Chemical petrology of ophiolites in southern Tuscany

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Authors:Grohmann, N.; Klemm, Dietrich D.; Topitsch, W.; Wagner, J.
Author Affiliations:Primary:
Univ. München, Inst. Allgemeine Angewandte Geol., Munich, Federal Republic of Germany
Volume Title:Ophiolites and actualism; Proceedings of the meeting
Volume Authors:Bortolotti, V., editor
Source:Ofioliti, 7(2-3), p.241-266; Ophiolites and actualism; meeting, Florence, Italy, Dec. 18-19, 1981, edited by V. Bortolotti. Publisher: Pitagora Editrice, Bologna, Italy. ISSN: 0391-2612
Publication Date:1982
Note:In English. 2 p. refs.; illus. incl. 50 anal., 4 tables, sketch map, block diag.
Summary:About 250 new analyses of ophiolites from S Tuscany were plotted in different major- and trace-element diagrams. For the basalts, the results contrasted with the published literature. Although some samples resemble ocean-floor types, on their chemistry most of the basalts are transitional ocean-floor basalts and the Eastern Mediterranean ophiolite nappe basalts. The dyke basalts show a close relation to these ophiolite nappe basalts, as well as to differentiated komatiites, marianites and boninites; they also crystallize between the tholeiitic and calc-alkaline trends. The distribution pattern of gabbros, dyke basalts, massive basalts and pillow basalts runs across the well-known fractionation trends. The major elements show the above pattern, but they may have changed through spilitization. Selected 'immobile' trace-elements more obviously show this effect. The gabbros show a similar chemistry to komatiites, which cannot be explained by accumulation. A new CIPW-normative Cross-diagram is presented, allowing primary magmas of different alkalinity to be distinguished, also their differentiation and spilitization, and therefore can be used to determine the petrology of the unspilitized differentiates and primary basalt types. Observed and calculated spilitization trends of samples of the same differentiation stage are in good agreement. Some of the basalts and gabbros, which plot in the alkaline or komatiite field, are examined more closely. The serpentinized peridotites are compared with literature-cited dunites, harzburgites and mantle-lherzolites. Most of then can be regarded as former lherzolites, depleted in Al2O3 and CaO during serpentinization. (Authors' abstract) [C.N.]
Subjects:Basalts; Gabbros; IGCP; Igneous rocks; Metasomatism; Ophiolite; Petrology; Phase equilibria; Plutonic rocks; Serpentine group; Sheet silicates; Silicates; Spilitization; Ultramafics; Volcanic rocks; Europe; Italy; Southern Europe; Tuscany Italy; Southern Tuscany
Abstract Numbers:87M/5029
Record ID:1985081309
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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