کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
6430862 1634838 2011 9 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Coupled silicon-oxygen isotope fractionation traces Archaean silicification
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علوم زمین و سیاره ای (عمومی)
پیش نمایش صفحه اول مقاله
Coupled silicon-oxygen isotope fractionation traces Archaean silicification
چکیده انگلیسی

Silica alteration zones and cherts are a conspicuous feature of Archaean greenstone belts worldwide and provide evidence of extensive mobilisation of silica in the marine environment of the early Earth. In order to understand the process(es) of silicification we measured the silicon and oxygen isotope composition of sections of variably silicified basalts and overlying bedded cherts from the Theespruit, Hooggenoeg and Kromberg Formations of the Barberton Greenstone Belt, South Africa.The δ30Si and δ18O values of bulk rock increase with increasing amount of silicification from unsilicified basalts (−0.64‰ < δ30Si < −0.01‰ and + 8.6‰ < δ18O < + 11.9‰) to silicified basalts (δ30Si and δ18O values as high as + 0.81‰ and + 15.6‰, respectively). Cherts generally have positive isotope ratios (+ 0.21‰ < δ30Si < + 1.05‰ and + 10.9 < δ18O < + 17.1), except two cherts, which have negative δ30Si values, but high δ18O (up to + 19.5‰).The pronounced positive correlations between δ30Si, δ18O and SiO2 imply that the isotope variation is driven by the silicification process which coevally introduced both 18O and 30Si into the basalts. The oxygen isotope variation in the basalts from about 8.6‰ to 15.6‰ is likely to represent temperature-dependent isotope fractionation during alteration. Our proposed model for the observed silicon isotope variation relies on a temperature-controlled basalt dissolution vs. silica deposition process.

Research Highlights►Silicification process introduces coupled 18O and 30Si in precursor rocks. ►18O-30Si values caused by temperature-controlled dissolution/precipitation processes. ►Positive δ30Si in silicified rocks may be a complementary reservoir to BIF values.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Earth and Planetary Science Letters - Volume 301, Issues 1–2, 3 January 2011, Pages 222-230
نویسندگان
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