Garnet Geochronology

**Download Ethan Baxter's "Garnet: Tree Rings of Crustal Processes" powerpoint here

Garnets contain the "tree-rings" of tectonic and metamorphic processes. Each garnet crystal is a history book spanning potentially millions of years waiting to be read and interpreted - the bigger the garnet, the longer the history. In this way, garnets contain otherwise inaccessible information about evolving prograde metamorphic conditions, processes, and their driving forces. We have developed integrated methodologies to chemically map, microsample, and date the growth of zoned garnets using the Sm-Nd isotopic system. New TIMS analytical developments permit precise measurement of very small quantities of Neodymium (Nd) isotopes permitting high resolution geochronology on multiple concentric growth zones within single garnet crystals. Individual age precision better than ±1 million years is now usually achieved. See our recent paper that describes the details of our microsampling and Sm-Nd geochronologic methods.

We are also pushing the limits on sample size and precision even further in developing the geochronology of detrital garnet grains in the ancient sedimentary (and metasedimentary) record. Detrital garnet geochronology would help inform us of the rates and conditions of the planet’s very first tectonic and metamorphic activity, as well as regional patterns of prograde metamorphic timing in more recent orogens.

If you are interested in potential collaborative research involving garnet geochronology in the BU TIMS Facility, please contact me directly.

Relevant Grant Support

NSF Grant EAR-1250497 "Collaborative Research: Field-Based Quantification of Dehydration Flux from Subducting Lithologies, Syros and Sifnos, Greece", 1/1/13, PI: Baxter; Co-PIs: Caddick

NSF Grant EAR-1049350 “Detrital Garnet Sm/Nd Geochronology: A New Window into Earth's Tectonic Past”, 9/1/10; PI: Baxter

NSF Grant EAR-0948308 “Collaborative Research: Testing for Rapid Pulses of Crustal-scale Heat and Mass Transfer by Fluids in Metamorphic "Hot Spots", New Hampshire, USA”, 8/1/10, PI: Ague; Co-PIs: Baxter, Chamberlain

NSF Grant EAR-0911582 “Collaborative Research: Developing a Practical and Quantitative Method for Measurement of Metamorphic Porphyroblast Crystallization Kinetics and Strain Rate”, 7/1/09, PI: Hirsch; Co-PIs: Stowell, Baxter

NSF Grant EAR-0547999 “CAREER: Rates and Timescales of Metamorphic Reactions at Convergent Plate Boundaries”, 1/1/06, PI: Baxter

NSF Grant EAR-0521266 “Acquisition and Development of a Thermal Ionization Mass Spectrometer Facility at Boston University”, 9/15/05, PI: Baxter; Co-PIs: Kurtz, Plank, Murray

Selected Publications

Dragovic B, Samanta LM, Baxter EF, Selverstone J, 2012. Using Garnet to Constrain the Duration and Rate of Water-Releasing Metamorphic Reactions During Subduction: An Example from Sifnos, Greece. Chemical Geology, v. 314-317. p. 9-22. (link to paper)

Pollington AD and Baxter EF, 2011. High precision microsampling and preparation of zoned garnet porphyroblasts for Sm-Nd geochronology. Chemical Geology, 281, 270-282. (PDF)

Pollington AD and Baxter EF, 2010. High resolution Sm/Nd garnet geochronology reveals the uneven pace of tectonometamorphic processes. EPSL, 293, 63-71. PDF

Peterman EM, Hacker BR, and Baxter EF, 2009. Phase transformations of continental crust during subduction and exhumation: Western Gneiss Region, Norway. Eur J Mineral, 21, 1097-1118. PDF

Harvey J and Baxter EF, 2009. An improved method for TIMS high precision neodymium isotope analysis of very small aliquots (1 – 10 ng). Chem Geol, 258, 251-257. PDF

Lancaster PJ, Baxter EF, Ague JJ, Breeding CM, and Owens TL, 2008. Synchronous peak Barrovian metamorphism driven by syn-orogenic magmatism and fluid flow in southern Connecticut, USA. J Met Geol, 26, 527-538. PDF

Baxter EF, Ague JJ, and DePaolo DJ, 2002. Prograde Temperature-Time Evolution in the Barrovian Type-Locality Constrained by Precise Sm/Nd Garnet Ages from Glen Clova, Scotland. J Geol Soc Lond, 159, 71-82. PDF