Geochemistry, petrology and origin of Neoproterozoic ironstones in the eastern part of the Adelaide Geosyncline, South Australia

نویسنده

  • B. G. Lottermoser
چکیده

The eastern part of the Adelaide Geosyncline contains well preserved glaciomarine sequences of the Sturtian glaciation (:750–700 Ma) including calcareous or dolomitic siltstone, manganiferous siltstone, dolostone and diamictite units and the associated Braemar ironstone facies. The ironstone facies occurs as matrix to diamictites and as massive to laminated ironstones and comprises abundant Fe oxides (hematite, magnetite) and quartz, minor silicates (muscovite, chlorite, biotite, plagioclase, tourmaline), carbonate and apatite, and detrital mineral grains and lithic clasts. Micro-textures indicate that magnetite and hematite are of metamorphic origin. They are intergrown with silicates and carbonates, with the mineral assemblage indicative of greenschist facies (biotite grade) metamorphism. Chemical compositions of ironstones vary greatly and reflect changes from silica-, alumina-poor ironstones formed by predominantly chemical precipitation processes to silica-, alumina-rich examples with a significant detrital component. Silica-, alumina-poor ironstones are characterised by low concentrations of transition metals and large ion lithophile and high field strength elements and display REE signatures of modern coastal seawater. The Braemar facies accumulated in a marine basin along the border of a continental glaciated highland and a low-lying weathered landmass. Wet-based glaciers originated from the Palaeoproterozoic to Mesoproterozoic metamorphic basement and debouched into a fault-controlled depocentre, the Baratta Trough. The intimate association of dolostones, manganiferous siltstones, ironstones and diamictites can be explained by a transgressive event during a postglacial period. Hydrothermal exhalations added significant amounts of Fe and other metals to Neoproterozoic seawater. Melting of floating ice led to an influx of clastic detritus and deposition of glaciomarine sediments from wet-based glaciers and to oxygenation of ferriferous (9manganiferous), carbonate and CO2 charged coastal waters. Release of CO2 to the atmosphere from the oxygenated waters resulted in the precipitation of carbonate as dolostones and oxygenation of ferriferous (9manganiferous) waters led to the precipitation of Fe oxides as laminated ironstones and as matrix of diamictic ironstones. Further increases in Eh conditions led to the precipitation of Mn oxides or carbonates and their incorporation in clastic sediments. Thus the Braemar ironstone facies is the result of chemical precipitation of dissolved Fe (and Mn) during a postglacial, transgressive period and formed in a near-coastal environment under www.elsevier.com/locate/precamres * Corresponding author. Fax: +61-7-40421284. E-mail address: [email protected] (B.G. Lottermoser) 0301-9268/00/$ see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0301 -9268 (99 )00098 -4 B.G. Lottermoser, P.M. Ashley / Precambrian Research 101 (2000) 49–67 50 significant terrestrial influences. © 2000 Elsevier Science B.V. All rights reserved.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

The Petrology and Geochemistry of Granitoid Rocks of Troud Area in South-West of Shahrood

The area of study is located 120 Km north-east of Shahrood city. In terms of structure and geological classification, this area is located in the northern part of central Iran zone. Granitoids of Troud ranging from monzonite to granite. The main minerals of granitoids are quartz, plagioclase, and orthose. The accessory minerals are biotite, hornblende, sphene, and opaque minerals. Various textu...

متن کامل

Petrology, Geochemistry and Tectonomagmatic Evolution of Hezar Igneous Complex (Rayen- South of Kerman- Iran): the First Description of an Arc Remnant of the Neotethyan Subduction Zone

The Hezar Igneous Complex (HIC) in the south-eastern part of Urumieh-Dokhtar magmatic arc, is the most prominent magmatic feature in the Kerman Porphyry Copper Belt, that understanding magmatic evolution of which may shed light on the tectonomagmatic development of this less-studied part of an important magmatic arc in the Neotethys realm. The HIC has been developed in the the intersection of t...

متن کامل

Petrology and geochemistry of gabbro part of Samsour Ophiolite, South East of Iran

Samsour ophiolite is located in Sistan and Baluchestan Province, about 210 Km southwest of Zahedan city. Based on structural and sedimentary classification of Iran, this ophiolite is located adjacent to NosratAbad-Karvandar fault and belongs to Sistan suture zone.  Rock units of this ophiolite are mainly composed of ultramafic, including gabbro (Layerd and massive) and doleriteic. In the micros...

متن کامل

Petrology, geochemistry, and petrogenesis of mafic dykes from the Kermanshah Ophiolite in Sahneh-Harsin area of Western Iran

The Kermanshah ophiolite complex is a part of the Mediterranean–Zagros–Oman Tethyan ophiolites, located in the structural–tectonic zone of western Iran in the northern part of the Zagros main thrust. Doleritic sheeted dykes are well exposed within the ophiolite in the south of Sahneh. These dykes contain high MgO, Na2O, low TiO2 (2O5, and K2O contents, and high FeOt/MgO and LILE/HFSE ratios. Th...

متن کامل

Phylogeny of Onobrychis sect. Hymenobrychis (Fabaceae) based on chloroplast DNA sequence data

Phenetic analysis of morphological characters in different species of Onobrychis Miller sect. Hymenobrychis DC. (Fabaceae), classified them in two main groups based on corolla features. To determine the phylogenetic relationships among the 13 species, chloroplast DNA sequences were used. Analysis of these data resulted in a well-resolved and well-supported phylogeny. Phylogenies generated by ma...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2000