Mineralogical-Petrographical Record of Melt-Rock Interaction and P–T Estimates from the Ozren Massif Ophiolites (Bosnia and Herzegovina)

Abstract

The Dinaride Ophiolite Belt formed from the Jurassic part of the Neotethys. The investigated Ozren ophiolite complex in Bosnia and Herzegovina consists of peridotites, plagioclase peridotites, plagiogranites, troctolites and other gabbroic rocks, and fewer basalts. Lherzolites and harzburgites contain corroded ortho- and clinopyroxene1 porphyroclasts enclosed in the olivine matrix. The boundaries between olivine aggregates and pyroxene1 and spinel1 are infilled by medium-grained undeformed aggregates of clinopyroxene2, less orthopyroxene2, spinel2, and often clinopyroxene3-spinel3 symplectites. These textures indicate the final crystallization of peridotite in subsolidus conditions. Partial dissolution of deformed pyroxene1 porphyroclasts and coarse-grained spinel1 most likely occurred due to their reaction with the rest melt present in the grain boundaries. The Al decrease from pyroxene1 to pyroxene2 and 3, or the Cr decrease and Al increase from spinel1 to spinel2 and 3 is characteristic. Peridotites are associated with inferred remnants of a gabbro-dolerite layer, whereas basalts and radiolarites occur as rare dm-size fragments in an ophiolitic breccia. Troctolites display interstitial crystallization of plagioclase, clinopyroxene, less Na-Ti-rich amphiboles, and phlogopite in the olivine-spinel matrix, indicating the replacive character of impregnating melt within the dunite layers. Clinopyroxene-plagioclase-ilmenite-±amphibole gabbroic and fewer basaltic dykes in peridotites formed due to subridge extension, mantle thinning, and the deeper mantle melting. Iron-enriched olivines occur in the peridotite-dyke interfaces and troctolites. Hydrated ultramafics and mafics contain amphiboles, biotite, phlogopite, clinozoisite, epidote, and chlorite aggregates. Estimated magmatic to subsolidus T from peridotite two-pyroxene thermometry are 1000–850 °C, for the spinel facies. Ca-in-orthopyroxene1 thermometry provided T of 1028–1068 °C, and Ca-in-orthopyroxene2 thermometry gave 909–961 °C at estimated P of 1.1–0.9 GPa. However, the gabbroic dyke magmatic crystallization T was constrained to 1200–1100 °C at P of 0.45–0.15 GPa by single clinopyroxene thermobarometry. The obtained P–T conditions constrained the deeper mantle environment for the formation of peridotites than troctolites and crosscutting dykes. The ophiolitic thrust-sheet hanging wall conditions in an obduction-related accretionary wedge were estimated from amphibolites at 620 °C and 0.85 GPa by Ti-in-amphibole thermometry and amphibole-plagioclase thermobarometry. 300 °C and 0.5 GPa were determined from an exhumation shear zone using a combination of chlorite thermometry and Si-in-phengite barometry.

Amphibole Group Minerals in the Ozren Massif Ophiolites of Bosnia and Herzegovina as Petrogenetic Indicators

“…The Amp generation of Krs to Fkrs and Phl replaces the Spl of the troctolites (Figure 4f) within the host dunite layers in peridotite. We reported troctolitization of dunite layers in peridotite by percolating basaltic melts, which crystallized Cpx and Pl in the interstitials of Ol and Spl [8]. This situation suggests that basaltic and plagiogranitic melts might have caused the formation of the Amp3 and 4 generations in the gabbro layer and similar Amp types also in the underlying, often Pl-bearing peridotites and dunites.…”

“…The Ozren ophiolite complex (OOC) in Bosnia and Herzegovina is part of the Dinaridic Ophiolite Belt [8,[10][11][12][13][14][15][16][17][18][19][20][21][22][23]. This complex shows a polystage mantle evolution and revealed an almost complete ophiolitic cross-section composed of peridotites, plagioclase peridotites, plagiogranites, troctolites, and other gabbros, gabbroic, doleritic, and fewer basaltic dykes.…”

“…Table 2. Mineral chemistry of amphiboles in the Ozren ophiolite complex from [8]. Amphibole 1 to 5 types were determined in the gabbro layer mafic rocks (gabbros and dolerites) and basalts, while Amp6 from the sole amphibolites.…”

“…The Ozren ophiolite complex (OOC) is one of the six known ophiolite complexes in Bosnia and Herzegovina and the second largest (Figure 1; [8]). In this paper, we focused on the determination of representative amphiboles in plagiogranite (P5B), gabbro (P13B1), dolerite (P17C), troctolite (P18A), harzburgite (P21), and amphibolite (P10F), including the definition of amphibole chemistry by using electron probe micro-analysis (EPMA), as well as a description of the measured spectra and bands by using micro-Raman spectroscopy.…”

“…We estimated the formation P-T conditions of amphiboles using the chosen amphibole geothermobarometers. (4) in Central Dinaridic Ophiolite Belt ( [8]; map modified after [10,11]). Figure 1.…”