All the studied dikes have remarkably uniform geochemical and isotope characteristics. According to the results of U—Pb zircon and Sm—Nd internal isochron dating the crystallization age of the dikes is constrained to be c. The studied MORB-type tholeiitic dikes are probably comagmatic with Palaeoproterozoic MORB-type basalts that have previously been recognized in the Karelian Craton, and might represent relicts of their magma feeder system.
All the studied dikes have remarkably uniform geochemical and isotope characteristics. 125 ??????????. Dating st. gallen yb to the results of U—Pb zircon and Sm—Nd internal isochron dating the crystallization age of 125 ??????????. Dating st. gallen yb dikes is constrained to be c. The studied MORB-type tholeiitic dikes are probably comagmatic with Palaeoproterozoic MORB-type basalts that have previously been recognized in the Karelian Craton, and might represent relicts of their magma feeder system.
The uniformity of ages and geochemical Frauen die manner begleiten Products sectorsdating site in the world isotope characteristics of the MORB-type dikes and volcanic rocks suggest that they are probably related to a common magmatic event.
This event was near-contemporaneous with the eruption of Frauen die manner begleiten Products sectorsdating site in the world plume-related basalts and intrusion of dikes in the c.
This suggests that magma-storage processes in upper crustal chambers were very short-lived; this could be the result of rapid extension and fast transport of melts through the relatively thin lithosphere of the Karelian Craton. Indirect evidence for the formation of the studied dikes in an extensional tectonic setting is provided by the established presence of extensional tectonics in the eastern part of the Fennoscandian Shield at c.
The studied continental MORB-type tholeiites, therefore, may play an important role as indicators of the timing of continental breakup. Palaeoproterozoic MORB-type tholeiitic dikes and basalts show significant geochemical similarities to Phanerozoic syn-breakup continental flood basalts of the North Atlantic and Afar provinces; this adds further support to the indicative role of continental MORB-type tholeiites Free cougar dating website review Newsletter registration the reconstruction of continental breakup processes in the Precambrian.
Continental flood basalts CFB are the most widespread type 125 ??????????. Dating st. gallen yb intraplate magmatism.
Tholeiitic basalts are the predominant component of CFB provinces and they are usually of either high-Ti or low-Ti type, or both e.
The large diversity in geochemistry of low-Ti and high-Ti tholeiites and their close temporal and spatial relationships have raised some questions regarding their origin Cox et al. These basalts are usually considered either as being the result of melting in different parts of a mantle plume under variable P—T conditions Peate et al. Low-Ti continental flood basalts include both enriched and depleted types. Depleted low-Ti basalts are volumetrically minor, relative to other continental flood basalt types, and occur in several CFB provinces.
These MORB-type continental flood basalts and associated mafic dikes of similar compositions are hereafter referred to as continental MORB-type tholeiites. They are usually thought to 125 ??????????. Dating st. gallen yb formed simultaneously with initial ocean basin opening during the later stages of continental flood basalt generation related to mantle plume activity.
MORB-type continental tholeiitic basalts are thought to have formed as a result of melting of depleted mantle components in mantle-plume source regions Daoud et al. Palaeoproterozoic mafic dikes and metabasalts compositionally similar to continental MORB-type tholeiites have also been described from Precambrian terranes. These include the c. The main goals of this study are to estimate the distribution of Palaeoproterozoic continental MORB-type tholeiites in the Karelian Craton, to evaluate lateral variations in their geochemical and isotope characteristics, and to compare these with well-studied modern analogues to place some additional constraints on the tectonic evolution of the Karelian Craton in the Palaeoproterozoic.
Volcano-sedimentary sequences of c. The loss on ignition LOI values were determined gravimetrically. Powdered samples were digested in an acid mixture following standard procedures described by Karandashev et al. The accuracy for most trace elements was c. Zircon grains selected for this study were washed in ethanol, acetone, and 1 M HNO 3. Before decomposition, the zircons were spiked with a mixed Pb— U spike.
Digestion of the zircons and U and Pb extractions were performed following a modified technique after Krogh The isotopic analyses were performed using a Triton TI multicollector TIMS system and either Faraday 125 ??????????. Dating st. gallen yb in static mode or an electron multiplier in peak-jumping mode. The zircons were mounted in epoxy along with zircon standards Wiedenbeck et al.
The inner structure of the zircons was examined using optical microscopy and cathodoluminescence. Regions devoid of visible cracks and inclusions in euhedral crystals were chosen for analysis. A mixed Sm— Nd spike was added to the sample 125 ??????????. Dating st. gallen yb digestion. The bulk REE fraction was first extracted and purified using standard cation exchange chromatography and then the Sm and Nd fractions were separated and further purified using HDEHP resin.
The accuracy and precision of the Nd isotope compositions were 125 ??????????. Dating st. gallen yb by replicate analyses of an in-house Nd standard. At the Max-Planck-Institute for Chemistry in Mainz, the analytical techniques used closely followed those described by Puchtel et al.
The Karelian Craton is a large segment of Archaean continental crust in the southeastern Fennoscandian Shield, bounded by the Svecofennian and Lapland—Kola Paleoproterozoic orogens Fig. The craton comprises Paleo- Meso- and Neoarchean terranes. The initial development of rift-related volcano-sedimentary belts with komatiitic, basaltic, and felsic volcanic rocks at c.
It is generally assumed that mantle melting was associated with the ascent of a mantle plume that affected an extensive area in the Fennoscandian and Canadian Shields Puchtel et al.
This period is characterized by several 125 ??????????. Dating st. gallen yb of mafic magmatism that include rare c. It is generally assumed that the c. The magmatic activity at c. Widespread and extremely Romantic pics from russian dating site Formula Recipe Management, plume-related mafic complexes that include picrites, high- and low-Ti tholeiites, subalkaline basalts, carbonatites, and kimberlites Puchtel et al.
This event is usually considered as unrelated to the c. Intraplate magmatic activity in the Palaeoproterozoic was followed by continental breakup in the eastern part of the Fennoscandian Shield and the opening of the Lapland—Kola and Svecofennian oceanic basins Fig.
Collapse of the Svecofennian and Lapland—Kola orogens at the end of the Late Palaeoproterozoic resulted in transtension in the Karelian Craton, sedimentation, emplacement of mafic sills at c. Cpx, clinopyroxene; Pl, plagioclase; Amph, amphibole; Ilm, ilmenite; Ol, olivine. In the northern and central parts of the Karelian Craton, dikes are well preserved and metamorphic overprinting is limited and localized in narrow zones Fig. The inner structure of the dikes is usually simple. Chilled margin Face-to-Face-Dating in Bonn per Video erklart consist of Ol-free, fine-grained Cpx—Pl dolerite.
Central parts consist of Ol-bearing fine- to coarse-grained gabbro. Almost all dikes contain gabbro—pegmatite schlieren. Hornblende, intermediate composition plagioclase and quartz are the main minerals of the late material that either fills interstices between earlier minerals or occurs as small up to 1—2 cm across segregations that probably crystallized from trapped residual melt.
Accessory zircon, baddeleyite, and apatite crystallized simultaneously with the late liquidus phases and are often included in interstitial magmatic amphibole. The compositions of the plagioclase, pyroxene, olivine, and hornblende are reported in Supplementary Data. In the Kianta terrane, dikes were studied from three localities Fig. In the northeastern part of the Kianta terrane, they form a narrow NNE—SSW-oriented swarm, which was sampled in the northern Allajarvi locality and southern parts Pirtguba locality.
The Pirtguba locality is situated near the Upper Kuito Lake in the eastern part of the Kianta terrane. Here, the tholeiitic dikes are hosted by c. The quenched contacts consist of fine-grained, aphyric or slightly porphyritic dolerite that contains rare euhedral plagioclase An 83—60 phenocrysts. The fine-grained groundmass consists of plagioclase laths An 73—54subhedral 125 ??????????.
Dating st. gallen yb both augite and low-Ca pyroxene and magnetite grains. The central part of the dike is composed of medium-grained, olivine-bearing, massive dolerite and contains rare gabbro—pegmatite schlieren, up to 50 cm in width.
In the central part of the dike, hornblende is an essential part of the late magmatic assemblage. The Allajarvi locality is situated in the northeastern part of the Kianta terrane. The quenched contacts of the dike are extensively amphibolitized and are composed of fine-grained metadolerite.
The central part of the dike is well preserved, and consists of medium-grained, massive, olivine-bearing dolerite with gabbro—pegmatite schlieren of up to 10 cm in width. The Kostomuksha locality is situated in the southern part of the Kostomuksha greenstone belt. Samples of a dolerite dike were collected from the core of an exploration borehole drilled through mafic metavolcanic rocks.
The quenched contacts of the dike consist of massive, porphyritic microdolerite Fig. The phenocrysts usually show normal magmatic zoning Klagenfurt Gay Men, Klagenfurt Gay Dating, Klagenfurt Gay Personals, Klagenfurt Gay Chat. Away from the contact, the microdolerite is replaced by Cpx—Pl-porphyritic dolerite. The contact between the Pl-porphyritic and Cpx—Pl-porphyritic dolerite is sharp Fig.
The presence of Pl laths in the early Cpx grains in the chilled margin zone of the dike indicates that Pl was one of early crystallizing phases. Large Cpx crystals in the quenched rocks also contain inclusions of irregular morphology composed of iddingsite, which probably replaced early formed olivine. Pyroxene in this dike can be subdivided into two groups: The Hatunoiya locality is situated in the southern part of the Jalonvaara—Ilomantsi greenstone belt in the southern part of the Central Karelian terrane.
Metavolcanic rocks within the greenstone belt are cut by late tectonic, c. Two generations of cross-cutting mafic dikes with different orientations were studied in the Hatunoiya locality. The younger high-Ti tholeiitic dike is possibly related to the c. The older dikes have a MORB-type chemical affinity. The contacts of the dikes commonly display apophyses 125 ??????????. Dating st. gallen yb different thickness forming a complex network in the host rocks.
The largest dike contains small gabbro—pegmatite schlieren. The dolerites have been 125 ??????????. Dating st. gallen yb altered; pyroxenes are amphibolitized and plagioclase and ilmenite are replaced 125 ??????????. Dating st. gallen yb saussurite and leucoxene, respectively. An interesting feature of the Hatunoiya locality dikes is the Online dating partnersuche online dating compatibility test of up to three inner chilled contacts in the margins of thick dikes and apophyses.
Chilled rocks preserve relics of porphyritic textures, amphibolitized Cpx, and plagioclase phenocrysts. The central parts of the dikes are composed of medium- and coarse-grained gabbros with rare gabbro—pegmatite schlieren.
The Central locality is situated 125 ??????????. Dating st. gallen yb the Hautovaara greenstone belt in the southwestern part of the Vodlozero terrane. These dikes are intensively amphibolitized, but preserve massive structures and relicts of gabbroic textures and fine-grained quenched marginal zones.
The dolerites are cut by quartz veins 125 ??????????. Dating st. gallen yb are metasomatically altered along their contacts. The chilled zones are composed of intensively amphibolitized, fine-grained metadolerite, whereas the central parts consist of medium-grained metadolerite. In these rocks, pyroxene is completely replaced by amphibole, but relicts of plagioclase are preserved. In each locality, the dikes selected for this study were systematically sampled.
Samples were collected from quenched contact zones, fine- to coarse-grained central parts, and from gabbro—pegmatite schlieren, where present. Concentrations of major elements and lithophile trace elements are presented in Table 1.
Other unaltered dikes appear to preserve their primary LILE concentrations; however, for the sake of consistency, these elements are not discussed further. LOI, 125 ??????????. Dating st. gallen yb on ignition. Zr is obtained by XRF. Primitive mantle-normalized abundances of selected trace and rare earth elements in MORB-type tholeiitic dikes from the Karelian Craton.
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