Re-investigating the Barrovian metamorphic rocks of the Isbjørnhamna Group, Svalbard Caledonides

2021 ◽  
Author(s):  
Margot Patry ◽  
Iwona Klonowska ◽  
Karolina Kośmińska ◽  
Jarosław Majka
Keyword(s):  
High Arctic ◽  
Metamorphic Rocks ◽  
Metamorphic History ◽  
South West ◽  
Science Centre ◽  
National Science ◽  
History Of ◽  
Orogenic Events ◽  
Preliminary Phase

<p>The Isbjørnhamna Group, which crops out in the south-west of Svalbard in the High Arctic, is crucial for understanding Svalbard’s regional geology. It can be traced in southern Wedel Jarlsberg Land and Sørkapp Land, and it consists of a Barrovian-type series of metapelites that were metamorphosed during the Torellian (c. 640Ma; Majka et al. 2008) and overprinted during the Caledonian orogenesis (Majka & Kośmińska, 2017). Although relatively recent petrological study exists, there are certain gaps in it. In order to fill these gaps, we decided to re-investigate these rocks using the most up-to-date petrochronological approach. Hence, we aim to determine the metamorphic history of these rocks in detail, test the hypothesis if there are indeed several orogenic events registered by these rocks and what was a possible exhumation mechanism responsible for uplift of this sequence.</p><p>The studied garnet-bearing mica schists preserve four different parageneses, ranging from chloritoid to kyanite metamorphic zones. Here we report on the samples containing chlorite and chloritoid, kyanite, staurolite and both staurolite and kyanite. The studied samples are the same exact rocks that have been previously studied by Majka et al. (2008, 2010) using both geothermobarometry and petrogenetic grids in the KFMASH system. According to those authors the estimated pressure-temperature conditions (P-T) were c. 655°C at 11kbar for the kyanite-bearing shist, c. 624°C at 6.6 to 8.7kbar for the staurolite + kyanite pelite and c. 580°C at 8-9kbar for the staurolite-bearing rock. The chloritoid schist has not been studied previously.</p><p>Our preliminary phase equilibrium modelling in the MnNCKFMASHTO system using the Theriak-Domino software indicates P-T conditions of c. 660°C at 7 kbar for the kyanite-schist and c. 575°C at 8 to 9.5kbar for the staurolite-schist, respectively. The chloritoid schist yielded conditions of c. 560°C at 7.5kbar. Further P-T modelling coupled with in-situ Ar-Ar and U-Pb geochronology should allow for much better understanding of the complex geological history of these rocks as well as potential flaws in the previous studies.</p><p> </p><p>Research funded by National Science Centre (Poland) project no. 2019/33/B/ST10/01728.</p><p> </p><p>References:</p><p>Majka & Kośmińska (2017): Arktos, 3:5, 1.17.</p><p>Majka et al. (2008): Geological Magazine, 145, 822-830.</p><p>Majka et al. (2010): Polar Research, 29, 250-264.        </p>

Five tombs at Knossos

1963 ◽  
Vol 58 ◽  
pp. 30-43 ◽  
Author(s):  
J. N. Coldstream
Keyword(s):  
Good Condition ◽  
Good Deal ◽  
Lower Edge ◽  
Water Pipe ◽  
The West ◽  
Light In August ◽  
South West ◽  
History Of ◽  
The Temple

On the east slope of Lower Gypsades hill, about 100 metres west of the Temple Tomb, a chamber tomb came to light in August 1958, when a cutting for a new water pipe was driven through the area (A in Plate 9 a). In the course of this operation, part of a plain larnax (iii) was sliced off, and much earth removed from the west end of the collapsed chamber: at no point, however, had the municipal workmen penetrated to the tomb floor.The chamber was approached by a sloping dromos (Plate 9 a: length 2·80 metres; max. width 1 metre), roughly cut into the natural kouskouras rock: its walls were approximately perpendicular. Although the gradient varied a good deal, there was no suggestion of a stairway.The blocking wall was found in good condition. Of especial interest were the numerous fragments of larnakes that had been built into its fabric: some of them could be recognized as belonging to each of the three fragmentary larnakes (i, ii, v) whose scattered pieces were found below and around the two undisturbed burials in the chamber (iii, iv). We may thus distinguish two periods in the history of the tomb: larnakes i, ii, and v were evidently smashed up in order to make room for iv and iii, which must have been deposited in that order. The debris of v was found under iv, with a few adult bones in its wreckage. Part of i lay on the floor near the south-west corner, where two plain vases (2, 3) were found in situ, hence, also, came most of the fragments of the fine L.M. IIIA 2 stirrup vase (1), although its other pieces were scattered all over the floor of the tomb. This small group of offerings may belong to the disturbed adult skeleton, whose skull lay up against the lower edge of iii. Curiously, some fragments of i and ii were also found above the broken lid of iv (Plate 9 b): perhaps the lid of the later larnax was accidentally smashed at the time of the funeral, in which case the debris from earlier burials could have been piled up above it, as a rough and ready means of protection.

First in-situ Rb-Sr dating of metasedimentary rocks from the Pontiac subprovince, Superior Craton, Canada. Implications towards the regional metamorphic evolution of the sequence.

2020 ◽  
Author(s):  
Nicholas Leventis ◽  
Thomas Zack ◽  
Iain Pitcairn ◽  
Johan Högmalm
Keyword(s):  
Accretionary Prism ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
Accuracy And Precision ◽  
Icp Ms ◽  
Age Variations ◽  
History Of ◽  
Peak Metamorphism ◽  
Superior Craton

<p>The Pontiac subprovince consists of metaturbidites, plutons and thin ultramafic rock layers of Archean age and lies south of the Cadillac-Larder Lake (C-LL) fault zone which is the boundary between the Pontiac and the extensively mineralized Abitibi Greenstone Belt. The sediments show a Barrovian metamorphic gradient which increases southwards, away from the C-LL fault. The most likely tectonic provenance for the Pontiac sedimentary rocks is that they represent a relic accretionary prism with material derived from both the Abitibi and an older terrane. Zircon U-Pb dating shows that deposition occurred not later than 2685±3 Ma ago and recent, robust Lu-Hf dating of garnets bracketed Pontiac's peak metamorphic conditions at 2658±4 Ma. For this study we used a recently developed LA-ICP-MS/MS method for in-situ Rb-Sr dating of biotite and plagioclase in samples ranging in metamorphic grade (biotite to sillimanite zones) from the Pontiac subprovince. Calibration of the instrument was achieved by repeated ablations on several reference materials (see Hogmalm et al. 2017) which also provided the monitoring of accuracy and precision throughout the analyses. Results show a range in dates between 2550 Ma and 2200 Ma with an average of 2440±50 Ma (2σ). Samples from the staurolite and kyanite zones have a larger range with respect to the other zones, but no significant differences are observed in the data with any method of data handing. These dates are ≈300Ma younger than the peak metamorphism in the area and this is attributed to either overgrowth and re-setting of the Rb-Sr system by a second metamorphic/hydrothermal event, or diffusional resetting with core-rim age variations. Possible influence from the adjacent late syntectonic to post-tectonic monzodiorite-monzonite-granodiorite-syenite (MMGS) plutons dated 2671±4 Ma and the garnet-muscovite-granite series (GMG) dated ≈2650 Ma cannot be ruled out. This study provides insights about the metamorphic history of the sequence and supports previous findings regarding resetting of some isotopic systems with relatively low closure temperatures (≈350-400°C) by later thermal events.</p>

How Himalayan collision stems from subduction

Geology ◽  
2021 ◽  
Author(s):  
M. Soret ◽  
K.P. Larson ◽  
J. Cottle ◽  
A. Ali
Keyword(s):  
Foreland Basin ◽  
Continental Collision ◽  
Ultrahigh Pressure ◽  
Metamorphic Rocks ◽  
Conductive Heat ◽  
Plate Interface ◽  
Continental Subduction ◽  
Metamorphic History ◽  
Orogenic Wedge ◽  
History Of

The mechanisms and processes active during the transition from continental subduction to continental collision at the plate interface are largely unknown. Rock records of this transition are scarce, either not exposed or obliterated during subsequent events. We examine the tectono-metamorphic history of Barrovian metamorphic rocks from the western Himalayan orogenic wedge. We demonstrate that these rocks were buried to amphibolite-facies conditions from ≤47 Ma to 39 ± 1 Ma, synchronously with the formation (46 Ma) and partial exhumation (45–40 Ma) of the ultrahigh-pressure eclogites. This association indicates that convergence during continental subduction was accommodated via development of a deep orogenic wedge built through successive underplating of continental material, including the partially exhumed eclogites, likely in response to an increase in interplate coupling. This process resulted in the heating of the subduction interface (from ~7 to ~20 °C/km) through advective and/or conductive heat transfer. Rapid cooling of the wedge from 38 Ma, coeval with the formation of a foreland basin, are interpreted to result from indentation of a promontory of thick Indian crust.

XIX.—Metamorphic History of the Schichallion Complex (Perthshire)

1958 ◽  
Vol 63 (2) ◽  
pp. 413-431 ◽  
Author(s):  
N. Rast
Keyword(s):  
Regional Metamorphism ◽  
Igneous Rocks ◽  
Metamorphic Rocks ◽  
Present Contribution ◽  
Scottish Highlands ◽  
Metamorphic History ◽  
Fine Grain ◽  
Tectonic History ◽  
History Of ◽  
Garnet Zone

SynopsisThe Schichallion complex is situated in the Central Highlands of Scotland between the villages Struan and Kinloch Rannoch. The area is of considerable geological interest and has been investigated stratigraphically and structurally by E. M. Anderson and Bailey and McCallien. As a consequence of their researches a complete stratigraphical succession has been established. Thus, the metamorphic rocks of the area are classified into the Moinian and Dalradian systems, which are separated by a plane of tectonic discontinuity known as the Boundary Slide. The Moinian rocks are quartz-felspathic granulites, whereas the Dalradian system includes pelitic schists, quartzites, limestones as well as a variety of meta-igneous rocks.In his previous research the present author has established the tectonic history of the complex. In particular three episodes of folding (F1to F3) and a much later episode of faulting (F4) were recognized. Of these the F3episode is of least significance. Consequently, events after the F2movements can be in many cases regarded as post-folding.The present contribution is concerned essentially with the mapping of the metamorphic zones (garnet and staurolite-kyanite) and with a detailed study of the mineralogical evolution of regionally metamorphosed rocks within these zones.In the field it is possible to prove that the staurolite-kyanite zone is essentially post-folding, since the kyanitepegmatites are found to cut across the minor F2-folds. In this respect textural studies confirm the field observations. The study of the internal inclusions in garnets indicates that the garnet zone has a much longer history, since pre-F2garnets are found in the southern part of the complex and throughout the central part of the area syn-tectonic F2garnets are apparent. The pre-F2garnets contain a very fine-grain F1fabric. Hence the garnets in relation to the F1movements are post-tectonic. Thus, the regional metamorphism can be subdivided into three phases: the F1metamorphism, the F2metamorphism and the post-F2metamorphism. The latter, on structural evidence appears to be at least in part contemporaneous with the F3movements.The meta-igneous rocks of the area are grouped into the hornblende-schists and granular epidiorites. The hornblende-schists appear to have suffered deformation and recrystallization during F1and F2episodes of movement. On the other hand the granular epidiorites are later than the F1and the F2movements. Although in the southern parts of the district the epidiorites have been slightly deformed, elsewhere they preserve the original ophitic texture and cut across the F1and F2folds. The deformation in the south is attributed to the effects of the F3folding. The epidiorites have been evidently emplaced as dolerites after the F2movements and before the F3metamorphism.The localized retrogressive metamorphism is associated with the F4movements, which are responsible for the Loch Tay Fault. The Fault is later than the minor intrusives associated with the Younger Granites of the Scottish Highlands and is suggested to be of a Lower or Middle O.R.S. age.On the basis of the chemical composition of the plagioclase felspars it is proposed to include all the staurolite and kyanite bearing rocks into the epidote-amphibolite facies. In this respect temperature and the hydrostatic pressure are assumed to have been the main factors, since similar minerals came into existence during static and dynamic stages of metamorphism alike.

Some observations on the use of zircon U-Pb geochronology in the study of granitic rocks

1992 ◽  
Vol 83 (1-2) ◽  
pp. 447-458 ◽  
Author(s):  
Ian S. Williams
Keyword(s):  
Igneous Rocks ◽  
Granitic Rocks ◽  
Metamorphic Rocks ◽  
Ion Microprobe ◽  
Zircon Population ◽  
Metamorphic History ◽  
Ion Probe ◽  
Isotopic Analyses ◽  
Single Zircon

ABSTRACTIn situ, microscale, U-Pb isotopic analyses of zircon using the SHRIMP ion microprobe demonstrate both the potential and the limitations of zircon U-Pb geochronology. Most zircons, whether from igneous or metamorphic rocks, need to be considered as mixed isotopic systems. In simple, young igneous rocks the mixing is principally between isotopically disturbed and undisturbed zircon. In polymetamorphic rocks, several generations of zircon growth can coexist, each with a different pattern of discordance. A similar situation exists for igneous rocks rich in inherited zircon, as these contain both melt-precipitated zircon and inherited components of several different ages. Microscale analysis by ion probe makes it possible to sample the record of provenance, age and metamorphic history commonly preserved within a single zircon population. It also indicates how the interpretation of conventionallymeasured bulk zircon isotopic compositions might be improved.

Unfriendly and polemical elements in Augustine’s correspondence with other clerics

2018 ◽  
Vol 22 (1) ◽  
pp. 110-124
Author(s):  
Stanisław Adamiak
Keyword(s):  
Late Antique ◽  
Science Centre ◽  
National Science ◽  
History Of

Abstract: Nearly half of the letters written by Augustine were directed to other clerics. The paper analyses how polemical intentions could be hidden behind friendly formulas. Particular consideration is given to the correspondence between Augustine and Donatist clerics, whom he treated as his peers and brothers.<fnote> The research was funded by the Polish National Science Centre grants: “The Presbyters in the Late Antique West” (2013/10/E/HS3/00202) and “The History of the Donatist Schism” (2015/19/D/HS3/00626).</fnote>

scholarly journals XRD graphitization degrees: a review of the published data and new calculations, correlations, and applications

2021 ◽  
Vol 50 (1) ◽  
pp. 11-35
Author(s):  
Alexander Vlahov
Keyword(s):  
Chemical Composition ◽  
Structural State ◽  
Tectonic Stress ◽  
Metamorphic Rocks ◽  
Published Data ◽  
Metamorphic History ◽  
Metamorphic Temperature ◽  
History Of ◽  
Carbon Matter

A system for transformation, correlation, and unification of subordinations between d002 (Å) of semi-graphite and graphite, graphitization degrees and metamorphic temperature was created. The existing equations in the literature were analyzed and new equations, which determine correlation relationships between these parameters, were formulated. The effect of factors that control graphitization processes (temperature, general pressure and tectonic stress, structure and origin of primary carbon matter, orientation of carbon formations, fluids, mineral and chemical composition, and duration of processes) was also considered. It was concluded that the structural state of semi-graphite and graphite is reversible, and this can be used for facies diagnostics and studying of metamorphic history of graphite-bearing metamorphic rocks. A new scale for graphitization degrees was proposed.

scholarly journals Testing the rocks loosening process by undercutting anchors

2020 ◽  
Vol 42 (3) ◽  
pp. 276-290
Author(s):  
Michał Siegmund ◽  
Marek Kalita ◽  
Domink Bałaga ◽  
Krzysztof Kaczmarczyk ◽  
Jonak Józef
Keyword(s):  
Load Capacity ◽  
List Type ◽  
Test Results ◽  
Capacity Design ◽  
In Situ Tests ◽  
In Situ Test ◽  
Modeling Process ◽  
Science Centre ◽  
National Science

AbstractThe method of unconventional solid rock loosening with undercutting anchors and the literature analysis of the problem are presented. The tests and test results of the rocks loosening process with a fixed undercutting anchor are described. The tests were carried out within the RODEST project, OPUS 10 competition No. 2015/19/B/ST10/02817, financed by the National Science Centre. Numerical modeling process as well as a series of laboratory and in situ tests were carried out. The test stand equipment and methodology for the in situ tests are presented. The tests were conducted in four mines, which allowed to obtain and determine the following characteristics: loosening force as a function of anchoring depth (for a given type of rock),the range of rock loosening in a function of anchoring depth (for a given type of rock), andloosened rock volume as a function of anchoring depth (for a given type of rock).The in situ test results are compared with the concrete capacity design (CCD) model used for the calculation of anchor load capacity in concrete.

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