A Discussion on global tectonics in Proterozoic times - Late Proterozoic cratonization in southwest Saudi Arabia

1976 ◽  
Vol 280 (1298) ◽  
pp. 517-527 ◽  
Keyword(s):  
Saudi Arabia ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Granulite Facies ◽  
Greenschist Facies ◽  
Arabian Shield ◽  
Granulite Facies Metamorphism ◽  
Quartz Monzonite ◽  
Facies Metamorphism ◽  
Global Tectonics

Early cratonal development of the Arabian Shield of southwestern Saudi Arabia began with the deposition of calcic to calc-alkalic, basaltic to dacitic volcanic rocks, and immature sedimentary rocks that subsequently were moderately deformed, metamorphosed, and intruded about 960 Ma ago by dioritic batholiths of mantle derivation (87Sr/86Sr = 0.7029). A thick sequence of calc-alkalic andesitic to rhyodacitic volcanic rocks and volcanoclastic wackes was deposited unconformably on this neocraton. Regional greenschistfacies metamorphism, intensive deformation along north-trending structures, and intrusion of mantle-derived (87Sr/86Sr = 0.7028) dioritic to granodioritic batholiths occurred about 800 Ma. Granodiorite was emplaced as injection gneiss about 785 Ma (87Sr/86Sr = 0.7028- 0.7035) in localized areas of gneiss doming and amphibolite to granulite facies metamorphism. Deposition of clastic and volcanic rocks overlapped in time and followed orogeny at 785 Ma. These deposits, together with the older rocks, were deformed, metamorphosed to greenschist facies, and intruded by calc-alkalic plutons (87Sr/86Sr = 0.7035) between 600 and 650 Ma. Late cratonal development between 570 and 550 Ma involved moderate pulses of volcanism, deformation, metamorphism to greenschist facies, and intrusion of quartz monzonite and granite. Cratonization appears to have evolved in an intraoceanic, island-arc environment of comagmatic volcanism and intrusion.

HRTEM Study of Zircon from Eliseev Anorthosite Complex, Antarctica

1996 ◽  
Vol 54 ◽  
pp. 668-669
Author(s):  
R. Wirth ◽  
H. Kämpf ◽  
A. Höhndorf
Keyword(s):  
Sedimentary Rocks ◽  
Age Determination ◽  
Radioactive Decay ◽  
Granulite Facies ◽  
Radioactive Isotopes ◽  
Accessory Mineral ◽  
Granulite Facies Metamorphism ◽  
Facies Metamorphism ◽  
Thorium Content ◽  
Anorthosite Complex

Zircon is a common accessory mineral in magmatic, metamorphic and sedimentary rocks. The crystal structure is tetragonal with space group I41/amd. Zircon contains minor amounts of U and Th and can be dated by a variety of techniques yielding ages of crystallization, cooling, and redistribution of radioactive isotopes and their daughter products. The precision of the radiogenic age determination strongly depends on the ability of zircon to retain the daughter products which were produced by the radiogenic decay of U and Th.Zircon-bearing rocks of this study are metamorphic oxide-apatite gabbronorites (OAGN) from the Eliseev Anorthosite Complex, Wohlthat-Massif, East Antarctica (Kampf et al., 1995). These unusual rocks are strongly enriched in accessory minerals (apatite: < 10 vol.%; zircon: < 1 vol.%, Owens & Dymek, 1992). Three steps in the evolution of these rocks are distinguished: a magmatic formation, followed by a granulite facies metamorphism and finally a tectonomagmatic overprint. The zircon crystals of this study are brown colored, up to 12 mm in length and up to 3 mm wide (Fig.1). Petrological investigations show that zircon has formed during the granulite facies event. Optical microscopy and cathodoluminiscence microscopy reveal a rhythmic zoning and many microcracks. The concentrations of uranium and thorium are low (U: 34-89 ppm and Th: 3-9 ppm). The radiation damage by radioactive decay of U and Th is expected to be minor due to the low uranium and thorium content.

A metamorphosed, layered alpine-type peridotite in the Langavat Valley, South Harris, Outer Hebrides

1976 ◽  
Vol 40 (313) ◽  
pp. 493-499 ◽  
Author(s):  
A. Livingstone
Keyword(s):  
Trace Element ◽  
Trace Element Content ◽  
Granulite Facies ◽  
Greenschist Facies ◽  
Trace Element Data ◽  
Granulite Facies Metamorphism ◽  
Facies Metamorphism ◽  
Outer Hebrides ◽  
Main Period ◽  
Mineral Analyses

SummaryA layered aipine-type peridotite, of pre-Scourian age(?), has been metamorphosed in the granulite facies then partially retrogressed to greenschist facies assemblages. Following granulite facies metamorphism of the dunite-harzburgite peridotite, granitization and metasomatism modified the peridotite by adding calcium and generated olivine-tremolite rocks. Anthophyllite-rich rocks developed from localized orthopyroxene-rich zones. The main epoch of serpentinization followed after tremolite formation and removed a portion of the calcium previously added, but with negligible effect upon the original trace-element content. Between tremolite generation and the main period of serpentinization greenschist facies assemblages formed. The layered rocks possess a repetitive, chemical variation normally attributable to basic igneous processes, although they may have formed either by vein metasomatism or by metasomatism of a disrupted layered igneous series. Twelve rock and five mineral analyses are presented, and trace element data for twenty-one rocks.

Uranium and thorium in the Precambrian basement of western Canada. II. Petrologic and tectonic controls

1979 ◽  
Vol 16 (3) ◽  
pp. 472-483 ◽  
Author(s):  
R. A. Burwash
Keyword(s):  
Granulite Facies ◽  
Western Canada ◽  
Precambrian Basement ◽  
Granulite Facies Metamorphism ◽  
Frequency Distributions ◽  
Peace River ◽  
Quartz Monzonite ◽  
Facies Metamorphism ◽  
Northeastern Alberta ◽  
Two Populations

Analyses of 182 basement cores, when plotted as log U and log Th, show bimodal frequency distributions. Cumulative frequency plots indicate an approximate 35–65% split between the two populations. Histograms of numbers of samples in various rock classes vs. log U fail to explain the bimodal distribution.A plot of log K vs. log U provides easy visual separation of rocks with varying K/U ratios and U contents. K/U values greater than 3 × 104 are ascribed principally to granulite facies metamorphism. K/U values less than 5 × 103 represent U-enrichment either in granitic melts or K-metasomatized gneisses. Factor analysis indicates a strong correlation between U, Th. Rb, Pb, and K.The geographic distribution of samples with K/U values greater than 3 × 104 can be related to relict Kenoran granulite facies terranes in the subsurface of northeastern Alberta and west central Saskatchewan similar to those mapped on the exposed Shield in northwestern Saskatchewan. These relict granulites could account for most of the samples in the smaller of the two sample populations.The U-enriched rocks are concentrated in three areas: (1) the epizonal, porphyritic granitic plutons of southwestern Saskatchewan, (2) linear quartz monzonite batholiths along the Kasba Lake – Edmonton gravity low, and (3) K-rich gneisses in the Peace River High of northwestern Alberta. In none of these areas is assimilation of large volumes of Aphebian sedimentary rocks indicated.

scholarly journals Supplemental Material: Building a continental arc section: Constraints from Paleozoic granulite-facies metamorphism, anatexis, and magmatism in the northern margin of the Qilian Block, northern Tibet Plateau

2021 ◽  
Author(s):  
Yinbiao Peng ◽  
Yu Shengyao ◽  
et al.
Keyword(s):  
Volcanic Rocks ◽  
Granulite Facies ◽  
Tibet Plateau ◽  
Granulite Facies Metamorphism ◽  
Northern Margin ◽  
Icp Ms ◽  
Continental Arc ◽  
Facies Metamorphism ◽  
Data Tables ◽  
Representative Samples

Tables S1–S4: Representative electron microprobe data; Tables S5–S16: Zircon U‐Th‐Pb LA‐ICP‐MS data for nine representative samples; Tables S17–S22: LA‐MC‐ICP‐MS Lu‐Hf isotope data for 6 representative samples; Table S23: Major and trace element compositions of plutons and volcanic rocks.

scholarly journals Supplemental Material: Building a continental arc section: Constraints from Paleozoic granulite-facies metamorphism, anatexis, and magmatism in the northern margin of the Qilian Block, northern Tibet Plateau

2021 ◽  
Author(s):  
Yinbiao Peng ◽  
Yu Shengyao ◽  
et al.
Keyword(s):  
Volcanic Rocks ◽  
Granulite Facies ◽  
Tibet Plateau ◽  
Granulite Facies Metamorphism ◽  
Northern Margin ◽  
Icp Ms ◽  
Continental Arc ◽  
Facies Metamorphism ◽  
Data Tables ◽  
Representative Samples

Tables S1–S4: Representative electron microprobe data; Tables S5–S16: Zircon U‐Th‐Pb LA‐ICP‐MS data for nine representative samples; Tables S17–S22: LA‐MC‐ICP‐MS Lu‐Hf isotope data for 6 representative samples; Table S23: Major and trace element compositions of plutons and volcanic rocks.

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