See more from this Division: Topical Sessions
See more from this Session: Alpine Concepts in Geology and the Evolution of Geological Thought
Abstract:
At the time when Steinmann (1905) described the close association of serpentinites, diabase, and radiolarites in Eastern Switzerland and then in the Northern Apennines, ophiolites were considered as intrusions of mafic-ultramafic magmas emplaced during folding of oceanic sediments deposited in the axial part of geosynclines. Following Bailey and MacCallien's (1950, 1953) definition of the Steinmann trinity, the ophiolitic tripartite was redefined as the association of serpentinite/peridotite, gabbro, and dolerite/spilite.
Ultramafic rocks in ophiolites were originally interpreted as intrusive-extrusive rocks, reminiscent of the alpine-type peridotites interpreted as plutons intruded into folded geosynclinal sediments (Benson, 1926). Subsequently, Hess (1954) and de Roever (1957) suggested that ultramafics in ophiolites represented mantle rocks. Structural studies of the Troodos and Oman ophiolites and seismic refraction studies in modern oceans demonstrated the stratified nature of the oceanic lithosphere.
The advent of plate tectonics led to the establishment of an idealized four-layer pseudostratigraphy of ophiolites, including oceanic sedimentary cover (layer 1), extrusive sequence and sheeted dike complex (layer 2), gabbroic complex (layer 3), and upper mantle (layer 4), matching the geophysical structure of the oceanic lithosphere (Anonymous, 1972).
The ophiolite concept and the Steinmann trinity as originally established in the Alps and Apennines consisted of an incomplete pseudostratigraphy in comparison to the Penrose-type oceanic lithosphere. However, ophiolite studies and marine investigations in recent years have shown that the structure and composition of the oceanic lithosphere vary significantly depending on the geodynamic environments of formation and different magmatic and tectonic processes involved in these diverse settings.
See more from this Division: Topical Sessions
See more from this Session: Alpine Concepts in Geology and the Evolution of Geological Thought