The Burdigalian to Serravallian turbiditic succession of the upper Gonfolite Lombarda Group exposed in the Brianza region has been sampled to analyze the petrographic composition and the detrital apatite fission-track record. The ultimate goal of this study is to define constraints for the provenance of the clastic sediments of the Gonfolite Lombarda and for the exhumation processes of the Central Alps during the Miocene. The petrographic analysis is still in progress, but preliminary results indicate that the Serravallian Gonfolite sediments include boulders from the Periadriatic Triangia (Sondrio) pluton that was emplaced at ca. 30 Ma. The fission-track-age distribution of the detrital apatites from the Burdigalian to Serravallian succession exhibits two age components: a approximately 30 Ma age component recorded by the largest fraction of grains in all samples, and a 53-106 Ma component shown only by two samples. The Burdigalian to Langhian samples include some detrital apatite ages close to the depositional age, suggesting possible partial annealing. Although the maximum burial conditions of the analyzed succession are not known, we tentatively interpret the fission-track-age distribution as not significantly affected by partial annealing. The approximately 30 Ma component is interpreted as related to the exhumation mainly of the Periadriatic intrusive rocks and of the adjacent Austroalpine units, but also of the portions of the Southalpine basement overprinted by the low-temperature Cenozoic thermal signature. The 53-106 Ma component is interpreted as related to the unroofing of the Variscan basement and the Permian volcanic rocks of the Southern Alps recording the Mesozoic thermotectonic signature. We conclude that the basement rocks of the Southern Alps were subject to erosion at least since the Early Miocene. Indeed, detrital apatites from the Gonfolite succession reveal a Southalpine provenance, but the dominant signal during the Early to Middle Miocene is likely derived mostly from the Periadriatic intrusives and the surrounding Austroalpine units.
Fellin, M., Sciunnach, D., Tunesi, A., Ando', S., Garzanti, E., Vezzoli, G. (2005). Provenance of detrital apatites from the upper Gonfolite Lombarda Group (Miocene, NW Italy). GEOACTA, 4, 43-56.
Provenance of detrital apatites from the upper Gonfolite Lombarda Group (Miocene, NW Italy)
TUNESI, ANNALISA MARIA;ANDO', SERGIO;GARZANTI, EDUARDO;VEZZOLI, GIOVANNI
2005
Abstract
The Burdigalian to Serravallian turbiditic succession of the upper Gonfolite Lombarda Group exposed in the Brianza region has been sampled to analyze the petrographic composition and the detrital apatite fission-track record. The ultimate goal of this study is to define constraints for the provenance of the clastic sediments of the Gonfolite Lombarda and for the exhumation processes of the Central Alps during the Miocene. The petrographic analysis is still in progress, but preliminary results indicate that the Serravallian Gonfolite sediments include boulders from the Periadriatic Triangia (Sondrio) pluton that was emplaced at ca. 30 Ma. The fission-track-age distribution of the detrital apatites from the Burdigalian to Serravallian succession exhibits two age components: a approximately 30 Ma age component recorded by the largest fraction of grains in all samples, and a 53-106 Ma component shown only by two samples. The Burdigalian to Langhian samples include some detrital apatite ages close to the depositional age, suggesting possible partial annealing. Although the maximum burial conditions of the analyzed succession are not known, we tentatively interpret the fission-track-age distribution as not significantly affected by partial annealing. The approximately 30 Ma component is interpreted as related to the exhumation mainly of the Periadriatic intrusive rocks and of the adjacent Austroalpine units, but also of the portions of the Southalpine basement overprinted by the low-temperature Cenozoic thermal signature. The 53-106 Ma component is interpreted as related to the unroofing of the Variscan basement and the Permian volcanic rocks of the Southern Alps recording the Mesozoic thermotectonic signature. We conclude that the basement rocks of the Southern Alps were subject to erosion at least since the Early Miocene. Indeed, detrital apatites from the Gonfolite succession reveal a Southalpine provenance, but the dominant signal during the Early to Middle Miocene is likely derived mostly from the Periadriatic intrusives and the surrounding Austroalpine units.
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