Geochronology of the Neogene intrusive magmatism of the Oaș—Gutâi Mountains, Eastern Carpathians (NW Romania)

Abstract

Earlier geological work in the Oa -Gutâi Mts (OG), Eastern Carpathians, has revealed the extensive presence of shallow subvolcanic intrusive bodies, both exposed on the surface and covered by Paleogene-Neogene sedimentary sequences and Neogene volcanic formations. This study is based on detailed mapping and sampling of the OG Neogene intrusive magmatic rocks. Thirty seven representative intrusions (sills, dykes, microlaccoliths, etc.) were selected for radiometric dating. These intrusions show a wide variety of petrographic rock-types: from microgabbros to microgranodiorites and from basalts to andesites. However, the intrusions consist of typical calc-alkaline, medium-K rocks, similar to the volcanic rocks which outcrop in the same areas. The K-Ar age determinations on whole-rock samples of intrusions yielded ages between 11.9 Ma and 7.0 Ma (from Late Sarmatian to Middle Pannonian). The results are in good agreement with the common assumption, based on the biostratigraphic and geological data, that large volumes of intrusions have formed during the paroxysm of the intermediate volcanic activity in the OG. Except for the Firiza basalt intrusive complex of the Gutâi Mts (8.1-7.0 Ma), the OG intrusions show similar K-Ar ages as the intrusions of the "Subvolcanic Zone" and Călimani Mts from Eastern Carpathians. The timing of the OG intrusive magmatism partially overlaps with the timing of the intrusive magmatic activity in the Eastern Moravia and Pieniny Mts. The systematic radiometric datings in the whole OG give clear evidence that the hydrothermal activity related to the epithermal systems always postdates intrusion emplacement.

Origin of the Laleaua Albă dacite (Baia Sprie volcanic area and Au-Pb-Zn ore district, Romania): evidence from study of melt inclusions

“…The K-Ar and Ar-Ar isotope ages of the Laleaua Albà rocks are among the youngest in the area (8.5-8.0 Ma; Pécskay et al 2006), and are similar to the age (9.4-7.9 Ma; Kovacs et al 1997) of the nearby ore deposits.…”

“…1) are situated in the Neogene calc-alkaline magmatic rocks, which intruded the basement of Lower Cambrian metamorphic rocks, the Paleogene Trans-Carpathian flysch sequence, and Neogene molasse sediments (Sàndulescu 1988). Ore mineralization also shows a progressive younging from the west to the east: deposits located in the western part of the district (Ilba, Nistru and Sàsar) were formed within 11.5-10 Ma, whereas those in the eastern part (Herja, Baia Sprie, Şuior and Cavnic) define ages within 9.4-7.9 Ma (Kovacs et al 1997).…”

“…According to K-Ar dating this event was subsequently followed by extrusion (13.4-9 Ma) of basaltic andesites, dacites, and andesites, and small basaltic intrusions in the Sarmatian and Pannonian (8.0-6.9 Ma; Edelstein et al 1992Edelstein et al , 1993Lang et al 1994;Pécskay et al 1995;Kovacs et al 1997). Chiefly andesitic volcanism (14-7 Ma) in the Baia Mare ore district is linked to the moderate-K, calc-alkaline association with high LILE and LREE contents.…”

“…According to numerous publications (Borcoş et al 1995;Damian et al 1995;Kovacs et al 1995Kovacs et al 1997etc. ), the gold-polymetallic ores show various structures (banded, drusy, and less commonly disseminated and stockwork).…”

“…We are taking into consideration the spatial association and the time of emplacement of Laleaua Albà similar with those of mineralization (~9-8 Ma) (e.g. Kovacs et al 1997).…”