The Idaho Batholith is a granitic and granodioriticbatholith of Cretaceous-Paleogene age that covers approximately 25,000 square kilometres (9,700 sq mi) of central Idaho and adjacent Montana. The batholith has two lobes that are separate from each other geographically and geologically. The Bitterroot lobe is the smaller lobe and the larger lobe is the Atlanta lobe. The Bitterroot lobe is in the north and is separated from the larger Atlanta lobe in the south by the Belt Supergroupmetamorphic rocks that compose the Salmon River Arch.[1] Much of the Atlanta and Bitterroot lobes are in the Idaho Batholith ecoregion.[2]
Castle Peak is the highest point on the Idaho Batholith
(Left) Geologic map showing the Late Cretaceous Plutonic Rocks corresponding to the Kaniksu Batholith, and the Bitterroot and Atlanta lobes of the Idaho Batholith. (Right) Geologic map of the Salmon River Arch separating the Idaho Batholith lobes.
Generalized map of the Idaho Batholith showing the Atlanta lobe, the Bitterroot lobe, and the Challis suite.
The overall intrusive event that created the Idaho batholith lasted for around 55 million years from Late Cretaceous to the Eocene (98 to 43 Ma) of magmatism and includes the younger Challis suite which is not considered to be part of the Idaho Batholith.[3] The Challis suite intruded both the Atlanta and Bitterroot lobes of the Idaho Batholith as well as the surrounding areas to the east of the Atlanta lobe.[3] The Challis suite is more petrologically diverse and contains a range of rocks from gabbro to granite.[3][4]
The Atlanta lobe was formed in the Late Cretaceous, 98 to 68 million years ago.[5][1] The early metaluminous suite (98-87 Ma) makes up the southeastern edge of the Atlanta pluton.[4] The boarder zone suite (92-85 Ma) makes up the western edge of the Atlanta pluton.[4] The Atlanta peraluminous suite (83-67 Ma) makes up the majority of the Atlanta lobe that stretches farther south than the early metaluminous suite and ends farther north than the early metaluminous suite.[3][6]
Structures
The Atlanta lobe lacks uniform deformation and foliation across the lobe but contains small areas of localized deformation.[7]
Petrology
The Atlanta lobe is petrologically homogeneous overall.[3] The magma from the Atlanta peraluminous suite (which makes up the majority of the Atlanta Lobe) is made almost entirely of preexisting continental material and contains biotite-containing granodiorite and two-mica granite.[3] However, the early metaluminous suite (which makes up the southern edge of the Atlanta lobe) is petrologically different from the early metaluminous suite and contains tonalite, granodiorite and quartz diorite.[4][3] The early metaluminous suite is also distinguished from the Atlanta peraluminous suite by the presence of hornblende and 10 cm long potassium feldspar megachrysts.[4] Like the early metaluminous suite, the border zone suite (which makes up the western edge of the Atlanta Lobe) is made of tonalite, granodiorite and quartz diorite.[6]
Bitterroot lobe
Age
The Bitterroot lobe was formed in the Late Cretaceous and Paleocene, 75 to 53 million years ago.[5][1] The Late metaluminous suite (75-69 Ma) makes up a small portion of the Bitterroot lobe that borders the greater Bitterroot lobe.[3][4] The Bitterroot lobe is mostly made from the Bitterroot peraluminous suite (66-53 Ma) consisting of the central portion of the Bitterroot lobe.[3][4]
Structures
The Bitterroot lobe shows regional strain with foliation that strikes to the northwest and dips to the northeast, which is parallel with other natural features in the area such as the Lewis and Clark line.[7][3] The Lewis and Clark line is a area of weakened crust where major faulting has occurred with steep or vertical dipping and striking to the northwest.[8] This deformation is attributed to the western Idaho shear zone.[4]
Petrology
The Bitterroot lobe is petrologically similar to the Atlanta lobe.[4][3] The Bitterroot peraluminous suite (which makes up the majority of the Bitterroot lobe) mostly consists of biotitegranodiorite, but with less muscovite-bearing granite than the Atlanta lobe.[4] The late metaluminous suite (which borders the Bitterroot lobe) is made of a range of diorite from, quartz diorite to granodiorite.
^ abcGaschnig, R.M.; Vervoort, J.D.; Lewis, R.S.; McClelland, W.C. (2010). "Migrating magmatism in the northern US Cordillera: in situ U–Pb geochronology of the Idaho batholith". Contributions to Mineralogy and Petrology. 159 (6): 863–883. doi:10.1007/s00410-009-0459-5. S2CID 128413910.
^"Ecoregions of Idaho" (PDF). U.S. Environmental Protection Agency. (PDF) from the original on April 18, 2021. Retrieved December 22, 2014.
^ abcdefghijkByerly, A.; Tikoff, B.; Kahn, M.; Jicha, B.; Gaschnig, R.; Fayon, A.K. (2016). "Internal fabrics of the Idaho batholith, USA". Lithosphere. 9 (2): 283–298. doi:10.1130/L551.1. ISSN 1941-8264.
^ abcdefghijGaschnig, Richard M.; Vervoort, Jeffrey D.; Lewis, Reed S.; Tikoff, Basil (2011). "Isotopic Evolution of the Idaho Batholith and Challis Intrusive Province, Northern US Cordillera". Journal of Petrology. 52 (12): 2397–2429. doi:10.1093/petrology/egr050. ISSN 1460-2415.
^ abFoster, D.A.; Fanning, C.M. (1997). "Geochronology of the northern Idaho Batholith and the Bitterroot metamorphic core complex: magmatism preceding and contemporaneous with extension". Geological Society of America Bulletin. 109 (4): 379–394. doi:10.1130/0016-7606(1997)109<0379:GOTNIB>2.3.CO;2.
^ abGaschnig, Richard M.; Vervoort, Jeffrey D.; Lewis, Reed S.; Tikoff, Basil (2011-12-01). "Isotopic Evolution of the Idaho Batholith and Challis Intrusive Province, Northern US Cordillera". Journal of Petrology. 52 (12): 2397–2429. doi:10.1093/petrology/egr050. ISSN 0022-3530.
^ abKahn, Maureen; Fayon, Annia K.; Tikoff, Basil (2020-07-01). "Constraints on the post-orogenic tectonic history along the Salmon River suture zone from low-temperature thermochronology, western Idaho and eastern Oregon". Rocky Mountain Geology. 55 (1): 27–54. doi:10.24872/rmgjournal.55.1.27. ISSN 1555-7340. S2CID 225560269.
^Harrison, J.E.; Griggs A.B.; Wells J.D. (1986). "Geologic and Structure Maps of the Wallace 1(degree) x 2 (degree) Quadrangle, Montana and Idaho". U.S. Geological Survey. Map I-1509-A: sheet 2 of 2.
January 31, 2023
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The Idaho Batholith is a granitic and granodioritic batholith of Cretaceous Paleogene age that covers approximately 25 000 square kilometres 9 700 sq mi of central Idaho and adjacent Montana The batholith has two lobes that are separate from each other geographically and geologically The Bitterroot lobe is the smaller lobe and the larger lobe is the Atlanta lobe The Bitterroot lobe is in the north and is separated from the larger Atlanta lobe in the south by the Belt Supergroup metamorphic rocks that compose the Salmon River Arch 1 Much of the Atlanta and Bitterroot lobes are in the Idaho Batholith ecoregion 2 Idaho BatholithStratigraphic range Cretaceous to PaleogeneTypePlutonLithologyPrimaryGranite and GranodioriteOtherQuartz diorite and TonaliteLocationRegionCentral IdahoCountry United StatesCastle Peak is the highest point on the Idaho Batholith Left Geologic map showing the Late Cretaceous Plutonic Rocks corresponding to the Kaniksu Batholith and the Bitterroot and Atlanta lobes of the Idaho Batholith Right Geologic map of the Salmon River Arch separating the Idaho Batholith lobes Generalized map of the Idaho Batholith showing the Atlanta lobe the Bitterroot lobe and the Challis suite The overall intrusive event that created the Idaho batholith lasted for around 55 million years from Late Cretaceous to the Eocene 98 to 43 Ma of magmatism and includes the younger Challis suite which is not considered to be part of the Idaho Batholith 3 The Challis suite intruded both the Atlanta and Bitterroot lobes of the Idaho Batholith as well as the surrounding areas to the east of the Atlanta lobe 3 The Challis suite is more petrologically diverse and contains a range of rocks from gabbro to granite 3 4 Contents 1 Atlanta lobe 1 1 Age 1 2 Structures 1 3 Petrology 2 Bitterroot lobe 2 1 Age 2 2 Structures 2 3 Petrology 3 See also 4 ReferencesAtlanta lobe EditAge Edit The Atlanta lobe was formed in the Late Cretaceous 98 to 68 million years ago 5 1 The early metaluminous suite 98 87 Ma makes up the southeastern edge of the Atlanta pluton 4 The boarder zone suite 92 85 Ma makes up the western edge of the Atlanta pluton 4 The Atlanta peraluminous suite 83 67 Ma makes up the majority of the Atlanta lobe that stretches farther south than the early metaluminous suite and ends farther north than the early metaluminous suite 3 6 Structures Edit The Atlanta lobe lacks uniform deformation and foliation across the lobe but contains small areas of localized deformation 7 Petrology Edit The Atlanta lobe is petrologically homogeneous overall 3 The magma from the Atlanta peraluminous suite which makes up the majority of the Atlanta Lobe is made almost entirely of preexisting continental material and contains biotite containing granodiorite and two mica granite 3 However the early metaluminous suite which makes up the southern edge of the Atlanta lobe is petrologically different from the early metaluminous suite and contains tonalite granodiorite and quartz diorite 4 3 The early metaluminous suite is also distinguished from the Atlanta peraluminous suite by the presence of hornblende and 10 cm long potassium feldspar megachrysts 4 Like the early metaluminous suite the border zone suite which makes up the western edge of the Atlanta Lobe is made of tonalite granodiorite and quartz diorite 6 Bitterroot lobe EditAge Edit The Bitterroot lobe was formed in the Late Cretaceous and Paleocene 75 to 53 million years ago 5 1 The Late metaluminous suite 75 69 Ma makes up a small portion of the Bitterroot lobe that borders the greater Bitterroot lobe 3 4 The Bitterroot lobe is mostly made from the Bitterroot peraluminous suite 66 53 Ma consisting of the central portion of the Bitterroot lobe 3 4 Structures Edit The Bitterroot lobe shows regional strain with foliation that strikes to the northwest and dips to the northeast which is parallel with other natural features in the area such as the Lewis and Clark line 7 3 The Lewis and Clark line is a area of weakened crust where major faulting has occurred with steep or vertical dipping and striking to the northwest 8 This deformation is attributed to the western Idaho shear zone 4 Petrology Edit The Bitterroot lobe is petrologically similar to the Atlanta lobe 4 3 The Bitterroot peraluminous suite which makes up the majority of the Bitterroot lobe mostly consists of biotite granodiorite but with less muscovite bearing granite than the Atlanta lobe 4 The late metaluminous suite which borders the Bitterroot lobe is made of a range of diorite from quartz diorite to granodiorite See also EditBitterroot National Forest List of mountain ranges in Montana List of mountain ranges in Idaho Idaho portal Mountains portal Pacific Northwest portalReferences Edit a b c Gaschnig R M Vervoort J D Lewis R S McClelland W C 2010 Migrating magmatism in the northern US Cordillera in situ U Pb geochronology of the Idaho batholith Contributions to Mineralogy and Petrology 159 6 863 883 doi 10 1007 s00410 009 0459 5 S2CID 128413910 Ecoregions of Idaho PDF U S Environmental Protection Agency Archived PDF from the original on April 18 2021 Retrieved December 22 2014 a b c d e f g h i j k Byerly A Tikoff B Kahn M Jicha B Gaschnig R Fayon A K 2016 Internal fabrics of the Idaho batholith USA Lithosphere 9 2 283 298 doi 10 1130 L551 1 ISSN 1941 8264 a b c d e f g h i j Gaschnig Richard M Vervoort Jeffrey D Lewis Reed S Tikoff Basil 2011 Isotopic Evolution of the Idaho Batholith and Challis Intrusive Province Northern US Cordillera Journal of Petrology 52 12 2397 2429 doi 10 1093 petrology egr050 ISSN 1460 2415 a b Foster D A Fanning C M 1997 Geochronology of the northern Idaho Batholith and the Bitterroot metamorphic core complex magmatism preceding and contemporaneous with extension Geological Society of America Bulletin 109 4 379 394 doi 10 1130 0016 7606 1997 109 lt 0379 GOTNIB gt 2 3 CO 2 a b Gaschnig Richard M Vervoort Jeffrey D Lewis Reed S Tikoff Basil 2011 12 01 Isotopic Evolution of the Idaho Batholith and Challis Intrusive Province Northern US Cordillera Journal of Petrology 52 12 2397 2429 doi 10 1093 petrology egr050 ISSN 0022 3530 a b Kahn Maureen Fayon Annia K Tikoff Basil 2020 07 01 Constraints on the post orogenic tectonic history along the Salmon River suture zone from low temperature thermochronology western Idaho and eastern Oregon Rocky Mountain Geology 55 1 27 54 doi 10 24872 rmgjournal 55 1 27 ISSN 1555 7340 S2CID 225560269 Harrison J E Griggs A B Wells J D 1986 Geologic and Structure Maps of the Wallace 1 degree x 2 degree Quadrangle Montana and Idaho U S Geological Survey Map I 1509 A sheet 2 of 2 Retrieved from https en wikipedia org w index php title Idaho Batholith amp oldid 1107797575, wikipedia, wiki, book, books, library,
