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>

Coupling thermodynamic modeling and high-resolution in situ LA-ICP-MS monazite geochronology: evidence for Barrovian metamorphism late in the Grenvillian history of southeastern Ontario

2014 ◽  
Vol 108 (6) ◽  
pp. 741-758 ◽  
Author(s):  
Travis McCarron ◽  
Fred Gaidies ◽  
Christopher R. M. McFarlane ◽  
R. Michael Easton ◽  
Peter Jones
Keyword(s):  
High Resolution ◽  
Thermodynamic Modeling ◽  
Icp Ms ◽  
History Of

Assessment of elemental fractionation and matrix effects during in situ Rb–Sr dating of phlogopite by LA-ICP-MS/MS: implications for the accuracy and precision of mineral ages

2021 ◽  
Author(s):  
Ahmad Redaa ◽  
Juraj Farkaš ◽  
Sarah Gilbert ◽  
Alan S. Collins ◽  
Ben Wade ◽  
...  
Keyword(s):  
Matrix Effects ◽  
Chemical Properties ◽  
Elemental Fractionation ◽  
Physical Chemical ◽  
Accuracy And Precision ◽  
Icp Ms

The effect of physical/chemical properties and Rb/Sr elemental fractionation on the accuracy of in situ Rb–Sr dating via LA-ICP-MS/MS.

Rb–Sr geochronology and metamorphic history of Proterozoic to early Archean rocks north of the Cape Smith Fold Belt, Quebec

1987 ◽  
Vol 24 (4) ◽  
pp. 813-825 ◽  
Author(s):  
Ronald Doig
Keyword(s):  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Iron Formation ◽  
Fold Belt ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
The North ◽  
Basement Rocks ◽  
History Of ◽  
Wide Zone

The Churchill Province north of the Proterozoic Cape Smith volcanic fold belt of Quebec may be divided into two parts. The first is a broad antiform of migmatitic gneisses (Deception gneisses) extending north from the fold belt ~50 km to Sugluk Inlet. The second is a 20 km wide zone of high-grade metasedimentary rocks northwest of Sugluk Inlet. The Deception gneisses yield Rb–Sr isochron ages of 2600–2900 Ma and initial ratios of 0.701–0.703, showing that they are Archean basement to the Cape Smith Belt. The evidence that the basement rocks have been isoclinally refolded in the Proterozoic is clear at the contact with the fold belt. However, the gneisses also contain ubiquitous synclinal keels of metasiltstone with minor metapelite and marble that give isochron ages less than 2150 Ma. These ages, combined with low initial ratios of 0.7036, show that they are not part of the basement, as the average 87Sr/86Sr ratio for the basement rocks was about 0.718 at that time.The rocks west of Sugluk Inlet consist mainly of quartzo-feldspathic sediments, quartzites, para-amphibolites, marbles, and some pelite and iron formation. In contrast to the Proterozoic sediments in the Deception gneisses, these rocks yield dates of 3000–3200 Ma, with high initial ratios of 0.707–0.714. These initial ratios point to an age (or a provenance) much greater than that of the Archean Deception gneisses. The rocks of the Sugluk terrain are intruded by highly deformed sills of granitic rocks with ages of about 1830 Ma, demonstrating again the extent and severity of the Proterozoic overprint. The eastern margin of this possibly early Archean Sugluk block is a discontinuity in age, lithology, and geophysical character that could be a suture between two Archean cratons. It is not known if such a suturing event is of Archean age, or if it is related to the deformation of the Cape Smith Fold Belt.Models of evolution incorporating both the Cape Smith Belt and the Archean rocks to the north need to account for the internal structure of the fold belt, the continental affinity of many of the volcanic rocks, the continuity of basement around the eastern end of the belt, and the increase in metamorphism through the northern part of the belt into a broad area to the north. The Cape Smith volcanic rocks may have been extruded along a continental rift, parallel to a continental margin at Sugluk. Continental collison at Sugluk would have thrust the older and higher grade Sugluk rocks over the Deception gneisses, produced the broad Deception antiform, and displaced the Cape Smith rocks to the south in a series of north-dipping thrust slices.

Quartz deformation in the Marquette and Republic troughs, Upper Peninsula of Michigan

1984 ◽  
Vol 21 (7) ◽  
pp. 793-801 ◽  
Author(s):  
Janet Kappmeyer ◽  
David V. Wiltschko
Keyword(s):  
Subgrain Size ◽  
Stress Regime ◽  
Upper Peninsula ◽  
Metamorphic History ◽  
Dislocation Densities ◽  
History Of ◽  
Peak Metamorphism ◽  
Quartz Fabrics ◽  
Upper Peninsula Of Michigan ◽  
Northern Michigan

Quartz fabrics and microstructures in quartzites of the Mesnard and Goodrich formations were examined to better define the deformation and metamorphic history of the Marquette Synclinorium, northern Michigan. Fabric development is very weak in the whole-rock samples and indicates that mica contamination, extensive annealing, and (or) low imposed strains prevented the formation of distinct c-axis fabrics. However, well defined fabrics are preserved in five quartzite pebbles from the Goodrich conglomerate. Double maxima of varying intensities among these pebbles suggest that the northwest section of the district experienced inhomogeneous shear strain. Measured grain sizes yielded differential stresses ranging from 44 to 548 bar (4.4 to 54.8 MPa). Subgrain size data indicate stresses ranging from 151 to 248 bar (15.1 to 24.8 MPa). Dislocation densities determined by observed etch-pit densities using scanning electron microscopy indicate a range of stresses from 330 to 730 bar (33 to 73 MPa). Stress values from dislocation density measurements vary inversely with metamorphic intensity. Cumulatively, these microstructural data indicate that a low-stress regime of deformation preceded a cooler, higher stress pulse. The data also imply that deformation of the Marquette Synclinorium continued after peak metamorphism, contrary to early hypotheses.

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>

scholarly journals U-Pb, Ar-Ar, and Re-Os Geochronological Constraints on Multiple Magmatic–Hydrothermal Episodes at the Lake George Mine, Central New Brunswick

Minerals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 566 ◽  
Author(s):  
Carlin Lentz ◽  
Kathleen Thorne ◽  
Christopher R. M. McFarlane ◽  
Douglas A. Archibald
Keyword(s):  
New Brunswick ◽  
Zircon Geochronology ◽  
Weighted Mean ◽  
Metasedimentary Rocks ◽  
Quartz Veins ◽  
Icp Ms ◽  
Step Heating ◽  
Geochronological Constraints ◽  
Lake George

The Lake George antimony mine was at one time North America’s largest producer of antimony. Despite being widely known for the antimony mineralization, the deposit also hosts a range of styles of mineralization such as multiple generations of W-Mo bearing quartz veins as well as a system of As-Au bearing quartz–carbonate veins. In situ U-Pb zircon geochronology, using LA ICP-MS, of the Lake George granodiorite yielded a weighted mean 206Pb/238U age of 419.6 ± 3.0 Ma. Step heating of phlogopite separated from the lamprophyre dykes produced a 40Ar/39Ar plateau segment date of 419.4 ± 1.4 Ma. Single molybdenite crystal analysis for Re-Os geochronology was conducted on two W-Mo-bearing quartz veins, which cross-cut altered granodiorite and altered metasedimentary rocks and yielded two dates of 415.7 ± 1.7 Ma and 416.1 ± 1.7 Ma respectively. 40Ar/39Ar geochronology of muscovite from alteration associated with Au-bearing quartz–carbonate veins yielded one representative plateau segment date of 414.1 ± 1.3 Ma. The dates produced in this study revealed that the different magmatic–hydrothermal events at the Lake George mine occurred over approximately a 10-million-year period at the end of the Silurian and the start of the Devonian following the termination of the Acadian orogeny.

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.

scholarly journals LA-ICP-MS U–Pb Dating of Cenozoic Rutile Inclusions in the Yuanjiang Marble-Hosted Ruby Deposit, Ailao Shan Complex, Southwest China

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 433
Author(s):  
Tianjian Yang ◽  
Xiaoming Sun ◽  
Guiyong Shi ◽  
Ying Liu
Keyword(s):  
Southwest China ◽  
Mineral Deposits ◽  
Cooling History ◽  
Host Matrix ◽  
Icp Ms ◽  
Lateral Shearing ◽  
The World ◽  
History Of ◽  
Tectonic Belt

Among the marble-hosted ruby deposits in the Himalayan tectonic belt, which yields the highest-quality rubies in the world, the Yuanjiang deposit is the only economically viable one located in China. More attempts are necessary to put constraints on the ore-forming age of these marble-hosted ruby deposits. Here, we dated rutile inclusions in the Yuanjiang rubies using the LA-ICP-MS U–Pb method, which yielded a lower intercept 206Pb/238U age of 20.2 ± 1.2 Ma on the Tera-Wasserburg plot, close to the 22.5–22.2 Ma 40Ar/39Ar ages of phlogopite from the ruby host matrix assemblage. Our U–Pb rutile age put a constraint on the cooling history of the Yuanjiang rubies deposit. The new rutile age is consistent with our previous model that shows the ca. 28–22 Ma left lateral shearing plays an important role in transporting the ruby deposit toward the surface. This study provides the first example of in-situ U–Pb dating of rutile in the Himalayan tectonic belt, demonstrating the great potential of U–Pb rutile geochronology for Cenozoic mineral deposits.

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

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

<p>Deciphering the structural and metamorphic history of the Balsfjord Series in the Upper Allochthon of the Scandinavian Caledonides in northern Norway</p><p>Höpfl Stephan<sup>1</sup>, Konopásek Jiří<sup>1</sup>, Stünitz Holger<sup>1,2</sup> Bergh G., Steffen<sup>1</sup></p><p>UiT Norges arktiske universitet, Institutt for geovitenskap, [email protected]</p><p> </p><p><sup>1</sup>Department of Geosciences, UiT The Arctic University of Norway, Tromsø 9037, Norway</p><p><sup>2</sup>Institut des Sciences de la Terre (ISTO), Université d’Orleans, Orleans 45100, France</p><p> </p><p>The Balsfjord Series is located in the central part of Troms–Finnmark County, northern Norway, and is part of the upper allochthon of the Scandinavian Caledonides. It consists of an Ordovician–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 + Tromsø 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 + Tromsø Nappe Complex features metamorphic peak ages of ca. 455–450 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.</p><p>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–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.      </p><p>Observed thrust kinematics and penetrative retrogression at the bottom of the Nakkedal + Tromsø 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 + Tromsø Nappe Complex, the Balsfjord series and the underlying RNC.</p>

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