Istituto di Geoscienze e Georisorse     
Pinarelli L., Bergomi M., Boriani A., Giobbi E. Pre-metamorphic melt infiltration in metasediments: geochemical, isotopic (Sr, Nd, and Pb), and field evidence from Serie dei Laghi (Southern Alps, Italy). In: Mineralogy and Petrology, vol. 93 (3-4) pp. 213 - 242. Springer, 2008.
Gradual transitions from K-feldspar free gneisses to K-feldspar bearing augengneisses are sometimes observed in metamorphic terranes. They have been explained with metasomatic porphyroblastic growth connected with regional metamorphism, or with pre-metamorphic presence of magmatic megacrysts. A transition of this kind can be observed in the Serie dei Laghi (Southern Alps, Italy), where coarse-grained metaarenites (Cenerigneiss) grade into Ceneri augengneisses with large K-feldspar porphyroclasts, and banded amphibolites of the ''Strona Ceneri Border Zone'' grade into Hbl augengneisses rich in K-feldspar. The Ceneri augengneisses are chemically indistinguishable from the Cenerigneiss, but have higher 87Sr=86Sr (0.7256-0.7258 vs. 0.7215-0.7233), similar to those of the Ordovician granites that were intruded, before the regional metamorphism, into the protoliths of both Cenerigneiss and amphibolites. The Cenerigneiss contains two types of zircons:(1) highly luminescent, rounded grains or fragments, yielding U-Pb SHRIMP ages from 0.43 to 1.0 Ga; (2) euhedral grains with oscillatory zoning (magmatic), with U-Pb SHRIMP concordant ages of 466 13 Ma. This age coincides with the Rb-Sr whole rock emplacement age of the Ordovician granitoids (466 5Ma).
URL: http://https://link.springer.com/journal/710
Subject Italy
southern Alps
metamorphic phenomena
rock geochemistry
chemical data
isotopic data

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