THE ZONE OF INCIPIENT ⁴⁰AR* LOSS: INTRODUCING A NEW CONCEPT OF AR DEGASSING BEHAVIOR IN A CONTACT METAMORPHIC SETTING

[MnO|SiO2,Al2O3,FeO,MgO] balanced log-ratio in chlorites: a tool for chemo-stratigraphic mapping and proxy for the depositional environment

“…3; Table 1; Table S1). Grading of metamorphism was based on Kübler index (KI) measurements by X-ray diffraction (XRD;Süssenberger et al, 2017Süssenberger et al, , 2018. The transition from low-temperature regional to contact metamorphism as well as the transition between different stratigraphic units appear to be veiled by the very fine-grained, dark lithology and are intrinsically difficult to differentiate by macroscopic or microscopic means.…”

“…In the present case study, we examine the chemical composition of chlorite and whole rock from lowgrade metasediments of the Magallanes foreland basin in order to track changes in the depositional environment and to discriminate stratigraphic formations. The study includes chlorites affected by two distinct metamorphic events, by regional metamorphism with temperatures between 230 and 270°C (Süssenberger et al, 2017;Süssenberger, 2018) and/or by contact metamorphism (<370°C; Süssenberger et al, 2018) in order to evaluate whether metamorphic events alter proxies for stratigraphic discrimination. The Mn concentrations of chlorite and whole rock may be used to decipher depositional conditions.…”