scholarly journals Petrography and geochemistry of early Proterozoic granitoid rocks in Wisconsin magmatic terranes of Penokean Orogen, northern Wisconsin

1993 ◽  
Keyword(s):  
Early Proterozoic ◽  
Granitoid Rocks

Rb–Sr biotite and whole-rock data from the Kapuskasing uplift and their bearing on the cooling and exhumation history

1994 ◽  
Vol 31 (7) ◽  
pp. 1172-1181 ◽  
Author(s):  
J. A. Percival ◽  
Z. E. Peterman
Keyword(s):  
Fault Zone ◽  
Spatial Relationship ◽  
Paleomagnetic Data ◽  
Isotopic Ratios ◽  
The West ◽  
Rapid Cooling ◽  
Early Proterozoic ◽  
Granitoid Rocks ◽  
Relationship Of ◽  
Exhumation History

Rb–Sr isotopic ratios were measured on biotite and whole rocks from a suite of 21 granitoid rocks from the southern Kapuskasing uplift. Results of 18 of the whole-rock analyses fall on an isochron with an age of 2.677 ± 0.057 Ga and Sri = 0.70080. Biotite model ages range from 2.50 to 1.93 Ga in a general spatial relationship of decreasing age with depth in the structural section as calibrated with the igneous hornblende barometer for tonalitic rocks and garnet–pyroxene barometers for granulites. Near the Michipicoten belt in the west, biotite ages of ~ 2 Ga reflect disturbances also recorded by paleomagnetic and whole-rock Rb–Sr systems. To the east, in a 70 km long northwest–southeast transect toward the Ivanhoe Lake fault zone, ages decrease from 2.50 to 1.95 Ga. In a southern transect ages are in the range 2.30–2.38 Ga to within 15 km of the fault, reflecting consistent erosion levels corresponding to ~ 0.53 MPa, but decrease to 1.93 Ga to the east, in concert with paleopressures in the 0.7–1.0 GPa range.A plateau of low Rb–Sr biotite dates is not evident, suggesting that the Kapuskasing uplift event exposed a frozen-in cooling profile, rather than setting the Rb–Sr clock by rapid cooling of the rocks from above their closure temperature. The youngest biotite date of 1.93 Ga therefore provides a maximum age for uplift, consistent with paleomagnetic data from Archean rocks and Early Proterozoic dykes, but in conflict with some K–Ar and 40Ar/39Ar biotite age data.

Age and source of detrital zircons from the Missi Formation: a Proterozoic molasse deposit, Trans-Hudson Orogen, Canada

1992 ◽  
Vol 29 (12) ◽  
pp. 2583-2594 ◽  
Author(s):  
Kevin M. Ansdell ◽  
T. Kurtis Kyser ◽  
Mel R. Stauffer ◽  
Garth Edwards
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Detrital Zircons ◽  
Early Proterozoic ◽  
Minimum Age ◽  
Granitoid Rocks ◽  
Evaporation Technique ◽  
Single Zircon ◽  
Flin Flon ◽  
Felsic Volcanic

The Missi Formation in the Flin Flon Basin forms part of a discontinuous series of molasse-type sediments found throughout the Early Proterozoic Trans-Hudson Orogen in northern Saskatchewan and Manitoba. The Flin Flon Basin contains a sequence of proximal-fan to braided-stream fluvial conglomerates and sandstones, which unconformably overlie subaerially weathered Amisk Group volcanic rocks. Stratigraphic way-up indicators have been preserved, even though these rocks have undergone greenschist-facies metamorphism and polyphase deformation. The sedimentary rocks are crosscut by intrusive rocks, which provide a minimum age of sedimentation of 1840 ± 7 Ma.Detrital zircons from each of the six stratigraphic subdivisions of the Flin Flon Basin were analyzed using the single-zircon Pb-evaporation technique. Euhedral to slightly rounded zircons dominate each sample, and these zircons give ages of between about 1854 and 1950 Ma. The Missi sediments were thus deposited between 1840 and 1854 Ma. Possible sources for the detrital zircons are Amisk Group felsic volcanic rocks and post-Amisk granitoid rocks and orthogneisses in adjacent domains within the Trans-Hudson Orogen. However, the immature character of the sedimentary rocks, the composition of clasts, the euhedral character of many of the zircons, and the range in ages suggest that most were likely derived from Amisk Group and granitoid rocks in the western Flin Flon Domain. Rounded zircons are uncommon but provide evidence for the reworking of older Proterozoic sedimentary rocks, or a distant Archean or Early Proterozoic granitoid terrane.

Review of isotope data for Precambrian rocks from the Disko Bugt region, West Greenland

1999 ◽  
pp. 41-47 ◽  
Author(s):  
Feiko Kalsbeek ◽  
Paul N. Taylor
Keyword(s):  
Sr Isotope ◽  
Yield Model ◽  
Original Series ◽  
Early Proterozoic ◽  
West Greenland ◽  
Precambrian Rocks ◽  
Isotope Data ◽  
Metavolcanic Rocks ◽  
Granitoid Rocks ◽  
Data Yield

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Kalsbeek, F., & Taylor, P. N. (1999). Review of isotope data for Precambrian rocks from the Disko Bugt region, West Greenland. Geology of Greenland Survey Bulletin, 181, 41-47. https://doi.org/10.34194/ggub.v181.5110 _______________ Pb-Pb and Rb-Sr isotope data yield whole-rock isochron ages of c. 2800 Ma for two localities of granitoid rocks in the Disko Bugt region, with little evidence of strong later disturbance. Rb-Sr isotope data on Archaean metasediments from two localities, however, were strongly disturbed during the early Proterozoic. Sm-Nd whole-rock data for acid metavolcanic rocks within Archaean supracrustal sequences yield model ages of c. 2800 Ma. The early Proterozoic age of a younger sequence of supracrustal rocks (the Anap nunâ Group) is confirmed by Sm-Nd data, and Rb-Sr whole-rock data for albitised siltstones show that albitisation took place hundreds of millions of years after the peak of early Proterozoic orogenic activity.

scholarly journals Sinistral transpression and hydrothermal activity during emplacement of the Early Proterozoic Julianehåb batholith, Ketilidian orogenic belt, South Greenland

1994 ◽  
Vol 163 ◽  
pp. 5-22
Author(s):  
B Chadwick ◽  
P Erfurt ◽  
T Frisch ◽  
R.A Frith ◽  
A.A Garde ◽  
...  
Keyword(s):  
Shear Zones ◽  
Field Work ◽  
Hydrothermal Activity ◽  
Vertical Shear ◽  
Early Proterozoic ◽  
North West ◽  
North East ◽  
The North ◽  
Granitoid Rocks ◽  
Quartz Veining

The first systematic investigations of the central part of the Early Proterozoic Ketilidian orogen in the vicinity of Søndre Sermilik in the early 1960s suggested that this part of the orogen comprised a mixture of the Julianehåb granite, altered supracrustal rocks and older orthogneisses. Recent field work has shown that the area consists only of a variably deformed suite of granitic to dioritic plutonic rocks and a range of hornblende-bearing dykes of the appinite suite which all belong to the Julianehåb batholith. Steep to vertical shear zones with widths from a few centimetres to more than one kilometre are a significant element of the structure. The principal shear zones trend north-east and they are parallel to the schistosity and subhorizontal linear structures in the granitoid rocks. Kinematic indicators in many of the shear zones indicate sinistral transcurrent displacements. The relationships between granite fabrics, shear zones and mafic dykes suggest that the Julianehåb batholith was emplaced during subduction from the south towards the Archaean craton in the north-west in a sinistral transpressional system. Effects of hydrothermal alteration, mainly in the form of quartz veining, silicification, chloritisation, epidotisation and pyritisation, are common within and adjacent to the largest shear zones. These effects are believed to be related to late stages of the evolution of the batholith. Gold anomalies appear to be closely tied to the hydrothermal phenomena.

The first data on possible Mezozoic magmatism within the Western slope of the Southern Urals

2018 ◽  
pp. 24-34
Author(s):  
A. O. Khotylev ◽  
N. B. Devisheva ◽  
Al. V. Tevelev ◽  
V. M. Moseichuk
Keyword(s):  
Southern Urals ◽  
Western Slope ◽  
Isotopic Age ◽  
The Southern Urals ◽  
Early Proterozoic ◽  
Carbonate Formations ◽  
Two Bodies

Within the Western slope of the Southern Urals, there are plenty of basite dyke complexes of Riphean to Vendian among Precambrian terrigenous-carbonate formations. In metamorphic formations of the Taratash complex (Archean to Early Proterozoic, the northern closure of the Bashkirian meganticlinorium) there was observed the andesitic dyke with isotopic age of 71±1 Ma (U-Pb SHRIMP II on zircons) and near Bakal two bodies of gabbroids with zircons of similar ages were found. These are the first evidence of possible Mezozoic magmatism in this region.

Sign in / Sign up

Export Citation Format

Share Document