New age data from the Dzirula massif, Georgia: Implications for the evolution of the Caucasian Variscides

Abstract

The Caucasus mountain belt has a complex tectono-thermal history that is as yet poorly understood due to the scarcity of reliable geochronological information. Here, we report new monazite and zircon data from the Dzirula massif in the southern Caucasus, which permit development of a model for Variscan LP-HT (low pressure-high temperature) metamorphism in this region. Data are presented for two key lithologies of the Dzirula massif: 1) a group of variably deformed granitoid (mainly granodioritic-tonalitic) rocks and 2) metapelitic LP-HT cordierite-biotitesillimanite migmatites and paragneisses. Electron-microprobe Th-U-total Pb monazite dating demonstrates that the LP-HT metamorphism in the Dzirula massif is Variscan, and occurred around 330 Ma. LA-ICP-MS zircon dating reveals that the granitoids include two different magmatic series. An older, mainly tonalitic, series is of Lower Cambrian age. Younger intrusions, including gabbros and diorites, but mainly tonalites and granodiorites, are Variscan in age. The older series show ductile deformation features and, along with the metapelites, experienced Variscan high-grade metamorphism that resulted in penetrative blastic recrystallization and anatexis. The younger series is generally undeformed, but often shows a magmatic foliation, and variable alteration under greenschist facies conditions. It is suggested that the Variscan intrusions facilitated the regional LP-HT metamorphic event at 330 to 340 Ma. Age and petrographic data from the Greater Caucasus imply a similar evolution as observed in the Dzirula massif. The Dzirula massif can thus be used as a proxy to model the evolution of the Caucasian Variscides.

Striking Variation in the Provenance of the Lower and Upper Cretaceous Turbidites in the Central Pontides (Northern Turkey) Related to the Opening of the Black Sea

“…Most of them cluster in the range of 330–290 Ma (late Carboniferous‐early Permian; 57%). This age range is similar to the ages of the magmatic bodies from the Sakarya Zone and the Lesser Caucasus (e.g., Nzegge, ; Nzegge et al, ; Mayringer et al, ; Topuz et al, , ; Ustaömer et al, , ). The closest outcrops are the Deliktaş and Sivrikaya granites in the central Pontides, with U–Pb zircon ages of 303–275 Ma (Nzegge et al, ).…”

Relict basin closure and crustal shortening budgets during continental collision: An example from Caucasus sediment provenance

“…[] question the robustness of the Rb‐Sr and Sm‐Nd dates due to the extensive Variscan metamorphic overprint and protracted residence of the samples in the upper plate of a long‐lived Mesozoic subduction zone. In the Dzirula Massif, mafic to intermediate intrusive rocks record a crystallization age of ~540 Ma (upper intercept of U‐Pb zircon discordia chord) with a metamorphic overprint at 338 ± 5 Ma (concordant U‐Pb zircon rims), along with Variscan zircon crystallization ages of 335 to 320 Ma [ Mayringer et al ., ; Rolland et al ., ]. In the Khrami Massif, zircons from a granodiorite reworked to migmatite yielded core ages of 474 ± 3 Ma and Variscan rims ages of 343 ± 2 Ma [ Rolland et al ., ].…”

“…The Dzirula-Khrami-Loki Massifs are fragments of Variscan and older basement very similar to the crystalline core of the Greater Caucasus (Figure 2a) [Gamkrelidze and Shengelia, 2001;Gamkrelidze et al, 1981;Mayringer et al, 2011;Rolland et al, 2016;Zakariadze et al, 2007]. In general, they expose Proterozoic to Carboniferousaged metamorphic and igneous rocks that are both intruded and overlain by Mesozoic to early Cenozoic volcanic and volcaniclastic units [Gamkrelidze and Shengelia, 2001;Zakariadze et al, 2007].…”

“…These peri-Gondwanan fragments are generally thought to have rifted from Gondwana via back-arc rifting above a south dipping subduction zone in the early Paleozoic. They were accreted to the southern margin of Eurasia by~350 Ma via closure of proto-Tethys, and were then subjected to high-pressure, low-temperature metamorphism from 329 to 337 Ma [Rolland et al, 2011] [Mayringer et al, 2011;Rolland et al, 2016]. In the Khrami Massif, zircons from a granodiorite reworked to migmatite yielded core ages of 474 AE 3 Ma and Variscan rims ages of 343 AE 2 Ma .…”

The formation and inversion of the western Greater Caucasus Basin and the uplift of the western Greater Caucasus: Implications for the wider Black Sea region

“…On the northern flank, the basement is unconformably overlain by either Late Carboniferous to Permian, Triassic, or Jurassic sediments [Lavrishchev et al, 2002;Somin, 2000]. On the southern flank, it is unconformably overlain by Late Carboniferous, Jurassic, Cretaceous, or Cenozoic sediments [Kandelaki and Kakhadze, 1956;Mayringer et al, 2011]. This indicates that these basement areas have been at or near surface for much of the Late Paleozoic to Cenozoic.…”