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JOURNAL U UEUFHYSIGAL KESEAKGH, VUL. 87, NU. B8,I'AUES MY7-671U, AUGUST 10, 1982 Geological Evidence For The Geographical Pattern of Mantle Return Flow
 

Summary: JOURNAL U UEUFHYSIGAL KESEAKGH, VUL. 87, NU. B8,I'AUES MY7-671U, AUGUST 10, 1982
Geological Evidence For The Geographical Pattern of Mantle Return Flow
and the Driving Mechanism of Plate Tectonics
Department of Geology and Geopbsics, University of California, Berkeley, California 94720
Tectonic features at the earth's surface can be used to test models for mantle return flow and to
determine the geographic pattern of this flow. A model with shallow return flow and deep con-
tinental roots places the strongest constraints on the geographical pattern of return flow and
predicts recognizable surface manifestations. Because of the progressive shrinkage of the Pacific
(averaging 0.5 km2/yr over the last 180 m y . ) this model predicts upper mantle outflow through the
three gaps in the chain of continents rimming the Pacific (Caribbean, Drake Passage, Australian-
Antarctic gap). In this model, upper mantle return flow streams originating at the western Pacific
trenches and at the Java Trench meet south of Australia, filling in behind this rapidly northward-
moving continent and providing an explanation for the negative bathymetric and gravity anomalies
of the 'Australian-Antarctic Discordance'. The long-continued tectonic movements toward the east
that characterize the Caribbean and the easternmost Scotia Sea may be produced by viscous cou-
pling to the predicted Pacific outflow through the gaps, and the Caribbean floor slopes in the
predicted direction. If mantle outflow does pass through the gaps in the Pacific perimeter, it must
pass beneath three seismic zones (Central America, Lesser Antilles, Scotia Sea); none of these
seismic zones shows foci below 200 km. Mantle material flowing through the Caribbean and Drake
Passage gaps would supply the Mid-Atlantic Ridge, while the Java Trench supplies the Indian Ocean

  

Source: Alvarez, Walter - Department of Earth and Planetary Science, University of California at Berkeley

 

Collections: Geosciences