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2 Geological Quarterly

2 2022

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Magmatic signature of the closure of the northern branch of Neo-Tethys : Upper Paleocene-Middle Eocene magmatism at the boundary of Tavşanlı-Sakarya Zone (Turkey)

Güllü Bahattin, Kadiıoğlu Yusuf Kağan

Geological Quarterly

2022

Vol. 66, No. 2

art. no. 13

Numerous plutons composed of granite, granodiorite, diorite-porphyry, monzonite, granodiorite-porphyry and diorite/microdiorite-porphyry occur at the boundary of the TavêanlÏ-Sakarya Zone, in the eastern part of the northwestern Anatolian magmatic belt, Turkey. These rocks belong to two different types: a medium-K calc-alkaline granodiorite series (with associated dykes and sub-volcanic rocks) and a shoshonitic series of granites. The rocks of the shoshonitic series have SiO₂from 67.5 to 75.6 wt.% with Mg# from 35.1 to 59.5, whereas the medium-K calc-alkaline series rocks have SiO₂ between 54.6 and 67.7 wt.% with Mg# from 43.5 to 60.8. There is a clear enrichment of LILE with respect to the HFSE in all magmatic units of the region. These magmatic rocks reflect properties of collision-related arc magmatism in the various geochemical discrimination diagrams. The initial Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd istopic ratios of the magmatic units range from 0.705506 to 0.710902 and 0.512178 to 0.512594, respectively. Collision-related granitoids yielded a ⁴⁰Ar/³⁹Ar cooling age age of 59.13 ±1.87 Ma, and arc-related granitoids and associated sub-volcanic units 44.3 ±0.47 and 44.11 ±0.89 Ma. The data obtained revealed that continent-continent collision in the Paleocene together with the initiation of the closure of the Neo-Tethys took place between the Anatolide-Tauride Platform and Sakarya Plate from the end of the Cretaceous. The shoshonotic granite may cooled in the Middle Paleocene, as regards the subduction-accretion zone in which subduction impacts have been observed. The medium-K calc-alkaline magmatic products in the region were formed by partial melting of the continental lithospheric mantle caused by the upwelling of asthenospheric mantle after the subducted slab was delaminated.

Constraints on the nature and evolution of the volcanic fields of the Andahua Group, Central Volcanic Zone, southern Peru

Gałaś Andrzej, Németh Károly, Lewińska Paulina

Geological Quarterly

2022

Vol. 66, No. 3

art. no. 25

The Andahua Group is a distinct cluster of typically monogenetic volcanoes located in the northernmost part of the Central Volcanic Zone in the Andes, characterized by small-volume lava domes and scoria cones. Seven volcanic clusters have been distinguished. Using satellite imagery, geological mapping, and fieldwork, we found a total of 103 lava domes, 43 scoria cones, and 3 small composite volcanoes. Most of the lava domes are monogenetic but 9 were formed by multiple eruptions. Petrogenetic models have been developed for the magma evolution of the Andahua Group. They show local crustal influence on the magmas generated, and possible controls on the magma pathway to the surface, and potential segregation. Local compositional variation of the crustal rocks is inferred to have a strong influence on the magma that ascends through the thick continental crust. Assimilation and contamination by deeply seated granitoids of the Arequipa and Paracas massifs are also inferred to play a role in the final magmatic products. Future activity with gas emissions from the Andahua Group volcanoes may cause hazardous conditions for tourists.