TY - JOUR

T1 - Interstitial carbonates in pillowed metabasaltic rocks from the Pilbara Craton, Western Australia: A vestige of Archean seawater chemistry and seawater-rock interactions

AU - Marin, Chris S.

AU - Jäger, Oliver

AU - Tusch, J.

AU - Viehmann, Sebastian

AU - Surma, Jakub

AU - Van Kranendonk, Martin

AU - Münker, Carsten

N1 - Funding Information: C.S. Marien and C. Münker acknowledge funding by the DFG project Mu1406/18 (SPP 1833 “Building a Habitable Earth”). F. Wombacher, J. Barosch and other laboratory support staff are thanked for their support at the microprobe and maintenance of the MC-ICP-MS lab. We thank N. Tepe and T. Hoffmann for their support at the University of Vienna and A. Pack, J. Reitner, and N. Albrecht at the University of Göttingen. We thank Wilson Teixeira for editorial handling and gratefully acknowledge the constructive reviews by Alexandre R. Cabral and Desiree L. Roerdink. Funding Information: C.S. Marien and C. Münker acknowledge funding by the DFG project Mu1406/18 (SPP 1833 “Building a Habitable Earth”). F. Wombacher, J. Barosch and other laboratory support staff are thanked for their support at the microprobe and maintenance of the MC-ICP-MS lab. We thank N. Tepe and T. Hoffmann for their support at the University of Vienna and A. Pack, J. Reitner, and N. Albrecht at the University of Göttingen. We thank Wilson Teixeira for editorial handling and gratefully acknowledge the constructive reviews by Alexandre R. Cabral and Desiree L. Roerdink. All data related to this article are published as table in the manuscript or supplemental information. Data tables can also be requested without charge from the corresponding author.

PY - 2023/8/15

Y1 - 2023/8/15

N2 - Calcites hosted in the interpillow void spaces of extremely well preserved, 3.47–3.12 Ga pillow lavas of the Archean Pilbara Craton, Australia, provide new geochemical insights into the composition of Archean seawater and its interaction with basaltic crust. We present a comprehensive dataset of major and trace elements, radiogenic 147Sm- 143Nd, 87Rb- 87Sr, and stable C-O isotopes for these calcites. Based on their elemental composition and Post-Archean Australian Shale-normalized rare earth element and yttrium (REY PAAS) patterns, two types of calcites can be distinguished. Type I (n = 9) are coarse-grained calcites with elevated Mn concentrations (478–14,790 ppm) and high REY concentrations that match the basaltic host rock compositions. Petrographic textures in combination with geochemical data indicate precipitation from boiling seawater trapped between pillows during basalt eruption. Small light-REY PAAS depletions, only slightly super-chondritic Y/Ho (34.5–39.1), and low δ 18O (VSMOW2) (9.25–16.66 ‰) suggest relatively high fluid-rock interactions of boiling seawater with the basaltic host rock. These characteristics are similar to those of interstitial carbonates found in modern mid-ocean ridge basalts. Type II carbonates (n = 6) are fine-grained, low-Mn (13.7–420 ppm) calcites that exhibit comparably high Sr concentrations (825–2,516 ppm) and anoxic modern seawater-like REY PAAS patterns, strong super-chondritic Y/Ho (39.1–55.8) and δ 18O (VSMOW2) values of 9.10–13.18 ‰. These features hint to direct calcite precipitation from seawater within the degassing space with little fluid-rock interaction. Almost all (Type I and Type II) of the calcites investigated here, combined with their respective host rocks, yield well-defined Sm-Nd isochron ages for the Apex (3,466 ± 23 Ma), Euro (3,365 ± 43 Ma), Honeyeater (3,187 ± 33 Ma), and Bradley (3,131 ± 24 Ma) formations. Only calcites from the Mt. Ada Basalt and their associated host rocks show a ∼ 100 Ma younger Sm-Nd isochron age (3,361 ± 22 Ma) compared to the U-Pb zircon age of formation. Highly radiogenic initial Sr isotope compositions of the high-Mn calcites (Type I) and low Sr concentrations, suggest Sr remobilization for these calcites. In contrast, the low-Mn calcite (Type II) exhibit higher Sr concentrations and lower 87Sr/ 86Sr (i) of 0.7010–0.7011 at 3.34 Ga and 0.70137 at 3.12 Ga, suggesting increasing influence of crustal weathering on the composition of Paleoarchean seawater through time, and progressive decoupling from the Archean mantle ( 87Sr/ 86Sr (i) = 0.7003–0.7007).

AB - Calcites hosted in the interpillow void spaces of extremely well preserved, 3.47–3.12 Ga pillow lavas of the Archean Pilbara Craton, Australia, provide new geochemical insights into the composition of Archean seawater and its interaction with basaltic crust. We present a comprehensive dataset of major and trace elements, radiogenic 147Sm- 143Nd, 87Rb- 87Sr, and stable C-O isotopes for these calcites. Based on their elemental composition and Post-Archean Australian Shale-normalized rare earth element and yttrium (REY PAAS) patterns, two types of calcites can be distinguished. Type I (n = 9) are coarse-grained calcites with elevated Mn concentrations (478–14,790 ppm) and high REY concentrations that match the basaltic host rock compositions. Petrographic textures in combination with geochemical data indicate precipitation from boiling seawater trapped between pillows during basalt eruption. Small light-REY PAAS depletions, only slightly super-chondritic Y/Ho (34.5–39.1), and low δ 18O (VSMOW2) (9.25–16.66 ‰) suggest relatively high fluid-rock interactions of boiling seawater with the basaltic host rock. These characteristics are similar to those of interstitial carbonates found in modern mid-ocean ridge basalts. Type II carbonates (n = 6) are fine-grained, low-Mn (13.7–420 ppm) calcites that exhibit comparably high Sr concentrations (825–2,516 ppm) and anoxic modern seawater-like REY PAAS patterns, strong super-chondritic Y/Ho (39.1–55.8) and δ 18O (VSMOW2) values of 9.10–13.18 ‰. These features hint to direct calcite precipitation from seawater within the degassing space with little fluid-rock interaction. Almost all (Type I and Type II) of the calcites investigated here, combined with their respective host rocks, yield well-defined Sm-Nd isochron ages for the Apex (3,466 ± 23 Ma), Euro (3,365 ± 43 Ma), Honeyeater (3,187 ± 33 Ma), and Bradley (3,131 ± 24 Ma) formations. Only calcites from the Mt. Ada Basalt and their associated host rocks show a ∼ 100 Ma younger Sm-Nd isochron age (3,361 ± 22 Ma) compared to the U-Pb zircon age of formation. Highly radiogenic initial Sr isotope compositions of the high-Mn calcites (Type I) and low Sr concentrations, suggest Sr remobilization for these calcites. In contrast, the low-Mn calcite (Type II) exhibit higher Sr concentrations and lower 87Sr/ 86Sr (i) of 0.7010–0.7011 at 3.34 Ga and 0.70137 at 3.12 Ga, suggesting increasing influence of crustal weathering on the composition of Paleoarchean seawater through time, and progressive decoupling from the Archean mantle ( 87Sr/ 86Sr (i) = 0.7003–0.7007).

KW - Archean

KW - Archean seawater

KW - Interpillow carbonates

KW - Pilbara Supergroup

KW - Stable and radiogenic isotopes

KW - Trace elements

UR - http://www.scopus.com/inward/record.url?scp=85161544901&partnerID=8YFLogxK

U2 - 10.1016/j.precamres.2023.107109

DO - 10.1016/j.precamres.2023.107109

M3 - Article

VL - 394

JO - Precambrian research

JF - Precambrian research

SN - 0301-9268

M1 - 107109

ER -