yb. Mostly approved for the rock compositions with SiO2 < 63 wt. %, the new plots are capable of distinguishing igneous rocks formed above zones of subduction at an island arc and continental margin (related to convergent margins), from those formed in the tectonic setting of transform margins along continents or island arcs.

Plutonium isotopes in marine sediments and some biota from the Sudanese coast of the Red Sea

2008 ◽  
Vol 131 (4) ◽  
pp. 414-417 ◽  
Author(s):  
D. A. Sirelkhatim ◽  
A. K. Sam ◽  
R. K. Hassona
Keyword(s):  
Red Sea ◽  
Marine Sediments ◽  
Plutonium Isotopes

Evolution of the Martian Crust

2017 ◽  
Author(s):  
John C. Bridges
Keyword(s):  
Plate Tectonics ◽  
Chemical Weathering ◽  
Compositional Data ◽  
Crustal Contamination ◽  
Planetary Science ◽  
Mantle Metasomatism ◽  
Igneous Rocks ◽  
Forthcoming Article ◽  
Physical Weathering ◽  
Igneous Activity

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.Mars, which has a tenth of the mass of Earth, has cooled as a single lithospheric plate. Current topography gravity maps and magnetic maps do not show signs of the plate tectonics processes that have shaped the Earth’s surface. Instead, Mars has been shaped by the effects of meteorite bombardment, igneous activity, and sedimentary—including aqueous—processes. Mars also contains enormous igneous centers—Tharsis and Elysium, with other shield volcanoes in the ancient highlands. In fact, the planet has been volcanically active for nearly all of its 4.5 Gyr history, and crater counts in the Northern Lowlands suggest that may have extended to within the last tens of millions of years. Our knowledge of the composition of the igneous rocks on Mars is informed by over 100 Martian meteorites and the results from landers and orbiters. These show dominantly tholeiitic basaltic compositions derived by melting of a relatively K, Fe-rich mantle compared to that of the Earth. However, recent meteorite and lander results reveal considerable diversity, including more silica-rich and alkaline igneous activity. These show the importance of a range of processes including crystal fractionation, partial melting, and possibly mantle metasomatism and crustal contamination of magmas. The figures and plots of compositional data from meteorites and landers show the range of compositions with comparisons to other planetary basalts (Earth, Moon, Venus). A notable feature of Martian igneous rocks is the apparent absence of amphibole. This is one of the clues that the Martian mantle had a very low water content when compared to that of Earth.The Martian crust, however, has undergone hydrothermal alteration, with impact as an important heat source. This is shown by SNC analyses of secondary minerals and Near Infra-Red analyses from orbit. The associated water may be endogenous.Our view of the Martian crust has changed since Viking landers touched down on the planet in 1976: from one almost entirely dominated by basaltic flows to one where much of the ancient highlands, particularly in ancient craters, is covered by km deep sedimentary deposits that record changing environmental conditions from ancient to recent Mars. The composition of these sediments—including, notably, the MSL Curiosity Rover results—reveal an ancient Mars where physical weathering of basaltic and fractionated igneous source material has dominated over extensive chemical weathering.

A marginal Late Proterozoic ocean basin in the Welsh region

1973 ◽  
Vol 110 (5) ◽  
pp. 447-455 ◽  
Author(s):  
J. W. Baker
Keyword(s):  
Subduction Zone ◽  
Ocean Basin ◽  
Ocean Floor ◽  
Late Proterozoic ◽  
Igneous Activity ◽  
Simple Deformation

SummaryRe-assessment of the idea that the Monian and Longmyndian accumulated along the margin of a palaeo-ocean suggests that Monian sedimentation occurred near the eastern shoreline of a micro-continent. If Monian igneous activity, metamorphism and deformation are attributed to an underlying subduction zone, this must have dipped northwestwards away from a small ocean basin to the southeast. Consumption of this ocean floor brought about collision with the continental shield and simple deformation of the Longmyndian.

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