Rb-Sr and K-Ar ages on minerals at temperatures of 300°-400°C from deep wells in the Larderello geothermal field (Italy)

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Authors:Del Moro, A.; Puxeddu, M.; Radicati di Brozolo, F.; Villa, I. M.
Author Affiliations:Primary:
CNR Ist. Geocronol.. Geochim. Isot., 56100 Pisa, Italy
Ist. Int. Ric. Geoterm., Italy
Cent. Stud. Problemi Orogeno Alpi Occidentali, Italy
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 81(4), p.340-349. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1982
Note:In English. 67 refs.; illus. incl. 15 anal., 4 tables, geol. sketch map
Summary:Rb/Sr and K/Ar ages were obtained on 6 biotites, 2 muscovites and 1 hornblende from mica schist, gneiss and amphibolite of Lower Palaeozoic to Precambrian age at a depth >2000 m in the basement rocks of the Larderello-Travale geothermal region. Most of the data cluster in the 2.5-3.7 m.y. range, revealing the existence of a Pliocene thermal event to which the origin of the field is attributed. The duration of the Larderello geothermal field is unexpectedly long. In the basement levels of two wells examined, unstabilized minimum T of 290° and 380°C were measured. All the biotites show almost complete 40Ar and 87Sr retention at the measured well T. Petrological evidence and experimental data also favour a closure T > 400°C for Rb/Sr and K/Ar in biotites. For the last 3 m.y., mean geothermal gradients of 120°-150°C/km were evaluated in the first 2-3 km, and 60°-65°C/km in the underlying 2 km. Total cooling in the last 3 m.y. was estimated to have been 120°C at 2500 m depth and 50°C at 4000 m in Sasso 22 well. A mean uplift rate of approx 0.22 mm/yr was calculated independently. [P.Br.]
Subjects:Absolute age; Amphibole group; Amphibolites; Biotite; Cenozoic; Chain silicates; Clinoamphibole; Cooling; Dates; Geochronology; Geothermal energy; Geothermal fields; Geothermal gradient; Granites; Heat flow; Hornblende; Igneous rocks; K/Ar; Metamorphic rocks; Metapelite; Metasedimentary rocks; Mica group; Muscovite; Neogene; Pliocene; Plutonic rocks; Rb/Sr; Sheet silicates; Silicates; Tertiary; Variscan Orogeny; Europe; Italy; Larderello; Southern Europe; Tuscany Italy; Wells
Coordinates:N432300 N432300 E0105300 E0105300
Abstract Numbers:83M/4043
Record ID:1986003460
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from PASCAL, Institute de l'Information Scientifique et Technique
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