Development of inverted metamorphic gradient in the internal domain of the Taconian belt, Gaspé Peninsula

G. Camiré

doi:10.1139/e95-005

Development of inverted metamorphic gradient in the internal domain of the Taconian belt, Gaspé Peninsula

Canadian Journal of Earth Sciences ◽

10.1139/e95-005 ◽

1995 ◽

Vol 32 (1) ◽

pp. 37-51 ◽

Cited By ~ 9

Author(s):

G. Camiré

Keyword(s):

Dissipative Heating ◽

Thrust Fault ◽

Passive Margin ◽

Prograde Metamorphism ◽

Metavolcanic Rocks ◽

Mineral Assemblages ◽

Gaspe Peninsula ◽

Metamorphic Gradient ◽

Internal Domain ◽

Deformational Event

The Mont Logan Nappe is part of the Taconian internal domain of the Quebec Appalachians, and is entirely made up of synrift to passive margin elastics and volcanics of the Shickshock Group. Rocks of the Mont Logan Nappe were affected by both Taconian and Acadian deformations but regional prograde metamorphism is Taconian and limited to the D1 deformational event. Thermobarometry and mineral assemblages indicate that the metasedimentary and metavolcanic rocks of the Mont Logan Nappe have recorded peak temperatures in the range 610–700 °C under pressures of approximately 600–700 MPa, and that prograde metamorphism was accompanied by the development of an inverted metamorphic gradient of −40 to −75 °C/km. The preferred interpretation of the cause of the inverted gradient is dissipative heating accompanying deformation along an intracontinental synmetamorphic thrust fault located at the top of the inverted metamorphic sequence.

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Zircon ages of the metavolcanic rocks and metagranites of the Ollo de Sapo Domain in central Spain: implications for the Neoproterozoic to Early Palaeozoic evolution of Iberia

Geological Magazine ◽

10.1017/s0016756807003858 ◽

2007 ◽

Vol 144 (6) ◽

pp. 963-976 ◽

Cited By ~ 68

Author(s):

P. Montero ◽

F. Bea ◽

F. González-Lodeiro ◽

C. Talavera ◽

M. J. Whitehouse

Keyword(s):

Passive Margin ◽

Variscan Orogeny ◽

Compositional Variation ◽

The West ◽

Middle Ordovician ◽

Pan African ◽

Metavolcanic Rocks ◽

High Fraction ◽

Early Palaeozoic ◽

High Level

AbstractDating the pre-Middle Ordovician metavolcanic rocks and metagranites of the Ollo de Sapo Domain has, historically, been difficult because of the small compositional variation, the effects of the Variscan orogeny and, as revealed in this paper, the unusually high fraction of inherited zircon components. The first reliable zircon data (U–Pb ion microprobe and Pb–Pb stepwise evaporation) indicate that the Ollo de Sapo volcanism spanned 495±5 Ma to 483±3 Ma, and was followed by the intrusion of high-level granites from 483±3 Ma to 474±4 Ma. In both metavolcanic rocks and metagranites, no less than 70–80% of zircon grains are either totally Precambrian or contain a Precambrian core overgrown by a Cambro-Ordovician rim. About 80–90% of inherited zircons are Early Ediacaran (602–614 Ma) and derived from calc-alkaline intermediate to felsic igneous rocks generated at the end of the Pan-African arc–continent collision. In the Villadepera region, located to the west, both the metagranites and metavolcanic rocks also contain Meso-Archaean zircons (3.0–3.2 Ga) which ultimately originated from the West African Craton. In the Hiendelaencina region, located to the east, both the metagranites and metavolcanic rocks lack Meso-Archaean zircons, but they have two different inherited zircon populations, one Cryogenian (650–700 Ma) and the other Tonian (850–900 Ma), which suggest older-than-Ediacaran additional island-arc components. The different proportion of source components and the marked variation of the 87Sr/86Srinit. suggest, at least tentatively, that the across-arc polarity of the remnants of the Pan-African arc of Iberia trended east–west (with respect to the current coordinates) during Cambro-Ordovician times, and that the passive margin was situated to the west.

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Deciphering the structural and metamorphic history of the Balsfjord Series in the Upper Allochthon of the Scandinavian Caledonides in northern Norway

10.5194/egusphere-egu21-7179 ◽

2021 ◽

Author(s):

Stephan Höpfl ◽

Jiří Konopásek ◽

Holger Stünitz ◽

Steffen G. Bergh

Keyword(s):

The Arctic ◽

Low Grade ◽

Prograde Metamorphism ◽

Northern Norway ◽

Metamorphic History ◽

Scandinavian Caledonides ◽

Nappe Complex ◽

History Of ◽

Peak Metamorphism ◽

Metamorphic Gradient

Deciphering the structural and metamorphic history of the Balsfjord Series in the Upper Allochthon of the Scandinavian Caledonides in northern NorwayH&#246;pfl Stephan1, Konop&#225;sek Ji&#345;&#237;1, St&#252;nitz Holger1,2 Bergh G., Steffen1UiT Norges arktiske universitet, Institutt for geovitenskap, [email protected]&#160;1Department of Geosciences, UiT The Arctic University of Norway, Troms&#248; 9037, Norway2Institut des Sciences de la Terre (ISTO), Universit&#233; d&#8217;Orleans, Orleans 45100, France&#160;The Balsfjord Series is located in the central part of Troms&#8211;Finnmark County, northern Norway, and is part of the upper allochthon of the Scandinavian Caledonides. It consists of an Ordovician&#8211;Silurian metsedimentary sequence lying on top of the mostly gabbroic Lyngen Magmatic Complex (LMC). The unit exhibits an inverted metamorphic gradient, where the metamorphic conditions increase from the base to the top, from very low grade in the southeast to medium grade in the west and northwest. The Balsfjord Series is sandwiched between two high-grade units, the Nakkedal + Troms&#248; Nappe Complex in the hanging wall and the Nordmannvik Nappe as the top part of the Reisa Nappe Complex (RNC) in the footwall. The Nakkedal + Troms&#248; Nappe Complex features metamorphic peak ages of ca. 455&#8211;450 Ma and the Nordmannvik Nappe of ca. 430 Ma. The peak metamorphism of the Balsfjord Series has never been dated and the role of the inverted metamorphic gradient is not yet understood. One of the main motivations in this project is to resolve the Caledonian deformation history in the Balsfjord Series, ideally leading to a regional tectonic model explaining the tectonostratigraphic and metamorphic relationships between the abovementioned units.The Balsfjord Series features two main discernible folding phases. The earlier phase displays tight to isoclinal folds with flat lying axial surfaces parallel to the penetrative foliation. Observed fold axes are parallel with the stretching lineation. These folds are best preserved in the northwestern, upper part of the unit and are syn-metamorphic in certain areas, as they fold original bedding (transposed foliation). A later folding phase is represented by mainly open folds with inclined to steep axial surfaces. Their fold axes are gently plunging with a predominant NE&#8211;SW orientation. We interpret these two folding events to be genetically related but slightly diachronous. The earlier folding phase with flat lying axial surfaces was likely generated during nappe thrusting and peak metamorphism of the Balsfjord Series. The subsequent open folding with inclined to steep axial surfaces is explained as a result of continued shearing and shortening of the weaker metapelitic Balsfjord Series against the more rigid gabbroic part of the LMC during the late stages of the Caledonian nappe thrusting.&#160;&#160;&#160;&#160;&#160;&#160;Observed thrust kinematics and penetrative retrogression at the bottom of the Nakkedal + Troms&#248; Nappe Complex suggest that its final exhumation took place during prograde metamorphism of the underlying Balsfjord Series. The ongoing dating of the prograde metamorphism in the Balsfjord series will provide important information about a possible continuity between the timing of peak metamorphism in the Nakkedal + Troms&#248; Nappe Complex, the Balsfjord series and the underlying RNC.

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The Tremolite Isograd near Marble Lake, Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e73-082 ◽

1973 ◽

Vol 10 (6) ◽

pp. 936-947 ◽

Cited By ~ 16

Author(s):

Ian Hutcheon ◽

J. M. Moore

Keyword(s):

Vapor Phase ◽

Experimental Work ◽

Lake Ontario ◽

Amphibolite Facies ◽

High Angle ◽

Grenville Province ◽

Metavolcanic Rocks ◽

Mineral Assemblages ◽

Total P

Marble, metavolcanic rocks, and pelite are found in a northeasterly trending belt near Marble Lake, in the Grenville Province, Ontario. The rocks have been metamorphosed to the lower amphibolite facies in the southwest, the grade increasing to the mid-amphibolite facies towards the northeast. Northwest-trending isograds in the metavolcanic rocks are at a high angle to the northeast-trending tremolite isograd in the marbles. Mineral assemblages indicate total pressures between 4 and 5 kbar and temperatures ranging from approximately 350 °C to over 600 °C. Temperatures estimated by calcite–dolomite solvus geothermometry and applied to experimental work in the system CaO–MgO–SiO2–CO2–H2O indicate: (i) P(total) = P(CO2) + P(H2O) was greater than 3 kbars; (ii) temperatures on the tremolite isograd were from approximately 450 to 550 °C and indicate that the tremolite isograd is not isothermal; (iii) the composition of the vapor phase present during metamorphism was approximately X(CO2) = 0.7 – 0.8; (iv) temperatures in the belt were from less than 400 °C in the southwest to more than 600 °C in the northeast.

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Proterozoic metamorphism in the Grenville Province: a study in the Double Mer – Lake Melville area, eastern Labrador

Canadian Journal of Earth Sciences ◽

10.1139/e88-178 ◽

1988 ◽

Vol 25 (11) ◽

pp. 1895-1905 ◽

Cited By ~ 12

Author(s):

C. F. Gower ◽

P. Erdmer

Keyword(s):

Granulite Facies ◽

High Grade ◽

Structural Configuration ◽

Geochronological Data ◽

Granitic Gneiss ◽

Grenville Province ◽

Accessory Minerals ◽

Mineral Assemblages ◽

Host Rocks ◽

Metamorphic Gradient

A regional metamorphic gradient from upper greenschist to granulite facies is identified south of the Grenville front in the Double Mer – Lake Melville area of eastern Labrador. Mineral assemblages in politic–granitic gneiss, amphibole-bearing quartzo-feldspathic gneiss, and coronitic metagabbro allow three major metamorphic domains to be established. These are collectively divisible into 11 subdomains. Geothermobarometry applied to the higher grade domains suggests that each is characterized by specific P–T conditions, which achieved 1000–1100 MPa and 700–800 °C in the deepest level rocks.The problem of reconciling geochronological data (which record a major orogenic event at 1650 Ma) with the occurrence of high-grade mineral assemblages in 1426 Ma metagabbro (which suggests a pervasive Grenvillian event) is discussed in terms of three models. The preferred model envisages crustal stabilization at 1650–1600 Ma to give high-grade mineral assemblages seen in the host rocks and with which mineral assemblages in coronitic metagabbro equilibrated after their emplacement at 1426 Ma. During Grenvillian orogenesis (1080–920 Ma) the present structural configuration was achieved by thrust stacking. This imparted a sporadic metamorphic and structural overprint and Grenvillian ages in selected accessory minerals.

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Structural evolution and tectonic setting of the Porongos belt, southern Brazil

Geological Magazine ◽

10.1017/s0016756805001433 ◽

2006 ◽

Vol 143 (1) ◽

pp. 59-88 ◽

Cited By ~ 28

Author(s):

K. SAALMANN ◽

M. V. D. REMUS ◽

L. A. HARTMANN

Keyword(s):

Continental Crust ◽

Tectonic Setting ◽

Structural Evolution ◽

Sedimentary Basins ◽

Passive Margin ◽

Ductile Deformation ◽

Geochemical Data ◽

Northwestern Part ◽

Metavolcanic Rocks ◽

Significant Contamination

The SW–NE-striking Porongos belt, located between juvenile Neoproterozoic rocks in the west and the Dom Feliciano belt, characterized by intense reworking of older crust, in the east, comprises a greenschist to amphibolite-facies metavolcano-metasedimentary succession (Porongos sequence) of unknown age with some exposures of Palaeoproterozoic gneisses (Encantadas gneisses). High-temperature ductile deformation of the basement gneisses comprises at least two magmatic events followed by three deformational phases including folding and shearing (DT1–DT3) and can be attributed to the Palaeoproterozoic Trans-Amazonian orogeny. The deformation of the Porongos sequence occurred during the Neoproterozoic Brasiliano orogeny and comprises four ductile deformation phases (DB1–DB4), including two phases of isoclinal folding associated with shearing recorded in mylonitic layers, followed by closed NW-vergent folding and thrusting leading to formation of a thrust stack. Uplift of the basement and formation of late tectonic sedimentary basins occurred as a result of semi-ductile to brittle block faulting in a sinistral strike-slip regime. The Porongos sequence can be subdivided into a southeastern and a northwestern part. Trace element analyses as well as Sm–Nd and Rb–Sr geochemical data indicate partial melting and significant contamination by old continental crust for the metavolcanic rocks. The metavolcanic rocks show εNd(t=780 Ma) values of −20.64 and −21.72 (northwestern units) and −6.87 (southeastern sequence). The metasedimentary rocks were derived from late Palaeoproterozoic to Archaean sources, and the data indicate different sources for the northwestern and southeastern rock units of the Porongos sequence. εNd(t=780 Ma) are −6.25 and −6.85 in the southeastern units, with TDM model ages between 1734 and 1954 Ma, and vary between −14.72 and −17.96 in the northwestern parts, which have TDM model ages between 2346 and 2710 Ma. High 87Sr/86Sr(t) values between 0.7064 and 0.7286 confirm reworking of older crust. Isotopic signatures of the Porongos sequence do not show indications for a significant contribution from a Neoproterozoic juvenile source. A passive margin or continental rift environment is suggested for the tectonic setting of the Porongos belt, which is compatible with both deposition of shallow marine to deep marine sediments and stretching of continental crust leading to volcanism which is characterized by significant contamination by old continental crust.

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Petrology of Metavolcanic Rocks in the Bishop Corners – Donaldson Area, Grenville Province, Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e73-061 ◽

1973 ◽

Vol 10 (5) ◽

pp. 589-614 ◽

Cited By ~ 17

Author(s):

K. Sethuraman ◽

John M. Moore Jr.

Keyword(s):

Alkali Basalt ◽

Bulk Composition ◽

Metamorphic Grade ◽

Chemical Analyses ◽

Grenville Province ◽

Clastic Rocks ◽

Carbonate Sedimentation ◽

Metavolcanic Rocks ◽

Apparent Thickness ◽

Mineral Assemblages

A calc-alkalic suite, with an apparent thickness of 7 km, varies from alkali basalt and tholeiite composition in the lowest part exposed, through andesite flows and pyroclastic rocks, to rhyodacite pyroclastics at the top. Sixty-two chemical analyses demonstrate a single volcanic cycle. Volcanism was succeeded by carbonate sedimentation and intrusion of granodiorite plutons. After deposition of clastic rocks, the entire succession was deformed and metamorphosed in the amphibolite facies.Isograds divide the metavolcanic rocks into five mineral zones: chlorite, biotite, blue-green hornblende, green hornblende, and diopside. Equivalent zones in the pelites are: chloritoid–staurolite, kyanite–staurolite, and sillimanite–muscovite.Fe in epidote, Ca in plagioclase, K and Na in hornblende, and ferric/ferrous ratio in rocks, biotite, and hornblende all increase in mafic and intermediate rocks, with increasing metamorphic grade. In biotite and hornblende, octahedral Al decreases with grade, whereas other chemical variables are related to bulk composition. Mineral assemblages and hornblende compositions indicate metamorphic conditions between Abukuma and classical Barrovian facies series.

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