Increased solubility of quartz following ferrous–ferric iron reactions
A knowledge of the solubility of quartz and silicates in natural waters is important to the understanding of many gelogical processes. Here we provide experimental data to support an earlier hypothesis1, that during the supergene enrichment of banded iron-formations, redox reactions involving iron result in a much more rapid dissolution of quartz than would be predicted from its known solubility in water. The process is relevant not only to iron ore genesis but also to the much wider field of chemical weathering— for example, to the genesis of laterites and soils from quartz-bearing rocks. In addition, the reactions may offer a mechanism by which quartz is pseudomorphed by iron oxides.
Silicon isotopes and the origin of the Archaean cherts
The first detailed investigation of silicon isotope systematics in Archaean cherts shows that silicon isotope variability in 3.0-3.5 Ga cherts of the Pilbara craton is significant on sub-centimetre to kilometre scales. A total delta30Si range of -2.4 to +1.3‰ was established. The silicon isotope compositions were determined with high precision (
Mesozoic rifting and basin inversion along the northern African Tethyan margin: an overview
Abstract The northern African Tethyan margin registered three major rifting episodes from the latest Palaeozoic-earliest Mesozoic to the earliest Cenozoic. Break-up of Gondwana was initiated in the late Carboniferous. Along the northern African-Arabian plate margin rifting propagated westward from the northeastern Arabian margin to Morocco during the Permian and Triassic, and was accompanied by Mid-Late Triassic-earliest Liassic extensive alkaline flow basalts. Rifting continued during the Liassic, e.g. in the Moghrebian Atlas troughs. A second stage of rifting occurred in the Late Jurassic and continued into, or was rejuvenated during, the Early Cretaceous. Along the east Mediterranean margin, some large E-W trending rifts formed, often with associated volcanism, e.g. southern Sirt and Abu Gharadig. Most researchers believe the oceanization of the eastern Mediterranean basin occurred at this time. Flexural subsidence affected the Moghrebian Atlas, including the Riffian-Tellian domain, where a thick flysch series was deposited. Two short-lived, but widespread and tectonically important, compressional or wrench-dominated events occurred during the Santonian and the latest Maastrichtian. From Morocco to Oman, most sedimentary basins were folded and inverted at these times. The Santonian event resulted from onset of the collision between the African-Arabian and Eurasian plates. New stress-fields favoured NE-SW extension along the African plate margin, generating or rejuvenating some rifts, e.g. in the Euphrates trough and in the Libya-Tunisia region (northwestern Sirt, Pelagian Sea). Rifting and magmatism continued in these regions into the Paleocene. During the Mesozoic, therefore, the northern margin of the African-Arabian plate registered both rifting resulting in the oceanization of the Tethys and rifting resulting from the initiation of the closure of the Tethys. The intraplate domain exhibited echoes of the tectonic events affecting the margin.