Downhole variation of lithium and oxygen isotopic compositions of oceanic crust at East Pacific Rise, ODP Site 1256

Y. Gao; F. Vils; K. M. Cooper; N. Banerjee; M. Harris; J. Hoefs; D. A.H. Teagle; J. F. Casey; T. Elliott; C. Laverne; J. C. Alt; K. Muehlenbachs

doi:10.1029/2012gc004207

Downhole variation of lithium and oxygen isotopic compositions of oceanic crust at East Pacific Rise, ODP Site 1256

Y. Gao^*, F. Vils, K. M. Cooper, N. Banerjee, M. Harris, J. Hoefs, D. A.H. Teagle, J. F. Casey, T. Elliott, C. Laverne, J. C. Alt, K. Muehlenbachs

^*Corresponding author for this work

School of Geography, Earth and Environmental Sciences

Research output: Contribution to journal › Article › peer-review

Abstract

Bulk rock lithium and oxygen isotope compositions from ODP Site 1256 were analyzed to investigate the seawater circulation in the upper oceanic crust formed at the East Pacific Rise (EPR). The upper extrusive basalts have δ18O values from +6.1‰ to +9.2‰, reflecting alteration of oceanic crust by seawater at low temperatures (<200–250°C). Bulk rocks from the sheeted dike complex and plutonic section have overall lower δ18O values (+3.0‰–+5.5‰). In the sheeted dike complex bulk rock δ18O values gradually decrease with depth, and then increase toward the fresh MORB δ18O value after reaching a minimum of +3.0‰ at ∼1350 m below seafloor (mbsf). The entire sampled crust is dominated by rocks with low lithium contents relative to fresh MORBs except for a few localized Li enrichment. The upper volcanic zone is characterized by a spread of δ7Li from low to high values relative to average unaltered MORB values (δ7Li = +3.4 ± 1.4‰). The presence of rocks with low δ7Li values in the upper crust most likely indicates zones of upwelling of relatively hot (∼200–250°C) hydrothermal fluids. In the sheeted dike complex, bulk rock δ7Li values show wide range of variation, but exhibit a general trend from enriched to depleted values at ∼1280 mbsf and then return to that for fresh MORB within the upper tens of meters of the plutonic section at the bottom of the after reaching a minimum at ∼1350 mbsf (δ7Li = −1.6‰). The downhole pattern of δ7Li principally reflects variations in water‐rock ratio (w/r) together with a downhole increase of temperature. Seawater flow in the upper volcanic zone is likely to be channeled with generally small but variable w/r ratios. The w/r ratios increase rapidly with depth in the lower volcanic section into the sheeted dike complex indicating water dominated pervasive hydrothermal flow due to intensive upwelling of hydrothermal fluids.

Original language	English
Number of pages	0
Journal	Geochemistry, Geophysics, Geosystems
Volume	13
Issue number	10
DOIs	https://doi.org/10.1029/2012gc004207
Publication status	Published - Oct 2012

Access to Document

10.1029/2012gc004207

Cite this

@article{b7c9aea40f244e5c9bae9e4d52b6514a,

title = "Downhole variation of lithium and oxygen isotopic compositions of oceanic crust at East Pacific Rise, ODP Site 1256",

abstract = "Bulk rock lithium and oxygen isotope compositions from ODP Site 1256 were analyzed to investigate the seawater circulation in the upper oceanic crust formed at the East Pacific Rise (EPR). The upper extrusive basalts have δ18O values from +6.1‰ to +9.2‰, reflecting alteration of oceanic crust by seawater at low temperatures (<200–250°C). Bulk rocks from the sheeted dike complex and plutonic section have overall lower δ18O values (+3.0‰–+5.5‰). In the sheeted dike complex bulk rock δ18O values gradually decrease with depth, and then increase toward the fresh MORB δ18O value after reaching a minimum of +3.0‰ at ∼1350 m below seafloor (mbsf). The entire sampled crust is dominated by rocks with low lithium contents relative to fresh MORBs except for a few localized Li enrichment. The upper volcanic zone is characterized by a spread of δ7Li from low to high values relative to average unaltered MORB values (δ7Li = +3.4 ± 1.4‰). The presence of rocks with low δ7Li values in the upper crust most likely indicates zones of upwelling of relatively hot (∼200–250°C) hydrothermal fluids. In the sheeted dike complex, bulk rock δ7Li values show wide range of variation, but exhibit a general trend from enriched to depleted values at ∼1280 mbsf and then return to that for fresh MORB within the upper tens of meters of the plutonic section at the bottom of the after reaching a minimum at ∼1350 mbsf (δ7Li = −1.6‰). The downhole pattern of δ7Li principally reflects variations in water‐rock ratio (w/r) together with a downhole increase of temperature. Seawater flow in the upper volcanic zone is likely to be channeled with generally small but variable w/r ratios. The w/r ratios increase rapidly with depth in the lower volcanic section into the sheeted dike complex indicating water dominated pervasive hydrothermal flow due to intensive upwelling of hydrothermal fluids.",

author = "Y. Gao and F. Vils and Cooper, {K. M.} and N. Banerjee and M. Harris and J. Hoefs and Teagle, {D. A.H.} and Casey, {J. F.} and T. Elliott and C. Laverne and Alt, {J. C.} and K. Muehlenbachs",

year = "2012",

month = oct,

doi = "10.1029/2012gc004207",

language = "English",

volume = "13",

journal = "Geochemistry, Geophysics, Geosystems",

issn = "1525-2027",

publisher = "John Wiley and Sons Inc.",

number = "10",

}

TY - JOUR

T1 - Downhole variation of lithium and oxygen isotopic compositions of oceanic crust at East Pacific Rise, ODP Site 1256

AU - Gao, Y.

AU - Vils, F.

AU - Cooper, K. M.

AU - Banerjee, N.

AU - Harris, M.

AU - Hoefs, J.

AU - Teagle, D. A.H.

AU - Casey, J. F.

AU - Elliott, T.

AU - Laverne, C.

AU - Alt, J. C.

AU - Muehlenbachs, K.

PY - 2012/10

Y1 - 2012/10

N2 - Bulk rock lithium and oxygen isotope compositions from ODP Site 1256 were analyzed to investigate the seawater circulation in the upper oceanic crust formed at the East Pacific Rise (EPR). The upper extrusive basalts have δ18O values from +6.1‰ to +9.2‰, reflecting alteration of oceanic crust by seawater at low temperatures (<200–250°C). Bulk rocks from the sheeted dike complex and plutonic section have overall lower δ18O values (+3.0‰–+5.5‰). In the sheeted dike complex bulk rock δ18O values gradually decrease with depth, and then increase toward the fresh MORB δ18O value after reaching a minimum of +3.0‰ at ∼1350 m below seafloor (mbsf). The entire sampled crust is dominated by rocks with low lithium contents relative to fresh MORBs except for a few localized Li enrichment. The upper volcanic zone is characterized by a spread of δ7Li from low to high values relative to average unaltered MORB values (δ7Li = +3.4 ± 1.4‰). The presence of rocks with low δ7Li values in the upper crust most likely indicates zones of upwelling of relatively hot (∼200–250°C) hydrothermal fluids. In the sheeted dike complex, bulk rock δ7Li values show wide range of variation, but exhibit a general trend from enriched to depleted values at ∼1280 mbsf and then return to that for fresh MORB within the upper tens of meters of the plutonic section at the bottom of the after reaching a minimum at ∼1350 mbsf (δ7Li = −1.6‰). The downhole pattern of δ7Li principally reflects variations in water‐rock ratio (w/r) together with a downhole increase of temperature. Seawater flow in the upper volcanic zone is likely to be channeled with generally small but variable w/r ratios. The w/r ratios increase rapidly with depth in the lower volcanic section into the sheeted dike complex indicating water dominated pervasive hydrothermal flow due to intensive upwelling of hydrothermal fluids.

AB - Bulk rock lithium and oxygen isotope compositions from ODP Site 1256 were analyzed to investigate the seawater circulation in the upper oceanic crust formed at the East Pacific Rise (EPR). The upper extrusive basalts have δ18O values from +6.1‰ to +9.2‰, reflecting alteration of oceanic crust by seawater at low temperatures (<200–250°C). Bulk rocks from the sheeted dike complex and plutonic section have overall lower δ18O values (+3.0‰–+5.5‰). In the sheeted dike complex bulk rock δ18O values gradually decrease with depth, and then increase toward the fresh MORB δ18O value after reaching a minimum of +3.0‰ at ∼1350 m below seafloor (mbsf). The entire sampled crust is dominated by rocks with low lithium contents relative to fresh MORBs except for a few localized Li enrichment. The upper volcanic zone is characterized by a spread of δ7Li from low to high values relative to average unaltered MORB values (δ7Li = +3.4 ± 1.4‰). The presence of rocks with low δ7Li values in the upper crust most likely indicates zones of upwelling of relatively hot (∼200–250°C) hydrothermal fluids. In the sheeted dike complex, bulk rock δ7Li values show wide range of variation, but exhibit a general trend from enriched to depleted values at ∼1280 mbsf and then return to that for fresh MORB within the upper tens of meters of the plutonic section at the bottom of the after reaching a minimum at ∼1350 mbsf (δ7Li = −1.6‰). The downhole pattern of δ7Li principally reflects variations in water‐rock ratio (w/r) together with a downhole increase of temperature. Seawater flow in the upper volcanic zone is likely to be channeled with generally small but variable w/r ratios. The w/r ratios increase rapidly with depth in the lower volcanic section into the sheeted dike complex indicating water dominated pervasive hydrothermal flow due to intensive upwelling of hydrothermal fluids.

U2 - 10.1029/2012gc004207

DO - 10.1029/2012gc004207

M3 - Article

SN - 1525-2027

VL - 13

JO - Geochemistry, Geophysics, Geosystems

JF - Geochemistry, Geophysics, Geosystems

IS - 10

ER -

Downhole variation of lithium and oxygen isotopic compositions of oceanic crust at East Pacific Rise, ODP Site 1256

Abstract

Access to Document

Fingerprint

Cite this