TY - JOUR
T1 - Boron isotope variations of Franciscan serpentinites, northern California
AU - Yamada, Chinatsu
AU - Tsujimori, Tatsuki
AU - Chang, Qing
AU - Kimura, Jun Ichi
N1 - Funding Information:
We thank Steve Kirby and John Wakabayashi for their kind assistances for collecting serpentinite samples. We also thank Bob Coleman for his information about serpentinites in New Idria. This research was supported by the Center for Northeast Asian Studies, Tohoku University and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in part by grants from the MEXT/JSPS KAKENHI JP15H05212 and JP18H01299 to T. Tsujimori and JP15H02148, JP16H01123, and JP18H04372 to J.-I. Kimura. The fieldwork was supported in part by the Collection Building Fellowship of the National Museum of Nature and Science, Tokyo; we thank Kenichiro Tani for this opportunity. We appreciate for constructive reviews from Céline Martin, Yuji Ichiyama, and an anonymous reviewer. We extend our appreciation to Ryosuke Oyanagi and Noriyoshi Tsuchiya for their assistance on the micro Raman spectroscopy. We also thank Daniel Pastor-Galán for feedback.
Funding Information:
We thank Steve Kirby and John Wakabayashi for their kind assistances for collecting serpentinite samples. We also thank Bob Coleman for his information about serpentinites in New Idria. This research was supported by the Center for Northeast Asian Studies, Tohoku University and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in part by grants from the MEXT/JSPS KAKENHI JP15H05212 and JP18H01299 to T. Tsujimori and JP15H02148 , JP16H01123 , and JP18H04372 to J.-I. Kimura. The fieldwork was supported in part by the Collection Building Fellowship of the National Museum of Nature and Science, Tokyo; we thank Kenichiro Tani for this opportunity. We appreciate for constructive reviews from Céline Martin, Yuji Ichiyama, and an anonymous reviewer. We extend our appreciation to Ryosuke Oyanagi and Noriyoshi Tsuchiya for their assistance on the micro Raman spectroscopy. We also thank Daniel Pastor-Galán for feedback.
Publisher Copyright:
© 2019 Elsevier B.V.
PY - 2019/6/1
Y1 - 2019/6/1
N2 - Serpentinites and serpentinized mantle peridotites with various tectonic origins occur in the Franciscan Complex of the Northern California Cordillera, USA. Boron isotopes of serpentinites differentiate with fluid-mediated processes, and have great potential for key geologic markers in convergent margins. To understand boron isotope behavior within the Franciscan subduction zone system, we apply a newly developed ablation volume correction (AVC) method for in-situ isotope/elemental analyses using a laser-ablation multiple collector inductively-coupled-plasma mass spectrometry (LA-MC-ICPMS) on seventeen different Franciscan serpentinites (sensu lato) collected from eight separate areas. Boron abundances and isotope compositions of the studied serpentinites show large variations B = 1.6–239 μg·g −1 , δ 11 B = −12.0 to +24.4‰, which allow to discriminate the serpentinites into two groups: (1) a lighter δ 11 B of −12.0 to +8.8‰ with a lesser B < ~56 μg·g −1 and (2) a heavier δ 11 B of +7.2 to +24.4% with a greater B ~34–239 μg·g −1 . These groups lithologically correspond to the presence or absence of associated blueschist-facies metamorphic rocks, respectively. The blueschist-bearing and/or blueschist-associated serpentinites might have been affected by a deep forearc slab fluids in the depth of > ~2 GPa. Preferential partitioning of 11 B into fluids released from the subducted slab at shallow leaves lighter δ 11 B in the slab resulting in lighter δ 11 B in the deep slab fluids. In contrast, the blueschist-absent serpentinites with heavier δ 11 B may have formed at a shallow environment where shallow slab or hydrothermal fluids with heavier 11 B were present. Lesser versus greater amounts of B in the deep versus shallow serpentinites are also consistent with the dehydration profile of B from a slab. Our results show the versatility of boron isotopes and composition for identification of the origin of serpentinite in Pacific-type orogenic belts.
AB - Serpentinites and serpentinized mantle peridotites with various tectonic origins occur in the Franciscan Complex of the Northern California Cordillera, USA. Boron isotopes of serpentinites differentiate with fluid-mediated processes, and have great potential for key geologic markers in convergent margins. To understand boron isotope behavior within the Franciscan subduction zone system, we apply a newly developed ablation volume correction (AVC) method for in-situ isotope/elemental analyses using a laser-ablation multiple collector inductively-coupled-plasma mass spectrometry (LA-MC-ICPMS) on seventeen different Franciscan serpentinites (sensu lato) collected from eight separate areas. Boron abundances and isotope compositions of the studied serpentinites show large variations B = 1.6–239 μg·g −1 , δ 11 B = −12.0 to +24.4‰, which allow to discriminate the serpentinites into two groups: (1) a lighter δ 11 B of −12.0 to +8.8‰ with a lesser B < ~56 μg·g −1 and (2) a heavier δ 11 B of +7.2 to +24.4% with a greater B ~34–239 μg·g −1 . These groups lithologically correspond to the presence or absence of associated blueschist-facies metamorphic rocks, respectively. The blueschist-bearing and/or blueschist-associated serpentinites might have been affected by a deep forearc slab fluids in the depth of > ~2 GPa. Preferential partitioning of 11 B into fluids released from the subducted slab at shallow leaves lighter δ 11 B in the slab resulting in lighter δ 11 B in the deep slab fluids. In contrast, the blueschist-absent serpentinites with heavier δ 11 B may have formed at a shallow environment where shallow slab or hydrothermal fluids with heavier 11 B were present. Lesser versus greater amounts of B in the deep versus shallow serpentinites are also consistent with the dehydration profile of B from a slab. Our results show the versatility of boron isotopes and composition for identification of the origin of serpentinite in Pacific-type orogenic belts.
KW - Boron isotope
KW - California Coast Ranges
KW - Franciscan complex
KW - Serpentinites
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U2 - 10.1016/j.lithos.2019.02.004
DO - 10.1016/j.lithos.2019.02.004
M3 - Article
AN - SCOPUS:85063501900
SN - 0024-4937
VL - 334-335
SP - 180
EP - 189
JO - Lithos
JF - Lithos
ER -