Age and composition of the Ruisseau Isabelle Mélange along the Shickshock Sud fault zone: constraints on the timing of mélanges formation in the Gaspé Appalachians

2001 ◽  
Vol 38 (1) ◽  
pp. 21-42 ◽  
Author(s):  
Michel Malo ◽  
Pierre A Cousineau ◽  
Paul E Sacks ◽  
J FV Riva ◽  
Esther Asselin ◽  
...  
Keyword(s):  
Black Shale ◽  
Sedimentary Rock ◽  
Rock Type ◽  
Accretionary Prism ◽  
Structural Features ◽  
Late Ordovician ◽  
Ultramafic Rocks ◽  
Serpentinized Peridotite ◽  
Tectonic Position ◽  
Tectonic Origin

Mélanges are common in the Humber and Dunnage zones of the Quebec Appalachians. Humber Zone mélanges are spatially associated with Taconian nappes and believed to be of tectonic origin. Dunnage Zone mélanges are interpreted as relicts of an Ordovician accretionary prism. The Ruisseau Isabelle Mélange (RIM) in the Gaspé Appalachians was first interpreted as a Dunnage Zone mélange, because of its tectonic position along the Baie Verte – Brompton Line and lithological components, such as dark mudstone, blocks of ultramafic rocks, and greenish chromite-bearing sandstone. The RIM comprises sedimentary rock assemblages (Composite Shale, Black Shale, and Chromite-Bearing Sandstone assemblages), an Exotic Block, a Pebbly Mudstone Assemblage and slivers of Serpentinized Peridotite, and Metamorphic Tectonite. Most mélanges of the Dunnage Zone in the Quebec Appalachians contain partly similar rocks, but their age is not well constrained. Recent work on the RIM and Cap-Chat Mélange of the Humber Zone and new fossil finds in the RIM rock assemblages allow us to conclude that previous distinction between mélanges of the Dunnage and Humber zones on the basis of rock-type associations is not valid. According to the age of the RIM rock assemblages, mélanges in the northern Gaspé Appalachians continued forming after the mid-Caradocian, later than the Dunnage Zone mélanges of southern Gaspé Appalachians. The juxtaposition and structural features of the RIM rock assemblages result from repeated faulting along the Shickshock Sud fault from Late Ordovician to Middle Devonian.

scholarly journals Gravity Analysis for Subsurface Characterization and Depth Estimation of Muda River Basin, Kedah, Peninsular Malaysia

2021 ◽  
Vol 11 (14) ◽  
pp. 6363
Author(s):  
Muhammad Noor Amin Zakariah ◽  
Norsyafina Roslan ◽  
Norasiah Sulaiman ◽  
Sean Cheong Heng Lee ◽  
Umar Hamzah ◽  
...  
Keyword(s):  
River Basin ◽  
Rock Type ◽  
Gravity Data ◽  
Power Spectral Analysis ◽  
Depth Estimation ◽  
Structural Features ◽  
Peninsular Malaysia ◽  
Gravity Survey ◽  
Basement Rock ◽  
Geophysical Techniques

Gravity survey is one of the passive geophysical techniques commonly used to delineate geological formations, especially in determining basement rock and the overlying deposit. Geologically, the study area is made up of thick quaternary alluvium deposited on top of the older basement rock. The Muda River basin constitutes, approximately, of more than 300 m of thick quaternary alluvium overlying the unknown basement rock type. Previous studies, including drilling and geo-electrical resistivity surveys, were conducted in the area but none of them managed to conclusively determine the basement rock type and depth precisely. Hence, a regional gravity survey was conducted to determine the thickness of the quaternary sediments prior to assessing the sustainability of the Muda River basin. Gravity readings were made at 347 gravity stations spaced at 3–5 km intervals using Scintrex CG-3 covering an area and a perimeter of 9000 km2 and 730 km, respectively. The gravity data were then conventionally reduced for drift, free air, latitude, Bouguer, and terrain corrections. These data were then consequently analyzed to generate Bouguer, regional and total horizontal derivative (THD) anomaly maps for qualitative and quantitative interpretations. The Bouguer gravity anomaly map shows low gravity values in the north-eastern part of the study area interpreted as representing the Main Range granitic body, while relatively higher gravity values observed in the south-western part are interpreted as representing sedimentary rocks of Semanggol and Mahang formations. Patterns observed in the THD anomaly and Euler deconvolution maps closely resembled the presence of structural features such as fault lineaments dominantly trending along NW-SE and NE-SW like the trends of topographic lineaments in the study area. Based on power spectral analysis of the gravity data, the average depth of shallow body, representing alluvium, and deep body, representing underlying rock formations, are 0.5 km and 1.2 km, respectively. The thickness of Quaternary sediment and the depth of sedimentary formation can be more precisely estimated by other geophysical techniques such as the seismic reflection survey.

The Mid-Atlantic Ridge near 45 °N. VI. Remanent intensity, susceptibility, and iron content of dredged samples

1970 ◽  
Vol 7 (2) ◽  
pp. 226-238 ◽  
Author(s):  
E. Irving ◽  
W. A. Robertson ◽  
F. Aumento
Keyword(s):  
Iron Content ◽  
Rock Type ◽  
Chemical Change ◽  
Sampling Bias ◽  
Axial Zone ◽  
Mean Intensity ◽  
Basaltic Rocks ◽  
Active Volcanism ◽  
Serpentinized Peridotite ◽  
Mid Atlantic Ridge

Results from 27 dredge hauls (75 samples) spaced from 150 km west to 70 km east of the Median Valley of the Mid-Atlantic Ridge at about 45 °N are reported. Basalt is the most common rock type. The basalts have a mean remanent intensity of 92 × 10−4 and a mean susceptibility of 0.9 × 10−4 cgs cm−3. The remanence varies with distance from the axis, samples from the Median Valley (mean 574 × 10−4) being ten times more magnetic than samples at a greater distance. Most of this decrease of intensity occurs within a few kilometers (less than 6 km) of the central axis and within the zone of active volcanism. It is suggested that this dramatic drop in intensity is caused by viscous decay enhanced by thermal cycling or by chemical change in the narrow volcanic axial zone.Certain other properties of the basalts vary with distance; the blocking temperatures and stability (versus a.f. demagnetization) increase, and the ratio FeO/Fe2O3 decreases with distance. These changes are most marked at the inner slopes of the Crestal Mountains not within the narrow axial zone, and it is possible that they reflect sampling bias, the samples from the Median Valley being from flow margins, whereas the collections from the flanks contain material from the centers of flows.Non-basaltic rocks include serpentinized peridotite, greenstone, gabbro, and diabase. Serpentinized peridotite samples are strongly magnetic and have a mean intensity of 23 × 10−4 cgs cm−3. Greenstones, gabbros, and diabases are weakly magnetized, with mean intensities of about 10−4. Moreover, basalt showing partial alteration to greenstone has intermediate intensities showing that such a metamorphic process effectively demagnetizes a rock. This result is more consistent with the idea that Layer 3 is composed predominantly of gabbro and metamorphosed basalt rather than of serpentinized peridotite. The remanence and susceptibilities of 18 "erratic" samples, which are thought from other evidence to have been deposited by Pleistocene icebergs, have a wide and irregular spread.

scholarly journals The tectonostratigraphic architecture of the Serbo-Macedonian massif in the Vertiskos and Kerdilion mountains (Northern Greece)

2021 ◽  
Vol 57 (1) ◽  
pp. 1
Author(s):  
Anastasios Plougarlis ◽  
Markos Tranos ◽  
Lambrini Papadopoulou
Keyword(s):  
Cross Sections ◽  
Large Volume ◽  
General Trend ◽  
Shear Zones ◽  
Structural Features ◽  
Ultramafic Rocks ◽  
Northern Greece ◽  
Tectonic Contact ◽  
Western Side ◽  
Map Scale

The lithologies and structural features of the exposed rocks of the Serbo-Macedonian massif in the Vertiskos and Kerdilion Mts. have been studied in detail by carrying out km-long cross-sections. Moreover, a new tectonostratigraphic architecture for the massif is proposed, based on the migmatization and anatexis that the rocks pertain, under which the specific exposed rocks have been placed into the Vertiskos and Kerdilion Units. The latter approach differs from the traditional view, which is based solely on the lithological difference between the units. In particular, in the Vertiskos Mt., mica schists, garnet-bearing two-mica gneisses, and predominantly two-mica gneisses, without a sign of anatexis and migmatization, overlie tectonically, biotite gneisses and layered amphibolite gneisses into which migmatization and anatexis takes place. The former constitute the Vertiskos Unit, whereas the latter have been grouped into the Kerdilion Unit, since they are of similar lithologies and affinities with rocks of the Kerdilion Unit. The Kerdilion Mt. is a large antiform made up of biotite gneisses alternating with marbles, which are similarly characterized by intense migmatization and anatexis. These rocks are intruded by the Oreskia granite, which is foliated and follows the general trend of the country rocks. All the rocks are folded with isoclinal to tight folds, and the contact between the two units is a mylonitic shear zone with a top-to-the-SW sense-of-shear. Also, a large volume of ultramafic rocks occurs between the Vertiskos and Kerdilion Mts., including metamorphosed rocks like metagabbros to massive amphibolites, which is assigned to the Therma-Volvi-Gomati Complex (TVGC). These rocks have been found in tectonic contact, i.e., shear zones with top-to-the-SW sense-of-shear, only with the rocks of the Kerdilion Unit. Taking into account our new tectonostratigraphic architecture, the contact between the Vertiskos and Kerdilion Units is not located along the western side of the marbles, as the latter are exposed in the Kerdilion Mt. It is traced westerly in the Vertiskos Mt. dipping with intermediate angles towards the SW, due to NW-trending, map-scale, isoclinal folding. The ultramafic rocks of the TVGC are in tectonic contact with the rocks of the Kerdilion Unit, but not the two-mica gneisses of the Vertiskos Unit, and the Arnea granite intrudes not only the Vertiskos Unit as previously considered, but the rocks of the Kerdilion Unit, as well.

Stratigraphie et paléogéographie d'un bassin d'avant-arc ordovicien, Estrie-Beauce, Appalaches du Québec

1994 ◽  
Vol 31 (2) ◽  
pp. 435-446 ◽  
Author(s):  
Pierre A. Cousineau ◽  
Pierre St-Julien
Keyword(s):  
Volcanic Rock ◽  
Accretionary Prism ◽  
Late Ordovician ◽  
Coarse Grained ◽  
Magmatic Arc ◽  
Rock Fragments ◽  
Felsic Volcanic Rock ◽  
Volcaniclastic Rocks ◽  
Felsic Volcanic ◽  
Quartz Grains

Two new formations, the Frontière and Etchemin formations, have been found to lie below the Beauceville and Saint-Victor formations, the two known formations of the Magog Group. The Frontière Formation, at the base of the group, is made up of centimeter-thick beds of medium- to coarse-grained litharenite and of greyish green mudstone; the sandstone, greyish green, contains abundant felsic volcanic rock fragments and chromite grains. The Etchemin Formation is composed mostly of centimeter-thick dusky yellow green siliceous mudstone; at the base, there is also a purple mudstone, and meter-thick beds of dusky green volcaniclastic rocks rich in intermediate to felsic volcanic rock fragments and crystals of feldspar and quartz occur near its top. The Beauceville Formation consists of interbedded centimeter-thick beds of black clayslate and centimeter- to meter-thick beds of black volcaniclastic rocks. The Saint-Victor Formation consists of classic turbidite beds with few meter-thick yellowish volcaniclastic rock beds similar to those of the Beauceville Formation; the sandstone is a litharenite rich in quartz grains and sedimentary rock fragments. Most rocks of the Frontière and Etchemin formations as well as the volcaniclastic rocks of the Beauceville and Saint-Victor formations were derived from a magmatic arc located to the southeast. However, the shale of the Beauceville Formation and the turbidites of the Saint-Victor Formation were derived from an orogenic source located to the northwest. The Magog Group is located between the Saint-Daniel Mélange and the Ascot Complex interpreted as remnants of an accretionary prism and a magmatic arc, respectively. The sediments of this group were thus deposited in a fore-arc basin active during the Taconian orogeny of the Middle to Late Ordovician.

scholarly journals Cambrian–Silurian stratigraphy of Børglum Elv, Peary Land, eastern North Greenland

1977 ◽  
Vol 82 ◽  
pp. 1-48
Author(s):  
R.L Christie ◽  
J.S Peel
Keyword(s):  
Black Shale ◽  
Lower Cambrian ◽  
Late Ordovician ◽  
Dolomitic Limestone ◽  
Carbonate Mounds ◽  
Middle Ordovician ◽  
Clastic Rocks ◽  
Shale Formation ◽  
Lower Palaeozoic ◽  
North Greenland

A sequence of Lower Palaeozoic carbonate and clastic rocks is described from Børglum Elv, Peary Land, eastem North Greenland, and briefly compared to Lower Palaeozoic sections elsewhere in Greenland and in Spitsbergen. Lower Cambrian clastic rocks of the Buen Formation are followed by dolomite of the Lower Cambrian Brønlund Fjord Formation (125 m). Succeeding dolomite and dolomitic limestone of the Wandel Valley Formation (320 m) of Early to Middle Ordovician age are overlain by limestone of the Børglum River Formation (430 m) of Middle to Late Ordovician age. Un-narned Early Silurian dolomite and limestone formations (150 m and 320 m respectively) are followed by an un.narned Middle Silurian black shale formation (c. 100 m) and at least 800 m of a late Middle Silurian and younger un-named flysch formation. Carbonate mounds, originating in the highest beds of the un-named Silurian limestone formation, occupy stratigraphic levels through the overlying black shale formation and into the flysch formation.

Clumped isotope thermometry reveals diagenetic origin of the dolomite layer within late Ordovician black shale of the Guanyinqiao Bed (SW China)

2021 ◽  
pp. 120641
Author(s):  
Xiaolong Hu ◽  
Inigo A. Müller ◽  
Ankun Zhao ◽  
Martin Ziegler ◽  
Qing Chen ◽  
...  
Keyword(s):  
Black Shale ◽  
Late Ordovician ◽  
Sw China ◽  
Clumped Isotope

Stratigraphy and graptolites of the Upper Ordovician Point Leamington Formation, central Newfoundland

1991 ◽  
Vol 28 (4) ◽  
pp. 581-600 ◽  
Author(s):  
S. Henry Williams
Keyword(s):  
Debris Flow ◽  
Black Shale ◽  
Strong Relationship ◽  
Late Ordovician ◽  
Black Shales ◽  
Upper Ordovician ◽  
Several Intervals

The Point Leamington Formation, as redefined herein, comprises a thick sequence of siliciclastic turbidites containing occasional Upper Ordovician graptolites and lies with the Exploits Subzone of the Dunnage Zone in central Newfoundland. The base of the unit is marked by the first coarse- to medium-grained sandstone, at a level that varies from the Dicranograptus clingani Zone to the Pleurograptus linearis Zone. Several intervals of interbedded black shales and siltstones higher in the formation yield assemblages characteristic of the P. linearis, Dicellograptus complanatus and Dicellograptus anceps zones. Debris-flow breccias occur at several levels within the Point Leamington Formation—some contain graptolitic, black shale clasts derived from the underlying Lawrence Harbour Formation—and range in age from Nemagraptus gracilis Zone to D. clingani Zone. Both the graptolite assemblages and lithostratigraphic succession of the Point Leamington Formation are similar to those of coeval rocks in southern Scotland, confirming a strong relationship between the two areas during the Late Ordovician.

Early Palaeozoic metamorphic history of the Midland Valley, Southern Uplands–Longford-Down massif and the Lake District, British Isles

1984 ◽  
Vol 75 (2) ◽  
pp. 245-258 ◽  
Author(s):  
G. J. H. Oliver ◽  
J. L. Smellie ◽  
L. J. Thomas ◽  
D. M. Casey ◽  
A. E. S. Kemp ◽  
...  
Keyword(s):  
Accretionary Prism ◽  
Late Ordovician ◽  
Ocean Floor ◽  
Lower Grade ◽  
Lake District ◽  
Reflectance Measurement ◽  
Early Ordovician ◽  
Metamorphic History ◽  
History Of ◽  
Early Palaeozoic

ABSTRACTA model for the early Palaeozoic metamorphic history of the Midland Valley and adjacent areas to the S in Scotland, England and Ireland is based on the results of new field mapping, thin section petrography, electron probe microanalysis, X-ray diffractometry, conodont and palynomorph colouration and graptolite reflectance measurement.The oldest metamorphic rocks of the Midland Valley of Scotland, excluding xenoliths in post-Silurian lavas, are possibly the blueschist occurrences in the melange unit of the Ballantrae complex. These may be tectonised remnants of (?)pre-Arenig ocean-floor subducted during closure of the Iapetus Ocean. In the early Ordovician, the melange terrane was dynamothermally metamorphosed during obduction of newly-formed ocean crust. The obduction process piled up a thick sequence of various ocean-floor types such that burial metamorphism in parts reached pumpellyite-actinolite facies; elsewhere prehnite-pumpellyite and zeolite facies was attained.Whilst the Midland Valley acted as an inter- or fore-arc basin during the Late Ordovician and Silurian and experienced burial metamorphism, an accretionary prism was formed to the S. Accretion, tectonic burial and metamorphism of ocean-floor and trench sediment was continuous in the Southern Uplands and the Longford-Down massif of Ireland through Late Ordovician to Late Silurian times. Rocks at the present-day surface vary from zeolite facies to prehnitepumpellyite facies. Silurian trench-slope basin sediments can be recognised in part by their lower grade of burial metamorphism. Greenschist facies rocks of the prism probably lie close to the surface.The Lake District island-arc terrane of Northern England has an early Ordovician history of burial metamorphism up to prehnite-pumpellyite facies. The Late Ordovician and Silurian metamorphic history is one of sedimentary burial complicated by tectonism and intrusion of granite plutons to a relatively high level. The Iapetus suture is marked by a weak contrast in metamorphic grade.

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