Search results for "Continent"

Has the East African Orogen Played Any Role in the Formation and Breakup of the Supercontinent Rodinia and the Amalgamation of Gondwana? New Evidence…

2001

African, southern Indian and South American cratons were not part of the Rodinia supercontinent: evidence from field relationships and geochronology

2003

We discuss the question whether the late Mesoproterozoic and early Neoproterozoic rocks of eastern, central and southern Africa, Madagascar, southern India, Sri Lanka and South America have played any role in the formation and dispersal of the supercontinent Rodinia, believed to have existed between about 1000 and 750 Ma ago. First, there is little evidence for the production of significant volumes of ~1.4–1.0 Ga (Kibaran or Grenvillian age) continental crust in the Mozambique belt (MB) of East Africa, except, perhaps, in parts of northern Mozambique. This is also valid for most terranes related to West Gondwana, which are made up of basement rocks older than Mesoproterozoic, reworked in th…

Early Pan-African evolution of the basement around Elat, Israel,and the Sinai Peninsula revealed by single-zircon evaporation dating, and implication…

1990

We report 2<r7Pb/206Pb single-zircon evaporation ages for early Pan-African rocks from southern Israel and the northeastern Sinai Peninsula, the northernmost extension of the Arabian-Nubian shield. The oldest rocks are metamorphic schists of presumed island-arc derivation; detrital zircons date the source terrain at ca. 800-820 Ma. A major phase of tonalite-trondhjemite plutonism occurred at ca. 760-780 Ma; more evolved granitic rocks were emplaced at about 745 Ma. A metagabbro-met adiorite complex reflects the youngest igneous phase at ca. 640 Ma. We Find no evidence for pre-Pan-African crust, and our data document important crust-forming events that correlate with similar episodes elsewhe…

Formation of Hercynian subplates, possible causes and consequences

1976

WITH the exception of the microplate models of Badham and Halls1 and Riding2 models of Hercynian plate tectonics3–7 have assumed the existence of only one plate, that is, South Europe, between Africa and the Tethys in the south and North America–Europe and the Mid-European Ocean in the north. The South European plate has generally been considered as a stable unit. Studies of the Alpine system8, however, suggest that such an assumption may not be valid. I assume here that during the Carboniferous, South Europe was originally an elongated plate with nearly straight margins and internal structures. Collision with the irregular continental margins of the bounding plates North America–Europe and…

Reassessment of continental growth during the accretionary history of the Central Asian Orogenic Belt

2014

We argue that the production of mantle-derived or juvenile continental crust during the accretionary history of the Central Asian Orogenic Belt (CAOB) has been grossly overestimated. This is because previous assessments only considered the Palaeozoic evolution of the belt, whereas its accretionary history already began in the latest Mesoproterozoic. Furthermore, much of the juvenile growth in Central Asia occurred in late Permian and Mesozoic times, after completion of CAOB evolution, and perhaps related to major plume activity. We demonstrate from zircon ages and Nd–Hf isotopic systematics from selected terranes within the CAOB that many Neoproterozoic to Palaeozoic granitoids in the accre…

Structure, Composition and Evolution of the South Indian and Sri Lankan Granulite Terrains from Deep Seismic Profiling and Other Geophysical and Geol…

2005

We here argue the need for a multidisciplinary, integrated geophysical/geological survey across southern India and Sri Lanka, part of the largest exposed Neoproterozoic high-grade metamorphic terrain in the world. The purpose is to stimulate deep seismic profiling and other geophysical and geological investigations in order to better understand the structure, composition and evolution of a keystone of Precambrian continental crust and the role it played in the amalgamation and subsequent break-up of the Gondwana supercontinent. Of particular importance is that this lithospheric fragment records a 2 billion year long history of magmatism, sedimentation, deformation and metamorphism and now e…

Structural framework and crustal characteristics of the Sardinia Channel Alpine transect in the central Mediterranean

2000

Abstract The submerged area located between the Sardinia Channel and the western Sicily offshore has been investigated based on deep crustal and conventional seismic lines with the aim of illustrating the relationships between the crust and its overlying crystalline and sedimentary thrust wedge. Analyses of seismic attributes and reflector pattern, supported by dredge hauls, also provided data in areas where stratigraphic and lithologic control is absent. Crustal geometries, tectonic processes and timing of the deformation are discussed here. North of the Elimi chain (central Sardinia Channel) the reflecting body consists of superposed tectonic wedges of crystalline rocks and their Meso-Cen…

High-pressure metamorphism in the Aegean, eastern Mediterranean: Underplating and exhumation from the Late Cretaceous until the Miocene to Recent abo…

2003

[1] We report 40Ar/39Ar ages from various tectonic units in the Aegean and westernmost Turkey. On the basis of published geochronologic data and our 40Ar/39Ar ages we propose that the Aegean is made up of several high-pressure units, which were successively underplated from the Late Cretaceous until the Miocene. Ages for high-pressure metamorphism range from 80–83 Ma in parts of the Vardar-Izmir-Ankara suture zone in the north to 21–24 Ma for the Basal unit in the Cyclades and the external high-pressure belt on Crete in the south. Published seismic data suggest that high-pressure metamorphism is currently occurring underneath Crete. Younging of high-pressure metamorphism in a southerly dire…

Late Hercynian Plate and Intraplate Processes within Europe

1987

The Hercynian orogenic belt of Europe consists of a central crystalline ridge which is accompanied on both sides by a rather unmetamorphosed foldbelt. It is speculated that the crystalline ridge represents some kind of island arc system underlain by a segment of continental crust. On both sides this island arc system was involved in subduction of oceanic crust, first of the Mideuropean Sea in the North and then of the Paleotethys in the South. When the continental areas to the north and south of the oceanic areas (North America/Northern Europe and Africa) finally got involved in the subduction processes, continent/continent collision took place on both sides of the island arc system. The tw…

Potassium-rich magmatism from a phlogopite-free source

2017

The generation of strongly potassic melts in the mantle is generally thought to require the presence of phlogopite in the melting assemblage. In the Mediterranean region, trace element and isotope compositions indicate that continental crustal material is involved in the generation of many potassium-rich lavas. This is clearest in ultrapotassic rocks like lamproites and shoshonites, for which the relevant chemical signals are less diluted by extensive melting of peridotite. Furthermore, melting occurs here in young lithosphere, so the continental crust was not stored for a long period of time in the mantle before reactivation. We have undertaken two types of experiments to investigate the r…