Geology and chemical variations in tourmaline from the quartz-tourmaline breccias within the Kerkenez granite-monzonite massif, Central Anatolian Crystalline Complex, Turkey

A hydrothermal breccia zone 6 km long and 2 km wide, crossed by quartz-tourmaline veins, occurs to the south of the Late Cretaceous Kerkenez granite-monzonite massif in the northern part of the Central Anatolian Crystalline Complex, Yozgat, Turkey. This breccia zone is characterized by numerous veins, a few millimeters to l meter in width, and display typical microtectonic features of multiple brecciation. Trace amounts of albite, K-feldspar, epidote, muscovite and rutile are associated with quartz and tourmaline. Petrographic features indicate three successive stages of tourmaline generation. The first generation is represented by feruvite, and the second and third generations consist of schorl. These distinct generations of tourmaline show successive enrichment in Al and Na, and depletion in Ti and Ca. The Na/(Na + Ca) values vary in the range 0.41-0.49 in the first generation, and 0.53-0.86 and 0.91-0.99 in the second and third generations. The development of the breccia zone and formation of three successive generations of tourmaline are most probably related to fluid-assisted brecciation and infiltration of low-to medium-pH hydrothermal fluids under subsolidus conditions. Successive enrichment in Na and Al in the younger generations is ascribed to late-stage fractionation in the B-rich granitic source.