Coronitic metagabbro and eclogite from the Grenville Province of western Quebec: interpretation of U–Pb geochronology and metamorphism

1997 ◽  
Vol 34 (7) ◽  
pp. 891-901 ◽  
Author(s):  
Aphrodite Indares ◽  
Greg Dunning
Keyword(s):  
High Pressure ◽  
Mineral Chemistry ◽  
Metamorphic Grade ◽  
Structural Level ◽  
Structural Units ◽  
Grenville Province ◽  
Mafic Rocks ◽  
High Pressure Metamorphism ◽  
Accreted Terranes ◽  
Laurentian Margin

We present new U–Pb and metamorphic data on high-pressure coronitic metagabbros from three distinct structural settings in the Parautochthonous Belt of the Grenville Province in western Quebec. Intrusive ages are (i) [Formula: see text], for metagabbro close to the Grenville Front, correlative with the Sudbury dykes, defined in Ontario; (ii) [Formula: see text] for an eclogitized lens at the base of the highest structural level (SL4), a new age for mafic magmatism in the western Grenville; and (iii) [Formula: see text] for metagabbro from SL4, interpreted as correlative with metagabbros from the Algonquin and Shawanaga domains in Ontario. Metamorphism in all cases is Grenvillian, with the best constrained age of 1069 ± 3 Ma for the metagabbro of SL4. Metamorphic grade increases from the Grenville Front to the south. The mafic rocks preserve relict igneous textures overprinted by garnet + clinopyroxene that developed as coronas and (or) pseudomorphs after igneous phases. The highest grade metagabbros contain omphacite and some lack primary plagioclase, therefore being eclogites. However, interpretation of textures and mineral chemistry indicates that they were equilibrated during decompression (at 1350 MPa and 720 °C, sample 51; and at 1200 MPa and 740 °C, sample 29), so maximum depths of burial remain unconstrained. Their evolution is interpreted as follows: (i) high-pressure metamorphism by burial of the Laurentian margin under accreted terranes thrust toward the northwest between 1080 and 1060 Ma; (ii) residence at intermediate crustal levels, for a few tens of millions of years; and (iii) rapid exhumation by renewed thrusting that led to the emplacement of the high-pressure units over the northerly adjacent structural units of the Parautochthonous Belt.

Mafic and ultrapotassic rocks from the Canyon domain (central Grenville Province): geochemistry and tectonic implications

2012 ◽  
Vol 49 (2) ◽  
pp. 412-433 ◽  
Author(s):  
Carolina Valverde Cardenas ◽  
Aphrodite Indares ◽  
George Jenner
Keyword(s):  
Tectonic Setting ◽  
Source Region ◽  
Crustal Contamination ◽  
Granulite Facies ◽  
Grenville Province ◽  
Mafic Rocks ◽  
Isotopic Signatures ◽  
Late Evolution ◽  
Grenvillian Orogeny ◽  
Laurentian Margin

The Canyon domain and the Banded complex in the Manicouagan area of the Grenville Province preserve a record of magmatic activity from ∼1.4 to 1 Ga. This study focuses on 1.4–1.2 Ga mafic rocks and 1 Ga ultrapotassic dykes. Geochemistry and Sm–Nd isotopic signatures were used to constrain the origin of these rocks and evaluate the changing role of the mantle with time and tectonic setting from the late evolution of the Laurentian margin to the Grenvillian orogeny, in the Manicouagan area. The mafic rocks include layers inferred to represent flows, homogeneous bodies in mafic migmatite, and deformed dykes, all of which were recrystallized under granulite-facies conditions during the Grenvillian orogeny. In spite of the complexities inherent in these deformed and metamorphosed mafic rocks, we were able to recognize suites with distinctive geochemical and isotopic signatures. Integration of this data along with available ages is consistent with a 1.4 Ga continental arc cut by 1.2 Ga non-arc basalts derived from depleted asthenospheric mantle, with varied degrees of crustal contamination and inferred to represent magmatism in an extensional environment. The 1 Ga ultrapotassic dykes postdate the Grenvillian metamorphism. They are extremely enriched in incompatible elements, have negative Nb anomalies, relatively unradiogenic Sr-isotopic compositions (initial 87Sr/86Sr ~ 0.7040) and εNd –3 to –15. Some dykes have compositional characteristics consistent with derivation from the mantle, ruling out crustal contamination as a major process in their petrogenesis. The most likely source region for the ultrapotassic dykes is a metasomatized subcontinental lithospheric mantle, with thermal input from the asthenosphere in association with post-orogenic delamination.

The High Pressure belt in the Grenville Province: architecture, timing, and exhumation

2002 ◽  
Vol 39 (5) ◽  
pp. 867-893 ◽  
Author(s):  
Toby Rivers ◽  
John Ketchum ◽  
Aphrodite Indares ◽  
Andrew Hynes
Keyword(s):  
High Pressure ◽  
Seismic Reflection ◽  
Extensional Flow ◽  
Upper Crust ◽  
Grenville Province ◽  
Extensional Faulting ◽  
Laurentian Margin ◽  
Two Stages ◽  
Tectonic Extrusion ◽  
Lower Crustal

We propose that the Grenvillian allochthonous terranes may be grouped into High Pressure (HP) and Low Pressure (LP) belts and examine the HP belt in detail in the western and central Grenville Province. The HP belt is developed in Paleo- and Mesoproterozoic rocks of the pre-Grenvillian Laurentian margin and characterized by Grenvillian eclogite and co-facial HP granulite in mafic rocks. Pressure–temperature (P–T) estimates for eclogite-facies conditions in well-preserved assemblages are about 1800 MPa and 850°C. In the central Grenville Province, HP rocks formed at ~1060–1040 Ma and underwent a single stage of unroofing with transport into the upper crust by ~1020 Ma, whereas farther west they underwent two stages of unroofing separated by penetrative mid-crustal recrystallization before transport to the upper crust at ~1020 Ma. Unroofing processes were comparable in the two areas, involving both thrusting and extensional faulting in an orogen propagating into its foreland by understacking. In detail, thrusting episodes preceded extension in the western Grenville Province, whereas in the central Grenville Province, they were coeval, resulting in unroofing by tectonic extrusion. In the central Grenville Province, the footwall ramp is well preserved, but any former ramp in the western Grenville Province was obliterated by later lower crustal extensional flow. Continuation of the HP belt into the eastern Grenville Province is not established, but likely on geological grounds. However, the pattern of deep crustal seismic reflection in the Lithoprobe Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT) line contrasts with that father west, suggesting that, if present, the HP rocks were exhumed by a different mechanism.

Eclogitized gabbros from the eastern Grenville Province: textures, metamorphic context, and implications

1993 ◽  
Vol 30 (1) ◽  
pp. 159-173 ◽  
Author(s):  
Aphrodite Indares
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Grenville Province ◽  
Mafic Rocks ◽  
Deep Burial ◽  
Mineral Assemblages ◽  
First Occurrence ◽  
Intrusive Suite ◽  
Very High

Undeformed lenses of olivine–orthopyroxene–gabbro belonging to the 1429 Ma Shabogamo Intrusive Suite (Parautochthonous Belt of the eastern Grenville Province) host the first occurrence of eclogite mineral assemblages reported from the Grenville Province. These rocks preserve igneous textures overprinted by eclogite mineralogy and by textures related to subsequent unloading. High-pressure signatures include omphacite pseudomorphs after augite, plagioclase replacement by garnet + kyanite + corundum, and orthopyroxene–omphacite–garnet coronas between olivine and plagioclase. Transformations related to decompression include replacement of garnet + kyanite + corundum by spinel + plagioclase, growth of plagioclase collars between clinopyroxene and garnet, and de-jadeitization of omphacite. Clinopyroxenes with numerous plagioclase inclusions and garnets surrounded by clinopyroxene–plagioclase symplectites in granoblastic mafic rocks from the same area are also evidence of decompression from high pressures. These rocks record pressure–temperature (P–T) conditions of 1600 MPa at 700–800 °C and steep subsequent P–T paths. It is suggested that the entire parautochthon in this part of the Grenville Province experienced deep burial during the Grenvillian metamorphism. In contrast, the Grenvillian metamorphic signature in the overlying allochthonous sheet is known to be minor, thus precluding any relationship between its emplacement and very high Grenvillian pressures in the parautochthon.

Mineral chemistry, geothermobarometry and pre-Alpine high-pressure metamorphism of eclogitic amphibolites and mica schists from the Schobergruppe, Austroalpine basement, Eastern Alps

1993 ◽  
Vol 57 (387) ◽  
pp. 189-202 ◽  
Author(s):  
Bernhard Schulz
Keyword(s):  
High Pressure ◽  
Mineral Chemistry ◽  
Eastern Alps ◽  
Upper Ordovician ◽  
Progressive Deformation ◽  
Tauern Window ◽  
High Pressure Metamorphism ◽  
Facies Metamorphism ◽  
Austroalpine Basement ◽  
T Path

AbstractAlternating eclogitic amphibolites, mica schists and orthogneisses in the Schobergruppe to the south of the Tauern Window suffered a post-Upper-Ordovician progressive deformation D1-D2which produced parallel planar-linear structures in all the rocks. Zoned garnets, preferentially oriented zoned clinopyroxenes (Jd 35-42%) and albite (An 7-9%) give evidence of high-pressure metamorphism (550-650°C 14-16 kbar) of the metabasites. Ca-amphiboles crystallized during subsequent decompression. In a kyanite-staurolite-garnet mica schist 300 metres below the metabasites, garnetbearing assemblages grew synchronous with the development of foliations S1and S2. Garnets are zoned with increasing XMgand decreasing-increasing-rcdecreasing Xcafrom cores to rims. Albitic plagioclase (An 1-3%) and micas are enclosed in garnet cores and rims, are in contact with garnet, and occur with garnet in microlithons. When these minerals are used for geothermobarometry, a prograde P-T evolution (460 to 680°C with coeval pressure variations which reach high-pressure conditions can be estimated. This suggests that garnet-plagioclase geobarometry with albitic plagioclase works in the relevant P-T field. Similar garnet zonation trends and a similarly shaped P-T path from mica schists of an adjacent region with late-Variscan cooling ages, points to an eady-Variscan age of the syn-D1-D2high-pressure and subsequent amphibolite-facies metamorphism.

The occurrence and timing of high-pressure metamorphism on Margarita Island, Venezuela: a constraint on Caribbean-South America interaction

2009 ◽  
Vol 328 (1) ◽  
pp. 705-741 ◽  
Author(s):  
Walter V. Maresch ◽  
Rolf Kluge ◽  
Albrecht Baumann ◽  
James L. Pindell ◽  
Gabriela Krückhans-Lueder ◽  
...  
Keyword(s):  
High Pressure ◽  
South America ◽  
High Pressure Metamorphism
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