Abstract
Boron concentrations and isotope compositions of fluids and lavas from subduction-zone settings show great potential for elucidating mass flux at Earth's modern convergent margins. However, the fluid-mineral-melt behavior of B and its two stable isotopes remains relatively poorly understood. Boron isotope analyses of tourmaline in metasedimentary rocks subducted to 15-90 km depths (1) demonstrate the ability of this mineral to retain information regarding prograde devolatilization history in even highly retrograded rocks and (2) indicate the importance of tourmaline in affecting whole-rock B loss and B isotope evolution during subduction-zone metamorphism. The B lost from micas during metamorphism of subducting sedimentary rocks and altered oceanic crust is isotopically more enriched in 11B than the B retained in the micas. Beneath forearcs and volcanic arcs, the B from micas is either removed from the subduction-zone rocks via metamorphic fluids or sequestered by growing tourmaline, in which the B can be entrained to even greater depths. Here we demonstrate that these metamorphic fluids could contribute to the relatively high δ11B signatures observed in most arc lavas and the across-arc trends of decreasing δ11B observed in several arcs.
| Original language | English |
|---|---|
| Pages (from-to) | 407-410 |
| Number of pages | 4 |
| Journal | Geology |
| Volume | 31 |
| Issue number | 5 |
| DOIs | |
| Publication status | Published - May 2003 |
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Keywords
- B/B
- Metamorphism
- Secondary ion mass spectrometry
- Subduction zones
- Tourmaline
ASJC Scopus subject areas
- Geology
Cite this
Record in metamorphic tourmalines of subduction-zone devolatilization and boron cycling. / Edward Bebout, Gray; Nakamura, Eizou.
In: Geology, Vol. 31, No. 5, 05.2003, p. 407-410.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Record in metamorphic tourmalines of subduction-zone devolatilization and boron cycling
AU - Edward Bebout, Gray
AU - Nakamura, Eizou
PY - 2003/5
Y1 - 2003/5
N2 - Boron concentrations and isotope compositions of fluids and lavas from subduction-zone settings show great potential for elucidating mass flux at Earth's modern convergent margins. However, the fluid-mineral-melt behavior of B and its two stable isotopes remains relatively poorly understood. Boron isotope analyses of tourmaline in metasedimentary rocks subducted to 15-90 km depths (1) demonstrate the ability of this mineral to retain information regarding prograde devolatilization history in even highly retrograded rocks and (2) indicate the importance of tourmaline in affecting whole-rock B loss and B isotope evolution during subduction-zone metamorphism. The B lost from micas during metamorphism of subducting sedimentary rocks and altered oceanic crust is isotopically more enriched in 11B than the B retained in the micas. Beneath forearcs and volcanic arcs, the B from micas is either removed from the subduction-zone rocks via metamorphic fluids or sequestered by growing tourmaline, in which the B can be entrained to even greater depths. Here we demonstrate that these metamorphic fluids could contribute to the relatively high δ11B signatures observed in most arc lavas and the across-arc trends of decreasing δ11B observed in several arcs.
AB - Boron concentrations and isotope compositions of fluids and lavas from subduction-zone settings show great potential for elucidating mass flux at Earth's modern convergent margins. However, the fluid-mineral-melt behavior of B and its two stable isotopes remains relatively poorly understood. Boron isotope analyses of tourmaline in metasedimentary rocks subducted to 15-90 km depths (1) demonstrate the ability of this mineral to retain information regarding prograde devolatilization history in even highly retrograded rocks and (2) indicate the importance of tourmaline in affecting whole-rock B loss and B isotope evolution during subduction-zone metamorphism. The B lost from micas during metamorphism of subducting sedimentary rocks and altered oceanic crust is isotopically more enriched in 11B than the B retained in the micas. Beneath forearcs and volcanic arcs, the B from micas is either removed from the subduction-zone rocks via metamorphic fluids or sequestered by growing tourmaline, in which the B can be entrained to even greater depths. Here we demonstrate that these metamorphic fluids could contribute to the relatively high δ11B signatures observed in most arc lavas and the across-arc trends of decreasing δ11B observed in several arcs.
KW - B/B
KW - Metamorphism
KW - Secondary ion mass spectrometry
KW - Subduction zones
KW - Tourmaline
UR - http://www.scopus.com/inward/record.url?scp=0037645855&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0037645855&partnerID=8YFLogxK
U2 - 10.1130/0091-7613(2003)031<0407:RIMTOS>2.0.CO;2
DO - 10.1130/0091-7613(2003)031<0407:RIMTOS>2.0.CO;2
M3 - Article
AN - SCOPUS:0037645855
VL - 31
SP - 407
EP - 410
JO - Geology
JF - Geology
SN - 0091-7613
IS - 5
ER -