engleski

Ages and Trace Element Patterns of Apatite and Zircon in a Diorite from the Mt. Papuk metamorphic complex (Pannonian Basin Basement in Croatia, CE Europe)

Small decameter-sized I-type plutonic bodies occur in the eastern part of the Mt. Papuk metamorphic complex of the Pannonian Basin Basement (Croatia). We studied a body of a cataclazed (meta)diorite composed of plagioclase (andesine and albite), amphibole, quartz, partially chloritized biotite, K-feldspar, clinozoisite, ilmenite, and titanite. Accessories zircon and apatite were analyzed and dated by laser-ablation ICP mass-spectrometry. The host rock contains only 80 ppm REE and shows negative Th, Nb, Ce, Pr, and Ti and positive U, Pb, Sr, Zr, and Eu (Eu/Eu*=1.03) anomalies in the primitive mantle-normalized diagram. Zircon is characterized by {;100};>>{;110}; prisms, {;101};<<{;211}; bipyramids, and an aspect ratio of 2.5:1. The average length of the analyzed zircon grains is 180 μm. REE patterns of zircon normalized to chondrite reveal positive Ce (Ce/Ce*=16.6) and negative Eu (Eu/Eu*=0.44) anomalies, whereas other trace element patterns of zircon and host rock are similar. High mean U (455 ppm) and Th (138 ppm) values, ratios of Th/U=0.30 and Zr/Hf=30.3 as well as Zr saturation (800°C) and Ti-in-zircon (760°C) temperatures suggest that zircon has crystallized at relatively high temperature. The 206Pb/238U age obtained on zircon is 554±13.2 Ma (RMSD). Apatite forms prismatic crystals with relatively low contents of Sr, Mn and Y (400, 345, 254 ppm, respectively). The total REE content in apatite (70-1900 ppm) varies but the chondrite-normalized REE patterns always show an enrichment of the MREE compared to the HREE, a negative Eu anomaly of 0.53 and a depletion of LREE in contrast to the host rock. The competition for REE with titanite explains the LREE depletion in apatite. The average of the obtained 206Pb/238U ages is 326±22.7 Ma (RMSD). Based on comparison of our data and data for the surrounding metamorphic rocks we conclude that the studied diorite intruded the crust in the Cambrian, was metamorphosed at medium grade by the Variscan orogeny, and only slightly affected by a low-grade Alpine event in the Cretaceous. Support by the Croatian Science Foundation (IP-2014-09-9541) is acknowledged.

age dating, apatite, zircon, Mt. Papuk

nije evidentirano