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The compositional properties of garnet probably preserve the most extensive records of the pressure-temperature-time (P-T-t) history of metamorphic rocks. There are a number of cation-exchange and discontinuous reactions involving garnet that have been extensively used to decipher the P-T conditions or P-T paths of the host rocks as these were buried and exhumed (e.g., Ganguly and Saxena 1987; Spear 1993). However, as metamorphic garnets commonly show compositional zoning, the choice of composition within a zoned garnet to retrieve peak metamorphic conditions requires consideration of its diffusion kinetic properties (Dasgupta et al. 2004, 2009), as does the issue of whether the peak condition is at all preserved in the compositional property of a garnet of a given grain size (e.g., Spear 1991; Ganguly and Tirone 1999; Tirone and Ganguly 2010). Diffusion kinetic modeling of the major-element compositional zonings of garnets leads to important constraints on the time scales of metamorphic processes such as heating and cooling rates (e.g., Florence and Spear 1993; Ganguly et al. 2000; Faryad and Chakraborty 2005; Augue and Baxter 2007), from which one may infer the burial and exhumation rates, respectively (e.g., Ganguly et al. 2000; Faryad and Chakraborty 2005), and time scales of deformation (Camacho et al. 2009).
In addition, the presence of garnet in the source region of a basaltic magma imparts a characteristic signature, often referred to as the “garnet signature,” to its rare earth element (REE) pattern. In addition to providing an important constraint on the depth of the source region of a basaltic magma, since garnet is stable below ~50 km depth in the Earth’s interior (e.g., Saxena and Eriksson 1983), the REE pattern of basaltic magma with “garnet signature” is often used to infer …