Standardisation, calibration and correlation of the Kübler-index and the vitrinite/bituminite reflectance: An inter-laboratory and field related study

Abstract

A multiple inter-laboratory calibration with illite Kübler-Frey-Kisch "crystallinity" index and related standards is presented and compared with CIS standards used in the last two decades in very low-grade metamorphic studies. Comparing CIS values with KI standards the CIS values show a higher full width at half-high maximum peak intensity. In all cases due to broadening effects on the Kübler-index, zone-limits, specifically the diagenetic zone/anchizone boundary, a shift is produced in geographical dimensions in a metamorphic map-view. Combining standardised Kübler-index and vitrinite-bituminite reflectance measurements a coherent data set for compilation studies can be generated from the data of different research groups. This attempt to establish a unified database of independent measures to determine diagenetic/metamorphic zones with different analytical instrumental methods are indispensable to present metamorphic maps at very low-grade conditions. Given that the Kübler-Frey-Kisch standards are difficult to preserve for the future and presumably they will be replaced with ongoing time by the CIS standards, a rescue of the laboratory settings from Frey, Kübler and others is done. After having compiled the Kübler-index-vitrinite reflectance zones in the Alps for the "New Metamorphic Map of the Alps", the presented calibration and inter-laboratory correlation gives a chance to save the KI values obtained by very different preparation procedures applied. This is an important step for further studies in an area like the Central Alps with a very high data grid. This correlation study will also make it possible that nearly 90 % of Kübler-index data from Switzerland can be compared in future work. Using the same calibration and preparation technique no fundamental problem in data comparison is achieved for the vitrinite/bituminite reflectance data operation. The main problem arises when rock maturity is compared with CIS calibrated Kübler-index values. Kübler-index values obtained by the so-called CIS calibration are not compatible with Kübler-Frey-Kisch (Árkai, Aprahamian, Brime, Ferreiro Mählmann, H. Krumm, Leoni, Petschick) calibrated Kübler-Indices. Applying both standardisation approaches for field studies, partially different results are obtained. © 2012 Swiss Geological Society.