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Chlorine isotope evidence for syn-subduction modification of serpentinites by interaction with sediment-derived fluid Jane Selverstone and Zachary Sharp.

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Presentation on theme: "Chlorine isotope evidence for syn-subduction modification of serpentinites by interaction with sediment-derived fluid Jane Selverstone and Zachary Sharp."— Presentation transcript:

1 Chlorine isotope evidence for syn-subduction modification of serpentinites by interaction with sediment-derived fluid Jane Selverstone and Zachary Sharp University of New Mexico NSF grant EAR during exhumation

2 °C Lago di Cignana: dia+coe GPa Zermatt-Saas ophiolite, Aosta, Italy P-T data from Cartwright & Barnicoat 2002, Li et al. 2004, Angiboust et al. 2009, Groppo et al Z-S ophiolite Combin ?

3 Chlorine Isotope Data serpentinization via seawater serpentinization via sedimentary pore fluids Zermatt-Saas data A simple story?

4 Textural Types (Li et al. 2004) Type A Type B F.O.V. = 4 mm for all photos Type B/C seafloor pseudomorphic replacement mylonitization ± folding during subduction recrystallization during initial exhumation greenschist overprint Type C Type D Ol+TiClh

5 Type A Type B Type C Type D Serpentine compositions correlate with textural types Texturally youngest serp in each sample has lowest Al and highest Mg# Serpentine analyses D A A B B C C

6 Chlorine Isotopes Revisited °C LdC GPa Serpentinite stages: Li et al. 2004, JMG A A

7 Chlorine Isotopes Revisited °C LdC GPa Serpentinite stages: Li et al. 2004, JMG B B A A

8 Chlorine Isotopes Revisited °C LdC GPa Serpentinite stages: Li et al. 2004, JMG B B C C A A

9 Chlorine Isotopes Revisited °C LdC GPa Serpentinite stages: Li et al. 2004, JMG B B C C E E D D A A 1σ error in δ 37 Cl

10 Single fluid? Multiple fluids? Bulk Composition Constraints on Fluid History High LOI = carbonate-bearing sed-derived? ???

11 Chlorine Isotopes Revisited A A B B C C D D

12 A A B B C C D D Ti-clh oliv FIs Type C&D

13 Chlorine Isotopes Revisited Type C&D A A B B C C D D Calcmica schist with diamond- bearing Mn layers

14 Chlorine Isotopes Revisited A A B B C C D D mixing between reservoirs + +

15 Faccenda et al )Bending stresses induce mantle serpentinization via seawater δ 37 Cl serp 0 2)± Local mantle serpentinization via sedimentary pore fluids δ 37 Cl serp 0 3)Uppermost sedimentary layer modified by extensive interaction with pore fluids from accretionary prism δ 37 Cl metased << 0 A Physical Scenario Consistent with the Chemical Data Seawater-dominated Sedimentary pore fluid 2 2

16 A Physical Scenario Consistent with the Chemical Data Faccenda et al ) Unbending stresses create regime of slab- parallel fluid flow in serpentinites during subduction δ 37 Cl serp constant 5) Onset of exhumation moves rocks into regime of cross-slab fluid flow: fluids from metasediments locally modify serpentinites δ 37 Cl serp <<

17 Conclusions °C LdC GPa B B C C E E D D A A Serpentinites preserved seafloor δ 37 Cl values during subduction phase Fluid-rock interaction during exhumation caused localized shifts to lower δ 37 Cl values Fluids likely derived from nearby metasedimentary rocks in subduction channel Switch from burial to exhumation expanded length scales of fluid-rock interaction and facilitated flow across lithologic boundaries Cl allows us to see chemical interaction between downgoing slab and accretionary wedge fluids δ 37 Cl


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