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Extreme oxygen isotope zoning in garnet and zircon from a metachert block in mélange reveals metasomatism at the peak of subduction metamorphism

2019; Geological Society of America; Volume: 47; Issue: 7 Linguagem: Inglês

10.1130/g46135.1

1943-2682

F. Zeb Page, E. M. Cameron, Clara Margaret Flood, Jeffrey Dobbins, Michael J. Spicuzza, Kouki Kitajima, Ariel Strickland, T. Ushikubo, Christopher G. Mattinson, John W. Valley,

Geochemistry and Geologic Mapping

Research Article| May 13, 2019 Extreme oxygen isotope zoning in garnet and zircon from a metachert block in mélange reveals metasomatism at the peak of subduction metamorphism F. Zeb Page; F. Zeb Page 1Geology Department, Oberlin College, Oberlin, Ohio 44074, USA Search for other works by this author on: GSW Google Scholar Emilia M. Cameron; Emilia M. Cameron 1Geology Department, Oberlin College, Oberlin, Ohio 44074, USA2Wisconsin Secondary Ion Mass Spectrometer Laboratory (WiscSIMS), Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar Clara Margaret Flood; Clara Margaret Flood 1Geology Department, Oberlin College, Oberlin, Ohio 44074, USA Search for other works by this author on: GSW Google Scholar Jeffrey W. Dobbins; Jeffrey W. Dobbins 1Geology Department, Oberlin College, Oberlin, Ohio 44074, USA Search for other works by this author on: GSW Google Scholar Michael J. Spicuzza; Michael J. Spicuzza 2Wisconsin Secondary Ion Mass Spectrometer Laboratory (WiscSIMS), Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar Kouki Kitajima; Kouki Kitajima 2Wisconsin Secondary Ion Mass Spectrometer Laboratory (WiscSIMS), Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar Ariel Strickland; Ariel Strickland 2Wisconsin Secondary Ion Mass Spectrometer Laboratory (WiscSIMS), Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar Takayuki Ushikubo; Takayuki Ushikubo 2Wisconsin Secondary Ion Mass Spectrometer Laboratory (WiscSIMS), Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar Christopher G. Mattinson; Christopher G. Mattinson 3Department of Geological Sciences, Central Washington University, Ellensburg, Washington 98926, USA Search for other works by this author on: GSW Google Scholar John W. Valley John W. Valley 2Wisconsin Secondary Ion Mass Spectrometer Laboratory (WiscSIMS), Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar Geology (2019) 47 (7): 655–658. https://doi.org/10.1130/G46135.1 Article history received: 08 Feb 2019 rev-recd: 28 Mar 2019 accepted: 17 Apr 2019 first online: 13 May 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation F. Zeb Page, Emilia M. Cameron, Clara Margaret Flood, Jeffrey W. Dobbins, Michael J. Spicuzza, Kouki Kitajima, Ariel Strickland, Takayuki Ushikubo, Christopher G. Mattinson, John W. Valley; Extreme oxygen isotope zoning in garnet and zircon from a metachert block in mélange reveals metasomatism at the peak of subduction metamorphism. Geology 2019;; 47 (7): 655–658. doi: https://doi.org/10.1130/G46135.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A tectonic block of garnet quartzite in the amphibolite-facies mélange of the Catalina Schist (Santa Catalina Island, California, USA) records the metasomatic pre-treatment of high-δ18O sediments as they enter the subduction zone. The block is primarily quartz, but contains two generations of garnet that record extreme oxygen isotope disequilibrium and inverse fractionations between garnet cores and matrix quartz. Rare millimeter-scale garnet crystals record prograde cation zoning patterns, whereas more abundant ∼200-μm-diameter crystals have the same composition as rims on the larger garnets. Garnets of both generations have high-δ18O cores (20.8‰–26.3‰, Vienna standard mean ocean water) that require an unusually high-δ18O protolith and lower-δ18O, less variable rims (10.0‰–11.2‰). Matrix quartz values are homogeneous (13.6‰). Zircon crystals contain detrital cores (δ18O = 4.7‰–8.5‰, 124.6 +1.4/−2.9 Ma) with a characteristic igneous trace element composition likely sourced from arc volcanics, surrounded by zircon with metamorphic age (115.1 ± 2.5 Ma) and trace element compositions that suggest growth in the presence of garnet. Metamorphic zircon decreases in δ18O from near-core (24.1‰) to rim (12.4‰), in equilibrium with zoned garnets. Collectively, the data document the subduction of a mixed high-δ18O siliceous ooze and/or volcanic ash protolith reaching temperatures of 550–625 °C prior to the nucleation of small garnets without influence from external fluids. Metasomatism was recorded in rims of both garnet and zircon populations as large volumes of broadly homogeneous subduction fluids stripped matrix quartz of its extremely high oxygen isotope signature. Thus, zoned garnet and zircon in high-δ18O subducted sediments offer a detailed window into subduction fluids. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.