Date of Degree

1995

Document Type

Dissertation

Degree Name

Ph.D.

Program

Earth & Environmental Sciences

Advisor

Kathleen Crane

Committee Members

Somdev Bhattacharji

Millard F. Coffin

Subject Categories

Environmental Sciences

Abstract

The predominance of large-scale paleo-shear zones in the Norwegian-Greenland Sea is thought to be the major cause of asymmetric seafloor spreading in this region. Plate reconstructions suggest that nascent mid-ocean ridges propagated into these obliquely oriented shear zones causing transtension to occur. The asymmetric evolution of the northern Norwegian-Greenland Sea is evident from both the morphology of the seafloor as well as its geophysical characteristics. The eastern passive margins of the northern Norwegian-Greenland Sea are punctuated by volcanic plateaus which have significantly higher heat flow than the western passive margins. It is hypothesized that marginal volcanic plateaus formed originally in response to deviatoric stress developed at nascent mid-ocean ridge/shear zone intersections along transtensional margins causing lava to pond upwards on the eastern flank of the intersections. In addition, not only did paleo-shear zones serve as loci for the extrusion of seafloor basalts, but the distal limbs of these shear zones appear to be present-day sites for the emanation of heat from the seafloor thus thermally rejuvenating the eastern margins in the process. Heat flow analyses suggest that the thermal interactions between the Aegir and paleo-Mohns Ridges with the Eastern Jan Mayen Fracture Zone System created the Voring Plateau and rejuvenated the adjacent continental crust (to a thermal age of 16 my). The subsequent northward propagation of the paleo-Mohns Ridge into/and along the paleo-Senja Shear Zone, probably underplated the Svalbard Platform, and thus caused a broad thermal swell in the region. Multiple intrusions from this northward propagating asthenosphere probably occurred along deep-seated faults in and adjacent to the Svalbard Platform and the northern Svalbard-Nordaustlandet margin. Thermal modeling results also reveal that a secondary detachment fault system cuts the southern Yermak Plateau and intersects the Spitsbergen Shear Zone and could have acted as a conduit for the upward propagation of the Knipovich Ridge-related asthenosphere. Recent northward propagation of the Knipovich Ridge caused rejuvenation of the southern Yermak Plateau (35-11 mybp). SeaMARC-II, and geophysical data also suggest diffuse intrusion and thermal rejuvenation along the northern Svalbard-Nordaustlandet margin creating the Yermak Seamount, Mosby Peak and the Nordaustlandet Volcanic Terrain (30-37 mybp) in the process.

Comments

Digital reproduction from the UMI microform.

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