Temporal‐Geochemical Evolution of the Persani Volcanic Field, Eastern Transylvanian Basin (Romania): Implications for Slab Rollback Beneath the SE Carpathians

Abstract

The Quaternary Persani volcanic field (PVF) consists of alkali basalts formed in an extensional basin at the SE end of the Transylvanian basin, near an important anomaly in the European mantle, the Vrancea slab, a seismically active near-vertical lithospheric fragment of debated origin. The PVF is the only basaltic field regionally, has been studied geochemically in the past, and is also known for the presence of abundant mantle xenoliths. Here, we describe new geochemical data on rocks recently dated by Ar-Ar chronometry and show that while we can reproduce virtually all previous results, there is a clear temporal evolution of the magmatic system. There is an increase of over 80°C in temperatures determined by the Si activity thermometer, from 1,300°C to 1,380°C during the~0.5-Myr duration of volcanic activity, which is accompanied by several coherent trends in geochemistry, among which the decrease of Zn/Fe and 87 Sr/ 86 Sr ratios over time. Earlier, higher Zn/Fe ratios are indicative of a pyroxenite/eclogite-dominated source, which gradually changed to a peridotite-dominated source. These characteristics are typical of a dynamic mantle in which vertical mantle lithosphere tectonics, either due to slab rollback or mantle dripping plays a role and are not consistent with simple decompression melting of asthenosphere. Synchronous adakitic rocks found about 25-30 km east of PVF are presumed to be slab melts and are consistent with the Vrancea slab rollback as the trigger for mantle melting responsible for the PVF.

Dehydration-induced earthquakes identified in a subducted oceanic slab beneath Vrancea, Romania

“…Additionally, the SE Carpathian region is characterized by enhanced electrical conductivity that likely highlights enhanced water percolation within the suture zone of the Carpathian belt and surrounding areas 34 , 35 . In contrast, decompressional melting, which occurs in case of lithospheric delamination, results in basaltic volcanism 7 , 32 . The origin of the East Carpathians recent magmatism 3 has been highly debated since there is no evidence of oceanic subduction in the area since the Miocene 7 .…”

“…In contrast, decompressional melting, which occurs in case of lithospheric delamination, results in basaltic volcanism 7 , 32 . The origin of the East Carpathians recent magmatism 3 has been highly debated since there is no evidence of oceanic subduction in the area since the Miocene 7 . The Ciomadul volcano is located at the SE extremity of the Călimani-Gurghiu-Harghita volcanic chain (NW–SE line).…”

Estimates of the Temperature and Melting Conditions of the Carpathian‐Pannonian Upper Mantle From Volcanism and Seismology

“…The colored data (symbols as in Figure 1) are those selected according to the screening criteria outlined in the main text. Published whole‐rock data (Ali & Ntaflos, 2011; Ali et al., 2013; Dobosi & Jenner, 1999; Dobosi et al., 1995; Downes et al., 1995; Ducea et al., 2020; Embey‐Isztin, Dobosi, et al., 1993; Embey‐Isztin, Downes, et al., 1993; Harangi et al., 1994, 2013, 2015; Harangi, Vaselli, et al., 1995; Ivan & Hovorka, 1993; Jankovics et al., 2015, 2019; Rosenbaum et al., 1997; Tschegg et al., 2010) are listed in the supporting information.…”

“…Data sets for this research are included in the supporting information file of this paper. In‐text citation references are as follows: basalt compositions (Ali & Ntaflos, 2011; Ali et al., 2013; Dobosi et al., 1995; Dobosi & Jenner, 1999; Downes et al., 1995; Ducea et al., 2020; Embey‐Isztin, Dobosi, et al., 1993; Embey‐Isztin, Downes, et al., 1993; Harangi et al., 1994, 2013, 2015; Harangi, Vaselli, et al., 1995; Ivan & Hovorka, 1993; Jankovics et al., 2015, 2019; Rosenbaum et al., 1997; Tschegg et al., 2010); nodule compositions and mineralogy (Aradi et al., 2017; Dobosi et al., 2010; Downes et al., 1992; Embey‐Isztin et al., 1989, 1990; Embey‐Isztin et al., 2014; Faccini et al., 2020; Liptai et al., 2017; Ntaflos et al., 2017; Szabó & Taylor, 1994; Szabó et al., 1995; Vaselli et al., 1995, 1996); mineral‐melt partition coefficients (Beattie, 1993; Johnson, 1998; Mallmann & O'Neill, 2009; McKenzie & O'Nions, 1991, 1995); melt sources (Gibson & Richards, 2018; McKenzie & O'Nions, 1991, 1995). Software for this research, that is, the INVMEL scheme formulated by McKenzie and O'Nions (1991, 1995), has since its conception been expanded to include the mantle melting parameterization of Katz et al.…”

“…The colored data (symbols as in Figure 1) are those selected according to the screening criteria outlined in the main text. Published whole-rock data (Ali & Ntaflos, 2011;Ali et al, 2013;Dobosi & Jenner, 1999;Dobosi et al, 1995;Downes et al, 1995;Ducea et al, 2020;Harangi et al, 1994Harangi et al, , 2013Harangi et al, , 2015Harangi, Vaselli, et al, 1995;Ivan & Hovorka, 1993;Jankovics et al, 2015Jankovics et al, , 2019Rosenbaum et al, 1997;Tschegg et al, 2010) are listed in the supporting information. sourced from the asthenosphere and that some were modified by interaction with the lithospheric mantle during ascent (Embey-Isztin, Harangi et al, 2015;Seghedi et al, 2004).…”