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21.
The Canary and Cape-Verde archipelagos are two groups of volcanic islands often cited as case examples of the surface expression
of two distinct hot-spot plumes. However, several considerations that␣we enumerate suggest a link between the two archipelagos.
Using seismic profiles we describe a continuous morphological basement ridge that exists between the two archipelagos. We
then examine the stratigraphic record available from field data on Fuerteventura Island (Canary) and Maio Island (Cape-Verde)
and from a few Deep Sea Drilling Project (DSDP) holes. The geological history of these volcanic islands is very similar since
the formation of their oceanic basement during the Late Jurassic. They share the same and synchronious sedimentary evolution
(subsidence, uplift and emersion) as well as very similar timing of volcanism and deformation. The two distinct hot-spots
model does not appear adapted to account for the formation of these structures as it ignores the existence of the ridge, as
well as most of the geological coincidences. By describing the coinciding geological incidents, we argue that it is misleading
to treat these two regions apart. 相似文献
22.
Patriat Philippe Sauter Daniel Munschy Marc Parson Lindsay 《Marine Geophysical Researches》1997,19(6):457-480
The study of very low-spreading ridges has become essential to ourunderstanding of the mid-oceanic ridge processes. The Southwest Indian Ridge(SWIR) , a major plate boundary of the world oceans, separating Africa fromAntarctica for more than 100 Ma, has such an ultra slow-spreadingrate. Its other characteristic is the fast lengthening of its axis at bothBouvet and Rodrigues triple junctions. A survey was carried out in thespring of 1993 to complete a multibeam bathymetric coverage of the axisbetween Atlantis II Fracture Zone (57° E) and the Rodrigues triplejunction (70° E). After a review of what is known about the geometry,structure and evolution of the SWIR, we present an analysis of the newalong-axis bathymetric data together with previously acquiredacross-axis profiles. Only three transform faults, represented byAtlantis II FZ, Novara FZ, and Melville FZ, offset this more than 1000 kmlong section of the SWIR, showing that the offsets are more generallyaccommodated by ridge obliquity and non-transform discontinuities. From comparison of the axial geometry, bathymetry, mantle Bouguer anomaly and central magnetic anomaly, three large sections (east of Melville FZ, between Melville FZ and about 65°30 E, and from there to the Rodrigues triple junction) can be distinguished. The central member, east of Melville FZ, does not resemble any other known mid-oceanic ridge section: the classical signs of the accretion (mantle Bouguer anomaly, central magnetic anomaly) are only observed over three very narrow and shallow axis sections. We also apply image processing techniques to the satellite gravity anomaly map of Smith and Sandwell (1995) to determine the off-axis characteristics of the Southwest Indian Ridge domain, more especially the location of the triple junction and discontinuities traces. We conclude that the large-scale segmentation of the axis has been inherited from the evolution of the Rodrigues triple junction. 相似文献
23.
Lindsay M. Parson Philippe Patriat Roger C. Searle Anne R. Briais 《Marine Geophysical Researches》1993,15(4):265-282
The present morphology and tectonic evolution of more than 1500 kilometres of the Central Indian Ridge are described and discussed following the integration of GLORIA side-scan sonographs with conventional geophysical datasets. Segmentation of the ridge occurs by a series of ridge axis discontinuities ranging in periodicity along strike from 275 km to less than 30 km. These segment boundaries we have classified into two types: first order fracture zones of offsets greater than 50 km which bound five major (mega-) segments, and smaller scale structures of a variety of offset styles and amplitudes which cut four of these segments. We refer to these as ridge-axis discontinuities. The frequent opposite sense of offset identified between the first order structures and the subordinate discontinuities between these major structures is interpreted as resulting from the adjustment to new kinematic parameters after magnetic anomaly 20. As far as our data allows us to determine, the central major segment is not subdivided by minor ridge axis discontinuities, which we suggest is a result of its proximity to the Rodriguez hotspot. 相似文献
24.
Lucien Leclaire Yannis Bassias Micheline Denis-Clocchiatti Hugh Davies Isabelle Gautier Bernard Gensous Pierre-Jean Giannesini Philippe Patriat Jacques Segoufin Michel Tesson Jacques Wannesson 《Geo-Marine Letters》1987,7(4):169-176
Geological samples from the southern Kerguelen Plateau include Lower Cretaceous basalt and lava breccia, probable Lower Cretaceous conglomerate and shelf limestone, Upper Cretaceous chert with dolomite, Upper Cretaceous-Eocene ooze, and Tertiary conglomerate. Neogene sediments are only a few hundred m thick, and include foraminiferal and diatomaceous ooze, and ice-rafted debris. In conjunction with seismic reflection profiles, the samples indicate Early Cretaceous near-shore volcanism, followed by erosion, sedimentation, and subsidence through Cretaceous; arching of the plateau at the end of Cretaceous; subsidence through Paleogene; widespread emergence in mid-Tertiary; and slow subsidence through Neogene. 相似文献
25.
Rommevaux-Jestin Céline Deplus Christine Patriat Philippe 《Marine Geophysical Researches》1997,19(6):481-503
A three-dimensional analysis of gravity andbathymetry data has been achieved along the Southwest Indian Ridge (SWIR)between the Rodriguez Triple Junction (RTJ) and the Atlantis II transform,in order to define the morphological and geophysical expression ofsecond-order segmentation along an ultra slow-spreading ridge(spreading rate of 8 mm/yr), and to compare it with awell-studied section along a slow-spreading ridge (spreadingrate of 12.5 mm/yr): the Mid-Atlantic Ridge (MAR) between 28°and 31°30 N.Between the Atlantis II transform and theRTJ, the SWIR axis exhibits a deep axial valley with an 30°oblique trend relative to the north–south spreading direction. Onlythree transform faults offset the axis, so the obliquity has to beaccommodated by the second-order segmentation. Alongslow-spreading ridges such as the MAR, second-order segmentshave been defined as linear features perpendicular to the spreadingdirection, with a shallow axial valley floor at the segment midpoint,deepening to the segment ends, and are associated with Mantle BouguerAnomaly (MBA) lows. Along the SWIR, our gravity study reveals the presenceof circular MBA lows, but they are spaced further apart than expected. Thesegravity lows are systematically centred over narrow bathymetric highs, andinterpreted as the centres of spreading cells. However, along some obliquesections of the axis, the valley floor displays small topographicundulations, which can be interpreted as small accretionary segments frommorphological analysis, but as large discontinuity domains from thegeophysical data. Therefore, both bathymetry and MBA variations have to beused to define the second-order segmentation of an ultraslow-spreading ridge. This segmentation appears to be characterisedby short segments and large oblique discontinuity domains. Analysis of alongaxis bathymetric and gravimetric profiles exhibits three different sectionsthat can be related to the thermal structure of the lithosphere beneath theSWIR axis.The comparison between characteristics of segmentationalong the SWIR and the MAR reveals two major differences: first, the poorcorrelation between MBA and bathymetry variations and second, the largerspacing and amplitude of MBA lows along the SWIR compared to the MAR. Theseobservations seem to be correlated with the spreading rate and the thermalstructure of the ridge. Therefore, the gravity signature of the segmentationand thus the accretionary processes appear to be very different: there areno distinct MBA lows on fast-spreading ridges, adjacent ones on slowspreading ridges and finally separate ones on ultra slow-spreadingridges. The main result of this study is to point out that 2nd ordersegmentation of an ultra slow-spreading ridge is characterised bywide discontinuity domains with very short accretionary segments, suggestingvery focused mantle upwelling, with a limited magma supply through a cold,thick lithosphere. We also emphasise the stronger influence of themechanical lithosphere on accretionary processes along an ultra slow-spreading ridge. 相似文献
26.
From rifting to spreading in the eastern Gulf of Aden: a geophysical survey of a young oceanic basin from margin to margin 总被引：1，自引：0，他引：1
Sylvie Leroy Pascal Gente Marc Fournier Elia d'Acremont Philippe Patriat Marie-Odile Beslier Nicolas Bellahsen Marcia Maia Angelina Blais Julie Perrot Ali Al-Kathiri Serge Merkouriev Jean-Marc Fleury Pierre-Yves Ruellan Claude Lepvrier Philippe Huchon 《地学学报》2004,16(4):185-192
A geophysical survey in the eastern Gulf of Aden, between the Alula–Fartak (52°E) and the Socotra (55°E) transform faults, was carried out during the Encens–Sheba cruise. The conjugate margins of the Gulf are steep, narrow and asymmetric. Asymmetry of the rifting process is highlighted by the conjugate margins (horst and graben in the north and deep basin in the south). Two transfer fault zones separate the margins into three segments, whereas the present‐day Sheba Ridge is divided into two segments by a transform discontinuity. Therefore segmentation of the Sheba Ridge and that of the conjugate margins did coincide during the early stages of oceanic spreading. Extensive magma production is evidenced in the central part of the western segment. Anomaly 5d was identified in the northern and southern parts of the oceanic basin, thus confirming that seafloor spreading in this part of Gulf of Aden started at least 17.6 Ma ago. 相似文献
27.
W.Q. Limond F. Gray G. Grau J.P. Fail L. Montadert Ph. Patriat 《Earth and Planetary Science Letters》1974,23(3):357-368
This paper describes a series of two ship refraction experiments carried out in the Bay of Biscay in May 1970 to determine the crustal structure to the southeast of Gascony sea mount. The results show that the seismic structure is similar to that found on Line B further to the northwest, but that the mantle is deeper. The structure is oceanic showing that it is unlikely that this area of the Bay of Biscay has been formed by downfaulting of continental crust. 相似文献