International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

EVOLUTION OF THE NEOGENE GURGHIU MOUNTAINS VOLCANIC RANGE (EASTERN CARPATHIANS, ROMANIA), BASED ON K-Ar GEOCHRONOLOGY

Pages: 325 - 332

Authors: IOAN SEGHEDI, ALEXANDRU SZAKACS, NORMAN J. SNELLING,ZOLTAN PECSKAY

Abstract: K-Ar ages of rocks from the Gurghiu Mountains, the middle part of the longest volcanic chain in the Eastern Carpathians (Călimani–Gurghiu–Harghita), indicate an interval of volcanic activity between 9.4–5.4 Ma. Magmatic activity migrated from North to South and built the following volcanic centres: Jirca (J), Fâncel-Lăpusna (FL), Bacta (B), Seaca-Tătarca (ST), Borzont (BZ), Sumuleu (S) and Ciumani-Fierăstraie (CF). The timing of volcanic activity in each volcanic centre reflects the previously recognized overlapping age progression from North to South along the arc: J=9.2–7.0 Ma; FL=9.4–6.0 Ma; B=7.5–7.0 Ma; ST=7.3–5.4 Ma; BZ=6.8 Ma; S=6.8–6.2 Ma; CF=7.1–6.3 Ma. Two peripheral small intrusive bodies have also been dated (Ditrău — 7.9 Ma and Corund — 7.4 Ma). The duration of volcanic activity of each centre is ca. 1 Ma, with a larger interval of 2.5 Ma for the Fâncel-Lăpusna volcano. Volcanic activity in the southernmost volcanic centres (ST; BZ; S; CF) between 7–6 Ma was contemporaneous. Certain volcanological problems are pointed out: (i) the voluminous debris-avalanche deposit assumed to belong to the Călimani Mountains includes blocks of ca. 8 Ma up to the Gurghiu Valley and between 7.5–7.8 Ma south of the Gurghiu Valley (ii) the Fâncel-Lăpusna caldera was generated around 6.9 Ma and involved a post-caldera uplift and/or erosion of the caldera floor and younger domes; and (iii) the model based on volcanic facies distribution is consistent with the new age-data.

Keywords: Eastern Carpathians, Gurghiu Mountains, K-Ar data, volcanology, debris-avalanche

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Volume 55 no. 4 / August 2004

Volume 55 no. 4