Sm–Nd, Rb–Sr and Pb–Pb dating of silicic carbonates from the early Archaean Barberton Greenstone Belt, South Africa

Carbonaceous cherts of the Barberton Greenstone Belt, South Africa: Isotopic, chemical and structural characteristics of individual microstructures

“…Raman spectra of carbonaceous particles (Fig. 9) in the different Barberton cherts are all identical, suggesting that a uniform degree of structural order was attained during a regional metamorphic event as late as 2.7 Ga, when temperatures between 200 and 320°C were reached (Weis and Wasserburg, 1987;Xie et al, 1997;Toulkeridis et al, 1998;. The observed N/C-ratio of individual carbonaceous particles in the Barberton cherts is in the order of 0.001-0.006, which is in line with typical observed values in Archean carbonaceous cherts and is significantly lower than that of unmetamorphosed biologic material (N/C = 0.15, Redfield ratio C:N is 106:16).…”

Geochemistry of the Krivoy Rog Banded Iron Formation, Ukraine, and the impact of peak episodes of increased global magmatic activity on the trace element composition of Precambrian seawater

“…Due to scare data, a few incomplete REY data sets for Late Paleoproterozoic and Mesoproterozoic chemical sediments had also to be used. Data compiled from Fryer (1977), Appel (1983), Dymek and Klein (1988), Beukes and Klein (1990), Shimizu et al (1990), Danielson et al (1992), Alibert and McCulloch (1993), Hälbich et al (1993), Klein and Beukes (1993), Morris (1993), Graf et al (1994), Bau and Dulski (1996), Khan et al (1996), Bau et al (1997b), Tsikos and Moore (1997), Toulkeridis et al (1998), Lottermoser and Ashley (2000), Bolhar et al (2004b), Klein and Ladeira (2004), Bolhar et al (2005), Frei and Polat (2007) Gourcerol et al (2015), Zhu et al (2015). The depositional age of the chemical sediments was taken from the related publication.…”

“…Pure marine chemical sediments with seawater-like REYSN patterns suggest heterogeneous Nd (t) between −5 to +3 for Archean seawater and plot between calculated depleted mantle and continental crust, indicating variable contributions from both, hydrothermally altered oceanic crust and continental material to the Archean REY budget of seawater. Samarium-Nd isotope compositions of Archean seawater precipitates with seawater-like REYSN patterns and their related depositional age are taken from Shimizu et al (1990), Alibert and McCulloch (1993), Bau et al (1997b), Toulkeridis et al (1998), Kamber and Webb (2001), Hayashi et al (2004), Frei and Polat (2007), Alexander et al (2008), Alexander et al (2009), Døssing et al (2009), Viehmann et al (2013. Unfortunately, Nd isotope studies of pure Post-Archean BIFs are rare and do not yet allow reconstructing a meaningful Nd isotope evolution curve for seawater throughout the entire Precambrian.…”

Fluid inclusion analysis of silicified Palaeoarchaean oceanic crust – A record of Archaean seawater?

“…In early Archaean greenstone belts older than c. 3.0 Ga silicification of volcano-sedimentary sequences is pervasive and chert layers are ubiquitous (Hofmann and Harris, 2008;Hofmann and Wilson, 2007;Terabayashi et al, 2003;van den Boorn et al, 2007van den Boorn et al, , 2010. Most workers attribute the silicification to be a result of hydrothermal processes (Duchac and Hanor, 1987;Hanor and Duchac, 1990;Hofmann and Harris, 2008;van den Boorn et al, 2007van den Boorn et al, , 2010, but the nature of the fluids and processes of silicification are not fully understood.…”

“…Most workers attribute the silicification to be a result of hydrothermal processes (Duchac and Hanor, 1987;Hanor and Duchac, 1990;Hofmann and Harris, 2008;van den Boorn et al, 2007van den Boorn et al, , 2010, but the nature of the fluids and processes of silicification are not fully understood. Early Archaean chert and quartz precipitates associated with silicified components of greenstone belts have received attention because if they are derived from silica-saturated seawater, they potentially provide constraints on the composition and temperature of the Archaean ocean De Ronde et al, 1997;de Vries and Touret, 2007;Knauth and Lowe, 2003;Terabayashi et al, 2003).…”