Isotopic constraints on the thermal history of the Wind River Range, Wyoming: implications for Archean metamorphism

2006 ◽  
Vol 43 (10) ◽  
pp. 1511-1532 ◽  
Author(s):  
Stephen D Keane ◽  
Chris M Hall ◽  
Eric J Essene ◽  
Michael A Cosca ◽  
Charles P DeWolf ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Large Scale ◽  
Time Interval ◽  
High Grade ◽  
Wind River Range ◽  
Metamorphic History ◽  
History Of ◽  
High Grade Metamorphism ◽  
The Difference ◽  
Differential Uplift

Precise U–Pb monazite and 40Ar/39Ar hornblende ages have been obtained from three locations in the high-grade Archean core of the Wind River Range, Wyoming. Monazites from metapelites in the Paradise Basin, Medina Mountain, and Crescent Lake have U–Pb ages of 2718 ± 1, 2633 ± 5, and 2657 ± 2 Ma, respectively. Hornblendes from amphibolites and granulites from the same locations yield plateau 40Ar/39Ar isotope ages of 2652 ± 11, 2572 ± 9, and 2527 ± 8 Ma, respectively, and are interpreted as cooling ages from the last thermal event. The three localities experienced similar peak pressure–temperature conditions. The timing of high-grade metamorphism in the Paradise Basin is older than the emplacement of large subjacent batholiths at 2.63–2.67 Ga. Calculated cooling rates based on monazite–hornblende pairs of 3.4 ± 1.0 °C/Ma for Paradise Basin, 3.8 ± 1.2 °C/Ma for Medina Mountain, and 1.7 ± 0.4 °C/Ma for Crescent Lake cannot be used to rule out reheating during subsequent pluton emplacement. The markedly slower cooling rate inferred for Crescent Lake may indicate early differential uplift or may demark another regional metamorphic event. The difference in 40Ar/39Ar ages between hornblende (2652 ± 11 Ma) and biotite (2637 ± 11 Ma) suggests a more rapid cooling rate, 11 °C/Ma, for Paradise Basin between 2.65 and 2.63 Ga, which may be related to the time of large-scale batholith emplacement elsewhere in the terrane. Combining new data with other ages in the Wind River Range reveals an extended metamorphic history, punctuated by thermal events over a time interval of at least 700 Ma.

Archean crustal evolution of the northwestern Superior craton margin: U-Pb zircon results from the Split Lake Block

1999 ◽  
Vol 36 (12) ◽  
pp. 1973-1987 ◽  
Author(s):  
Christian O Böhm ◽  
Larry M Heaman ◽  
M Timothy Corkery
Keyword(s):  
Superior Province ◽  
High Grade ◽  
Grade Metamorphism ◽  
Metamorphic History ◽  
Zircon Growth ◽  
Growth History ◽  
Northwestern Margin ◽  
History Of ◽  
High Grade Metamorphism ◽  
Superior Craton

The Split Lake Block forms a partly retrogressed, granulite-grade basement segment located at the northwestern margin of the Superior Province in Manitoba. Unlike other segments along the craton margin, the effects of Proterozoic tectonism are relatively minor in the Split Lake Block, making it amenable to establishing firm temporal constraints for the Archean magmatic and metamorphic history of the northwestern Superior Province margin. Consequently, samples from the main lithological units within the Split Lake Block were selected for precise single-grain U-Pb zircon geochronology. Heterogeneous zircon populations isolated from representative enderbite, tonalite, and granodiorite samples reveal a complex growth history with pre-2.8 Ga protolith ages (e.g., 2841 ± 2 Ma tonalite), possibly as old as 3.35 Ga as indicated in a granodiorite sample. The youngest Archean granitic magmatism identified in the eastern Split Lake Block is represented by the 2708 ± 3 Ma Gull Lake granite. A U-Pb zircon age of 2695+4-1 Ma obtained for leucosome in mafic granulite is interpreted to reflect the timing of granulite-grade metamorphism in the Split Lake Block, supported by polyphase zircon growth and (or) lead loss at ca. 2.7 Ga in the enderbite sample. A younger phase of metamorphic zircon growth at ca. 2.62 Ga is documented in the tonalite and granodiorite zircon populations. The 2.70-2.71 Ga crust formation, the occurrence of ca. 2695 Ma high-grade metamorphism, and broadly contemporaneous Paleoproterozoic mafic dykes in both the Split Lake Block and Pikwitonei Granulite Domain imply a common evolution of these high-grade terrains along the northwestern Superior craton margin since the late Archean.

The Pikwitonei Granulite Domain, Manitoba: a giant Neoarchean high-grade terrane in the northwest Superior ProvinceThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.N. Machado, T.E. Krogh, and W. Weber are deceased.

2011 ◽  
Vol 48 (2) ◽  
pp. 205-245 ◽  
Author(s):  
L. M. Heaman ◽  
Ch. O. Böhm ◽  
N. Machado ◽  
T. E. Krogh ◽  
W. Weber ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Superior Province ◽  
High Grade ◽  
Metamorphic Zircon ◽  
Special Issue ◽  
Metamorphic History ◽  
Zircon Growth ◽  
The World ◽  
Northwestern Margin ◽  
History Of

The Pikwitonei Granulite Domain located at the northwestern margin of the Superior Province is one of the largest Neoarchean high-grade terranes in the world, with well-preserved granulite metamorphic assemblages preserved in a variety of lithologies, including enderbite, opdalite, charnockite, and mafic granulite. U–Pb geochronology has been attempted to unravel the protolith ages and metamorphic history of numerous lithologies at three main localities; Natawahunan Lake, Sipiwesk Lake, and Cauchon Lake. The U–Pb age results indicate that some of the layered enderbite gneisses are Mesoarchean (3.4–3.0 Ga) and the more massive enderbites are Neoarchean. The high-grade metamorphic history of the Pikwitonei Granulite Domain is complex and multistage with at least four episodes of metamorphic zircon growth identified: (1) 2716.1 ± 3.8 Ma, (2) 2694.6 ± 0.6 Ma, (3) 2679.6 ± 0.9 Ma, and (4) 2642.5 ± 0.9 Ma. Metamorphic zircon growth during episodes 2 and 3 are interpreted to be regional in extent, corresponding to M1 amphibolite- and M2 granulite-facies events, respectively, consistent with previous field observations. The youngest metamorphic episode at 2642.5 Ma is only recognized at southern Cauchon Lake, where it coincides with granite melt production and possible development of a major northeast-trending deformation zone. The timing and multistage metamorphic history recorded in the Pikwitonei Granulite Domain is similar to most Superior Province high-grade terranes and marks a fundamental break in Archean crustal evolution worldwide at the termination of prolific global Neoarchean greenstone belt formation.

Liquid supercoolings and droplet cooling rates of remelted argon-atomized Fe–30Ni powder particles

1988 ◽  
Vol 3 (3) ◽  
pp. 441-452 ◽  
Author(s):  
Matthew R. Libera ◽  
Pedro P. Bolsaitis ◽  
R. Erik Spjut ◽  
John B. VanderSande
Keyword(s):  
Standard Deviation ◽  
Cooling Rate ◽  
Metal Droplet ◽  
Liquid Droplets ◽  
Interfacial Velocity ◽  
Gas Atmosphere ◽  
History Of ◽  
Powder Particles ◽  
The Difference ◽  
Individual Particles

Individual particles of argon-atomized Fe-30Ni powder are electrodynamically levitated and remelted by a CO2 laser pulse. The thermal history of each droplet during remelting and solidification is monitored by single-color radiation pyrometry at each of three wavelengths (850, 750, and 550 nm). Experiments are done in an atmosphere of either air or nitrogen. The average supercooling of six experiments performed in nitrogen is 298 K with a standard deviation of 14 K. This value is of the same order as several others reported in the literature using bulk levitation and emulsification techniques. The average supercooling of seven experiments performed in air is 163 K with a standard deviation of 20 K. The difference suggests that oxides are forming in the air-remelting experiments and catalyzing nucleation at relatively low supercoolings. The average cooling rate of the liquid droplets prior to solidification in nitrogen is 1.5 × 105 K/s. This measured cooling rate is somewhat higher than that predicted by Newtonian heat flow modeling, and the difference is attributed to radiative losses not considered in the Newtonian model. The measured cooling rate is used to estimate the total heat transfer coefficient characterizing cooling of a small metal droplet in a quiescent gas atmosphere. A lower bound of 1.5 × 106 K/s on the droplet heating rate during recalescence and a minimum average liquid/solid interfacial velocity during recalescence of 0.1 m/s are estimated.

scholarly journals Noch einmal: Zum Verhältnis von Moralität und Sittlichkeit

2019 ◽  
Vol 67 (5) ◽  
pp. 729-743 ◽  
Author(s):  
Jürgen Habermas
Keyword(s):  
Political Theory ◽  
Social Relations ◽  
Large Scale ◽  
Frankfurt School ◽  
Point Of View ◽  
Ethical Life ◽  
Philosophical Discourse ◽  
History Of ◽  
The Difference ◽  
Relations Of Power

Abstract Ever since Hegel made poignant the difference between morality and ethical life (“Sittlichkeit”), philosophical discourse in the traditions that developed subsequently, up to and including the Frankfurt school, has oscillated between those poles. This paper starts out with a short exposition of autonomy as one of the few large-scale innovations in the history of philosophy and then proceeds to discuss Hegel’s concept of “Sittlichkeit” and the objections to be raised against it from a Kantian point of view. Political theory, however, has to move beyond pure normativism and consider actual social relations of power, as Marx disclosed. Mapping out this winding trajectory from Kant to Marx provides some perspective that may be illuminating for challenging present-day issues.

scholarly journals Some Critical Remarks on the Inflationary Universe Concept

1988 ◽  
Vol 130 ◽  
pp. 63-65
Author(s):  
Gerhard Börner
Keyword(s):  
Large Scale ◽  
Higgs Field ◽  
Quantitative Model ◽  
Time Interval ◽  
Inflationary Universe ◽  
Fundamental Particle ◽  
The Standard Model ◽  
History Of ◽  
Simple Change ◽  
The Universe

The basic idea of inflation in cosmology is very simple: It is the assumption that the expansion factor R(t) of a Friedmann-Lemaltre cosmological model grows exponentially during a brief time interval in the very early universe. The phase of exponential growth is followed by a thermalizatlon stage and a subsequent “normal” evolution R(t)∼vt. This “Inflationary expansion“ can help to solve cosmological puzzles inherent in the standard model - such as the large-scale flatness, the horizon structure, the numerical value of the entropy in a comoving volume [for a review see Brandenberger 1985]. To turn this romantic idea of inflation into a quantitative model requires still a lot of work: The simple change in the thermal history of the universe must be derived from a fundamental particle theory. The models proposed so far do not inspire much confidence. In the following a few difficulties of the Higgs field idea, especially the Coleman-Weinberg formalism will be pointed out (section 1). In section 2 some problems connected with the investigation of initially strongly anisotropic or Inhomogeneous cosmological models will be mentioned.

A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies

1997 ◽  
Vol 9 (1) ◽  
pp. 74-91 ◽  
Author(s):  
S.L. Harley ◽  
L.P. Black
Keyword(s):  
Time Interval ◽  
Minor Importance ◽  
High Grade ◽  
Bay Area ◽  
Igneous Activity ◽  
High Grade Metamorphism ◽  
Ancient Times ◽  
Tectonothermal Event ◽  
Very High ◽  
Napier Complex

The long and complex Archaean evolution of the Napier Complex of Enderby Land, characterized by high-grade metamorphism and several strong deformations, is reassessed in the light of new SHRIMPU–Pb zircon dating results bearing on the ages of protoliths and possible regional extents of distinct Archaean tectonothermal events. Initial felsic igneous activity occurred over a significant time interval c. 3800 Ma ago. An age of 2980±9 Ma for the emplacement of charnockite at Proclamation Island might date the oldest tectonothermal event to be recognized in the Napier Complex. An ensuing, very-high grade, previously imprecisely dated tectonothermal event occurred at 2837±15 Ma. U–Pb zircon ages ranging from 2456+8/−5 Ma to 2481±4 Ma date a subsequent, protracted high-grade tectonothermal event. Whereas the ~2840 Ma event is of regional importance in the Amundsen Bay-Casey Bay area, it is possible that the ~2980 Ma event was of only moderate grade, minor importance, or even absent, in that part of the Complex. If so, the apparent trend to very-high temperature metamorphism in the Tula and Scott mountains compared with the Napier Mountains may reflect two distinct metamorphic events rather than a simple baric and thermal gradient. The oldest crustal component in the Napier Complex appears to have been of igneous derivation. Zircon populations in paragneisses at Mount Sones are similar to those in the nearby orthogneisses, which therefore may have been basement. Another paragneiss, in the Casey Bay area, yields no zircons older than 2840 Ma, probably indicating that pre-3000 Ma crust, which is now located nearby, was not exposed at the time of sedimentation there. The isotopic data are quite complex, particularly in rocks that experienced postcrystallization metamorphic temperatures of 1000°C or more. It is postulated that this complexity, which was largely the product of migration of radiogenic Pb within the zircon grains in ancient times, and produced local excesses of this element with respect to its parent U, was caused by volume diffusion at these abnormally high regional crustal temperatures.

scholarly journals The Archaean gneiss complex of northern Labrador A review of current results, ideas and problems

1991 ◽  
Vol 39 ◽  
pp. 153-166
Author(s):  
D. Bridgwater ◽  
L. Schiøtte
Keyword(s):  
Major Part ◽  
Granulite Facies ◽  
High Grade ◽  
Late Archaean ◽  
West Greenland ◽  
Metamorphic History ◽  
Gneiss Complex ◽  
History Of ◽  
Augen Gneiss ◽  
Dominant Phase

1. The early Archaean rocks in northern Labrador can be subdivided into the ea. 3.78 Ga Nulliak supracrus­tal association, the migmatitic Uivak I gneisses, the dominant phase of which was emplaced at ea. 3.73 Ga, and the Uivak II augen gneiss. Inherited low-U rounded inclusions within igneous zircons in the Uivak I gneisses have ages between 3.73 and 3.86 Ga and are more likely to have been derived from a pre-existing high-grade metamorphic gneiss complex than from the Nulliak association. In the early Archaean there were probably several rapid cycles of sedimentary deposition and volcanism followed by emplacement of major plutons. Mid Archaean gneisses are more abundant in northern Labrador than previously realised. The late Archaean metamorphic history of these gneisses is different from the history of the early Archaean gneisses. Whereas an important part of the mid Archaean suite was emplaced in granulite facies and retrogressed at the time of granitoid veining at ea. 2.99 Ga, the major part of the early Archaean rocks were reworked under granulite facies conditions in a sequence of closely spaced events between 2. 7 and 2.8 Ga. The two groups of gneisses had different metamorphic histories until ea. 2.7 Ga, but late and post-tectonic granites of 2.5- 2. 7 Ga age cut across both. It is suggested that the terrane model in southern West Greenland can be extended to Labrador and that tectonic intercalation of early and mid Archaean gneisses took place around 2.7 Ga. Correlation between the Maggo gneisses around Hopedale, mid Archaean gneisses in northernmost Labrador and gneisses from the Akia terrane in West Greenland is suggested. Like the Malene supracrustals in West Greenland the Upernavik supracrustals in Labrador are composite associations, the youngest of which are thought to have been deposited around 2. 7 Ga.

scholarly journals Search for Archaean basement in the Caledonian fold belt of North-East Greenland

1994 ◽  
Vol 162 ◽  
pp. 129-133
Author(s):  
A.P Nutman ◽  
F Kalsbeek
Keyword(s):  
High Grade ◽  
Metamorphic Zircon ◽  
Fold Belt ◽  
Pb Isotope ◽  
Zircon Age ◽  
East Greenland ◽  
Early Proterozoic ◽  
North East ◽  
History Of ◽  
High Grade Metamorphism

SHRIMP U-Pb isotope data on zircon crystals from a gneiss sample near Danmarkshavn, where the presence of Archaean rocks has earlier been documented, show that the rock has undergone a complex history of igneous and metamorphic zircon growth. At least three generations of zircon are present with ages of c. 3000 Ma, c. 2725 Ma and 1967 ±8 Ma (2 α). Apparently the rock was formed from an Archaean protolith which underwent high grade metamorphism during the early Proterozoic. Another sample from the easternmost exposures of the Caledonian basement, collected further north, yielded only early Proterozoic zircons with an age of 1963 ± 6 Ma. Together with a SHRIMP U-Pb zircon age of 1974 ± 17 Ma reported earlier, these results give evidence of a major igneous and metamorphic event in North-East Greenland about 1965 Ma ago.

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