Post-collisional magmatism in the Late Miocene Rodna-Bârgău subvolcanic district (East Carpathians) gave rise to a wide variety of rock compositions, allowing recognition of four groups of calcalkaline rocks with distinctive petrography, mineral chemistry, whole-rock geochemistry and Sr-Nd-Hf isotope features. New U-Pb zircon datings, together with literature data, indicate that the emplacement of the four rock groups was basically contemporaneous in the 11.5–8Ma time span. The lowpotassiumgroup (LKG) includes the most abundant lithotypes of the area, ranging frombasaltic andesite to dacite, characterized by K-poor tschermakiticamphibole,weak enrichment in LILE and LREE, relatively low 87Sr/86Sr, coupled with relatively high 143Nd/144Nd and 176Hf/177Hf. The high potassium group (HKG) includes amphibole-bearing microgabbro, amphibole andesite and amphiboleand biotite dacite, with K-richer magnesio-hastingsite to hastingsite amphibole, more marked enrichments in incompatible elements, higher 87Sr/86Sr and lower 143Nd/144Nd and 176Hf/177Hf. These two main rock groups seem to have originated from similar juxtaposed mantle sources, with the HKG possibly related to slightly more enriched domains (with higher H2O reflected by the higher modal amphibole) with respect to LKG (with higher plagioclase/amphibole ratios). The evolution of the two rock series involved also open-system processes, taking placemainly in the upper crust for the HKG, in the lower crust for LKG magmas. In addition, limited occurrences of generally younger strongly evolved peraluminous rhyolites and microgranites (Acid group) and sialicdominated “leucocratic” andesites and dacites (LAD group)were also recognized to the opposite outermost areas of the district. These two latter rock groupswere generated by the melting of a basicmetamorphic crustal source (respectively in hydrous and anhydrous conditions), favored by the heat released by mantle melts from the adjoining central area. The peculiar distribution of the products of the four rock groups in well defined sectors argues for a strong control of the local crustal tectonic regime on magmatism, influenced by the change from a transpressional to trastensional stage.
Post-collisional magmatism in the Late Miocene Rodna-Bârgău district (East Carpathians, Romania): geochemical constraints and petrogenetic models / Fedele, Lorenzo; Seghedi, I.; Chung, S. L.; Laiena, Fabio; Lin, T. H.; Morra, Vincenzo; Lustrino, M.. - In: LITHOS. - ISSN 0024-4937. - 266-267:(2016), pp. 367-382. [doi:10.1016/j.lithos.2016.10.015]
Post-collisional magmatism in the Late Miocene Rodna-Bârgău district (East Carpathians, Romania): geochemical constraints and petrogenetic models
FEDELE, LORENZO;LAIENA, FABIO;MORRA, VINCENZO;
2016
Abstract
Post-collisional magmatism in the Late Miocene Rodna-Bârgău subvolcanic district (East Carpathians) gave rise to a wide variety of rock compositions, allowing recognition of four groups of calcalkaline rocks with distinctive petrography, mineral chemistry, whole-rock geochemistry and Sr-Nd-Hf isotope features. New U-Pb zircon datings, together with literature data, indicate that the emplacement of the four rock groups was basically contemporaneous in the 11.5–8Ma time span. The lowpotassiumgroup (LKG) includes the most abundant lithotypes of the area, ranging frombasaltic andesite to dacite, characterized by K-poor tschermakiticamphibole,weak enrichment in LILE and LREE, relatively low 87Sr/86Sr, coupled with relatively high 143Nd/144Nd and 176Hf/177Hf. The high potassium group (HKG) includes amphibole-bearing microgabbro, amphibole andesite and amphiboleand biotite dacite, with K-richer magnesio-hastingsite to hastingsite amphibole, more marked enrichments in incompatible elements, higher 87Sr/86Sr and lower 143Nd/144Nd and 176Hf/177Hf. These two main rock groups seem to have originated from similar juxtaposed mantle sources, with the HKG possibly related to slightly more enriched domains (with higher H2O reflected by the higher modal amphibole) with respect to LKG (with higher plagioclase/amphibole ratios). The evolution of the two rock series involved also open-system processes, taking placemainly in the upper crust for the HKG, in the lower crust for LKG magmas. In addition, limited occurrences of generally younger strongly evolved peraluminous rhyolites and microgranites (Acid group) and sialicdominated “leucocratic” andesites and dacites (LAD group)were also recognized to the opposite outermost areas of the district. These two latter rock groupswere generated by the melting of a basicmetamorphic crustal source (respectively in hydrous and anhydrous conditions), favored by the heat released by mantle melts from the adjoining central area. The peculiar distribution of the products of the four rock groups in well defined sectors argues for a strong control of the local crustal tectonic regime on magmatism, influenced by the change from a transpressional to trastensional stage.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
