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Christensen, J. N.
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Christensen, J. N.
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- PublicationRestrictedEruptive history and petrologic evolution of the Albano multiple maar (Alban Hills, Central Italy)(2006)
; ; ; ; ; ; ; ; ; ;Freda, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Gaeta, M.; Dipartimento di Scienze della Terra, Universit`a degli Studi “La Sapienza” ;Karner, D. B.; Dept of Geology, Sonoma State University, ;Marra, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Renne, P. R.; Berkeley Geochronology Center, ;Taddeucci, J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Scarlato, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Christensen, J. N.; Lawrence Berkeley National Laboratory, ;Dallai, L.; CNR-Istituto di Geologia Ambientale e Geoingegneria; ; ; ; ; ; ; ; A comprehensive volcanological study of the Albano multiple maar (Alban Hills, Italy) using (i) 40Ar/39Ar geochronology of the most complete stratigraphic section and other proximal and distal outcrops and (ii) petrographic observations, phase analyses of major and trace elements, and Sr and O isotopic analyses of the pyroclastic deposits shows that volcanic activity at Albano was strongly discontinuous, with a first eruptive cycle at 69±1 ka producing at least two eruptions, and a second cycle with two peaks at 39±1 and 36±1 ka producing at least four eruptions. Contrary to previous studies, we did not find evidence of magmatic or hydromagmatic eruptions younger than 36±1 ka. The activity of Albano was fed by a new batch of primary magma compositionally different from that of the older activity of the Alban Hills; moreover, the REE and 87Sr/86Sr data indicate that the Albano magma originated from an enriched metasomatized mantle. According to the modeled liquid line of descent, this magma differentiated under the influence of magma/limestone wall rock interaction. Our detailed eruptive and petrologic reconstruction of the Albano Maar evolution substantiates the dormant state of the Alban Hills Volcanic District.245 30 - PublicationRestrictedTime-dependent geochemistry of clinopyroxene from Alban Hills (Central Italy): clues to source and evolution of ultrapotassic magmas.(2006)
; ; ; ; ; ; ; ;Gaeta, M.; Dipartimento di Scienze della Terra, Universita` degli Studi "La Sapienza" ;Freda, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Christensen, J. N.; Center for Isotope Geochemistry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 70A4418, Berkeley, CA 94720, USA ;Dallai, L.; CNR-Istituto di Geoscienze e Georisorse, Via Moruzzi 1, 56127 Pisa, Italy ;Marra, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Karner, D. R.; Department of Geology, Sonoma State University- 1801 East Cotati Avenue, Rohnert Park, CA 94985, USA ;Scarlato, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; ; ; We investigated chemical and isotopic compositions of clinopyroxene crystals from well age-constrained juvenile scoria clasts, lava flows, and hypoabyssal magmatic ejecta representative of the whole eruptive history of the Alban Hills Volcanic District. The Alban Hills is a Quaternary ultra-potassic district that was emplaced into thick limestone units along the Tyrrhenian margin of Italy. Alban Hills volcanic products, even the most differentiated, are characterised by low SiO2 content. We suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma/limestone interface. According to the liquid line of descent we propose, the differentiation process is driven by crystallisation of clinopyroxene+leuciteFapatiteFmagnetite coupled with assimilation of a small amount of calcite and/or with interaction with crustal CO2. By combining age, chemical data, strontium and oxygen isotopic compositions, and REE content of clinopyroxene, we give insights into the evolution of primitive ultrapotassic magmas of the Alban Hills Volcanic District over an elapsed period of about 600 kyr. Geochemical features of clinopyroxene crystals, consistent with data coming from other Italian ultrapotassic magmas, indicate that Alban Hills primary magmas were generated from a metasomatized lithospheric mantle source. In addition, our study shows that the 87Sr / 86Sr and LREE/HREE of Alban Hills magmas continuously diminished during the 600–35 ka time interval of the Alban Hills eruptive history, possibly reflecting the progressive depletion of the metasomatized mantle source of magmas.215 26