СПИСАНИЕ НА БЪЛГАРСКОТО ГЕОЛОГИЧЕСКО ДРУЖЕСТВО, год. 81, кн. 3, 2020, с. 66–68 REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, vol. 81, part 3, 2020, p. 66–68 Национална конференция с международно участие „ГЕОНАУКИ 2020“ National Conference with international participation “GEOSCIENCES 2020”

Middle Triassic crystallization of the Ivanovo granite, Harmanli block, Sakar- Strandzha zone, Кристализация през Среден Триас на Ивановски гранит, Харманлийски блок, Сакар-Странджанска зона, България Nikolay Bonev1, Petyo Filipov2 Николай Бонев1, Петьо Филипов2

1 University “St. Kliment Ohridski”, Department of Geology, Paleontology and Fossil Fuels, Sofia 1504, 15 Tzar Osvoboditel Bd.; Е-mail: [email protected] 2 Geological Institute, Bulgarian Academy of Sciences, Department of Geochemistry and Petrology, Sofia 1113, 24 Acad. Georgi Bonchev St.

Keywords: granitе, U-Pb zircon geochronology, Sakar-Strandzha Zone, Bulgaria.

Introduction et al. (1992) have mentioned K-Ar ages (likely unpublished) in the range 300–325 Ma and 150– Lower–Middle Triassic meta-sedimentary rocks 230 Ma for the Ivanovo granite. The host K-feld- in which have been intruded presumably Triassic spar porphyritic meta-granite crystallized at 240.6± granite and rhyolite bodies are known for the re- 2.3 Ma, while the leucocratic meta-granite has crys- gion along the river valley (Chatalov, 1961; tallization age of 243.3±5.8 Ma (Bonev et al., 2019). Chatalov, Stefanov, 1966; Kozhoukharov et al., 1969; Kozhoukharova, Kozhoukharov, 1978) of the Sakar-Strandzha Zone. Recently, along the Maritsa Results river valley was identified a Middle Triassic acid magmatism of ages ranging from 243 Ma to 238 Ma Field observations confirmed that the Ivanovo (Bonev et al., 2019), including the meta-granites of granite is undeformed and unmetamorphosed. The the Harmanli block that also belongs to the Sakar- Ivanovo granite is coarse-grained and contains Strandzha Zone. In this contribution we further con- biotite-rich microgranular enclaves. The porphy- firm the timing of Triassic magmatism with U-Pb ritic texture of the granite consists of a large (up to zircon geochronology of the Ivanovo granite in the 5–7 cm), sometimes zonal K-feldspar porphyres. Harmanli block (Fig. 1a). The granite also contains quartz, plagioclase (seric- itized) and biotite (partly chloritized), and all these main mineral constituents have preserved their orig- Geological outline inal igneous shape and size. A single sample (Lat. The Ivanovo granite forms a small east-west elon- N41°52'18.7", Long. E25°52'28.7") from the Ivano- gated body emplaced into the K-feldspar porphy- vo granite has been used for U-Pb zircon LA-ICP- ritic two-mica meta-granite of the Harmanli block MS geochronology. Zircons vary in size from 400 (Fig 1a), which block is also built by a leucocratic to 100 μm and mainly have prismatic forms of well- muscovite meta-granite. The Ivanovo granite is un- expressed magmatic oscillatory and sector zoning deformed and unmetamorphosed in contrast to the patterns (Fig. 1b). A single analysis of a zircon host rocks, and this was used earlier to infer that the grain out of thirty grains analyzed yielded a concor- Ivanovo granite is an important magmatic marker dia age of 238.3±4.2 Ma (Th/U = 0.50) that defines for the bulk metamorphic and tectonic evolution of the magmatic crystallization age of the Ivanovo the large-scale region of the Eastern Rhodope and granite (Fig. 1c). Other three zircon grains yielded Sakar mountains (Boyanov et al., 1963). Boyanov concordant age of 248.6±1.8 Ma. These concordant

66 Fig. 1. a, Geological map of the Maritsa river valley area compiled after Boyanov et al. (1992, 1993) showing the location of the Ivanovo granite. Numbers refer to U-Pb zircon ages after Bonev et al. (2019). Some unpublished U-Pb zircon age data have been incorporated into the map; b, selected cathodeluminescence image of dated zircons, where circles represent point analyses with corresponding ages; c, concordia U-Pb diagram.

grains have high Th/U ratios in the range of 0.10– pears as a textural variety of the K-feldspar porphy- 0.93. Five zircon antecrysts have concordant ages ritic meta-granite, while the crystallization age de- in the range of 263.4–253.2 Ma. Thirteen inherited fines emplacement of the Ivanovo granite as a late zircons yielded a concordant ages between 351.1 Ma magmatic body. and 279.4 Ma. Acknowledgments: The study was supported by the Sofia University “St. Kliment Ohridski” Fund Conclusion Scientific Research project no. 80-10-78/2020. The U-Pb zircon age result for the Ivanovo granite confirms the Middle Triassic magmatic phase (ca. References 243–238 Ma) recorded in the Harmanli block and Bonev, N., P. Filipov, R. Raicheva, R. Moritz. 2019. Triasic within adjacent areas of the Sakar-Strandzha Zone. magmatism along the Maritsa river valley, Sakar-Strandzha From field data and texture the Ivanovo granite ap- Zone, Bulgaria. – Rev. Bulg. Geol. Soc., 80, 3, 56–57.

67 Boyanov, I., B. Mavroudchiev, I. Vaptsarov. 1963. On the Chatalov, G., 1961. Triasiche kristalline schiefer und mag- structural and formational peculiarities of part of the East- magesteine zwischen and Dimitrovgrad. – C. R. ern Rhodope. – Bull. Inst. Geol., 12, 125–186 (in Bulgarian Acad. Bulg. Sci., 14, 5, 503–506. with Russian and English abstracts). Chatalov, G., S. Stefanov. 1966. Neue paläontologische An-ga- Boyanov, I., D. Kozhokharov, A. Goranov, E. Kozhoukharova, ben zum triassischen Alter eines Teiles der kristallinen M. Ruseva, G. Shiliafova. 1992. Explanatory Note to the Schiefer in Südostbulgarien. – Bull. Inst. Geol., 15, 269– Geological Map of Bulgaria on the Scale 1:100 000. Map 277 (in Bulgarian with Russian and German abstracts). Sheet Haskovo. Committee of Geology, Department of Ge- Kozhoukharov, D., I. Boyanov, S. Savov. 1969. Neuen daten über ophysical Prospecting and Geological Mapping (in Bulgar- die geologie der Marica störungszone östlich der schwelle ian with English abstract). von Cirpan. – C. R. Acad. Bulg. Sci., 22, 8, 927–930. Boyanov, I., A. Goranov, G. Shiliafova, M. Ruseva. 1993. Ex- Kozhoukharova, Е., D. Kozhoukharov. 1978. Notes on the planatory Note to the Geological Map of Bulgaria on the Triassic quartz-porphyry magmatism between the village Scale 1:100 000. Map Sheet Dimitrovgrad. Committee of Klokotnica and the town of Marica, Haskovo district. – Geology and Mineral Resources, Geology and Geophysics Rev. Bulg. Geol. Soc., 39, 3, 335–341 (in Bulgarian with Corp. (in Bulgarian with English abstract). English abstract).

68