scholarly journals Late Miocene magmatic activity in the Attic-Cycladic Belt of the Aegean (Lavrion, SE Attica, Greece): implications for the geodynamic evolution and timing of ore deposition

2009 ◽  
Vol 146 (5) ◽  
pp. 732-742 ◽  
Author(s):  
ANTHI LIATI ◽  
NIKOS SKARPELIS ◽  
GEORGIA PE-PIPER
Keyword(s):  
Late Miocene ◽  
Hanging Wall ◽  
Granulite Facies ◽  
Detachment Fault ◽  
Time Range ◽  
Crystallization Time ◽  
Ion Microprobe ◽  
Granulite Facies Metamorphism ◽  
Zircon Crystallization ◽  
Facies Metamorphism

AbstractNumerous post-metamorphic Miocene granitoids occur in the area of Lavrion, SE Attica, at the western end of the Attic-Cycladic Belt of the Aegean. U–Pb ion microprobe-dating (SHRIMP) of zircon from a granitoid sill in the hanging-wall of a regional detachment fault reveals two distinct ages: (1) 11.93 ± 0.41 Ma, obtained from inherited zircon cores with metamorphic characteristics (homogeneous cathodoluminescence, low Th/U ratios) and granulite-type (round/resorbed) morphology. This age is interpreted as the time of a likely granulite-facies metamorphism of the precursor rock. (2) 8.34 ± 0.20 Ma, obtained by oscillatory zoned zircon domains with cathodoluminescence and Th/U characteristics typical for magmatic origin. This age is interpreted as the crystallization time of the granitoid sills. Although a granulite-facies metamorphic event has not been recognized so far for rocks of the Attic-Cycladic Belt, it seems to be the most plausible hypothesis to explain both the zircon systematics and age results. This hypothesis is consistent with an extensional regime predominating in the Aegean from Late Miocene times onwards. A possible granulite-facies metamorphism can be related to magmatic underplating at the initial stages of extension, setting an upper age of c. 12 Ma for the operation of the detachment fault. The 8.34 ± 0.20 Ma zircon crystallization age is, statistically, marginally different to a previous K–Ar feldspar date of hornblende-bearing dykes (9.4 ± 0.3 Ma) and identical to a 8.27 ± 0.11 Ma K–Ar biotite date of the main granitoid stock in the area, thus being generally consistent with prior age constraints from the region. Operation of the detachment fault in the Lavrion area is therefore bracketed between c. 11.9 Ma and at least 8.3 Ma. This time range is in line with the time of operation of detachment faults suggested previously for the Cycladic islands. Carbonate-hosted replacement-type massive sulphide Pb–Zn–Ag ores are spatially associated with the detachment fault and related extensional structures in the Basal Unit. Therefore, these Pb–Zn–Ag ores probably also formed within the above time span of c. 11.9 to at least 8.3 Ma. U–Pb ion microprobe (SHRIMP) dating of zircon from an orthogneiss within the metaclastic subunit of the Basal Unit in Lavrion yielded a protolith age of 240 ±4 Ma, consistent with ages of Triassic volcanism elsewhere in Greece.

Geology and U–Pb geochronology of the Neoarchean Snare River terrane: tracking evolving tectonic regimes and crustal growth mechanisms

2005 ◽  
Vol 42 (6) ◽  
pp. 895-934 ◽  
Author(s):  
Venessa Bennett ◽  
Valerie A Jackson ◽  
Toby Rivers ◽  
Carolyn Relf ◽  
Pat Horan ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Detrital Zircon ◽  
Inductively Coupled Plasma ◽  
Granulite Facies ◽  
Crustal Thickening ◽  
Ionization Mass ◽  
Granulite Facies Metamorphism ◽  
Zircon Crystallization ◽  
Facies Metamorphism ◽  
Turbidite Sedimentation

U–Pb zircon crystallization ages determined by isotope dilution – thermal ionization mass spectrometry (ID–TIMS) and laser ablation microprobe – inductively coupled plasma – mass spectrometry (LAM–ICP–MS) for 13 intrusive units in the Neoarchean Snare River terrane (SRT) provide tight constraints on the timing of crust formation and orogenic evolution. Seven metaluminous plutons were emplaced over ~80 Ma from ca. 2674 to 2589 Ma, whereas six peraluminous bodies were emplaced in a ~15 Ma interval from ca. 2598 to 2585 Ma. A detrital zircon study yielded an age spectrum with peaks correlative with known magmatic events in the Slave Province, with the ca. 2635 Ma age of the youngest detrital zircon population providing a maximum estimate for the onset of sedimentation. This age contrasts with evidence for pre-2635 Ma sedimentation elsewhere in the SRT, indicating that sedimentation was protracted and diachronous. Evolution of the SRT can be subdivided into four stages: (i) 2674–2635 Ma — formation of a metaluminous protoarc in a tonalite–trondhjemite–granodiorite (TTG) – granite–greenstone tectonic regime (TR1) and coeval with early turbidite sedimentation; (ii) 2635–2608 Ma — continued turbidite sedimentation, D1/M1 juxtaposition of turbidites and protoarc lithologies prior to ~2608 Ma, and metaluminous granitoid plutonism; (iii) 2608–2597 Ma — onset of TR2, collision of Snare protoarc with Central Slave Basement Complex, D2/M2 crustal thickening and mid-crustal granulite-facies metamorphism, sychronous with metaluminous and peraluminous plutonism; and (iv) 2597–2586 Ma — orogenic collapse, D3/M3 mid-crustal uplift, granulite-facies metamorphism, and waning metaluminous and peraluminous plutonism. The distribution of igneous rocks yields an "orogenic stratigraphy" with an older upper crust underlain by a younger synorogenic mid-crust. These data can be used to provide constraints for the interpretation of the Slave – Northern Cordillera Lithospheric Evolution (SNORCLE) Lithoprobe transect.

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.

scholarly journals Mapping in the Fiskefjord area, southern West Greenland

1982 ◽  
Vol 110 ◽  
pp. 55-57
Author(s):  
A.A Garde ◽  
V.R McGregor
Keyword(s):  
Granulite Facies ◽  
Amphibolite Facies ◽  
Isotopic Age ◽  
Supracrustal Rock ◽  
Granulite Facies Metamorphism ◽  
West Greenland ◽  
Facies Metamorphism ◽  
Geological Work ◽  
Age Determinations

Previous geological work on the 1:100000 map sheet 64 V.l N (fig. 15) includes published maps of smaller areas by Berthelsen (1960, 1962) and Lauerma (1964), mapping by Kryolitselskabet Øresund A/S (Bridgwater et al., 1976) and mapping by GGU geologists for the 1:500000 map sheet Frederikshåb Isblink - Søndre Strømfjord (Allaart et al., 1977, 1978). The Amltsoq and Niik gneisses and Malene supracrustal rock units south and east of Godthåbsfjord have not so far been correlated with rocks in the Fiskefjord area. Godthåbsfjord separates the granulite facies gneisses in Nordlandet from amphibolite facies Nûk gneisses on Sadelø and Bjørneøen; the granulite facies metamorphism occurred at about 2850 m.y. (Black et al., 1973), while no published isotopic age determinations from the Fiskefjord area itself are available.

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