Allanite Crystals Research Articles

Petrogenesis and significance of late Caledonian granitoid magmatism in western Norway

Obduction of the late Ordovician Solund-Stavfjord Ophiolite Complex (443±3 Ma), west Norwegian Caledonides, involved generation and high-level emplacement of granitic and granodioritic dikes and plutons. Initial 87Sr/86Sr ratios in the granites are low (0.7042–0.7059), suggesting either a mantle component or a Rb-poor crustal source. Initial eNd (eNd(t)) ranges from-0.8 to-8.8, indicating that the granites represent recycling of old crustal rocks, which is supported by Precambrian inheritance in zircons from two of the studied granites. I argue that the Rb-Sr and the Sm-Nd isotope systems are decoupled in the sense that the Sr-and the Nd-isotopes derive their dominant signals from two different sources, a mantle source and a crustal source respectively. The granites are metaluminous to peraluminous and typically have high Sr, Ba and Na2O/K2O ratios. SiO2 contents range from 66 to 74 wt%. REE abundances are highly variable; the La contents range from ∼80 to ∼200 times chondrite, and are inversely correlated with the contents of SiO2. The concentration of Nd in the granites decreases asymptotically with decreasing eNd(t) suggesting fractional crystallization of accessory phases and assimilation of continental crust. This argument is supported by the presence of partly dismembered xenoliths in the granites with eNd(t)-values that are significantly lower than eNd(t)-values in the host granite. The following models are suggested for the granites. When the ophiolite complex obducted, an outboard subduction zone approached the continental margin, and subduction-related magmas accumulated beneath the continental margin, and probably intruded the overlying eugeosynclinal deposits. The mantle-derived magmas most likely evolved to granitoid composition by assimilation of these eugeosynclinal sediments and by fractional crystallization of amphibole, feldspar, sphene, and allanite. Alternatively, but less likely, the heat content of the mantle-derived magmas caused extensive melting of immature graywackes and calc-alkaline volcaniclastic rocks in the deepest portions of the eugeosyncline. Either way, during ascent, the compositions of the granitic melts were modified by fractional crystallization of LREE-rich phases and by assimilation of continental metasediments.

Primary allanite in andesitic rocks from the Poros Volcano, Greece

AbstractPrimary allanite crystals occurring in andesitic rocks from Poros, NE Peloponnese, Greece were studied. Although the allanite shows high REE content, its presence does not affect the whole-rock REE content of the andesite. It is suggested that the formation of allanite crystals reflects the crystallization history of the andesitic rocks where allanite occurs. These andesitic rocks are the most basic rocks in which allanite has been reported.

Light-rare-earth-element zoning in sphene and allanite during granitoid fractionation

Research Article| March 01, 1984 Light-rare-earth-element zoning in sphene and allanite during granitoid fractionation Wayne N. Sawka; Wayne N. Sawka 1Department of Geology, Australian National University, Canberra, ACT 2600, Australia Search for other works by this author on: GSW Google Scholar Bruce W. Chappell; Bruce W. Chappell 1Department of Geology, Australian National University, Canberra, ACT 2600, Australia Search for other works by this author on: GSW Google Scholar Keith Norrish Keith Norrish 2CSIRO Division of Soils, Adelaide, South Australia Search for other works by this author on: GSW Google Scholar Geology (1984) 12 (3): 131–134. https://doi.org/10.1130/0091-7613(1984)12<131:LZISAA>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Wayne N. Sawka, Bruce W. Chappell, Keith Norrish; Light-rare-earth-element zoning in sphene and allanite during granitoid fractionation. Geology 1984;; 12 (3): 131–134. doi: https://doi.org/10.1130/0091-7613(1984)12<131:LZISAA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Sphene and allanite rare-earth-element (REE) and whole-rock light-REE concentrations have been found to increase during granitoid fractionation. The REE concentrations in both sphene and allanite crystals are zoned, with relative depletion occurring at the crystal rims. The REE concentration variability and zoning in these minerals can be explained by changes in the melt structure that occur during differentiation and final solidification of the granitoid. Our data suggest that crystal-melt separation controls light-REE enrichment or depletion in granitoids and that the end result depends on liquidus, accessory, and/or restite phases present during the crystal-melt separation. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Boulder Creek Batholith, Colorado Part I: Allanite and its Bearing upon Age Patterns

Allanite is abundant and commonly attains unusually large size as a late-replacement mineral in: (1) the comagnatic rocks of the Precambrian Boulder Creek batholith; (2) associated amphibolite xenoliths and related hybrid rocks; and (3) distinctly younger intrusions of Silver Plume Granite that cut the complex. Allanite porphyroblasts develop by replacement of biotite, probably in the presence of emanations from the rare earth-rich and thorium-rich Silver Plume Granite. The largest allanite crystals are made up of nearly isotropic (metamict) cores and birefringent (recrystallized) rims. Smaller crystals are made up exclusively of birefringent material. The maximum birefringence is shown to be that expectable in allanite of Late Cretaceous to early Tertiary age. As plotted on maps, the birefringence increases, and the thorium and uranium contents of the allanite decrease toward a Laramide stock. The variation in birefringence is, therefore, largely relatable to variations in the post-Laramide radiation dosage brought about by differences in the amounts of uranium and thorium lost during recrystallization. The recrystallized allanite is itself partly replaced by epidote which characteristically occurs as a border between allanite and biotite. Total rare-earth oxides for the eight samples of allanite analyzed range from 17.5 to 21.3 percent by weight. In 13 samples, thorium ranged from 0.50 to 1.14 percent by weight, and uranium from 54 to 158 parts pparts per million. Ranges in optical measurements for 20 samples using the spindle stage are: Nα = 1.719–1.759, Nβ = 1.731-1.774, N γ = 1.741–1.784, birefringence = 0.020–0.032, 2V X (calc.) 70 ° –84 ° . Ranges for unit-cell data obtained on 8 samples are: a = 8.948–8.985A, b = 5.721-5.763A, c = 10.184–10.240A, β = 115°7.50′–115°25.89′ and volume = 473.02–478.43A 3 . The average value for the ratio a:b:c = 1.561:1:1.778.

On allanite crystals from Franklin Furnace, NJ

On allanite crystals from Franklin Furnace, NJ