Geochemistry and provenance of metasedimentary rocks from the Archean Golden Pond sequence (Casa Berardi mining district, Abitibi subprovince)

Abstract

The Archean Golden Pond sequence is made up of deformed and metamorphosed conglomerates, greywackes, and mafic volcanic rocks, and is overlain by ferrugineous metasedimentary rocks of the North iron formation. The clastic rocks were derived mainly from a volcanic source that had undergone weak chemical weathering. Their source area was dominated by the presence of 60–80% high-Al2O3 felsic volcanics having strongly fractionated [La/Sm]N (= 3.7 ± 0.3) and very low Ta/Th ratios (= 0.09 ± 0.02), with lesser proportions of basaltic (10–30%) and ultramafic volcanic rocks (1–10%). The ferrugineous metasedimentary rocks can be modelled by mixing 20–40% siliciclastic material, of the composition of the average Golden Pond greywacke, with an Fe- and Si-rich precipitate (molecular Fe/Si = 0.6 ± 0.2). The high-Al2O3 felsic source rocks were most likely produced by subduction processes within an oceanic arc environment, but the mafic and ultramafic volcanic rocks were derived by different processes from an asthenospheric mantle source, possibly in an oceanic rift environment. Therefore, it is suggested that the ultramafic, mafic, and felsic volcanic rocks were brought to the same erosional level by dissection of the arc system and rapid exhumation of the felsic arc lithologies and the deeper ocean floor. Intrabasinal hydrothermal activity associated with contemporaneous mafic volcanism and (or) graben development may have also been responsible for the local production of the Fe-rich precipitates of the North iron formation.

Contrasting provenance of Late Archean metasedimentary rocks from the Wutai Complex, North China Craton: detrital zircon U–Pb, whole-rock Sm–Nd isotopic, and geochemical data

“…8a), implying that weathering in the source area was simply the breakdown of plagioclase, corresponding to intermediate chemical weathering according to the scheme suggested by Fedo et al (1995). Preferential accumulation of heavy minerals, such as zircon, sphene, monazite, and apatite, in clastic sedimentary rocks can potentially bias the distributions of some chemical compositions and, consequently, can considerably complicate the interpretation of sedimentary provenance La Flèche and Camiré 1996). Generally, the main Zr-bearing minerals may be concentrated in the coarse fraction of the sediments, but the major Al-and Ti-bearing phases in the silts/clays by hydraulic sorting (La Flèche and Camiré 1996;Fralick 2003).…”

“…Preferential accumulation of heavy minerals, such as zircon, sphene, monazite, and apatite, in clastic sedimentary rocks can potentially bias the distributions of some chemical compositions and, consequently, can considerably complicate the interpretation of sedimentary provenance La Flèche and Camiré 1996). Generally, the main Zr-bearing minerals may be concentrated in the coarse fraction of the sediments, but the major Al-and Ti-bearing phases in the silts/clays by hydraulic sorting (La Flèche and Camiré 1996;Fralick 2003). Likewise, REE and Th abundances may depend on the accumulation of monazite, apatite, zircon or sphene (Camiré et al 1993;La Flèche and Camiré 1996).…”

“…Generally, the main Zr-bearing minerals may be concentrated in the coarse fraction of the sediments, but the major Al-and Ti-bearing phases in the silts/clays by hydraulic sorting (La Flèche and Camiré 1996;Fralick 2003). Likewise, REE and Th abundances may depend on the accumulation of monazite, apatite, zircon or sphene (Camiré et al 1993;La Flèche and Camiré 1996). A plot involving Al, Ti, and Zr (Fig.…”

“…Diagenetic reactions may include illitization, feldspar dissolution, cementation, Na-, K-, and Mg-metasomatism (e.g. Nesbitt and Young 1989;La Flèche and Camiré 1996;McLennan et al 2003;Nesbitt 2003). Fedo et al (1997) suggested that K-metasomatism is predominant in shales and reflects the illitization of kaolinite, whereas Na-metasomatism principally affects silt-and sand-sized particles.…”

“…CAS represents the field of calc-alkaline suites and SPG represents the field of strongly peraluminous granites (after Garcia et al 1994). b La/Sm-Th, c Tb/La-Ti and d Tb/Yb-Hf diagrams (after La Flèche and Camiré 1996) rocks which are responsible for the observed scatter of the data (Fig. 8).…”