Geochemistry of heavily altered Archean volcanic and volcaniclastic rocks of the Warrawoona Group, at Mt. Goldsworthy in the Pilbara Craton, Western Australia: Implications for alteration and origin

Abstract

The geochemical characteristics of Archean unusual siliceous rocks at Mt. Goldsworthy region in the Pilbara Craton were studied. The siliceous rocks have been assigned to the uppermost Warrawoona Group mafic volcanic rocks, and are overlain by quartz-rich sandstone units of the Strelley Pool Chert that probably represent continental margin sedimentation. The Warrwoona rocks have been heavily altered and are now composed dominantly of microcrystalline quartz, with subordinate mica, Fe-Ti oxides and unidentified silicates; original magmatic textures are only locally preserved. The complex alteration is assumed to result from multiple events including weathering during subaerial exposure, circulation of hydrothermal fluids, and metasomatic silicification. During alteration, Al, Ti, Zr, Th, Cr and Sc remained immobile, although their concentrations were lowered by a substantial increase in silica. Mutual ratios of these immobile elements such as Al 2 O 3 /TiO 2 Cr/Th, Th/Sc, Cr/Al 2 O 3 and Zr/TiO 2 and comparison with the least-altered contemporaneous maficultramafic rocks in the Pilbara Craton show that the altered rocks originated from high-MgO rocks such as komatiite and high-MgO basalt, possibly of Al-depleted type. The Mt. Goldsworthy rocks have significantly higher Th/Sc (0.024-0.1) values compared with primitive mantle values (0.005) and komatiite (0.01). This feature is interpreted as a result of crustal contamination, which is consistent with the early evolution of continental crust.

Life on Earth Originated Where Later Microbial Oxygenic Photosynthesis Precipitated Banded Iron Formation, Suppressing Life Diversification for 1.4 Ga

“…Likewise, the 3.5 -3.3-Ga-old Barberton greenstone belt in South Africa yielded evaporites and subaerial microbial mats formed on the surface of volcanic rocks [26,27]. Accordingly, the Phanerozoic tectonic processes producing mafic to ultramafic rocks mainly along oceanic spreading centers cannot be applied to similar Archean volcanic rocks [28], suggesting that the latter erupted onto continental basement [29]. These observations corroborate earlier conclusions on the evaporitic nature of the associated BIF [30,31].…”

Determination of rare earth elements by spectroscopic techniques: a review

“…There are many techniques dedicated to determination of rare earth elements. INAA, [80][81][82][83][84][85][86][87] RNAA, 88,89 XRF, [90][91][92][93] ICP-OES, 63,88,[94][95][96][97][98] ICP-MS, 63,84,95,[99][100][101][102][103][104][105][106] and UV-VIS 94,[107][108][109] are the most frequently employed analytical techniques for determination of REE in geological materials. Although ICP-MS and NAA are the most suitable techniques for determination of REE, which possess the ability to detect trace elements at sub-mg L À1 levels, they suffer from problems of ionization suppression by matrix elements, isobaric polyatomic interferences and clogging of the sample introduction system when the sample contains a high concentration of dissolved salts.…”

Petrography, geochemistry, and tectonics of a rifted fragment of Mainland Asia: evidence from the Lasala Formation, Mindoro Island, Philippines

“…Felsic rocks tend to have high concentrations of these compounds compared with mafic rocks. However, this tectonic diagram must be employed with caution because K 2 O, Na 2 O, and SiO 2 contents may be obscured by post-depositional processes such as silicification and K-metasomatism (Cullers et al 1993;Fedo et al 1995;Sugitani et al 2006). Results from this diagram may only be deemed reliable if it complements the petrography of the samples (Roser and Korsch 1986).…”