High‐Grade K‐Feldspar Veining in Granulites From the Ivrea‐Verbano Zone, Northern Italy: Fluid Flow in the Lower Crust and Implications For Granulite Facies Genesis

1998 ◽  
Vol 106 (4) ◽  
pp. 455-472 ◽  
Author(s):  
Leander Franz ◽  
Daniel E. Harlov
Keyword(s):  
Fluid Flow ◽  
Lower Crust ◽  
Granulite Facies ◽  
Northern Italy ◽  
High Grade

Mylonitic mafic granulite in fault megabreccia at Clarke Head, Nova Scotia: a sample of Avalonian lower crust?

1995 ◽  
Vol 132 (1) ◽  
pp. 81-90 ◽  
Author(s):  
Wes Gibbons ◽  
J. Brendan Murphy
Keyword(s):  
Nova Scotia ◽  
Lower Crust ◽  
Mafic Magma ◽  
Granulite Facies ◽  
Fault System ◽  
High Grade ◽  
Deep Crust ◽  
Clay Matrix ◽  
Meguma Terrane ◽  
North And South

AbstractThe Clarke Head fault megabreccia was produced within a major Late Palaeozoic transcurrent structure (the Minas fault system) which separates the displaced Meguma terrane of southern Nova Scotia from rocks more typical of the Avalon Superterrane. A large clast of anomalously high grade metabasite embedded in the clay matrix of the fault megabreccia displays a fresh granulite facies mineralogy (2-pyroxene + garnet + plagioclase) and mylonitic to ultramylonitic textures induced by anhydrous shearing deep in the roots of the fault zone. Whole rock geochemistry reveals the granulite protolith to have been a continental, within-plate mafic magma transitional between theoleiitic and alkaline. The original geochemical signature has survived strong dynamic recrystallization at granulite grade. Well-preserved REE abundances testify to a lack of metasomatic fractionation during high grade shearing under water-absent conditions. Sm—Nd data indicate that the basic granulite has a TDM age of c. 1 Ga. Isotopic comparisons with adjacent areas reveal similar TDM ages both north and south of the Minas fault system. The high grade clast may be typical of the lower crust in Nova Scotia and is thought to offer a rare window into the deep crust of the Avalon Superterrane in North America.

scholarly journals Granulite-Facies Xenoliths in Rift Basalts of Northern Tanzania: Age, Composition and Origin of Archean Lower Crust

2014 ◽  
Vol 55 (7) ◽  
pp. 1243-1286 ◽  
Author(s):  
A. T. Mansur ◽  
S. Manya ◽  
S. Timpa ◽  
R. L. Rudnick
Keyword(s):  
Lower Crust ◽  
Granulite Facies ◽  
Age Composition ◽  
Northern Tanzania

Zircon ages and the distribution of Archaean and Proterozoic rocks in the Rauer Islands

1993 ◽  
Vol 5 (2) ◽  
pp. 193-206 ◽  
Author(s):  
P. D. Kinny ◽  
L. P. Black ◽  
J. W. Sheraton
Keyword(s):  
Granulite Facies ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
High Grade ◽  
Ion Microprobe ◽  
Rock Interaction ◽  
Mafic Rocks ◽  
Grade Fluid ◽  
Vestfold Hills ◽  
Intrusive Suite

The application of zircon U-Pb geochronology using the SHRIMP ion microprobe to the Precambrian high-grade metamorphic rocks of the Rauer Islands on the Prydz Bay coast of East Antarctica, has resulted in major revisions to the interpreted geological history. Large tracts of granitic orthogneisses, previously considered to be mostly Proterozoic in age, are shown here to be Archaean, with crystallization ages of 3270 Ma and 2800 Ma. These rocks and associated granulite-facies mafic rocks and paragneisses account for up to 50% of exposures in the Rauer Islands. Unlike the 2500 Ma rocks in the nearby Vestfold Hills which were cratonized soon after formation, the Rauer Islands rocks were reworked at about 1000 Ma under granulite to amphibolite facies conditions, and mixed with newly generated felsic crust. Dating of components of this felsic intrusive suite indicates that this Proterozoic reworking was accomplished in about 30–40 million years. Low-grade retrogression at 500 Ma was accompanied by brittle shearing, pegmatite injection, partial resetting of U-Pb geochronometers and growth of new zircons. Minor underformed lamprophyre dykes intruded Hop and nearby islands later in the Phanerozoic. Thus, the geology of the Rauer Islands reflects reworking and juxtaposition of unrelated rocks in a Proterozoic orogenic belt, and illustrates the important influence of relatively low-grade fluid-rock interaction on zircon U-Pb systematics in high-grade terranes.

The Pikwitonei Granulite Domain, Manitoba: a giant Neoarchean high-grade terrane in the northwest Superior ProvinceThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.N. Machado, T.E. Krogh, and W. Weber are deceased.

2011 ◽  
Vol 48 (2) ◽  
pp. 205-245 ◽  
Author(s):  
L. M. Heaman ◽  
Ch. O. Böhm ◽  
N. Machado ◽  
T. E. Krogh ◽  
W. Weber ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Superior Province ◽  
High Grade ◽  
Metamorphic Zircon ◽  
Special Issue ◽  
Metamorphic History ◽  
Zircon Growth ◽  
The World ◽  
Northwestern Margin ◽  
History Of

The Pikwitonei Granulite Domain located at the northwestern margin of the Superior Province is one of the largest Neoarchean high-grade terranes in the world, with well-preserved granulite metamorphic assemblages preserved in a variety of lithologies, including enderbite, opdalite, charnockite, and mafic granulite. U–Pb geochronology has been attempted to unravel the protolith ages and metamorphic history of numerous lithologies at three main localities; Natawahunan Lake, Sipiwesk Lake, and Cauchon Lake. The U–Pb age results indicate that some of the layered enderbite gneisses are Mesoarchean (3.4–3.0 Ga) and the more massive enderbites are Neoarchean. The high-grade metamorphic history of the Pikwitonei Granulite Domain is complex and multistage with at least four episodes of metamorphic zircon growth identified: (1) 2716.1 ± 3.8 Ma, (2) 2694.6 ± 0.6 Ma, (3) 2679.6 ± 0.9 Ma, and (4) 2642.5 ± 0.9 Ma. Metamorphic zircon growth during episodes 2 and 3 are interpreted to be regional in extent, corresponding to M1 amphibolite- and M2 granulite-facies events, respectively, consistent with previous field observations. The youngest metamorphic episode at 2642.5 Ma is only recognized at southern Cauchon Lake, where it coincides with granite melt production and possible development of a major northeast-trending deformation zone. The timing and multistage metamorphic history recorded in the Pikwitonei Granulite Domain is similar to most Superior Province high-grade terranes and marks a fundamental break in Archean crustal evolution worldwide at the termination of prolific global Neoarchean greenstone belt formation.

scholarly journals U-Pb geochronology of rutile: deciphering the cooling history of the Oaxacan Complex granulites, southern Mexico

2020 ◽  
Vol 37 (2) ◽  
pp. 135-145
Author(s):  
Miguel Gerardo Adame-Martínez ◽  
Luigi Augusto Solari ◽  
Carlos Ortega-Obregón ◽  
Fanis Abdullin
Keyword(s):  
Sudden Change ◽  
Granulite Facies ◽  
High Grade ◽  
Southern Mexico ◽  
Cooling Rates ◽  
Clastic Rocks ◽  
The North ◽  
Precise Calculation ◽  
Fast Cooling ◽  
North And South

Rutile (TiO2) is a heavy mineral, commonly found as accessory in many lithologies, such as basic igneous rocks, high-grade metamorphic units, as well as a detritus in sedimentary clastic rocks. Its chemical composition is sensitive to the crystallization environment, allowing a characterization of either metabasic or metasedimentary protoliths in metamorphic rocks. Thanks to the capability to accept U in its crystalline network, at least in metasedimentary, high-grade protoliths, rutile can be dated by U-Pb geochronology. Furthermore, its closure temperature of ca. 600 °C for the U-Pb system makes rutile a suitable chronometer, complementary to zircon, to unravel provenance and exhumation paths in both sedimentary siliciclastic cover and basement units. Besides, the Zr-in thermometer allows for a very precise calculation of the rutile crystallization temperature. In the example case presented here, focused on granulite facies units of the Grenvillian Oaxacan Complex (OC), rutile crystallisation took place in the range 808–873 °C. Data for different localities indicate that cooling and exhumation after the Zapotecan granulite facies event (ca. 990 Ma) was heterogeneous among the different tectonic slices that constitute the OC. Cooling occurred in the central sector (Nochixtlán-Oaxaca) right after the granulite peak, with fast cooling rates of ca. 40 °C/Ma. To the north and south, the cooling to ca. 600 °C was much slower, with calculated cooling rates of ca. 3 °C/Ma for the northern OC outcrops in Coatepec (Puebla) to ca. 6 °C/Ma south of Ejutla (Oaxaca). This can be related to a combination of factors, such as an early collapse of some sectors of the orogen, a change of conditions in the subducing plate, or more in general, to a sudden change in the geodynamic conditions during the Zapotecan orogeny and Amazonia-Baltica amalgamation. This application example to some metasedimentary lithologies belonging to the OC demonstrates how the exhumation after the Zapotecan granulite facies event (ca. 990 Ma) was heterogeneous among the different tectonic slices that compose the OC, having occurred in the central sector (Nochixtlán-Oaxaca) right after the granulite peak, with fast cooling rates of ca. 40 ºC/M.y., whereas to the North and South the cooling to ca. 600 ºC was much slower, with calculated cooling rates of ca. 3 ºC/M.y. (north, OC outcrops in Coatepec, Puebla) to ca. 5.5 ºC/M.y. south of Ejutla (Oaxaca). This can be related to a combination of factors, such as an early collapse of some sectors of the orogen, change of conditions in the subjecting plate, or more in general, to a sudden change in the geodynamic conditions during the early stages of the Rodinia amalgamation. This example sharply illustrates the advantage of employing microanalytical techniques, able to resolve restricted crystal-domain chemical variations, to obtain accurate and precise temperature and age values. Furthermore, it is paramount to combine several mineral species with different closure temperatures, and collected in well-defined, recognized tectonic slices, to understand their behavior and construct meaningful cooling curves through geologic time, capable to better characterize and interpret their tectonic evolution.

Granulite facies xenoliths from the Yuhuashan complex, central Jiangxi, South China: constraints on Late Palaeozoic orogeny and middle-lower crust components

2016 ◽  
Vol 34 (1) ◽  
pp. 45-61 ◽  
Author(s):  
C. Zhang ◽  
J. Yu ◽  
S. Y. O'Reilly ◽  
W. L. Griffin ◽  
J. Qian ◽  
...  
Keyword(s):  
South China ◽  
Lower Crust ◽  
Granulite Facies ◽  
Late Palaeozoic

Crustal xenoliths in Triassic lamprophyre dykes in western Morocco: tectonic implications for the Rheic Ocean suture

2005 ◽  
Vol 142 (2) ◽  
pp. 159-172 ◽  
Author(s):  
J. DOSTAL ◽  
J. D. KEPPIE ◽  
M. A. HAMILTON ◽  
E. M. AARAB ◽  
J. P. LEFORT ◽  
...  
Keyword(s):  
Granulite Facies ◽  
West African ◽  
Granitic Rocks ◽  
High Grade ◽  
The West ◽  
West African Craton ◽  
Rheic Ocean ◽  
Western Morocco ◽  
Meguma Terrane ◽  
Crustal Xenoliths

Dykes of calc-alkaline lamprophyre cutting granite of the Hercynian Jebilet Massif of the Moroccan Meseta (western Morocco) contain crustal xenoliths. The xenoliths range in composition from mafic (cognate cumulates) and upper crustal granitic rocks through gneisses to middle crustal felsic granulites. SHRIMP U–Th–Pb zircon analyses of these rocks indicate that the dykes were likely intruded during Middle Triassic times (∼235 Ma), whereas the xenoliths contain zircons with concordant Carboniferous–Early Permian, Neoproterozoic and Palaeoproterozoic ages (280–328 Ma, c. 540–615 Ma, 700 Ma and ∼2000 Ma). The 280–328 Ma ages appear to record synchronous intrusive and high-grade (up to granulite facies) Variscan metamorphic events, suggesting that high-grade metamorphism may have facilitated the S-type granitic magmatism. On the other hand, the ∼540–615 Ma, 700 Ma and 2000 Ma ages correspond with Pan-African and Eburnian orogenic events recorded in the West African Craton. In a Triassic reconstruction, Morocco is juxtaposed against Nova Scotia (Canada), and some have proposed that the basement of the easternmost terrane (Meguma terrane) is a piece of the West African craton. However, lower crustal xenoliths from Devonian dykes (∼370 Ma) cutting the Meguma terrane have yielded Late Devonian, Neo- and Mesoproterozoic ages (378 Ma, 575–629 Ma, ∼880–1050 Ma and ∼1530 Ma). The presence of ∼1 Ga ages suggests that the basement of the Meguma terrane is Avalonian rather than West African, implying that in a Pangean reconstruction, the Rheic Ocean suture between NW Africa and Maritime Canada coincides with the Atlantic Ocean.

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