Geochemical investigation of Neogene volcaniclastic rocks from the south-eastern part of the Zărand Basin (Apuseni Mts., Romania) – implications for locating the source area

Abstract

Abstract.A geochemical study of the Neogene volcaniclastic deposits from the south-eastern part of the Zărand Basin (Apuseni Mts., Romania) was performed. The investigated rocks are represented by medium-K calc-alkaline andesites. Their geochemical features are similar with those of other Neogene volcanic rocks from the Apuseni Mts. However, the investigated rocks also display a few particularities: limited variation of some major oxides and trace elements content, much lower content of Nb or of light REE. As for the other Neogene volcanic rocks from Apuseni area, the geochemical evidence supports a magma source located close to the boundary between crust and garnetfree lithospheric mantle, minor fractional crystallization processes affecting the magma. A subduction signature was identified for the investigated samples, and, similar to other Neogene volcanic rocks from Apuseni Mts., was interpreted as being related to some enrichment in fluids of the magma source. Based on the location and geochemical similarities with those of other Neogene volcanic rocks from the Apuseni Mts, the assumed age range of volcanic activity generating the volcaniclastic rocks of the study area is 13.8-10 Ma, while the source of the volcaniclastic material is most probably the Bontău volcanic structure.

Construction and Destruction of Bontău Composite Volcano in the Extensional Setting of Zărand Basin during Miocene (Apuseni Mts., Romania)

“…According to the TAS and Peccerillo and Taylor diagrams, the samples range from basaltic andesite to andesite (Figure 9). The data are comparable with those already published before for the Bontău volcanic complex [2,20,41,48], however, the Bontău rocks show faintly lower K 2 O than most of the previously published data of Group 1-Z, but similar Na 2 O + K 2 O trend. The basaltic andesites are in the smallest amount, they were identified for the first time in the remnant of the CVW edifice and were mentioned as clasts in DADs and associated with distal WDA debris-flow deposits (e.g., [48]).…”