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Petrogenesis of Pre-caldera Mafic Lavas, Jemez Mountains Volcanic Field (New Mexico, USA) |
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| Authors: | WOLFF J A; ROWE M C; TEASDALE R; GARDNER J N; RAMOS F C; HEIKOOP C E |
| Institution: | 1 DEPARTMENT OF GEOLOGY, WASHINGTON STATE UNIVERSITY, PULLMAN, WA 99164, USA 2 DEPARTMENT OF GEOSCIENCES, OREGON STATE UNIVERSITY, 104 WILKINSON HALL, CORVALLIS, OR 97331, USA 3 DEPARTMENT OF GEOLOGICAL AND ENVIRONMENTAL SCIENCES, CALIFORNIA STATE UNIVERSITY, CHICO, CA 95929, USA 4 EARTH AND ENVIRONMENTAL SCIENCES, LOS ALAMOS NATIONAL LABORATORY, LOS ALAMOS, NM 87545, USA 5 DEPARTMENT OF EARTH SCIENCES, UNIVERSITY OF CALIFORNIA, SANTA CRUZ, CA, 95064, USA 6 DEPARTMENT OF GEOLOGY, McMASTER UNIVERSITY, 1280 MAIN STREET WEST, HAMILTON, ONTARIO L8S 4M1, CANADA |
| Abstract: | The Miocene–Quaternary Jemez Mountains volcanic field(JMVF), the site of the Valles caldera, lies at the intersectionof the Jemez lineament, a Proterozoic suture, and the CenozoicRio Grande rift. Parental magmas are of two types: K-depletedsilica-undersaturated, derived from the partial melting of lithosphericmantle with residual amphibole, and tholeiitic, derived fromeither asthenospheric or lithospheric mantle. Variability insilica-undersaturated basalts reflects contributions of meltsderived from lherzolitic and pyroxenitic mantle, representingheterogeneous lithosphere associated with the suture. The Kdepletion is inherited by fractionated, crustally contaminatedderivatives (hawaiites and mugearites), leading to distinctiveincompatible trace element signatures, with Th/(Nb,Ta) and La/(Nb,Ta)greater than, but K/(Nb,Ta) similar to, Bulk Silicate Earth.These compositions dominate the mafic and intermediate lavas,and the JMVF is therefore derived largely, and perhaps entirely,from melting of fertile continental Jemez lineament lithosphereduring rift-related extension. Significant variations in Pband Nd isotope ratios (206Pb/204Pb = 17·20–18·93;143Nd/144Nd = 0·51244–0·51272) result fromcrustal contamination, whereas 87Sr/86Sr is low and relativelyuniform (0·7040–0·7048). We compare theeffects of contamination by low-87Sr/86Sr crust with assimilationof high-87Sr/86Sr granitoid by partial melting, with Sr retainedin a feldspathic residue. Both models satisfactorily reproducethe isotopic features of the rocks, but the lack of a measurableEu anomaly in most JMVF mafic lavas is difficult to reconcilewith a major role for residual plagioclase during petrogenesis. KEY WORDS: Jemez Mountains volcanic field; Rio Grande rift; lithospheric mantle; crustal contamination; trace elements; radiogenic isotopes |
| Keywords: | : Jemez Mountains volcanic field Rio Grande rift lithospheric mantle crustal contamination trace elements radiogenic isotopes |
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