Geochronological scale and evolution of late Cenozoic magmatism within the Caucasian segment of the alpine belt

Abstract

Results of the isotope geochronological studies of the Late Cenozoic magmatism of Caucasus have been considered. The Neogene-Quaternary volcanic activity is found to have evolved during the last 15 m. y. being most intensive in the Middle-Late Pliocene. Within separate neovolcanic areas of the Cauca sus region, magmatism was of a clearly discrete character when intense eruption periods interchanged with prolonged (up to several million years) times of quiet conditions. Four stages of young magmatism of the Cau casus are recognized: the Middle Miocene (15-13 Ma), the Late Miocene (9-5 Ma), the Pliocene (4.5-1.6 Ma), and the Quaternary (less than 1.5 Ma). However, for certain areas the time limits of these stages were shifted relative to each other and overlap the whole age range from the mid Miocene to the end of the Quaternary period. Therefore, within the collision zone, the Neogene-Quaternary magmatism evolved almost continu ously during almost the last 9 m. y., but in the time interval of 13-9 Ma in the Caucasian segment, volcanic activity was possibly low. No evidence of directed lateral migration of volcanic activity within the entire Cau casus region was found. At the same time, in the Lesser Caucasus the young magmatism commenced earlier (~15 Ma), compared to the Greater Caucasus (~8 Ma).

Transition from a singly vergent to doubly vergent wedge in a young orogen: The Greater Caucasus

“…If the low modern convergence rate is representative of long‐term deformation, then there appears to be a discrepancy between the inferred low shortening rates and high elevations here, which have been variably attributed to either magmatic addition to the crust beneath Elbrus [e.g., Mosar et al ., ] or dynamic topography produced by either delamination of a crustal root [e.g., Ershov et al ., ] or slab detachment [e.g., Mumladze et al ., 2014]. Although there are several late Cenozoic volcanic centers in the western Greater Caucasus (Figure ) [e.g., Lebedev et al ., ], they are too poorly documented to independently quantify magmatic addition. A possible alternative approach is to compare cross‐sectional areas within and outside the volcanic region (Figure g): the area under Mount Elbrus (~250–375 km) has a cross‐sectional area of ~360 km 2 , whereas it is ~275 km 2 to the east (400–750 km), implying magmatic addition of ~85 km 2 .…”

Evidence of Unusual Geomagnetic Regimes Recorded in Plio‐Pleistocene Volcanic Sequences from the Lesser Caucasus (Southern Georgia)

“…These structures control the most recent kinematics and act as conduits through which the magma ascends, giving rise to most subaerial neovolcanic activity, with at least three different magmatic stages. The rocks from the present study belong to the second (Pliocene -Early Quaternary) stage of young volcanic activity in the Djavakheti highland and the adjacent Armenian block (Lebedev et al, 2011). Five phases of Pliocene volcanism separated by quiet periods of less than 300 000 years are recognized based on K-Ar dating: I, 3.75-3.55 Ma; II, 3.30-3.05 Ma; III, 2.85-2.45 Ma; IV, 2.25-1.95 Ma; and V, 1.75-1.55 Ma.…”

“…Five phases of Pliocene volcanism separated by quiet periods of less than 300 000 years are recognized based on K‐Ar dating: I, 3.75–3.55 Ma; II, 3.30–3.05 Ma; III, 2.85–2.45 Ma; IV, 2.25–1.95 Ma; and V, 1.75–1.55 Ma. Impulses of moderately acid and acid volcanism either preceded the major magmatism (phases III and IV) or were synchronous to it (phase II) or at the end of it (phase III) (Lebedev et al, ).…”

Upper mantle shear wave velocity structure of the east Anatolian-Caucasus region||Upper mantle shear wave velocity structure of the east Anatolian-Caucasus region

“…However, the volumes of the collision-related extrusive materials located in the Greater Caucasus are small in comparison with those in the Eastern Anatolian Plateau. The ages of the volcanic products vary from late Miocene to Holocene [e.g., Lebedev et al, 2011]. Their compositions are represented by calc-alkaline and subalkaline basalts, andesite-basalts, andesite-dacites and rhyolites; their parental melts were likely the products of interaction between contrasting mantle melts and crustal material [e.g., Lebedev et.…”

“…and Niemi, 2011]. Furthermore, this most rapidly uplifting part of the Greater Caucasus is characterized by Neogene-Quaternary mantle-derived volcanism [e.g., Lebedev et al, 2011;, which is absent in the other parts of the mountain range (i.e. the western and eastern Greater Caucasus).…”