Mantle Processes and Sources of Neogene Slab Window Magmas from Southern Patagonia, Argentina
Neogene plateau lavas in Patagonia, southern Argentina, east of the volcanic gap between the Southern and Austral Volcanic Zones at 46·5° and 49·5°S are linked with asthenospheric slab window processes associated with the collision of a Chile Ridge segment with the Chile Trench at 12 Ma. The strong...
| Published in: | Journal of Petrology |
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| Main Authors: | , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
2001
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| Subjects: | |
| Online Access: | http://petrology.oxfordjournals.org/cgi/content/short/42/6/1067 https://doi.org/10.1093/petrology/42.6.1067 |
| Summary: | Neogene plateau lavas in Patagonia, southern Argentina, east of the volcanic gap between the Southern and Austral Volcanic Zones at 46·5° and 49·5°S are linked with asthenospheric slab window processes associated with the collision of a Chile Ridge segment with the Chile Trench at 12 Ma. The strong ocean-island basalt (OIB)-like geochemical signatures (La/Ta <20; Ba/La <20; 87 Sr/ 86 Sr = 0·7035–0·7046; 143 Nd/ 144 Nd = 0·51290–0·51261; 206 Pb/ 204 Pb = 18·3–18·8; 207 Pb/ 204 Pb = 15·57–15·65; 208 Pb/ 204 Pb = 38·4–38·7) of these Patagonian slab window lavas contrast with the mid-ocean ridge basalt (MORB)-like, depleted mantle signatures of slab window lavas elsewhere in the Cordillera (e.g. Antarctic Peninsula; Baja California). The Patagonian lavas can be divided into a voluminous ∼12–5 Ma, tholeiitic main-plateau sequence (48–55% SiO 2 4–5% Na 2 O + K 2 O) and a less voluminous ∼7–2 Ma alkaline post-plateau sequence (43–49% SiO 2 5–8% Na 2 O + K 2 O). Moderately high FeO T (9–11%), and low heavy rare earth element (HREE), Y, and Sc concentrations in all lavas are consistent with melt generation just below the garnet–spinel transition at a depth of ∼70 km. The main-plateau lavas from the western back-arc can be modeled by ∼10–15% partial melting of an OIB-like asthenospheric mantle source with additions from slab fluid–melt components coupled with crustal contamination (AFC). A three-stage petrogenetic model is envisaged: (1) decompression melting and source region contamination of an OIB-like subslab asthenospheric source by slab melts of the trailing edge of the subducted Nazca Plate; (2) minor contamination of slab window melts with arc components ‘stored’ in the supraslab mantle wedge and/or basal continental lithosphere; (3) further modification by addition of crustal components during magma ascent. The main-plateau lavas from the eastern back-arc can be modeled by ∼7% partial melting of the same asthenospheric source as the influence of arc components diminishes and the intensity of mantle ... |
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