229-12 Isotopic Insights into Progressive Rodingitization in the Dun Mountain Ophiolite, Aotearoa New Zealand

Session: Crustal Petrology (Posters)

Poster Booth No.: 256

Presenting Author:

Charlie Hite

Authors:

Hite, Charlie¹, Lara Rivas, Jesus², Mims, David³, Hams, Jake⁴, Gevedon, Michelle⁵, Nistor, Claudiu⁶, Barnes, Jaime D.⁷, Stockli, Lisa Danielle⁸, Stockli, Daniel F.⁹, Dragovic, Besim¹⁰, Goswami (she/her), Nandana¹¹, Satkoski, Aaron¹²

(1) Colorado College Geology Department, Colorado Springs, CO, USA, (2) Colorado College Geology Department, Colorado Springs, CO, USA, (3) Colorado College Geology Department, Colorado Springs, CO, USA, (4) Colorado College Geology Department, Colorado Springs, CO, USA, (5) Colorado College Geology Department, Colorado Springs, CO, USA, (6) Department of Earth and Planetary Sciences, University of Texas at Austin, Austin, TX, USA, (7) Department of Earth and Planetary Sciences, University of Texas at Austin, Austin, TX, USA, (8) Department of Earth and Planetary Sciences, University of Texas at Austin, Austin, TX, USA, (9) Department of Earth and Planetary Sciences, University of Texas at Austin, Austin, TX, USA, (10) School of the Earth, Ocean & Environment, University of South Carolina, Columbia, SC, USA, (11) School of the Earth, Ocean & Environment, University of South Carolina, Columbia, SC, USA, (12) Department of Earth and Planetary Sciences, University of Texas at Austin, Austin, TX, USA,

Abstract:

Rodingites are Ca-rich metasomatic rocks commonly found as veins, pods, or dikes in serpentinized ultramafic terranes, formed via interaction of mafic protoliths with high-pH, Ca-rich fluids during serpentinization. Despite localized occurrence, rodingites provide critical records of fluid–rock interaction within the mafic crust and associated mantle and mantle wedge; they also contain underutilized petrogenetic indicator minerals that may constrain the timing and conditions of metasomatism. Rodingite samples were collected from the Dun Mountain Ophiolite Belt and associated mélanges, and display mineralogical evidence of variable degrees of rodingitization, with the progression of plagioclase, to hydrogrossular and andradite ± clinopyroxene, to vesuvianite (e.g., Li et al., 2004). We pair Raman spectra analysis, with oxygen, strontium, and calcium isotope ratios in garnet, pyroxene, vesuvianite and host serpentine to: (1) test whether rodingitization and serpentinization are truly concomitant processes by identifying serpentine polymorphs and testing for equilibrium among ẟ¹⁸O values of rodingite garnet and serpentinite phases; (2) determine whether progressive rodingitization may result in the wide range of isotopic compositions exhibited by rodingites; and (3) develop an understanding of the timing and tectonic position of the ophiolite and associated mélanges during rodingitization. ẟ¹⁸O ratios are consistent with those of altered ocean crust (2.3 to 7.3‰; n=31), and inter-mineral variability exceeds what can be accounted for by equilibrium fractionation or temperature effects alone; heterogeneity in ẟ^44/40Ca values of garnet and pyroxene approach that observed in crustal and mafic rocks globally (−1.38 to 2.88‰; n=15); ⁸⁷Sr/⁸⁶Sr ratios are dominated by mafic protolith compositions and indicate an influx of seawater (0.70340 to 0.7050; n=16).

Li, X.-P., Rahn, M., and Bucher, K., 2004, Metamorphic Processes in Rodingites of the Zermatt-Saas Ophiolites: International Geology Review, v. 46, p. 28–51, doi:10.2747/0020-6814.46.1.28.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10765

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