Sm-Nd geochronology and petrologic investigation of sub-ophiolite metamorphic sole from the Dinarides (Krivaja-Konjuh, Ophiolite Complex, Bosnia and Herzegovina)

Branimir Šegvić,Ralf Schuster,Damir Slovenec,Elvir Babajić,Luka Badurina,Boško Lugović

doi:10.4154/gc.2020.09

Abstract

The Dinaridic segment of Neotethys was affected by a widespread shortening and related subduction-accretion-obduction processes that commenced in the middle Jurassic. In the Dinarides, the Krivaja-Konjuh Ophiolite Complex (KKOC) stands as the largest ophiolite complex with a well-exposed metamorphic sole which is the key to understanding the dynamics of intraoceanic subduction initiation in this part of Neotethys. In this contribution we present Sm-Nd geochronology on a granulite facies amphibolite from the KKOC, as well as a detailed petrological description. A five-point isochrone age calculated from clinopyroxene, plagioclase, garnet, amphibole and whole rock is 162 ± 14 Ma (MSWD = 6.2), whereas garnet and whole rock yield 160 ± 7 Ma. Ages calculated from all data points except clinopyroxene are 162 ± 5 Ma (MSWD = 1.09). Petrographic investigations suggest that these ages date granulite facies metamorphic conditions (i.e. peak metamorphism of Grt-Cpx amphibolite) rather than post-peak exhumation or obduction processes. Phase textural relationships are in line with previous research, which indicated a peak metamorphism equilibration pressure and temperature of ~1 GPa and ~800 °C, respectively. Granulite facies conditions are elucidated for an igneous precursor, which underwent a multi-stage metamorphism that gave rise to recrystallization of igneous clinopyroxene and plagioclase, epitaxial growth of amphibole, and garnet blastosis. Taking into account the age of gabbronorite from the youngest segment of the KKOC oceanic crust (Taorcian to Bathonian) and ages of radiolarian assemblages from the KKOC melange (Bajocian to Bathonian), it may be inferred that within ~25 Ma the Dinaridic segment of Neotethys evolved rapidly from active ridge spreading through a stage of intraoceanic subduction and arc magmatism toward sub-ophioliteexhumation and further obduction along the Adria passive margin at the end of the Jurassic era.

Highlights

Stretching discontinuously for about 9500 km, from the European Alps to southern Tibet, the Tethyan ophiolites structurally overlie passive margin successions of collided continents and commonly show fully developed ophiolitic sequences, which include high-grade sub-ophiolite metamorphic rocks (DILEK & FURNES, 2019: Fig. 8b, and references therein)
The first argues for a derivation of both ophiolite belts from the same marginal segment of Neotethys, which led to the actual position of ophiolites within the Dinarides-Hellenides nappe stack (PAMIĆ et al, 1998; SCHMID et al, 2008; FAUL et al, 2014), while the second one favours the existence of two Neotethyan oceanic branches (e.g. LUGOVIĆ et al, 1991; ROBERTSON, 2004), which were defined in the Hellenides (FERRIÈRE et al, 2012)
Taking into account the Sm-Nd age of gabbronorite from the youngest segment of the Krivaja-Konjuh Ophiolite Complex (KKOC) oceanic crust, which is set to the Toarcian to Bathonian time (BABAJIĆ, 2009) we argue for a geodynamic evolution that resulted in intraoceanic subduction and closure of the major part of Neotethys by the end of the Jurassic

Summary

Introduction

Stretching discontinuously for about 9500 km, from the European Alps to southern Tibet, the Tethyan ophiolites structurally overlie passive margin successions of collided continents and commonly show fully developed ophiolitic sequences, which include high-grade sub-ophiolite metamorphic rocks (DILEK & FURNES, 2019: Fig. 8b, and references therein). The first argues for a derivation of both ophiolite belts from the same marginal segment of Neotethys, which led to the actual position of ophiolites within the Dinarides-Hellenides nappe stack (PAMIĆ et al, 1998; SCHMID et al, 2008; FAUL et al, 2014), while the second one favours the existence of two Neotethyan oceanic branches (e.g. LUGOVIĆ et al, 1991; ROBERTSON, 2004), which were defined in the Hellenides (FERRIÈRE et al, 2012). Both ophiolitic belts contain high-grade Jurassic metamorphic rocks Amphibolite and granulite dominate the metamorphic suite of the KKOC

Methods

Results

Discussion

Conclusion