Progressive Melting of a Metasedimentary Sequence: the Saint-Malo Migmatitic Complex, France

2015 ◽  
pp. 261-275
Author(s):  
Vojtěch Janoušek ◽  
Jean-François Moyen ◽  
Hervé Martin ◽  
Vojtěch Erban ◽  
Colin Farrow
Keyword(s):  
Metasedimentary Sequence

Pressure-temperature-fluid constraints for the Emmaville-Torrington emerald deposit, New South Wales, Australia: Fluid inclusion and stable isotope studies

2012 ◽  
Vol 4 (2) ◽  
Author(s):  
Lara Loughrey ◽  
Dan Marshall ◽  
Peter Jones ◽  
Paul Millsteed ◽  
Arthur Main
Keyword(s):  
Fluid Inclusion ◽  
New South ◽  
Two Phase ◽  
Quartz Veins ◽  
South Wales ◽  
Three Phase ◽  
Liquid Portion ◽  
Isotope Studies ◽  
Two Fluid ◽  
Metasedimentary Sequence

AbstractThe Emmaville-Torrington emeralds were first discovered in 1890 in quartz veins hosted within a Permian metasedimentary sequence, consisting of meta-siltstones, slates and quartzites intruded by pegmatite and aplite veins from the Moule Granite. The emerald deposit genesis is consistent with a typical granite-related emerald vein system. Emeralds from these veins display colour zonation alternating between emerald and clear beryl. Two fluid inclusion types are identified: three-phase (brine+vapour+halite) and two-phase (vapour+liquid) fluid inclusions. Fluid inclusion studies indicate the emeralds were precipitated from saline fluids ranging from approximately 33 mass percent NaCl equivalent. Formational pressures and temperatures of 350 to 400 °C and approximately 150 to 250 bars were derived from fluid inclusion and petrographic studies that also indicate emerald and beryl precipitation respectively from the liquid and vapour portions of a two-phase (boiling) system. The distinct colour zonations observed in the emerald from these deposits is the first recorded emerald locality which shows evidence of colour variation as a function of boiling. The primary three-phase and primary two-phase FITs are consistent with alternating chromium-rich ‘striped’ colour banding. Alternating emerald zones with colourless beryl are due to chromium and vanadium partitioning in the liquid portion of the boiling system. The chemical variations observed at Emmaville-Torrington are similar to other colour zoned emeralds from other localities worldwide likely precipitated from a boiling system as well.

Thematic interpretation of heliborne magnetic data for delineation of concealed regional structural fabric in the Narnaul-Palsana tract, North Delhi Fold Belt, India

2018 ◽  
Vol 6 (2) ◽  
pp. T367-T375
Author(s):  
Amit Kumar Pathak ◽  
G. V. Giridhar ◽  
Anand Kumar Chaturvedi
Keyword(s):  
Soil Cover ◽  
Magnetic Data ◽  
Fold Belt ◽  
Magnetic Minerals ◽  
Polyphase Deformation ◽  
The North ◽  
Magnetic Signature ◽  
Structural Fabric ◽  
Tectonic Sequence ◽  
Metasedimentary Sequence

The North Delhi Fold Belt (NDFB) exposure of the Delhi Supergroup of rocks is significant for its structurally controlled uranium mineralization. The Narnaul-Palsana tract within the Khetri subbasin of the NDFB comprises the arenaceous Alwar and argillaceous Ajabgarh Groups of the Delhi Supergroup. The metasedimentary sequence has been subjected to polyphase deformation and igneous intrusion. We used heliborne magnetic data to enhance our geologic understanding of the area. Total magnetic intensity data are gridded and enhanced to resolve the magnetic anomalies. The regional magnetic signature reveals a deep-seated fracture. Varying concentrations of magnetic minerals in different lithologies are reflected in the magnetic response and provide clues to the formational trends. Trend lines and breaks are extracted from the magnetic signature. Thematic analysis of trend lines reveals formational trends that indicate an antiformal and synformal fold pattern in different sectors of the study area. The spatial correlation of the fold patterns is used to decipher the tectonic sequence. Superimposition of antiformal folding over earlier antiform-synform structure and displacement due to later faulting is inferred. Magnetic data analysis is used as a tool to unravel the regional structural fabric of the area that is widely concealed below soil cover.

scholarly journals Caledonian and pre-Caledonian geology of the region between Grandjean Fjord and Bessel Fjord (75°–76°N), North-East Greenland

1989 ◽  
Vol 145 ◽  
pp. 90-97
Author(s):  
N Henriksen ◽  
J.D Friderichsen ◽  
R.A Strachan ◽  
N.J Soper ◽  
A.K Higgins
Keyword(s):  
Amphibolite Facies ◽  
Sedimentary Sequence ◽  
East Greenland ◽  
Early Proterozoic ◽  
Late Proterozoic ◽  
North East ◽  
The North ◽  
Group A ◽  
Metasedimentary Sequence

The area between Grandjean Fjord and Bessel Fjord was the focus in 1988 of regional geological investigations and 1:500000 mapping during the North-East Greenland project (Henriksen, 1989). The greater part of the area forms part of the East Greenland Caledonides and can be divided into three distinct rock groups: infracrustal gneisses and granites of possibie Archaean or early Proterozoic origin; a metasedimentary sequence which has probably suffered both mid-Proterozoic and Caledonian migmatisation and metamorphism; and the late Proterozoic Eleonore Bay Group, a thick sedimentary sequence which has undergone amphibolite facies Caledonian metamorphism in its lower parts and is intruded by Caledonian granites. Aspects of the stratigraphy and sedimentology of the Eleonore Bay Group are described by Sønderholm et al. (1989); only the structures affecting the sequence are described here.

Natural‐field and very low‐frequency tipper profile interpretation of contacts

Geophysics ◽  
1987 ◽  
Vol 52 (12) ◽  
pp. 1697-1707 ◽  
Author(s):  
Victor F. Labson ◽  
Alex Becker
Keyword(s):  
Numerical Models ◽  
Low Frequency ◽  
Washington State ◽  
Trial And Error ◽  
North Central ◽  
Natural Field ◽  
Very Low Frequency ◽  
Basement Faults ◽  
Vertical Contact ◽  
Metasedimentary Sequence

Anomalous vertical magnetic field (tipper) profiles acquired using natural or very low‐frequency (VLF) radio transmitter sources can be interpreted simply and rapidly for a number of geologic settings. The relations between computed numerical models, and outcropping dipping and buried vertical contacts are presented here in a series of interpretation charts. Use of the tipper phase in the analysis minimizes the effect of transmitter azimuth in the VLF case. Two examples illustrate the application to field data. An audiofrequency natural‐field tipper profile over a conductive bed in a north‐central Washington State metasedimentary sequence demonstrates the interpretation procedure for a dipping contact. VLF profiles over covered basement faults in Ontario demonstrate the application for a buried vertical contact. In both cases the quick results are in agreement with the much more laborious trial‐and‐error matching to two‐dimensional models.

scholarly journals Metamorfismo de alto gradiente P/T en la Sierra de Pie de Palo (Sierras Pampeanas, Argentina): modelado de equilibrio de fases minerales e implicancias geodinámicas en el antearco famatiniano

2019 ◽  
Vol 46 (3) ◽  
pp. 526
Author(s):  
Carlos Dino Ramacciotti ◽  
César Casquet ◽  
Edgardo Gaspar Baldo ◽  
Sebastián Osvaldo Verdecchia ◽  
Matías Martín Morales ◽  
...  
Keyword(s):  
Continental Margin ◽  
Active Continental Margin ◽  
Progressive Decrease ◽  
The West ◽  
Sierras Pampeanas ◽  
Magmatic Arc ◽  
Age Related ◽  
Grenvillian Orogeny ◽  
Western Side ◽  
Metasedimentary Sequence

The Sierra de Pie de Palo (SPP, Western Sierras Pampeanas) shows evidence of two regional metamorphisms: one Mesoproterozoic attributed to the Grenvillian orogeny and other of Ordovician age related to the Famatinian orogeny. The Neoproterozoic-to-Cambrian sedimentary successions that cover the Grenvillian basement only record the Ordovician event. One staurolite-schist from the Ediacaran Difunta Correa Metasedimentary Sequence collected in the southeastern side of the SPP allows to constrain, by means of pseudosections, a prograde evolution from ca. 3 kbar and 515 ºC up to ca. 9 kbar and 640 ºC corresponding to a high P/T gradient. The SPP and the immediately east Loma de Las Chacras outcrop were part of the famatinian forearc which shows a progressive decrease of P (from ca. 13 kbar to 6 kbar), T (from ca. 900 ºC to 450 ºC), and P/T gradient (from ca. 85 ºC/kbar to 35 ºC/kbar) towards the active continental margin on the west. The Caucete Group, in the western side of the SPP, represents the westernmost part of the forearc, near to the active continental margin. Metamorphism was apparently coeval with the Famatinian magmatism and with ductile underthrusting at ca. 470-465 Ma, which led to burial of the forearc beneath the magmatic arc.

scholarly journals The migmatites, granites and metasediments of Danmark Ø and adjacent areas of Milne Land and Gåse1and, East Greenland Caledonian fold belt

1979 ◽  
Vol 84 ◽  
pp. 1-36
Author(s):  
K Bucher-Nurminen
Keyword(s):  
Large Scale ◽  
Quartz Diorite ◽  
Granitic Rocks ◽  
Small Scale ◽  
Fold Belt ◽  
Thrust Sheet ◽  
East Greenland ◽  
Mineral Assemblages ◽  
Caledonian Orogeny ◽  
Metasedimentary Sequence

The mapped area (Danmark Ø, part of south-east Milne Land and eastern Gåseland) consists mainly of migmatites and granitic rocks forming part of a migmatitic zone within the East Greenland CaIedonian fold belt. The area ean be divided into various granitic and syenitic rocks, strongly migmatized paragneisses, a metasedimentary sequence, garnetiferous augen granite sheets, and a thrust sheet of hornblende quartz diorite. Some rock units may have been formed in Precambrian time, and others during the Caledonian orogeny. Large scale E-W trending folds occur in eastern Gåseland and small scale folds throughout the area. Mineral assemblages suggest several metamorphic events. No indications of economic mineralization were found.

Emplacement and differentiation of an Archean subvolcanic metapyroxenite–metagabbro sill in the Favourable Lake area, northwestern Ontario

1982 ◽  
Vol 19 (4) ◽  
pp. 837-858 ◽  
Author(s):  
M. Raudsepp ◽  
L. D. Ayres
Keyword(s):  
Titanium Oxide ◽  
Country Rock ◽  
Tholeiitic Basalt ◽  
Lake Area ◽  
Initial Composition ◽  
Northwestern Ontario ◽  
Volcanic Processes ◽  
Facies Metamorphism ◽  
Metasedimentary Sequence

A sequence of five fractionated, subvolcanic, pyroxenite–gabbro sills of tholeiitic basalt initial composition was intruded into the Archean Favourable Lake metavolcanic–metasedimentary sequence. Individual sills are up to 2.7 km long, range in thickness from 17 to 240 m, and are confined to a relatively thin lacustrine metachert and fine clastic unit. The sills were emplaced sequentially upward into water-rich, unlithified country rocks, with succeeding sills being emplaced prior to final consolidation of underlying sills. Sills are either in contact or separated by thin country-rock septa, but later sills did not intrude earlier sills.Greenschist facies metamorphism and pre-metamorphism alteration have destroyed primary mineralogy and have modified chemical variations, but primary textures are well preserved by pseudomorphs. Each sill comprises a lower ultramafic zone of clinopyroxene–olivine and clinopyroxene–orthopyroxene cumulates and an upper mafic zone of clinopyroxene–plagioclase – iron–titanium oxide and plagioclase – iron–titanium oxide cumulates. The upper part of the mafic zone is largely cumulus plagioclase that either accumulated in situ or floated upwards. The lower part of the ultramafic zone is relatively constant in composition and crystallization appears to have been largely in a closed system with only local magma flowage. In the mafic zone, crystallization was apparently in a more open system with surges of magma related to volcanic processes being derived either from elsewhere in the sills or externally. The most fractionated component is granophyric gabbro that is locally concentrated into large intrusive lenses.

Early recumbent folds in the northeastern part of the northern Labrador Trough

1978 ◽  
Vol 15 (2) ◽  
pp. 245-252 ◽  
Author(s):  
Andrew Hynes
Keyword(s):  
Northeastern Part ◽  
Gneiss Domes ◽  
Metasedimentary Sequence

In the northeastern part of the Labrador Trough northwest of Fort Chimo, Quebec, a polydeformed metasedimentary sequence structurally overlies feldspathic gneisses. The gneisses are probably basement to the sediments. Rocks of the metasedimentary sequence were deformed into north-northwest vergent, isoclinal, recumbent folds and then refolded about subhorizontal northwest trending axes during the Hudsonian orogeny. The presence of early recumbent folds, apparently not involving basement, is compatible with the occurrence of gneiss domes and tight keels of metasediments in the eastern trough, as described by Dimroth, Gelinas and others. Recumbent folds like these could in part account for both the high metamorphic grades observed in the eastern trough and the commonly faulted contacts between metasediments and possible basement gneisses.

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