Palaeomagnetism of the South Harghita volcanic rocks of the East Carpathians: implications for tectonic rotations and palaeosecular variation in the past 5 Ma

Abstract

SUMMARY Lavas of Pliocene–Quaternary age were sampled in the South Harghita Mountains, which form the southern end of the Călimani–Gurghiu–Harghita volcanic chain of the East Carpathians. The analyses of 68 volcanic sites in the South Harghita Mountains provided 62 sites with well‐constrained directional data (n > 5 and k > 50) in an age interval ranging from 0.5 to 4.3 Ma. The age and polarity for the 62 sites (38 normal and 24 reversed) are consistent with the Geomagnetic Reversal Time Scale and support the model of the southward migration of the volcanism. The distribution of the VGPs is Fisherian and the mean pole position, both from all contributing sites and from the 53 sites older than 2 Ma, includes the spin axis. This result is consistent with the absence of important vertical axis rotations after the emplacement of the volcanic rocks in agreement with tectonic models for the Pliocene–Quaternary evolution of the bending area of the East Carpathians. Virtual geomagnetic pole dispersions are consistently high compared with global values obtained between 40 and 55°N, but closer to the values obtained only from the Time Averaged geomagnetic Field Initiative studies for the same latitudinal band. Our data are compatible with the prediction of the statistical palaeosecular variation model TK03. The inclination anomaly is less than 1° in accord with the Total Average Field global data. These palaeomagnetic data from the South Harghita volcanic rocks are the first data from the southeastern Europe which can be considered in the databases for time averaged field and palaeosecular variation from lavas analyses in the last 5 Ma.

Seismic scattering and absorption mapping from intermediate-depth earthquakes reveals complex tectonic interactions acting in the Vrancea region and surroundings (Romania)

“…At the lowest frequency ( Figures 8 and 10, 3 Hz panel, in our assumption the frequency band sampling deepest Earth layers) absorption increases northwest and southeast of the epicentral area, crossing an area of average-to-strong scattering ( Figure 5). This anomaly is spatially correlated with the location of the hypothesised asthenospheric upwelling beneath the Neogene volcanic arc (Figure 1), which migrated from NW to SE Panaiotu et al 2012). Moesian Platform.…”

“…To better understand the meaning of the scattering/absorption contrasts at different the Ciomadul volcanic region, situated just NNW of the Vrancea region Panaiotu et al 2012). Such an high-absorption trend has been observed under the Cascadian volcanoes and related to the effect of a deep magmatic arc .…”

“…This observation is similar in space and nature to that of for the subducting Japanese crust, at least for the peak delay time, and consistent with the presence of a NNE-SSW-oriented sinking lithospheric fragment into the asthenosphere . In this framework, considering the investigated frequencies and Bouguer anomalies, the high scattering following the epicentral trend and extending to the west (Figure 13, 12 Hz and 18 Hz) is feasibly caused by either coupling between a subducting slab and the overlying crust or small-scale scattering phenomena within the upper portion of a subducted or detached Panaiotu et al 2012) lithospheric fragment, sinking into the asthenosphere.…”

Palaeomagnetism of the Upper Miocene- Lower Pliocene lavas from the East Carpathians: contribution to the paleosecular variation of geomagnetic field

“…To analyse the PSV between 4 and 6 Ma we have used the new data from the Northern Harghita Mountains and 7 sites from the norther part of the South Harghita Mountains 13 , which have an age greater than 4 Ma 16 ( Supplementary Table S1 and Supplementary Fig. S1 ).…”

“…Previous paleomagnetic results from the CGH volcanic chains were obtained from lava flows younger than 4 Ma 13 14 . In this paper we present new paleomagnetic results obtained from volcanic rocks erupted between 4 and 6 Ma.…”