TESTING OF CR-SPINEL STABILITY DURING WEATHERING, TRANSPORT, AND DIAGENESIS ON CONGLOMERATES WITH OPHIOLITIC DETRITUS: CONSEQUENCES FOR INTERPRETATION OF THE PROVENANCE OF EXOTIC FLYSCHES IN THE ALPINE-CARPATHIAN AREA

Abstract

Chrome-spinels are considered as valuable provenance indicators in heavy mineral analysis. Their importance is emphasized by the fact that they are ultrastable during weathering, transport and diagenesis. However, some earlier publications have inferred that high-Al/low-Cr spinels are less resistant which may have a strong influence on provenance studies. In the Western Carpathians and Eastern Alps, there is a remarkable contrast between Late Jurassic to mid-Cretaceous ophiolite-bearing sediments (so-called exotics) derived from the Neotethys that are depleted in high-Al/low-Cr spinels and primary ophiolitic occurrences of Meliata Unit (also a part of Neotethys) which display the entire spectra of the Cr-spinel chemistry. It was unknown, however, whether this difference was primary or secondary, caused by later removal
of high-Al/low-Cr spinels. Therefore, Cr-spinels from the Upper Cretaceous ophiolite-bearing conglomerates in the area of the Dobšiná Ice Cave derived from the Meliata Unit were analyzed to test their stability during weathering, transport and diagenesis. Parallel analysis of spinels from sandy and pebble material showed that the spinels from both fractions cover all the chemistry spectrum from high-Cr/low-Al to low-Cr/high-Al types, without any depletion. Good preservation of all sorts of Cr-spinels in the sandy material indicates that the depletion of Cr-spinel assemblages that was recorded in the Late Jurassic to mid-Cretaceous exotics all over the Alpine-Carpathian area appears to be primary. This was caused by lack of lherzolitic (MORB) ophiolites in the source area. Although the Meliata unit had formed a part of the same Neotethyan oceanic system, the analyzed ophiolites which include lherzolitic (MORB) types could not have been the source of Cr-spinels for the exotics-bearing flysches.