Detrital-Zircon Populations and Provenance of Mesoproterozoic Strata of East-Central Idaho, U.S.A.: Correlation with Belt Supergroup of Southwest Montana

Salmon River Arch revisited: new evidence for 1370 Ma rifting near the end of deposition in the Middle Proterozoic Belt basin

Canadian Journal of Earth Sciences ◽

10.1139/e96-079 ◽

1996 ◽

Vol 33 (7) ◽

pp. 1037-1052 ◽

Cited By ~ 44

Author(s):

P. Ted Doughty ◽

Kevin R. Chamberlain

Keyword(s):

Tectonic Setting ◽

Mafic Magma ◽

Isotopic Analysis ◽

Magma Intrusion ◽

Magmatic Complex ◽

East Central ◽

Salmon River ◽

Basin Subsidence ◽

Belt Supergroup ◽

Central Idaho

New U–Pb zircon dates on diabase, diorite, and migmatites within a large magmatic complex in east-central Idaho have refined the age and tectonic setting of the East Kootenay orogeny that affected the Belt basin ca. 1370 Ma. These data show that a large volume of mafic magma was injected into the basin in east-central Idaho and followed shortly thereafter by its own felsic differentiate and granitic plutons and metamorphism of the host sediments ca. 1370 Ma. These data show that the magmatic complex and associated gneisses in east-central Idaho are not pre-Belt basement, but contemporaneous in age with the Belt basin. Nd isotopic analysis of the magmatic rocks establishes that they are not derived from known Proterozoic or Archean basement terranes, but could have formed from the host Yellowjacket Formation or juvenile 1.7 Ga crust. Nd isotopic composition of gneisses and the Yellowjacket Formation are interpreted to support previous correlations between these rocks and the Belt Supergroup. Metamorphic barometry on 1370 Ma migmatites intercalated with the magmatic complex constrain the metamorphism to pressures of 450 MPa (14 km) initially and show that pressure increased to 650 MPa (20 km) before the end of metamorphism, which is consistent with magma intrusion into the bottom of the basin, followed by basin subsidence and sediment loading. We postulate that the East Kootenay orogeny is a pulse of bimodal magmatism, basin rifting, and renewed subsidence and sedimentation that shortly preceded the end of deposition in the Belt basin.

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

Canadian Journal of Earth Sciences ◽

10.1139/e10-049 ◽

2010 ◽

Vol 47 (11) ◽

pp. 1383-1404 ◽

Cited By ~ 24

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.

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