Neogene Patagonian plateau lavas: Continental magmas associated with ridge collision at the Chile Triple Junction
Extensive Neogene Patagonian plateau lavas (46.5° to 49.5°S) southeast of the modern Chile Triple Junction can be related to opening of asthenospheric “slab windows” associated with collisions of Chile Rise segments with the Chile Trench at ≈ 12 Ma and 6 Ma. Support comes from 26 new total‐fusion, w...
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| Published in: | Tectonics (Washington, D.C.) Vol. 16; no. 1; pp. 1 - 17 |
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| Main Authors: | , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Blackwell Publishing Ltd
01-02-1997
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Extensive Neogene Patagonian plateau lavas (46.5° to 49.5°S) southeast of the modern Chile Triple Junction can be related to opening of asthenospheric “slab windows” associated with collisions of Chile Rise segments with the Chile Trench at ≈ 12 Ma and 6 Ma. Support comes from 26 new total‐fusion, whole rock 40Ar/39Ar ages and geochemical data from back arc plateau lavas. In most localities, plateau lava sequences consist of voluminous, tholeiitic main‐plateau flows overlain by less voluminous, 2 to 5 million year younger, alkalic postplateau flows. Northeast of where the ridge collided at ≈12 Ma, most lavas are syncollisional or postcollisional in age, with eruptions of both sequences migrating northeastward at 50 to 70 km/Ma. Plateau lavas have ages from 12 to 7 Ma in the western back arc and from 5 to 2 Ma farther to the northeast. Trace element and isotopic data indicate main‐plateau lavas formed as larger percentage melts of a garnet‐bearing, oceanic island basalt (OIB) ‐like mantle than postplateau lavas. The highest percentage melts erupted in the western and central plateaus. In a migrating slab window model, main‐plateau lavas can be explained as melts that formed as upwelling, subslab asthenosphere which flowed around the trailing edge of the descending Nazca Plate and then interacted with subduction‐altered asthenospheric wedge and continental lithosphere. Alkaline, postplateau lavas can be explained as melts generated by weaker upwelling of subslab asthenosphere through the open slab window. Thermal problems of high‐pressure melt generation of anhydrous mantle can be explained by volatiles (H2O and CO2) introduced by the subduction process into slab window source region(s). An OIB‐like, rather than a mid‐ocean ridge basalt (MORB) ‐like source region, and the lack of magmatism northeast of where ridge collision occurred at ≈13 to 14 Ma can be explained by entrainment of “weak” plume(s) or regional variations in an ambient, OIB‐like asthenosphere. |
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| Bibliography: | istex:38D5B23C1D56A9C9CC08E1B1B16FBBE686400327 ark:/67375/WNG-FJ61V82G-T ArticleID:96TC03368 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 0278-7407 1944-9194 |
| DOI: | 10.1029/96TC03368 |