Ontologies constitute one of the most important and enabling components of the semantic Web, allowing geoscientists to explicitly and formally model their knowledge base for sharing and reuse over a global network. The geoscience community, realizing the need for such knowledge-enhancing technologies, has started developing a series of geoontologies for specific fields. We analyze the problems of designing geoontologies, emphasizing issues related to conceptual modeling and system architecture, and present the preliminary conceptual model of part of the structural geology ontology (StructuralGeoOntology). We discuss the ontology development process and identify a set of useful steps and activities that enhance and facilitate the development of any geoontology. Developing ontologies for any field in the geosciences becomes complex if all the concepts and their relationships in the field are included in a single, large ontology. To reduce complexity, we design the StructuralGeoOntology with a modular architecture involving multiple ontologies. This component-based ontology merges several homogeneous subontologies from allied subdisciplines in structural geology, and integrates ontologies from other fields. Each of the shared subontologies will have its corresponding relational database. The modular architecture leads to simplified and more efficient modeling, development, integration, maintenance, reasoning, and future extensibility for the ontologies and databases.

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Knowledge of the geologic evolution of the northern margin of South America has increased tremendously, inspired by the occurrence of huge hydrocarbon deposits. This margin originated in late Triassic time when the supercontinent of Pangea broke up and North and South America drifted apart. The passive margin accommodated a thick sequence of Jurassic to Tertiary sediments. During the latest Cretaceous to the Present, the Antilles volcanic arc, built upon the Caribbean plate, migrated southeastward and collided obliquely with South America. This collision resulted in the diachronous accretion of allochthonous terranes as well as diachronous formation of a fold and thrust belt. This belt was initiated in the west (Colombia) during the latest Cretaceous and progressively moved east and reached Trinidad only in Miocene time. In front of this thrust belt, diachronous foreland basins developed. The present paper reviews the geologic evolution of northern Venezuela and adjacent areas in the Caribbean Sea, based to a large extent on a huge amount of new data released by oil companies and data collected by universities.

The margin of northern Venezuela is a complex zone representing the orogenic events from basement formation to subsequent subduction and exhumation during transpressional collision. This boundary zone has six east-west–trending belts that each record a different segment of its development. This geologic complexity requires radiometric ages to unravel, and we herein provide 48 new ages including U-Pb (4), Rb-Sr (2), 40 Ar/ 39 Ar (24), zircon and apatite fission-track (17), and 14 C (1) ages to constrain the evolution of three of these belts. These three belts are the Cordillera de la Costa, Caucagua–El Tinaco, and Serranía del Interior belts. In the Cordillera de la Costa belt, U-Pb geochronologic data indicate portions of the basement igneous and metaigneous rocks formed in the Cambro-Ordovician (513–471 Ma). New 40 Ar/ 39 Ar data from Margarita Island indicate that some of the subduction complex was rapidly cooled and exhumed, whereas other portions indicate slower cooling. This contrasts with new 40 Ar/ 39 Ar data from the Puerto Cabello portion of the subduction complex that has Eocene to Oligocene (42–28 Ma) cooling ages. New fission-track data imply the entire Cordillera de la Costa belt from Puerto Cabello to La Guaira (∼150 km) was uplifted at the same time. In the Caucagua–El Tinaco belt, the oldest 40 Ar/ 39 Ar amphibole ages from the Tinaquillo ultramafic complex are Jurassic (190 Ma). Additional amphibole 40 Ar/ 39 Ar cooling ages are older than previously recorded in either the Tinaco or Tinaquillo complex. One amphibole 40 Ar/ 39 Ar cooling age for the Tinaco complex is similar to previous U-Pb results. New apatite fission-track results from the Serranía del Interior foreland fold and thrust belt are synchronous with exhumation in the Cordillera de la Costa belt. In addition, several zircon fission-track ages in the Serranía del Interior belt are older than their fossil ages, indicating a Cretaceous minimum provenance age for Miocene beds. Significant new findings from these geochronologic studies include (1) several igneous and metaigneous bodies that may be correlated with orogenic events in the Appalachians occur within the subduction mélange; (2) the Tinaquillo complex may record Jurassic rifting; (3) Cretaceous source rocks for the Serranía del Interior sedimentary strata; (4) exhumation of the subduction complex is segmented because two regions have significantly different cooling histories, with Margarita Island exhumed in the Cretaceous, whereas to the west, the Puerto Cabello region has widespread Paleogene cooling and exhumation ages; and (5) earthquake activity in 1812 caused uplift as recorded by exposure of Recent corals.

The Cordillera de la Costa eclogite belt, exposed along the Caribbean coastline of Venezuela near Puerto Cabello, consists of lensoid bodies and boudins of high pressure-temperature ( P-T ) metabasite in a heterogeneous matrix of mica schist and metacarbonate rocks. The metabasite bodies consist of eclogite and its retrogression products. Data for less mobile elements indicate that protoliths ranged from normal mid-oceanic-ridge basalt (N-MORB), to enriched (E)-MORB, to cumulate gabbro. Some eclogites and their retrogression products are enriched in large ion lithophile elements (LILE). The covariations of K and Ba are evidence that these elements were most likely incorporated into phengite, which has textures that suggest it crystallized from retrograde fluids. A similar style of LILE enrichment is also documented for eclogites of the Samana Peninsula, Dominican Republic, but not in eclogites from Isla de Margarita, Venezuela. Low- T, K-metasomatized basalts from the Bermuda Rise display different K-Ba systematics than the eclogite suites, which suggests that LILE enrichment of the latter rocks was not merely inherited from altered protoliths. In contrast to the LILE-enriched eclogites, some Cordillera de la Costa belt eclogite bodies have apparently been stripped of K, Rb, Ba, and U. Some metasedimentary rocks, in an outcrop that also contains LILE-poor metabasite, also show extreme LILE depletion relative to counterparts elsewhere in the Cordillera de la Costa. In this outcrop, LILE are most conspicuously depleted in a lens of kyanite + glaucophane schist that formed at P > 20 kb, T ∼600 °C. Although the rock has Al/Si ratios, rare earth element, and high field strength element abundances comparable to shale, it contains <0.3 wt% K 2 O. Some rocks of the Cordillera de la Costa eclogite belt thus appear to record LILE expulsion, probably at the “peak” P-T conditions of P > 20 kb at T ∼600 °C, whereas others chronicle LILE enrichment during retrogression at lower P-T conditions. Some outcrops show both effects. In a few outcrops, eclogitic blocks that appear to be LILE-depleted occur in metasedimentary host rocks that are not.

The Cordillera de la Costa belt, exposed for at least 600 km along the EW-trending coast of Venezuela, is a subduction mélange that contains fragments (knockers) of many rock types, notably eclogite and blueschist included in a matrix of mostly mica and graphite schist. The exhumation of the eclogite occurred in three stages. During the first stage (mid-Cretaceous), buoyancy forces drove the eclogite and its enclosing low-density matrix upward along the subduction zone from ∼75 to ∼25 km depth. During the second stage (Late Cretaceous), the mélange was severely fragmented by plate boundary–parallel stretching that caused the eclogite to ascend to ∼10 km depth. During the third stage (Oligocene-Miocene), the Cordillera de la Costa belt was thrust onto the South American plate and erosion was responsible for the ultimate exhumation of the eclogite.

New geochemical data from the Villa de Cura blueschist belt indicate that it is a subducted (and exhumed) oceanic island-arc terrane. The majority of the metabasalts were oceanic island-arc tholeiites (7–23 wt% MgO), though more evolved tholeiites are also found. Rare earth element (REE) and immobile trace element data from the Villa de Cura belt exhibit island-arc signatures, including (1) flat to light enriched REE patterns, and (2) enrichment of large ion lithophile elements relative to high field strength elements with a strongly negative Nb anomaly. Thus, the Villa de Cura belt is similar to other Albian-Aptian age oceanic island-arc tholeiites documented throughout the Caribbean in Cuba, Hispaniola, Puerto Rico, Tobago, and Bonaire. It is not related to the Cretaceous Caribbean-Colombian oceanic plateau. From our new geochemical data and previously published metamorphic data, we propose that the Villa de Cura blue-schist sequence represents two forearc slivers of the “Great Arc of the Caribbean” that were subsequently subducted and amalgamated during exhumation.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.