Título del libro: Topics In Igneous Petrology
Título del capítulo: Upper triassic karmutsen formation of western canada and alaska: A plume-generated oceanic plateau formed along a mid-ocean ridge nucleated on a late paleozoic active margin
JOHN DUNCAN KEPPIE MOORHOUSE;
Autores externos:
Idioma:
Inglés
Año de publicación:
2011
Resumen:
The 1-6 km thick Upper Triassic Karmutsen basalts extend ca. 2,400 km along the Cordillera from British Columbia to Alaska and are characteristic of the Wrangellia terrane. The basalts were erupted in less than 3.5 million years following rapid >1 km uplift of an extinct Devono-Carboniferous island arc. Eliminating transcurrent dispersal reduces its original distribution to an elliptical area, ca. 1,200 × 700 km2 in size. The convergent tectonic setting is inferred to be associated with amalgamation of Wrangellia out in the Pacific Ocean with its accretion to Laurentia occurring prior to Middle Jurassic. Geochemical data characterize the basalts as high-and low-Ti within-plate tholeiites derived from two components, an asthenospheric mantle plume at a depth ca. 80-100 km and partial melt of depleted lithospheric mantle enriched during the Paleozoic arc magmatism or of lower crust. Assuming that the ocean floor above the Paleozoic arc lay at a depth of ca. 4.5 km (i.e. 1 km above normal ocean floor) before passage over a plume, and accounting for extrusion of 6 km of basalt, the Karmutsen seamount experienced ca. 4 km of thermal uplift, was ca. 90 km wide and yielded a magma volume of ca. 15,600 km3. Although the 90 km width is similar to that on Vancouver Island, the predicted volume is only 1/60th of the estimated volume. This discrepancy could be explained if the 2,400 km length of the volcanic belt represents a migrating volcanic chain but no diachronism has been detected. Even using the ca. 1,200 × 700 km2 areal dimension prior to sinistral dispersal yields an unrealistic model plume size. This suggests that the Late Triassic magmatism formed as an oceanic plateau over a triple point or mid-oceanic ridge segment. However, the Karmutsen flood basalts are unusual as they formed over an extinct oceanic arc, which suggests that triple point or ridge may have nucleated on the extinct arc or trench. The modeling also shows that the bulk density of the lithosphere on which the oceanic plateau rests is never less than the asthenospheric density suggesting several possibilities for the plateau's preservation: (1) that the oceanic plateau jammed the trench causing the trench to jump oceanwards: this is consistent with the oceanic arc basement and the unimodal flood basalt magmatism; (2) th
Entidades citadas de la UNAM:
ISBN:
9789048195992
Editorial:
Springer Netherlands Nombre de la publicación:
Upper triassic karmutsen formation of western canada and alaska: A plume-generated oceanic plateau formed along a mid-ocean ridge nucleated on a late paleozoic active margin
Página inicial:
3
Página final:
27
