Boron isotope fractionation in magma via crustal carbonate dissolution

نویسندگان

  • Frances M. Deegan
  • Valentin R. Troll
  • Martin J. Whitehouse
  • Ester M. Jolis
  • Carmela Freda
چکیده

Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ(11)B values down to -41.5‰, reflecting preferential partitioning of (10)B into the assimilating melt. Loss of (11)B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports (11)B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ(11)B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Magma hybridization in the middle crust: Possible consequences for deep-crustal magma mixing

The 465 Ma Svarthopen pluton in northcentral Norway was emplaced under middle-crustal conditions (~700 MPa) into metasedimentary rocks of the Helgeland Nappe Complex. The pluton is characterized by zones of mingling and mixing of gabbro/ diorite with peraluminous, garnet-bearing biotite granite. Variation in bulk-rock Sr and Nd isotope ratios are consistent with simple mixing; however, nonunifo...

متن کامل

Re-evaluating boron speciation in biogenic calcite and aragonite using 11B MAS NMR

Understanding the partitioning of aqueous boron species into marine carbonates is critical for constraining the boron isotope system for use as a marine pH proxy. Previous studies have assumed that boron was incorporated into carbonate through the preferential uptake of tetrahedral borate B(OH)4 . In this study we revisit this assumption through a detailed solid state B magic angle spinning (MA...

متن کامل

Stable boron isotope fractionation between dissolved B(OH)3 and B(OH)4

The stable boron isotope ratio (B/B) in marine carbonates is used as a paleo-pH recorder and is one of the most promising paleo-carbonate chemistry proxies. Understanding the thermodynamic basis of the proxy is of fundamental importance, including knowledge on the equilibrium fractionation factor between dissolved boric acid, B(OH)3, and borate ion, B(OH)4 – ( B OH 3 B OH 4 , hereafter (B3–B4))...

متن کامل

Uranium-series isotope and thermal constraints on the rate and depth of silicic magma genesis

Uranium-series isotopes provide important constraints on the timescale of magma differentiation and this can be used to identify where in the crust and silicic magmas acquire their geochemical characteristics. Timescales of differentiation can be inferred from the observed co-variations of U-series disequilibria with differentiation indexes. When crustal assimilation of secular equilibrium mate...

متن کامل

PETROLOGICAL AND GEOCHEMICAL STUDY OF CRUSTAL XENOLITHS FROM 1961 ERUPTION OF CALBUCO VOLCANO, CHILE (LATITUDE 41 20 S )

Twenty four samples of xenoliths and country rocks from the 1961 lava flow of Calbuco volcano have been studied. Fourteen samples have been analyzed for major elements and P, Ni, Ba, Cr, V, Zr, Sc, Y, and Sr. Five of these samples were further analyzed for Sm, Nd, Sr, and Pb isotope ratios. Seventeen samples were analyzed under the microscope and three samples were analyzed by microprobe fo...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره 6  شماره 

صفحات  -

تاریخ انتشار 2016