Ophiolitic detritus in Cretaceous clastic formations of the Dinarides (NW Croatia): evidence from Cr-spinel chemistry

Abstract

Cr-spinel is a common heavy mineral in the sandstones of Cretaceous synorogenic sedimentary formations of the NW Dinarides, Croatia. The rocks occur in isolated exposures in the uplifted basement units of Medvednica, Ivanščica, Ž umberak and Samobor Mountains near Zagreb. In this area, evidence of the early Alpine evolution of the Dinarides is obscured due to strong dismemberment of pre-Tertiary tectonostratigraphic units resulting from an intense tectonic history, as well as due to the widespread sedimentary cover of the Pannonian Basin. Electron microprobe analyses of detrital Cr-spinels from the Oštrc Formation reveal that in the Early Cretaceous the ophiolitic source area was predominantly composed of harzburgite peridotites and associated cumulate rocks, which developed in a supra-subduction zone setting. The supply of Cr-spinels with the same chemical signature remained dominant until the end of the Cretaceous, suggesting that exposed remnants of the same ophiolite belt persisted through the Cretaceous and/or that recycling was significant. Similarities with data reported from the Northern Calcareous Alps and the Transdanubian Central Range imply that a rather extensive harzburgitic ophiolite belt probably extended along the Adriatic margin during the Early Cretaceous. A slight trend of increasing variation in the Cr# is observed from the Early to the latest Cretaceous, suggesting that the source areas became more heterogeneous with the ongoing Cretaceous tectonic evolution. Differences in Cr-spinel compositions in two contemporaneous latest Cretaceous formations are well in line with existing data on heavy mineral proportions, which together identify contrasting hinterland geology for these formations and strongly suggest the coeval existence of two separate basins.

Ophiolitic detritus in Kimmeridgian resedimented limestones and its provenance from an eroded obducted ophiolitic nappe stack south of the Northern Calcareous Alps (Austria)

“…Harzburgitic sources vastly predominate in most of the Cre- taceous synorogenic flysches all over the Alpine-CarpathianDinaridic belt (Pober & Faupl 1988;Árgyelán 1996;von Eynatten & Gaupp 1999;Jablonský et al 2001;Lužar-Oberiter et al 2009). There are some cases described in literature which showed that the Mg/(Mg+ Fe 2+ ) vs. Cr/(Cr + Al) provenance diagrams of Dick & Bullen (1984) and Pober & Faupl (1988) are not necessarily valid for all spinel sources.…”

Following the Amphibolite to Greenschist Metamorphic Path through the Structural Parameters of Spinels from Amsaga (Mauritania)

“…Cr-bearing spinels have been considered important petrogenetic indicators by many authors [65][66][67][68][69][70][71], due to their chemical variability in parental melt composition and/or crystallization conditions in igneous rocks, and as paleogeographic indicators in geodynamic reconstructions, because of their resistance to mechanical stress, weathering and diagenesis in sedimentary environments. Commonly-used diagrams for these purposes are the Cr# vs. Mg# and the TiO 2 vs. Al 2 O 3 [3,5] as well as the Cr-Fe 3+ -Al ternary plot.…”

Heavy minerals from sedimentary rocks of the Malcov Formation and their palaeogeographic implications for evolution of the Magura Basin (Western Carpathians, Slovakia) during the Late Eocene – Late Oligocene

“…Cr-spi nels orig i nat ing from cu mu late and ex tru sive volca nic rocks tend to have higher TiO 2 (Kamenetsky et al, 2001). High Fe 3+ and TiO 2 , along with lower Mg#, sug gest that the Cr-spi nels could have been the prod ucts of frac tional crystallisation and re-equil i bra tion at lower tem per a tures due to slow cool ing (Arai, 1992;Kamenetsky et al, 2001;Lužar-Oberiter et al, 2009), and thus prob a bly de rived from cumu late mem bers of an ophiolite source. The in creased con tents of TiO 2 in most Cr-spi nels from the Malcov Fm.…”