Spilites

Shimazu, M. (1971) On the authigenic minerals in the spilitic basalts in the inner belts of northeastern Japan. Proc, IMA-IAGOD Meeting 70, IMA Vol. Mineralog. Soc. Japan, Spec. Paper 1, 134-139. 

Metahasite group 7 = amphibolites, spilites, greenschists, amphibole gneisses (undifferentiated) 8 =... 

The jaspilite subformation developed in the spilite-diabase formation is known both in intrageosynclinal synclinorium zones and in the inner zones of the Krivoy Rog-Kremenchug marginal depression. 

In the Karelian zone of the Karelides, BIF are known in northern Finland in the spilite-diabase formation and are associated with basic volcanic rocks —pyroclastics, basaltic lavas and agglomerates—in northern Norway graphite schists and limestones are occasionally encountered in the sections. 

Despite the diversity of the BIF and the complexity of their interrelationships with the enclosing rocks, some general features have been established. In a detailed formational analysis, Chernov showed that the cherty iron-formations constitute the lower parts of the sections both in the Karelides and in the Svecofennides, and that their formation reflects the initial stages of geosynclinal development of the Baltic shield. In many areas the BIF are underlain by thick piles of conglomerates which rest on an old basement more than 2600 m.y. old. The BIF are overlain by volcanic rocks of the spilite-diabase series or by clastic flyschoid formations formed in the final stages of geosynclinal development. 

Chernov et al. (1970), who studied the cherty iron-formations of Karelia, concluded that they are related to volcanism not only of basic, but mainly also of acid composition. In turn, on the basis of the composition of the parent lavas, they distinguished spilite-diabase and leptite-porphyry formations among those of eugeosynclinal type, formed simultaneously but in different paleotectonic conditions. A large part of the formations of the spilite-diabase series of the Baltic shield is confined to the junctions between geosynclinal depressions and central massifs. The leptite-porphyry series of geosynclinal formations is characterized by a close association of acid and basic volcanics with iron cherts and less often with limestones and clastic sediments (Fig. 9). 

As in the case of iron, the hydrodynamic regime of the water basin has a considerable effect on the processes of accumulation of siUca. In the case of simultaneous deposition of silica and iron, the sols of their hydroxides are usually converted to gels having the composition of ferruginous chlorites. In the case of coagulation of silica sol around submarine active springs with constant discharge, only small lenticular intercalations of spilite are formed. 

Belevtsev, Ya.N. and Goroshnikov, B.I., 1969. On the rationality of the terms iron chert", ja.spilite , and ferruginous quartzite . In Problemy obrazovaniya zhelezistykh porod dokembriya (Problems of the Formation of the Prccambrian Iron Formations). Izd. Naukova Dumka, Kiev, pp. 299-303 (in Russian). 

Several important alteration environments, however, are not observed for in situ oceanic crust. These include spilites (Cann, 1969), a rock type that displays almost complete exchange of calcium for sodium, leading to formation of an albite-rich rock, and epidosites, the metal depleted epidote-quartz-chlorite assemblage that is likely to be characteristic of the reaction zones, or at least last equilibration zones of black-smoker fluids (e.g., Schiffman and Smith, 1988 Richardson et al., 1987 Bettison-Varga et al., 1992). In particular, the importance of spilites in chemical mass balances could be large, but they are effectively unknown for in situ oceanic crust. Spilites are therefore not considered in any mass balances. Epidosites are likely to be important for the mass balance of some trace metals in the... 

Cann J. R. (1969) Spilites form the Carlsberg Ridge, Indian Ocean. J. Petrol. 10, 1-19. 

The controls on carbon dioxide would have been somewhat different. Today, carbon dioxide is stored in carbonate minerals in the ocean floor and on the continental shelf. Subduction, followed by volcanism, cycles the carbon dioxide to the mantle and then restores the CO2 to the air. Metamorphic decarbonation of the lower crust also returns carbon dioxide. The carbon dioxide is then cycled back to the water, some via rain, some dissolved via wave bubbles. Erosion provides calcium and magnesium, eventually to precipitate the carbonate. In the earliest Archean, parts of this cycle may have been inefficient. The continental supply of calcium may have been limited however, subseafloor hydrothermal systems would have been vigorous and abundant, exchanging sodium for calcium in spilitization reactions, and hence providing calcium for in situ precipitation in oceanic crust. 

Hall A. (1989) Ammonium in spilitized basalts of southwest England and its implications for the recycling of nitrogen. Geochem. J. 23, 19—23. 

Coombs, D. S., "On the Mineral Facies of Spilitic Rocks and Their... 

The Shackleton Limestone is overlain by clastic sedimentary rocks that have been assigned to the Dick, Douglas, and Starshot formations. The Dick Formation is composed of siltstone, argillite, sandstone, and silty limestone. Rees et al. (1988) reported that sandstones of the Dick Formation are ripple-marked and cross-bedded and that interbedded shales contain rare mud-cracks. In addition, an outcrop of the Dick Formation located east of Mt. Dick (89°49 S, 159°32 E) and about 20 km south of the Byrd Glacier contains a lava flow that is 9 m thick and is composed of spilite (Skinner 1964, 1965). Rees et al. (1988) later interpreted this lava flow as a pillow basalt and noted that the contact between it and sedimentary rocks of the Byrd Group was covered by snow. They also reported that they had obtained a whole-rock K-Ar date of 586 20 Ma (Neoproterozoic), which is incompatible with the presence of Early Cambrian fossils in the underlying Shackleton Limestone. Therefore, Rees et al. (1988)... 

Lanthanide mobility has been suggested to occur during the low-temperature metamorphic conditions such as spilitization and submarine weathering of basalts... 

Many authors have also proposed different reactions for the contact of very hot seawater in the rocks of deep sea vents, including Hardie (1990) who considered the primary reaction to be with basalt to form spilitic greenstone. With vents and various other hot calcium chloride brines Shvartsev and Bukaty (1996), Stura (1977,1974), Azizov (1975), Kissin and Pakhomov (1969), and Pastushenko (1967) have proposed reactions with a wide variety of other rocks. Several authors have also discussed rock leaching, adsorption, precipitation or ion exchange to add or remove components in the dolomitization brine. 

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