The ultrapotassic rocks: Characteristics, classification, and constraints for petrogenetic models

A review of tufa and travertine deposits of the world

Some remarks on the movement of small melt fractions in the mantle

D\H and 18 O\ 16 O data have now been obtained on a wide variety of granitic batholiths of various ages. The primary δD values of the biotites and hornblendes are remarkably constant at about –50 to –85, identical to the values in regional metamorphic rocks, marine sediments and greeenstones, and most weathering products in temperate climates. Therefore the primary H 2 O in these igneous rocks is probably not ‘juvenile’, but is ultimately derived by dehydration and/or partial melting of the lower crust or subducated lithosphere. Most granitic rocks have δ 18 O = + 7.0 to +10.0, probably indicating significant involvement of high - 18 O metasedimentary or altered volcanic rocks in the melting process; such an origin is required for many other granodiorites and tonaloites that have δ 18 O = + 10 to +13. Gigantic meteoric-hydrothermal convective circulation systems were established in the epizonal portions of all batholiths, locally producing very low δ 18 O values (particularly in feldspars) during subsolidus exchange. Some granitic plutons in such environments also were emplaced as low- 18 O magmas probably formed by melting or assimilation of hydrothermally altered roofrocks. However, the water/rockratios were typically low enough that over wide areas the only evidence for meteoric H 2 O exchange in the batholiths is given by low D/H ratios (δD as low as –180); for example, because of latitudinal isotopic variations in meteoric waters, as one moves from through the Cordilleran batholiths of western North America an increasingly higher proportion of the granitic rocks haves δD values lower than –120. The lowering of δD values commonly correlates

Water/rock interactions and the origin of H2O in granitic batholiths Thirtieth William Smith lecture

The restless, resurgent Campi Flegrei nested caldera (Italy): constraints on its evolution and configuration

The 18O/16O ratios of rocks and coexisting minerals were measured for 93 samples of leucite-bearing lavas, pyroclastics, and related volcanic rocks from the Quaternary Roman Co-Magmatic Province, Italy. The δ18O values were found to generally increase northward in the sequence: Ischia (5.8 to 7.0); Somma-Vesuvius and Phlegrean Fields (7.3 to 8.3); Alban Hills (7.3 to 8.7); M. Sabatini (7.3 to 9.7); Vico Volcano (7.4 to 10.2); and M. Vulsini (8.1 to 11.7). The northward increase in δ18O parallels a similar increase in 87Sr/86Sr, and these data indicate that the Roman magmas have interacted strongly with high-18O continental crust. A marked increase in δ18O occurs just north of Rome where the Roman Province begins to overlap the calc-alkaline, oversaturated Tuscan Magmatic Province. Therefore, some of the observed 18O/16O and 87Sr/86Sr enrichments in the Roman magmas may have been facilitated by direct mixing with the high-18O Tuscan magmas or because the high-18O country rocks underwent widespread heating during a couple of million years of Tuscan igneous activity. Although many of the Roman magmas underwent fractional crystallization without appreciable change in δ18O, contamination has produced a correlation between δ18O and SiO2 content at several of the volcanic centers; thus the trachytes are typically higher in 18O than the undersaturated rocks. The major features of the oxygen isotope data can be explained in terms of a simple two-component mixing model in which one end-member was a primary, strongly undersaturated magma derived from the upper mantle, with δ18O≈+6, 87Sr/86Sr≈0.704 to 0.705, and SiO2<44wt.%. However, none of the analyzed samples have these values, as they have all been contaminated to some extent. The closest approach is found in some of the leucitepyroxenite ejecta from the Alban Hills. The second end-member, derived from the continental crust, had a variable composition with δ18O≈+12 to +20, 87Sr/86Sr≧0.712 to 0.720, and SiO2≧65wt.%, and it mixed in much greater proportions in the volcanoes north of Rome than in those of the Alban Hills or the Naples area. The widespread interactions between the Roman magmas and the continental crust are probably due to (1) the fact that such low-SiO2 magmas always have a very strong tendency to interact with quartz-bearing rocks of the continental crust, and (2) in Italy, these magmas were emplaced into a tectonically very active area containing poorly consolidated sedimentary rocks, and in the northern part of the belt there had been a prior history of extensive calc-alkaline igneous activity.

Oxygen isotope studies of potassic volcanic rocks of the Roman Province, Central Italy

Isotopic study of the origin of sulfur and carbon in Solfatara fumaroles, Campi Flegrei caldera

http://www.museucienciesnaturals.org/userFiles/File/Publicaciones/articles_cientifics/02Vesica_et_al_2000.pdf

Late Pleistocene Paleoclimates and sea-level change in the Mediterranean as inferred from stable isotope and U-series studies of overgrowths on speleothems, Mallorca, Spain

The 18O/16O ratios were measured for 60 rocks and coexisting minerals from the Plio-Pleistocene, calc-alkaline, Tuscan Magmatic Province, Italy. The δ18O values of these magmas were as follows: Elba, Giglio, and Montecristo granodiorites (11.4 to 12.1); M. Cimini rhyolites and trachytes (11.2 to 11.7); Roccastrada, S. Vincenzo, and M. Amiata rhyolites (12.3 to 13.4); and the Tolfa rhyolites and quartz latites (15.3 to 16.4). The latter are by far the highest δ18O values yet reported for primary volcanic rocks. The extremely high δ18O values in the Tuscan Province indicate that these magmas all formed by melting or large-scale assimilation of high-18O argillaceous sedimentary rocks, in agreement with previous evidence based on the high 87Sr/86Sr ratios and ubiquitous presence of cordierite. Low δ18O values (+5 to +6) were found in the feldspar, but not the quartz, of the small Porto Azzuro stock on Elba, as well as in the marginal facies of the M. Capanne stock, indicating that these bodies interacted with low-18O meteoric-hydrothermal fluids subsequent to solidification. The M. Cimini lavas apparently formed about 1 m.y. ago by mixing of high-18O Tuscan magmas containing large K feldspar crystals with potassic, undersaturated, low-18O magmas of the adjacent Roman Co-Magmatic Province. These large sanidine crystals did not completely equilibrate 18O/16O with the coexisting magma.

Bruno Turi

Papers

Oxygen isotope studies of potassic volcanic rocks of the Roman Province, Central Italy

Isotopic study of the origin of sulfur and carbon in Solfatara fumaroles, Campi Flegrei caldera

Late Pleistocene Paleoclimates and sea-level change in the Mediterranean as inferred from stable isotope and U-series studies of overgrowths on speleothems, Mallorca, Spain

High-18O igneous rocks from the Tuscan Magmatic Province, Italy

Oxygen isotope geochemistry of the potassic igneous rocks from the Roccamonfina volcano, Roman comagmatic region, Italy