Le Brioverien. Esquisse des caracteres stratigraphiques, metamorphiques, structuraux et paleographiques de l'Antecambrien recent dans le Massif armoricain

1962 ◽  
Vol S7-IV (3) ◽  
pp. 413-430 ◽  
Author(s):  
Jean Cogne

Abstract The stratigraphic characteristics of the Brioverian from Normandy to the Vendee reflect a complete geosynclinal cycle younger than the Pentevrian (Precambrian) but completed before the Cambrian transgression. The Brioverian is the basement rock of the Armorican massif, and thus has the largest areal extent of any Precambrian formation in France. The lower part consists of epimetamorphic basic rocks (ophiolites). The middle part is feldspathic sandstone, phtanite, quartzite, and phyllitic shale. After a short period of emergence, the upper beds were deposited, consisting of the Saint Germain-le-Gaillard rhyolite, the Granville tillite complex, and shale and sandstone at the top. Cadomian folding and granitic intrusion occurred, forming the Cadomian chain prior to Cambrian transgression, and thereby affecting the structure of the Armorican massif. The Brioverian clearly was a folded and partially granitized sole before the dawn of the Paleozoic, but the exact dates of the deposition of the Brioverian and of the Cadomian orogeny are still hypothetical.

2021 ◽  
Vol 33 (6) ◽  
pp. 703-716
Author(s):  
Leonid Shumlyanskyy ◽  
Gerhard Franz ◽  
Sarah Glynn ◽  
Oleksandr Mytrokhyn ◽  
Dmytro Voznyak ◽  
...  

Abstract. The origin of large miarolitic (also known as “chamber”) pegmatites is not fully understood although they may have great economic value. The formation of cavities in magmatic bodies is related to melt degassing and gas or fluid flow through partially solidified magma. In this paper, the origin of the Volyn pegmatite field, located in the Palaeoproterozoic Korosten anorthosite–mangerite–charnockite–granite (AMCG) complex, North-Western region of the Ukrainian Shield, is discussed. Pegmatites of the field host deposits of piezoelectric quartz that is accompanied by gem-quality beryl and topaz. The Volyn pegmatite field is confined to granites located in the south-western part of the Korosten complex and extends for 22 km along the contact with the anorthosite massif within the Korosten plutonic complex. Geological data indicate hybridization of basic melts and partly crystallized granites, as well as direct impact of fluids derived from basic melts on the chamber pegmatites. The new U–Pb zircon ages obtained for granites and pegmatites of the Korosten complex confirm that the rock assemblage in the northern part of the complex crystallized between 1800 and 1780 Ma, whereas rocks in the southern part intruded mainly between 1768 and 1755 Ma. U–Pb zircon ages for granites from the south-western part of the Korosten complex indicate that granites were emplaced at 1770–1765 Ma, a few million years prior to the intrusion of the gabbro–anorthosite massif (1762–1758 Ma), while chamber pegmatites in these granites crystallized at 1760 ± 3 Ma, coevally with the basic rocks. Ultimately, the formation of the chamber pegmatites was related to the reheating of the semi-crystallized granitic intrusion and to fluids migrating from the underlying gabbro–anorthosite massif.


Ars Adriatica ◽  
2013 ◽  
pp. 103
Author(s):  
Marijana Kovačević

This paper discusses an interesting silver fragment showing an image of a saint which was found a few years ago in the rectory of the island of Olib. Based on a thorough comparison of the fragment with similar liturgical objects from the wider area of Zadar, especially with the processional cross from Vlašići (Pag), the authoress proposes that the fragment once belonged to a Gothic proccessional cross dating from the end of the 14th century and that it was nailed as the middle part of its reverse side. The image of the saint depicted on this fragment is identified, based partly on the place of its discovery, with the patron saint of the parish of Olib, St.Anastasia. This identification is further strenghtened also by an iconographical analysis of various depictions of St. Ananstasia in Romanesque and Gothic art of Zadar and its area, especially in goldsmiths’ work of the time, where there are relatively many of her images considering that St. Anastasia was the patron saint of Zadar cathedral, where her relic was treasured for centuries, and also one of four main patron saints of this important Adriatic city. That analysis led to the conclusion that there was a certain evolutive change in the depiction of the saintly patroness during that era, and that, starting form ourfragment and the end of the 14th century, she is more often adorned with a book as her standard attribute.It was also noted that the image depicted on the Olib fragment may, perhaps, be identified with St. Catherine of Alexandria who was also often depicted with a book. Namely, she was the patron saint of a church in Novigrad, a small medieval town situated in the hinterland of Zadar,whence its inhabitants could have brought a whole cross, or solely this fragment, centuries after its making, as C. F. Bianchi recorded thet they brought to Olib a worshipped painting when fleeing from the Turks. This move of the local treasure from Novigrad to Olib in times of crisis and flight would thus coincide with the same practice of the move of the processional cross from Gorica to Pašman, as proposed by N. Jakšić. The stumbling stone of this theory is, of, course, the existence of the 14th century processional cross in Novigrad, with very similar image of St. Catherine on its reverse. Although she is iconographically coherent with the saintly image on the fragment from Olib, it is rather difficult toexplain the making of two similar processional crosses in such a short period of time, since the evident stylistic and tehnical differences between the two images allow only for a short time difference. On the other hand, if the saint on the Olib fragment indeed is St. Anastasia, this would mean that the parish church of Olib regularly refurbished its liturgical equipment during the period of less than two centuries, since one processional cross from Olib older than our fragment has also survived, still partly Romanesque in its morphology and iconography, as well as has survived the late 15th century cross attributed to Toma Martinov, goldsmith from Zadar, whose style is already Rennaissance in many aspects. In course of the search for the images of St. Anastasia in the medieval goldsmiths’ work of Zadar it was also observed that the long established iconographical identification of the figures depicted on the luxurious bishop’s staff of the archbishop Maffeo Vallaresso (1460) has to be partially revised.


Author(s):  
Hubert KIERSNOWSKI ◽  
Zdzisław Petecki

On the background of a critical review of earlier studies and concepts concerning the structure of the pre-Permian basement of LGOM, the authors’s own, modified version of its tectonic model is presented, accompanied by that explaining the sedimentation and areal extent of the Lower Permian sedimentary cover. Integrated sedimentological, structural and tectonic analysis was applied in conjunction with geophysical analysis based on gravimetric and magnetic data. As a result of the analysis, the pre-Permian basement of the LGOM area is interpreted to be part of the northern Variscan internides and, at the same time, to constitutea northerly extension of the Fore-Sudetic block (Sieroszowice block) . Within the LGOM area, in its southern part, there are middle Odra fault zone, comprising the southern middle Odra fault (Lubin trough) and northern middle Odra fault, separated with the Sieroszowice block. In the middle part of the LGOM area located is the Głogów trough, cut by the Silesia-Lubusz fault in its northern segment and by the southern part of the vast middle Odra deep fracture zone.


1990 ◽  
Vol 51 (1) ◽  
pp. 3-12 ◽  
Author(s):  
R. S. D’Lemos ◽  
R. A. Strachan ◽  
C. G. Topley

2021 ◽  
pp. 1-15
Author(s):  
Ulf Linnemann ◽  
Mandy Hofmann ◽  
Andreas Gärtner ◽  
Jessica Gärtner ◽  
Johannes Zieger ◽  
...  

Abstract In the Cadomian orogenic belt a package of glacigenic sedimentary deposits have been recently described in the Armorican Massif (Normandy, France). The Granville Tillite Member, the middle part of the upper Granville Formation, is late Ediacaran in age. Maximum depositional ages of the pre- and syn-glacial sedimentary deposits obtained by LA-ICP-MS U–Pb detrital zircon dating indicate a maximum age of 561 ± 3 Ma. Combined with geochronological data on the previously described glacial deposits in Cadomia, West Africa, Arabia and Iran, the Granville Tillite Member appears to represent an Upper Ediacaran Glacial Period in northern peri-Gondwana, clearly younger than the c. 580 Ma old Gaskiers glaciation. Detailed mapping and analysis of the depositional regime of two sections near the city of Granville are indicative of two independent glaciomarine lower and upper tillite deposits separated by a distinct conglomeratic marker horizon, evidently a massive gravel beach horizon deposited during an interglacial stage. Age spectra of detrital zircon U–Pb ages constrain the palaeogeographical position of the upper Granville Formation to the periphery of the West African Craton. Post-Gaskiers aged glaciations in Cadomia and in West Africa should be grouped into an Upper Ediacaran Glacial Period dated at c. 565 Ma. This glacial period seems not to be related to the negative δ13C Shuram–Wonoka anomaly. Sedimentary deposits formed during the Upper Ediacaran Glacial Period show a scattered distribution along the marginal orogens of the Gondwana supercontinent independent of palaeolatitude and are coupled most likely to contemporaneous orogenic processes and uplift.


2021 ◽  
Author(s):  
Karen Lythgoe ◽  
Muzi Muzli ◽  
Win Oo ◽  
Hongyu Zeng ◽  
Rahmat Triyono ◽  
...  

<p>Supershear earthquakes have significant implications for seismic hazard, in terms of  ground shaking and aftershock pattern. It has been suggested that supershear ruptures are associated with fewer aftershocks on the supershear rupture segment, however this needs to be tested using high resolution event locations. Current aftershock catalogues for the M7.5 Palu 2018 supershear rupture are not of sufficient resolution to identify any characteristic aftershock pattern. Additionally it is unclear whether the supershear rupture speed occurred from the time of earthquake initiation, or at a later time on a certain segment of the fault.</p><p>We deployed a nodal array to record aftershocks following the main event. The array comprised of twenty short-period nodes, which can be deployed rapidly, making them ideal for post-rupture investigations in areas of sparse coverage. We expand the earthquake catalogue by applying template matching to the nodal array data. We then relocate seismicity recorded by the array using a double difference method. We also relocate seismicity that occurred before the array was active, using a relative relocation method. To do this, we calibrate the more distant permanent stations using events well-located by the nodal array. We further derive moment tensors for the largest events by waveform modelling using short-period and broadband records.</p><p>Our results show that the aftershocks cluster at the northern and southern extents of rupture. There is a relative dearth of aftershocks in the middle part of the rupture, particularly in the Palu valley, where rupture terminated to the surface. The fault here is a long and straight distinctive geomorphic feature. Many secondary faults were triggered, particularly in the southern Sapu valley fault system. An earthquake swarm was triggered 1 month after the main event on a strike-slip fault 200km away.</p>


1990 ◽  
Vol 51 (1) ◽  
pp. 81-94 ◽  
Author(s):  
D. Rabu ◽  
J. Chantraine ◽  
J. J. Chauvel ◽  
E. Denis ◽  
P. Balé ◽  
...  

1938 ◽  
Vol 75 (4) ◽  
pp. 174-184 ◽  
Author(s):  
W. A. Deer

The Glen Tilt Complex, one of the larger masses of the Newer Granites of the Central Highlands, is included in sheet 64 of the Geological Survey of Scotland. The greater part of this complex is a granite which is bounded on the south-west and southeast by an earlier series of intermediate and basic rocks. The granites described in this contribution are restricted to a small area at the south-eastern margin of the large granitic intrusion generally known as the Beinn Dearc granite. The smaller and independent intrusion of the Sron a ‘Chro’ granite and a number of smaller masses of granite associated with the marginal strip of diorites on the north-western side of Glen Tilt have also been examined. These small isolated areas appear to be contemporaneous with the intrusion of the main Beinn Dearc mass and have been intruded between the earlier diorites and the margin of the intrusion, a feature not uncommon in many of the other Scottish Newer Granites. A small independent mass of muscovite-biotite-granite intruded into quartz-mica-diorite occurs on Conlach Mhor. Although these rocks are completely isolated from both the biotite- and muscovite-biotite-granites of the main Beinn Dearc intrusion their essential similarity with the latter leaves no reasonable doubt of their common origin.


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