Prolonged Magmatic and Tectonic Development of the Caribbean Igneous Province Revealed by a Diving Submersible Survey

Using the diving submersible survey NAUTICA we investigated the central part of the Caribbean large igneous province (CLIP) to observe and sample internal portions of this proposed oceanic plateau. Most of the samples are gabbroic and doleritic rocks; basalts are scarce. Radiometric dating by ⁴⁰Ar/³⁹Ar incremental heating experiments indicate that the intrusive rocks are Campanian in age (81–75 Ma). In some places these intrusive rocks underlie older Santonian (85–83 Ma) extrusive basaltic rocks, suggesting that the Campanian rocks represent a sill injection and an underplating episode. Results of the diving program supplemented by information from ODP and DSDP drilling sites document a 20 m.y. period (94–75 Ma) of igneous activity in the submerged portion of the Caribbean large igneous province (CLIP). In the northern part of the Beata Ridge late Campanian and/or post Campanian uplift is documented by prominent Maastrichtian (71–65 Ma) erosion and the establishment of a Paleocene-middle Eocene (65–49 Ma) carbonate platform. During and after the uplift an extensional period is indicated by seismic images and the subsidence (3 km depth) of the carbonate platform. Paleocene ages (55–56 Ma) determined on some volcanic samples are attributed to localised decompression mantle melting that accompanied the extension. We document a prolonged period of magmatic and tectonic events that do not fit with the current models of short-lived plateau formation during mantle plume initiation but shares many similarities with the constructional histories of other oceanic large igneous provinces.     

Alboran Sea late cenozoic tectonic and stratigraphic evolution

Analysis of airgun seismic profiles from the Alboran Sea reveals a complex morphostructure with margins, basins, and structural highs. North of the Alboran Ridge, south-facing margins have a passive style of evolution, with thick progradational sequences of post-Messinian deposits, whereas north-facing margins are tectonized along structural highs with reduced sediment cover. Basins are extensional features developed since the Early Miocene by mechanisms of tectonic escape and pull-apart, under generalized northwest-southeast to north-south compression. Depositional sequences in this semi-land-locked sea were controlled by the local tectonism and influenced by global sea-level oscillations.     

An alternative interpretation of the Cayman trough evolution from a reidentification of magnetic anomalies

Magnetic data were collected during the Wilkes (1973) and Seacarib II (1987) cruises to the Cayman trough. A new interpretation of magnetic data is carried out. An isochron pattern is drawn up from our anomaly identifications. An early Eocene age (49 Ma, Ypresian) for Cayman trough opening is proposed instead of the late Oligocene or middle Eocene ages suggested by previous studies. Our plate tectonic reconstruction is simpler and fits the on-land geology (Jamaica and Cuba) and the tectonics. Our reconstruction shows a southward propagation of the spreading centre between magnetic anomalies 8 and 6 (26 and 20 Ma). The trough width increases by 30 km in this period. The southward propagation of the Cayman spreading centre from the Middle Oligocene to the Early Miocene induced the development of the restraining bend of the Swan Islands, the formation of a 1 km high scarp on the eastern trace of the Cayman trough transform fault (Walton fault) and the formation of a pull-apart basin (Hendrix pull-apart). Magnetic anomalies and magnetization maps give information about the deformation and the rocks. The proposed evolutionary model of the Cayman trough from the inception of seafloor spreading to the present configuration is presented in relation to the tectonic escape of the northern boundary of the Caribbean plate from the Maastrichtian to the Present.     

Geological interpretation of combined Seabeam,Gloria and seismic data from Anegada Passage (Virgin Islands,north Caribbean)

The Anegada Passage (sensu lato) includes several basins and ridges from Southeast of Puerto Rico to the corner of the Virgin Islands Platform. Seabeam (Seacarib I) and Gloria long-range sidescan sonar surveys were carried out in this area. These new data allow us to propose an interpretation of the Anegada Passage.Most of the features described are related to wrench faulting:

Prélèvements systématiques et caractérisation des réflecteurs acoustiques: nouvelle étape dans la compréhension de la géologie de la Méditerranée occidentale

A sampling survey in the Ligurian Sea and north of the Balearic Islands (Mediterranean Sea) brought back samples containing the following elements: (1) lithified Quaternary crust and deep-lying corals; (2) Early Pliocene marls corresponding to reflector level M in some cases; (3) red sediments tentatively assimilated with the Messinian continental equivalent; (4) rocks coming from the basement; (5) volcanic rocks.For the first time, basalts with olivine were discovered in the Algero-Provencal Abyssal Plain.A volcano 500 m high was sampled by dredging north of Minorca.     

The Alboran Sea (Western Mediterranean) revisited with a view from the Moroccan Margin

This paper presents a new depth to acoustic basement map based on a grid of seismic profiles. In the Western Alboran Basin the basement is more than 10 km deep. An examination of a seismic profile of this region suggests that Late Oligocene–Early Miocene 5 km thick synrift formation has been accumulated in this basin. This West Alboran basin has been formed in an extensional setting, but in a fore‐arc position, south of the Balearic Islands then westwards transported behind a subduction zone.     

Sub-B″ layering in the Southern Caribbean: The Aruba Gap and Venezuela Basin

Multichannel seismic data in the Aruba Gap region near JOIDES/DSDP Site 153 verify the presence of a deep sub-B″ reflection. One multichannel seismic line trends NE-SW on and along the edge of Beata Ridge and passes within 1 km of Site 153, and another line runs N-S across the entire Aruba Gap with the drill site 4 km east from its northern end. Closely spaced velocity analyses indicate the presence of deep primary reflection events and enable calculation of interval velocities between the A″-B″ marker horizons. Deconvolved, true amplitude, normal incidence profiles sharply delineate the A″-B″ marker horizons and indicate the presence of the sub-B″ reflection event. On the NE-SW line, this deep reflector is best described as a “diffuse” discontinuous zone, relatively horizontal, lying about 0.8 seconds of two-way travel time below the B″ reflector, with an interval velocity of approximately 5.0 km/s between Horizon B″ and this reflection. The N-S line is more complex since the sub-B′' reflection event is masked by a strong internal multiple from the A″-B″ interval. In the central and western Venezuela Basin, deep primary reflections beneath Horizon B″ are also observed on the northern and western sides of what appears to be a major fault zone. This fault zone separates the smooth B″ and sub-B″ reflectors on the northern and western sides of this fault zone from what appears to be typical oceanic basement. The widespread presence of sub-B″ reflections yielding high interval velocities for the section between these events and Horizon B″ suggest that this material is probably igneous in origin.     

Ocean-continent boundary off the Iberian margin: A serpentinite diapir west of the Galicia Bank

A serpentinite diapir made of altered plagioclase-bearing lherzolites, has been emplaced west of the Galicia Bank at the boundary between oceanic crust and the probable thinned continental crust, that underlies the Iberian margin.