The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
The Late Archean (c. 2.54–2.52 Ga) high-K granitoids of the Rum Jungle Complex, Northern Australia, display the igneous mineral assemblage of K-feldspar, quartz, plagioclase, biotite, and magnetite, and accessories such as zircon, monazite, titanite, allanite, apatite, and ilmenite. The granites underwent a variably severe greenschist facies alteration and associated deformation during the Barramundi...
Neoarchean late to post-tectonic sanukitoid intrusions are found in the western part of the Karelian Province in Finland. Variable-sized, even-grained to K-feldspar porphyritic intrusions form a series of diorites, tonalites, and granodiorites, that are calc-alkaline to alkali-calcic, magnesian, and mostly peraluminous. The major and trace element geochemistry of the intrusions show typical sanukitoid...
A single-grain zircon U–Pb secondary ion mass spectrometer (SIMS) study of nine granitoid intrusions with sanukitoid geochemistry from the Finnish part of the Karelian Province shows their time-limited emplacement. The age results indicate emplacement at ~2715 and 2745Ma. We observed also a significant number of relict cores in the zircons with 207 Pb/ 206 Pb ages up to 3.2Ga, emphasizing...
The Fiskenæsset Complex, SW Greenland, is one of the best preserved layered Archean intrusions in the world, consisting of an association of ca. 550-meter-thick anorthosite, leucogabbro, gabbro, and ultramafic rocks (dunite, peridotite, pyroxenite, and hornblendite). Despite poly-phase deformation and amphibolite to granulite facies metamorphism, primary cumulate textures and igneous layering are...
Archean, Paleoproterozoic, and Mesoproterozoic rocks, assemblages, and structures differ greatly both from each other and from modern ones, and lack evidence for subduction and seafloor spreading such as is widespread in Phanerozoic terrains. Most specialists nevertheless apply non-actualistic plate-tectonic explanations to the ancient terrains and do not consider alternatives. This report evaluates...
Attempts to decipher the petrogenesis of Archean Trondhjemite–Tonalite–Granodiorite (TTG) and establish trends in their compositions over time typically do not assess the possible role of assimilation–crystal fractionation processes. Studies of TTG suites worldwide, however, demonstrate that reprocessing of older crust is common. Felsic volcanic and intrusive rocks from the North Caribou Lake area,...
The Likamännikkö quartz alkali feldspar syenite complex is located in eastern Finland, in the Suomussalmi district, within the Archean Karelian Craton. The intrusive complex covers an area of 2km 2 and is cut by both Neoarchean leucogranite and Paleoproterozoic dolerite dykes. Three zircon fractions define a concordant U–Pb age of 2741±2Ma for the quartz alkali feldspar syenite. The syenitic...
This study presents new geochemical and isotopic data from granitoids belonging to the Kianta Complex of the Western Karelian terrane, collected from the Suomussalmi district in eastern Finland. Geochemically the Archean granitoids can be divided into five groups: TTGs (tonalite–trondhjemite–granodiorite, sensu stricto), transitional TTGs, sanukitoids (high-Mg granitoids), quartz diorites and anatectic...
The formation of cratonic mantle peridotite of Archean age is examined within the time frame of Earth's thermal history, and how it was expressed by temporal variations in magma and residue petrology. Peridotite residues that occupy the lithospheric mantle are rare owing to the effects of melt-rock reaction, metasomatism, and refertilization. Where they are identified, they are very similar to the...
New whole-rock geochemistry and LA-MC-ICPMS and Pb-evaporation geochronological data were obtained on zircon from the Neoarchean Planalto suite granites and associated charnockitic rocks of the Canaã area of the Carajás province, eastern Amazonian craton, Brazil. The Pb-evaporation ages of three samples from the Planalto suite are around 2730Ma (2733±2Ma, 2731±1Ma and 2736±4Ma), whereas U–Pb LA-MC-ICPMS...
The 3.09–2.97Ga Murchison Greenstone Belt is one of several Archean volcano-sedimentary belts within the Kaapvaal Craton in southern Africa. Among the diverse ore deposits found within the belt, a set of Sb-(±Au) deposits are located in a major quartz-carbonate altered brittle–ductile structure known as the Antimony Line. The Antimony Line is thus clearly related to hydrothermal fluid circulation...
Partial melting experiments with models of Archean oceanic crust (MAOC; with 11, 13 and 15wt.% MgO) are used to investigate the role of metamorphism and melting of primary picritic compositions in the formation of TTG-like melts and continental crust on the early Earth. The approach investigates the possibility that the average early crust composition was comparatively MgO-rich and evolved to lower...
We integrate an updated worldwide compilation of U/Pb, Hf-isotope and trace-element data on zircon, and Re–Os model ages on sulfides and alloys in mantle-derived rocks and xenocrysts, to examine patterns of crustal evolution and crust–mantle interaction from 4.5Ga to 2.4Ga ago. The data suggest that during the period from 4.5Ga to ca 3.4Ga, Earth's crust was essentially stagnant and dominantly mafic...
The Jiaodong Terrane of the Eastern Shandong Complex in the Eastern Block of the North China Craton (NCC) consists predominantly of Archean granitoid gneisses with minor supracrustal rock enclaves or lenses. This study presents new zircon LA-ICP-MS U–Pb and Lu–Hf isotopic data for these lithologies, which help to better understand the Archean crustal evolution of the Eastern Block of the NCC. Magmatic...
Meso-Archean sedimentary sequences at Mt. Narryer and the Jack Hills of the Narryer Terrane in Western Australia's Yilgarn Craton contain detrital zircon grains with ages as old as 4.37Ga, the oldest preserved terrestrial matter. These grains are rare remnants of Hadean (4.5–4.0Ga) terrestrial crust and their survival stems from the crystallographic properties of zircon during crustal reworking: they...
Subduction processes on early earth are controversial, with some suggestions that tectonics did not operate until the earth cooled to a sufficient point around the Archean–Proterozoic boundary. One way of addressing this issue is to examine well-preserved successions of Archean supracrustal rocks. Here we discuss petrography, whole-rock chemical and isotopic data combined with zircon Hf isotopes from...
Dunhuang Block is previously considered to be an eastern part of the Tarim Craton, but now it is proposed to be the western extension of the Alxa Block of the NCC as a result of displacement along the Altyn Tagh fault. The oldest basement rocks of the Dunhuang Block, named Aketashitage Complex, were mainly exposed in the northern Altyn Tagh. Migmatites of the Aketashitage Complex are sodic and subalkaline...
Oxygen isotopes were measured in zircon crystals from a suite of Paleo- to Mesoarchean igneous and sedimentary rocks from the Pilbara Craton in order to test prevailing models of early Earth tectonic evolution. Our results indicate that igneous zircon crystals older than 3.2Ga in the Pilbara Craton have mantle-like oxygen isotope signatures, whereas zircon grains younger than c. 3.2Ga show, on average,...
Xenoliths retrieved from lamprophyric hosts in the Michipicoten belt fall into four groups defined by Al–Mg contents but do not include mantle peridotite. Based on immobile trace element abundances, the xenoliths are derived from magmas associated with the main phase of arc volcanism between 2.75 and 2.70Ga or are co-genetic with the orogenic shoshonite suite.Trace elements distinguish two styles...
Archean mafic–ultramafic melts, crystallized as layered intrusions in the upper crust and extruded as komatiitic flows, are primary probes of upper mantle chemistry. However, the message from their primary chemical composition can be compromised by different modes of contamination. Contaminants are typically cryptic in terms of their geochemical and isotopic signals but may be related to metasomatised...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.