Minor- and trace-element composition of trioctahedral micas: a review

More than 19,000 analytical data mainly from the literature were used to st udy statistically the distribution patterns of F and the oxides of minor an d trace elements (Ti, Sn, Sc, V, Cr, Ga, Mn, Co, Ni, Zn, Sr, Ba, Rb, Cs) in trioctahedral micas of the system phlogopite-annite/siderophyllite-polylit hionite (PASP), which is divided here into seven varieties, whose compositi onal ranges are defined by the parameter mgli (= octahedral Mg minus Li). p lots of trace-element contents vs. mgli reveal that the elements form disti nct groups according to the configuration of their distribution patterns. S ubstitution of most of these elements was established as a function of mgli . Micas incorporate the elements in different abundances of up to four orde rs of magnitude between the concentration highs and lows in micas of 'norma l' composition. Only Zn, Sr and Sc are poorly correlated to mgli. In compos itional extremes, some elements (Zn, Mn, Ba, Sr, Cs, Rb) may be enriched by up to 2-3 orders of magnitude relative to their mean abundance in the resp ective mica variety. Mica/melt partition coefficients calculated for Varisc an granites of the German Erzgebirge demonstrate that trace-element partiti oning is strongly dependent on the position of the mica in the PASP system, which has to be considered in petrogenetic modelling. This review indicates that for a number of trace elements, the concentratio n ranges are poorly known for some of the mica varieties, as they are for p articular host rocks (i.e, igneous rocks of A-type affiliation). The study should help to develop optimal analytical strategies and to provide a tool to distinguish between micas of 'normal' and 'abnormal' trace-element compo sition.