Other
Scientific paper
Sep 1980
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980e%26psl..49..193b&link_type=abstract
Earth and Planetary Science Letters, Volume 49, Issue 2, p. 193-204.
Other
2
Scientific paper
In the Mesozoic eugeosynclinal sequences of the Italian North Apennines, ophiolitic rocks are commonly stratigraphically overlain by thick bedded chert sequences of Late Jurassic age. The isotopic composition of Pb contained in upper basalts, lower ferruginous (and in places manganiferous) cherts, middle cherts and upper cherts indicates that simple mixing occurred in the sediments between basalt-derived Pb, and more radiogenic Pb provided by fine-grained terrigenous detritus, radiolarian silica and possibly seawater.
The most ferruginous cherts are those nearest the ophiolitic basement, which is interpreted as ocean crust formed early in the opening of the Apennine ocean. Hematite content, considered to represent original Fe hydroxy-oxide chemical precipitate in the sediment, decreases upwards in a general way to very low values in the upper cherts. The most ferruginous cherts also contain the highest volcanogenic Pb component and total Pb, whereas higher cherts contain mainly terrestrially-derived Pb. These relations indicate a volcanic-hydrothermal origin for a significant portion of the Pb in the basal to middle parts of the chert formation, and suggest a similar origin for the hematitic Fe. The vertical distribution of hematite and volcanogenic Pb suggests that some initial Fe precipitates, carrying such Pb, had a widespread lateral dispersal after formation at an active ridge.
Present address: Mineralogisches Institut, Abteilung Geochemie, Universität Tübingen, Wilhemstrasse 56, 7400 Tübingen, Federal Republic of Germany.
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