کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
6427566 1634714 2016 12 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Geochemistry and Nd isotopic characteristics of Earth's Hadean mantle and primitive crust
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علوم زمین و سیاره ای (عمومی)
پیش نمایش صفحه اول مقاله
Geochemistry and Nd isotopic characteristics of Earth's Hadean mantle and primitive crust
چکیده انگلیسی


- New high precision 142Nd isotopic data for the Isua boninite-like amphibolites.
- Highlights key differences for 142Nd datasets of SW Greenland vs. Nuvvuagittuq rocks.
- Geochemical and isotopic comparison between two of the earliest meta-volcanic belts.
- Common early-formed mantle source involved in crust formation in Hadean/Eoarchean.

The Isua supracrustal belt (ISB) and the Nuvvuagittuq greenstone belt (NGB) are among the oldest suites of mafic volcanic rocks preserved on Earth and are the best candidates for representing its early crust. Despite the possible 500 Ma age difference between the belts, these mantle-derived rocks show compositional similarities, with features resembling rocks formed in subduction initiation environments. With the addition of new 142Nd data for the Garbenschiefer unit of the ISB reported here, high precision 142Nd data are now available for all the mafic lithologies from both belts. Mantle-derived rocks from both the ISB and NGB belts exhibit a range of 142Nd/144Nd ratios. The datasets for the two belts, however, are significantly different, suggesting a different origin for their 142Nd anomalies. Nearly all ISB samples have excesses in 142Nd, including the newly analyzed Garbenschiefer boninitic amphibolites (mean of +12ppm). Excesses in 142Nd/144Nd compared to the Nd standard for all the ISB rocks range between +8 and +20ppm, with a near Gaussian distribution around +12ppm. This distribution could simply reflect the analytical error (±5 ppm) around a single 142Nd/144Nd ratio indicating that the samples formed after the extinction of 146Sm from a source with a nearly uniform 142Nd/144Nd ratio. In contrast, the NGB shows a range of 142Nd/144Nd ratios from +8 to −18ppm relative to the modern Nd standard and displays a flat distribution of 142Nd/144Nd ratios. The ISB samples show no significant correlation between their 142Nd/144Nd and Sm/Nd ratios, consistent with their formation in the Eoarchean via melting of a Hadean depleted mantle. In contrast, all NGB samples display a 142Nd/144Nd vs. Sm/Nd correlation, consistent with their crystallization in the Hadean. The mantle sources for both the ISB and NGB mantle-derived rocks have a similar 142Nd/144Nd ratio at the possible age of formation of the NGB (∼4.3 Ga) suggesting the derivation of ISB and NGB rocks from a common early-formed depleted mantle source formed between 4.47 and 4.42 Ga with a 147Sm/144Nd ratio ∼0.218. This mantle appears to have been an important source component involved in the formation of the primitive crust during most of the Hadean and Eoarchean eons.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Earth and Planetary Science Letters - Volume 442, 15 May 2016, Pages 194-205
نویسندگان
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