Geochronological Constraints on Mesoproterozoic and Neoproterozoic(?) High-Grade Metasedimentary Rocks of North-Central Idaho, U.S.A.

2007 ◽  
pp. 37-53 ◽  
Author(s):  
REED S. LEWIS ◽  
JEFFREY D. VERVOORT ◽  
RUSSELL F. BURMESTER ◽  
WILLIAM C. McCLELLAND ◽  
ZHAOSHAN CHANG
Keyword(s):  
High Grade ◽  
North Central ◽  
Metasedimentary Rocks ◽  
Geochronological Constraints ◽  
Central Idaho

Detrital zircon analysis of Mesoproterozoic and Neoproterozoic metasedimentary rocks of north-central Idaho: implications for development of the Belt–Purcell basin

2010 ◽  
Vol 47 (11) ◽  
pp. 1383-1404 ◽  
Author(s):  
Reed S. Lewis ◽  
Jeffrey D. Vervoort ◽  
Russell F. Burmester ◽  
Peter J. Oswald
Keyword(s):  
Detrital Zircon ◽  
Inductively Coupled Plasma ◽  
North Central ◽  
Inductively Coupled ◽  
Metasedimentary Rocks ◽  
The North ◽  
Basement Rocks ◽  
Two Samples ◽  
Belt Supergroup ◽  
Central Idaho

The authors analyzed detrital zircon grains from 10 metasedimentary rock samples of the Priest River complex and three other amphibolite-facies metamorphic sequences in north-central Idaho to test the previous assignment of these rocks to the Mesoproterozoic Belt–Purcell Supergroup. Zircon grains from two samples of the Prichard Formation (lower Belt) and one sample of Cambrian quartzite were also analyzed as controls with known depositional ages. U–Pb zircon analysis by laser ablation — inductively coupled plasma — mass spectrometry reveals that 6 of the 10 samples contain multiple age populations between 1900 and 1400 Ma and a scatter of older ages, similar to results reported from the Belt–Purcell Supergroup to the north and east. Results from the Priest River metamorphic complex confirm previous correlations with the Prichard Formation. Samples from the Golden and Elk City sequences have significant numbers of 1500–1380 Ma grains, which indicates that they do not predate the Belt. Rather, they are probably from a relatively young, southwestern part of the Belt Supergroup (Lemhi subbasin). Non-North American (1610–1490 Ma) grains are rare in these rocks. Three samples of quartzite from the Syringa metamorphic sequence northwest of the Idaho batholith contain zircon grains younger than the Belt Supergroup and support a Neoproterozoic age. A single Cambrian sample has abundant 1780 Ma grains and none younger than ∼1750 Ma. These results indicate that the likely protoliths of many high-grade metamorphic rocks in northern Idaho were strata of the Belt–Purcell Supergroup or overlying rocks of the Neoproterozoic Windermere Supergroup and not basement rocks.

Structural and geochronological constraints on the role of partial melting during the formation of the Shuswap metamorphic core complex at the latitude of the Thor-Odin dome, British Columbia

1999 ◽  
Vol 36 (6) ◽  
pp. 917-943 ◽  
Author(s):  
Olivier Vanderhaeghe ◽  
Christian Teyssier ◽  
Richard Wysoczanski
Keyword(s):  
Partial Melting ◽  
Metamorphic Core Complex ◽  
High Grade ◽  
Core Complex ◽  
Genetic Link ◽  
The Core ◽  
Lower Unit ◽  
Geochronological Constraints ◽  
Metamorphic Core ◽  
Middle Unit

At the latitude of the Thor-Odin dome, the Shuswap metamorphic core complex exposes a ~15 km thick structural section composed of an upper unit that preserved Mesozoic metamorphism, structures, and cooling ages, separated from the underlying high-grade rocks by low-angle detachment zones. Below the detachments, the core of the complex consists of an amphibolite-facies middle unit overlying a migmatitic lower unit exposed in the core of the Thor-Odin dome. Combined structural and super high resolution ion microprobe (SHRIMP) U-Pb geochronology studies indicate that the pervasive shallowly dipping foliation and east-west lineation developed in the presence of melt during Paleocene time. SHRIMP analyses of complexly zoned zircon grains suggest that the migmatites of the lower unit crystallized at ~56 Ma, and a syntectonic leucogranite at ~60 Ma. We suggest that leucogranite migrated upward from the migmatites through an array of dikes and sills that permeated the middle unit and ponded to form laccoliths spatially related to the detachment zones. The similarity in ages of inherited zircon cores in the two migmatite and the leucogranite samples suggests a genetic link consistent with the structural analysis. Following the crystallization of migmatites, the terrane cooled rapidly, as indicated by argon thermochronology. We propose that exhumation of the core of the Canadian Cordillera during the formation of the Shuswap metamorphic core complex occurred from ~60 to 56 Ma at a time when the crust was significantly partially molten. These structural and temporal relationships suggest a genetic link between mechanical weakening of the crust by partial melting, late-orogenic collapse, and exhumation of high-grade rocks in the hinterland of a thermally mature orogenic belt.

scholarly journals Foraging Ecology of Long-legged Myotis (Myotis volans) In North-central Idaho

2007 ◽  
Vol 88 (5) ◽  
pp. 1261-1270 ◽  
Author(s):  
Joseph S. Johnson ◽  
Michael J. Lacki ◽  
Michael D. Baker
Keyword(s):  
Foraging Ecology ◽  
North Central ◽  
Myotis Myotis ◽  
Central Idaho

Rb–Sr whole-rock geochronology of the Gamitagama area, north central Ontario

1981 ◽  
Vol 18 (2) ◽  
pp. 323-329 ◽  
Author(s):  
A. Turek ◽  
T. E. Smith ◽  
C. H. Huang
Keyword(s):  
Greenstone Belt ◽  
Complex Terrain ◽  
Regional Metamorphism ◽  
Superior Province ◽  
The South ◽  
Stratigraphic Sequence ◽  
North Central ◽  
Metasedimentary Rocks ◽  
Area North ◽  
Radiometric Ages

The Gamitagama greenstone belt is situated to the south of the Archean Wawa belt of the Superior Province, and is about 50 km south of Wawa, Ontario. The Rb–Sr ages being reported here show that the metavolcanic and associated metasedimentary rocks are older than 2665 ± 45 Ma, which is a whole-rock isochron age of the pretectonic or syntectonic trondhjemitic plutons. The Gamitagama Lake complex, a calcalkalic differentiated and multiple diorite pluton, postdates the regional metamorphism and gives an age of 2645 ± 100 Ma. Potassic granitoid stocks, which are considered to be coeval with the Gamitagama Lake complex, define an isochron age of 2590 ± 80 Ma. The greenstone belt and associated intrusives are adjacent to the Southern batholith, a complex terrain of gneisses and migmatites, for which an isochron age of 2570 ± 90 Ma has been obtained. The radiometric ages reported here support the established stratigraphic sequence and prove that the rocks are Archean in age.

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