Whole rock major element influences on monazite growth: examples from igneous and metamorphic rocks in the Menderes Massif, western Turkey

Monazite (LREEPO₄) is a radiogenic, rare-earth bearing mineral commonly used for geochronology. Here we examine the control of major element chemistry in influencing the crystallization of monazite in granites (Salihli and Turgutlu bodies) and garnet-bearing metamorphic assemblages (Bozdag and Bayindir nappes) from the Menderes Massif, western Turkey. In S-type granites from the massif, the presence of monazite correlates to the CaO and Al₂O₃ content of the whole rock. Granites with monazite only are low Ca (0.6-1.8 wt% CaO). As CaO increases (from 2.1-4.6 wt%), allanite [(Ce, Ca, Y)₂(Al, Fe³⁺)₃(SiO₄)₃ (OH)] is present. Higher Al₂O₃ (>15 wt%) rocks contain allanite and/or monazite, whereas those with lower Al₂O₃ contain monazite only. However, examining data reported elsewhere for A-type granites, the correlation between major element chemistry and presence of monazite is likely restricted to S-type lithologies. Pelitic schists of the Menderes Massif show no correlation between major element chemistry and presence of monazite. One Bayindir nappe sample contains both prograde garnets and those affected significantly by diffusion. These rocks have likely experienced a complicated multi-stage tectonic history, which influenced their current mineral assemblages. The presence of monazite in a metamorphic rock can be influenced by the number, duration, and nature of events that were experienced and the degree to which fluids were involved. The source of monazite in the Bayindir and Bozdag samples was likely reactions that involved allanite. These reactions may not have significantly changed the bulk composition of the rock.