Combined geologic and seismic reflection data from the Atka Basin region of the Aleutian forearc show that the upper 2-3 km of slightly deformed sediment filling the\ud
basin are probably of late Miocene to Holocene age. The depositional axis of the basin shifted arcward over time because of the progressive and differential rise of the\ud
basin's outer ridge. Units filling the basin unconformably overlie and, along the edges of the basin, onlap beds of Oligocene age and older(?). The basal units of the basin fill are characterized by little variation in thickness, somewhat irregular internal reflectors, fault offsets, and possible wedge outs against units of Eocene(?) age. A fault\ud
with at least 500 m of vertical displacement cuts the outer high of the forearc basin and displaces beds of the basin-filling series relative to those trenchward of the trenchslope break. The Atka Basin appears to have\ud
formed in response to a combination of (1) initiation of trench-floor-filling turbidite deposition, in part derived from glacial marine sedimentation from mainland Alaska;\ud
(2) an increased rate and normal component in Pacific plate subduction beneath the central Aleutian arc beginning in early Pliocene time; and (3) formation of a broad\ud
and thick accretionary wedge that progressively uplifted the outer high of the Aleutian terrace

Coffin, M.F.

Colwell, J.B.

Davies, H.L.

Hill, P.J.

Pigram, C.J.

Ramsay, D.C.

Stagg, H.M.J.

Single dates obtained on mollusk shells by the U-series nuclides method are highly unreliable, primarily because of the mobility of uranium isotopes. However, in several cases, a statistical approach was demonstrated to yield coherent chronologies in both continental and marine environments. We report on 34 new Th and U isotope measurements on Strombus bubonius and Glycymeris glycymeris fossils from raised marine terraces in the Almeria area, southeastern Spain. The results yield a coherent chronology that indicates the presence of the warm water S. bubonius fauna in the Mediterranean basin at the end of the Mindel-Riss interglacial (18O stage 7) and during each high sea-level episode of the Riss-Würm interglacial (18O stage 5). Reconsideration of the Tyrrhenian stratigraphy based on the presence of S. bubonius is thus required.Peer reviewe

Hillaire-Marcel, C.

Carro, Odette

Causse, Christiane

Goy, José Luis

Zazo, Caridad

Digital.CSIC

Geology

Th/U dating of Strombus bubonius-bearing marine terraces in southeastern Spain

Harbert, William

Scholl, D. W.

Vallier, T. L.

Stevenson, A. J.

Mann, D. M.

Name not available

Major evolutionary phases of a forearc basin of the Aleutian terrace:  Relation to North Pacific tectonic events and the formation of the Aleutian subduction complex

Zircon populations from two plagiogranites in the plutonic section of the Troodos ophiolite yield U-Pb dates between 90.3 ±0.7 and 92.4 ±0.7 Ma. Zircons from one of the two samples yield U-Pb dates of 90.3 ±0.7 and 92.1 ±0.7 Ma. This difference is greater than our analytical error, and the zircons are therefore considered to be slightly discordant. Two fractions from another sample are internally and externally concordant and have an average date of 91.6 ±1.4 Ma. This date is adopted as the age of plagiogranite crystallization. The plutonic section of the Troodos ophiolite is complex in that several generations of intrusion can be identified. The plagiogranites occur at the top of the intrusive section and represent fractionated residua of magma chambers related to the lower pillow lavas. They are possibly slightly older than small ultramafic layered complexes that represent the final intrusive episode within the Troodos ophiolite. There is good agreement between our results and the ages of radiolaria which occur in umbers intercalated with the upper pillow lavas of Troodos (Blome and Irwin, 1985). This shows that the 75 to 85 Ma K-Ar dates on the lavas and sheeted dikes (Desmet et al., 1978; Delaloye and Desmet, 1979; Delaloye et al., 1980; Staudigel et al., 1986) represent age resetting unrelated to ophiolite formation. The Troodos U-Pb zircon ages are slightly lower than U-Pb zircon ages from the Samail ophiolite in Oman, which vary between 93.5 and 97.9 Ma and average 95 Ma (Tilton et al., 1981). The small difference in age between the Troodos and the Samail ophiolites and the geochemical similarities of basalts from both complexes to island-arc volcanic rocks imply that a 3000-km axis of rift-related island arcs formed between 91 and 98 Ma. Emplacement of the ophiolites followed during the early Maastrichtian.</p

Mukasa, Samuel B.

Ludden, John N.

Heriot Watt Pure

Uranium-lead isotopic ages of plagiogranites from the Troodos ophiolite, Cyprus, and their tectonic significance

New geophysical data confirm the existence of marked structural and morphological differences between the northern and southern sectors of the Kerguelen Plateau. A major sedimentary basin (Raggatt Basin) covers an area of at least 30 000 km2 on the eastern part of the southern plateau. A deep oceanic basin (Labuan Basin) with extremely rough basement lies adjacent to the southeastern flank of the plateau. We suggest that this may be the former western extension or conjugate feature of the Diamantina zone. Samples of rock obtained by free-fall grabs suggest that the southern Kerguelen Plateau contains continental crust.<br/

Southampton (e-Prints Soton)

New findings from the Kerguelen Plateau

New geophysical data confirm the existence of marked structural and morphological differences between the northern and southern sectors of the Kerguelen Plateau. A major sedimentary basin (Raggatt Basin) covers an area of at least 30 000 km2 on the eastern part of the southern plateau. A deep oceanic basin (Labuan Basin) with extremely rough basement lies adjacent to the southeastern flank of the plateau. We suggest that this may be the former western extension or conjugate feature of the Diamantina zone. Samples of rock obtained by free-fall grabs suggest that the southern Kerguelen Plateau contains continental crust

NERC Open Research Archive

The southern volcanic zone (SVZ) of the Late Archean Abitibi belt of the Superior province of Canada is dominated by komatiitic to tholeiitic volcanic plateaus and large, bimodal, mafic-felsic volcanic centers. These volcanic rocks were erupted between about 2717 and 2700 Ma in a series of rift basins that formed as a result of wrench-fault tectonics. They overlie and juxtapose a volcano-plutonic assemblage characterized in the northern Abitibi belt. The age of the assemblage is about 2720 Ma or older, and it comprises basaltic to andesitic and dacitic subaqueous massive volcanics, cored by comagmatic sills and layered anorthositic complexes and overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 ± 2 Ma.A tectonic model is proposed in which the SVZ formed in a series of rift basins that dissected an earlier formed volcanic arc. Comparisons are made with rift environments that have been postulated for Phanerozoic areas such as the Hokuroko basin of Japan, the Taupo volcanic zone of New Zealand, and the Sumatra and Nicaragua arcs.</p

Ludden, J.

Hubert, C.

Geologic evolution of the Late Archaean Abitibi greenstone belt of Canada

The early breakup of western Pangea has been investigated by mapping the pattern of fracture zones and distribution of seismic reflectors within the sedimentary cover of the Atlantic between the Cape Verde Islands and the equator. Two distinct sets of transverse oceanic lineaments are present, separated by the Guinea Fracture Zone near lat 10°N. Lineaments to the north are associated with the formation of the central Atlantic in the Late Jurassic and Early Cretaceous; those in the south relate to the Cretaceous opening of the South Atlantic. The Guinea Fracture Zone is thus the conjugate of the Jurassic transform boundary under peninsular Florida, which linked the Atlantic with the Gulf of Mexico. The distribution of dated seismic reflectors suggests that deposition of deep-water sediments was confined to the region north of the Guinea transform until Aptian time, when the Sierra Leone Basin began to open. The latter started to widen at least 15 m.y. after the initiation of the Cape Basin off southwest Africa, an age difference that can be explained if a short-lived plate boundary developed in either Africa or South America during the Early Cretaceous. Neither the trends of the equatorial fracture zones nor the seismic stratigraphy supports the existence of a predrift gap between west Africa and Brazil

Jones, E. J. W.

OceanRep

Fracture zones in the equatorial Atlantic and the breakup of western Pangea

The tectonics of the southwestern Kuril arc are a result of the oblique subduction of the Pacific plate at the Kuril Trench. In association with forearc sliver migration caused by the oblique subduction, collision tectonics occur at the leading margin of the sliver and tensional tectonics take place at the tapering margin. As a result of the collision, a deep crustal section of island arc is observed at the leading margin of the forearc sliver. Tectonics of the Kuril arc related to oblique subduction are different from those of the western Sunda arc, where backarc spreading occurs at the leading margin. This difference is due to margin morphology of the oblique subduction zone

Kimura, Gaku

Oblique subduction and collision: Forearc tectonics of the Kuril arc

http://geology.geoscienceworld.org/content/14/9/757.abstract

MAJOR EVOLUTIONARY PHASES OF A FORE-ARC BASIN OF THE ALEUTIAN TERRACE - RELATION TO NORTH PACIFIC TECTONIC EVENTS AND THE FORMATION OF THE ALEUTIAN SUBDUCTION COMPLEX

MAJOR EVOLUTIONARY PHASES OF A FORE-ARC BASIN OF THE ALEUTIAN TERRACE - RELATION TO NORTH PACIFIC TECTONIC EVENTS AND THE FORMATION OF THE ALEUTIAN SUBDUCTION COMPLEX

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