Garnet: A Rock-Forming Mineral Petrochronometer
نویسندگان
چکیده
Garnet could be the ultimate petrochronometer. Not only can you date it directly (with an accuracy and precision that may surprise some), but it is also a common rock-forming and porphyroblast-forming mineral, with wide ranging—yet thermodynamically well understood— solid solution that provides direct and quantitative petrologic context. While accessory phase petrochronology is based largely upon establishing links to the growth or breakdown of key rockforming pressure–temperature–composition (P–T–X) indicators (e.g., Rubatto 2002; Williams et al. 2007), garnet is one of those key indicator minerals. Garnet occurs in a great variety of rock types (see Baxter et al. 2013) and is frequently zoned (texturally, chemically) meaning that it contains more than just a snapshot of metamorphic conditions, but rather a semi-continuous history of evolving tectonometamorphic conditions during its often prolonged growth. In this way, garnet and its growth zonation have been likened to dendrochronology: garnet as the tree rings of evolving tectonometamorphic conditions (e.g., Pollington and Baxter 2010).
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