Zeolite to prehnite-pumpellyite facies metamorphism of the late Proterozoic Zig-Zag Dal Basalt Formation, eastern North Greenland
19
Citation
26
Reference
10
Related Paper
Citation Trend
An area to the south of Dalsfjord has been mapped and four lithological units
differentiated. These are (from the top downwards) the Vardheia unit,
consisting of heterogeneous paragneisses; the Flekke unit, consisting of
metabasic, ultrabasic and oxide-rich rocks, frequently with corona structures;
the Gjorlanger unit, consisting of dioritic to granodioritic orthogneisses
with common metabasic bodies and websterites, and the Basal Gneisses, with
pink granodioritic to monzonitic orthogneisses, paragneisses and pegmatites.
The latter is separated from the overlying unit by a zone of protomylonites.
Eclogites are found in all the units.
Gradational or intrusive relationships show that all the units are mutually
autochthonous. Many eclogites had demonstrable low-pressure igneous
protoliths and/or intrusive relationships with the gneisses, indicating a
crustal, eclogite-facies metamorphism of all the lithologies mapped. Relics
of early granulite-facies assemblages occur in most lithologies.
Bulk-rock geochemistry of Gjorlanger unit lithologies indicates calc-alkaline
affinities, resembling magmatic arc rocks but possibly modified during
granulite-facies metamorphism. Associated eclogites have been metasomatically
altered but retain some tholeiitic characteristics. Websterites are
tentatively related to the orthopyroxene eclogites of More and Romsdal. The
Flekke unit rocks have affinities with some layered basic intrusions typical
of mid-Proterozoic anorthosite suites.
Protolith
Lithology
Cite
Citations (7)
Abstract The Central Indian Tectonic Zone (CITZ) comprises northern and southern Indian cratonic blocks and is a tectonic window that is suitable for investigating the Proterozoic crustal evolution because of the presence of a wide variety of lithologies. Geochemical and geochronological data on mafic granulites by previous workers do not ascertain the possibility of mafic protoliths and their coeval link to other CITZ units. Thus, determining the precise timing of the formation of mafic granulites may indicate a connection between metamorphism and fragmentation of the Columbian supercontinent. This study presents zircon U–Pb ages, Nd isotopes and the geochemistry of mafic granulites to evaluate their genesis and timing of metamorphism. The results show the tholeiitic affinity and primary magmatic differentiation of the parental melt. Depletion of Nb, P, Zr and Ti and positive enrichment of Ba, U and Pb indicate the derivation of mafic granulites from a variably enriched subcontinental lithospheric mantle (SCLM) source. The zircon U–Pb ages (1564 ± 8 to 1598 ± 9 Ma) are interpreted as a period of granulite-facies metamorphism. The T DM (depleted-mantle) model ages (2.9–3.4 Ga) of mafic granulites indicate the timing of mafic protolith extraction. The mineral isochron age c. 1.0 Ga indicates that these rocks underwent some events during an early Neoproterozoic period. Protolith of mafic granulites could be related to the evolution of melts derived from metasomatized SCLM through fractional crystallization processes.
Protolith
Geochronology
Cite
Citations (1)
The occurrence,mineralogy and geochemistry of eclogites in the Mt.Dabie area show that they were subjected to a high-pressure metamorphism together with the country rocks,but their petrochemistry and REE geochemistry show some difference from those of the country rocks.The geochemical characteristics of the eclogites are similar to those of bot continental tholeiitic basalt and oceanic tholeiitic basalt.The rocks probably subducted to the upper mantle with the Dabie metamorphic complex.When elevated to the surface,they were subjected to different staes of retrogressive metamorphism.
Petrogenesis
Petrochemistry
Cite
Citations (0)
Sediments of Ouachita facies extend subsurface from the Ouachita Mountains of Oklahoma and Arkansas to the Marathon and Solitario uplifts of extreme southwest Texas. Although these sediments have been subjected to strong dynamic metamorphism, the metamorphic grade attained is uniformly low. Sediments of Ouachita facies are essentially unaltered in some areas; elsewhere they range in degree of metamorphism as high as the biotite zone. Mineralogical change and cataclastic effects are key criteria for discerning the stages of progressive metamorphism in sediments of Ouachita facies. Metamorphic changes are most easily observed in shales and argillaceous sandstones--limestones and cherts react less conspicuously to metamorphic stress. Mineralogical change resulting from metamorphism reduces the porosity and non-fracture permeability of sandstones to such an extent that they are not good petroleum reservoirs. The petrography of the so-called schists of Luling field, Caldwell County, Texas, and of some other deep wells along the Luling-Mexia-Talco fault system is discussed briefly. It is shown that they are generally comparable in mineralogy and degree of metamorphism with sediments exposed in the Ouachita Mountains of McCurtain County, Oklahoma. End_of_Article - Last_Page 2626------------
Cite
Citations (0)
Abstract Orthopyroxene-bearing felsic gneiss occurs as foliation-parallel layers and bands together with aluminous granulite, mafic granulite, and quartzofeldspathic granulite in the Chilka Lake migmatite complex of the Proterozoic Eastern Ghats Belt, India. The rock was classified previously as charnockite which underwent granulite-facies metamorphism. Field and textural features of this rock show evidence of the partial melting of a biotite-bearing greywacke protolith. Orthopyroxene with/without garnet and cordierite were produced with K-feldspar as peritectic phases of incongruent melting of presumed metaluminous sediments. Fluid-inclusion data suggest the presence of high-density CO 2 -rich fluids during peak metamorphism, which are similar to those found in associated aluminous granulite. Whole-rock major and trace element data show wide variability of the source materials whereas REE distributions show enriched LREE and flat HREE patterns. Zircon grains from representative samples show the presence of inherited cores having spot dates (SHRIMP) in the range c. 1790–3270 Ma. The overgrowth on zircon was formed predominantly during c. 780–730 Ma and sporadically during c. 550–520 Ma. Some neoblastic zircons with c. 780–730 Ma ages are also present. U-rich dark zones surrounding cores appear partially metamictised, but spot ages from this zone vary within c. 1000–900 Ma. The <1000 Ma ages represent metamorphism that mirrors the events in associated aluminous granulite. The sources of metaluminous sediments are speculative as the rock compositions are largely modified under granulite-facies metamorphism and partial melting. Considering the accretionary tectonic setting of the Eastern Ghats Belt during the c. 1000–900 Ma time frame, a greywacke-type protolith for the migmatite complex has been proposed.
Migmatite
Felsic
Protolith
Cite
Citations (9)
Migmatite
Basement
Muscovite
Cordierite
Cite
Citations (132)
The Split Lake Block forms a partly retrogressed, granulite-grade basement segment located at the northwestern margin of the Superior Province in Manitoba. Unlike other segments along the craton margin, the effects of Proterozoic tectonism are relatively minor in the Split Lake Block, making it amenable to establishing firm temporal constraints for the Archean magmatic and metamorphic history of the northwestern Superior Province margin. Consequently, samples from the main lithological units within the Split Lake Block were selected for precise single-grain U-Pb zircon geochronology. Heterogeneous zircon populations isolated from representative enderbite, tonalite, and granodiorite samples reveal a complex growth history with pre-2.8 Ga protolith ages (e.g., 2841 ± 2 Ma tonalite), possibly as old as 3.35 Ga as indicated in a granodiorite sample. The youngest Archean granitic magmatism identified in the eastern Split Lake Block is represented by the 2708 ± 3 Ma Gull Lake granite. A U-Pb zircon age of 2695 +4 -1 Ma obtained for leucosome in mafic granulite is interpreted to reflect the timing of granulite-grade metamorphism in the Split Lake Block, supported by polyphase zircon growth and (or) lead loss at ca. 2.7 Ga in the enderbite sample. A younger phase of metamorphic zircon growth at ca. 2.62 Ga is documented in the tonalite and granodiorite zircon populations. The 2.70-2.71 Ga crust formation, the occurrence of ca. 2695 Ma high-grade metamorphism, and broadly contemporaneous Paleoproterozoic mafic dykes in both the Split Lake Block and Pikwitonei Granulite Domain imply a common evolution of these high-grade terrains along the northwestern Superior craton margin since the late Archean.
Geochronology
Protolith
Basement
Cite
Citations (16)
Abstract The granulite‐facies rocks in the Tomkinson Ranges of central Australia are dominated by layered felsic (quartzofeldspathic) gneisses with minor interbanded mafic, calcareous, ferruginous, and quartzitic granulites. They are regarded as representing a middle Proterozoic metasedimentary and/or metavolcanic sequence which has undergone anhydrous granulite‐facies metamorphism approximately 1200 m.y. ago. Conditions of metamorphism have been derived from a petrogenetic grid based on several experimentally determined reactions and give estimates of 10–11 kb pressure and 950–1000°C. Such metamorphism could take place close to the base of the crust with a moderate geothermal gradient of 25–30°C/km.
Felsic
Cite
Citations (18)
The occurrence, mineralogy and geochemistry of eclogites in the Mt. Dabie area show that they were subjected to a high-pressure metamorphism to- gether with the country rocks, but their petrochemistry and REE geochemistry show some difference from those of the country rocks. The geochemical charac- teristics of the eclogites are similar to those of both continental tholeiitic basalt and oceanic tholeiitic basalt. The rocks probably subducted to the upper mantle with the Dabie metamorphic complex. When elevated to the surface, they were subjected to different stages of retrogressive metamorphism.
Petrogenesis
Petrochemistry
Cite
Citations (0)