Major oxide, minor oxide, trace element, and geochemical data from rocks collected in a portion of the Fortymile mining district, Alaska, 1999

Szumigala, D. J.; Newberry, R. J.; Werdon, M.B.; Finseth, B. A.; Pinney, D. S.; Flynn, R. L.

doi:10.14509/2727

Cited by 2 publications

(6 citation statements)

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“…Older Early Jurassic 40 Ar/ 39 Ar plateau ages of 191 ± 2 Ma on Hbl and 196 ± 2 Ma on Bt were determined for a sample of Bt-Hbl Qtz diorite from the Chicken pluton, two km to the east of our sample ( Fig. 3; Szumigala et al 2000a). These older ages were determined using the laser heating method as opposed to the furnace heating method used on our sample 1.…”

Section: Jurassic Plutonic Samplesmentioning

confidence: 97%

“…Lacking the information necessary for thermal mod- 40 Ar/ 39 Ar ages and kinematic shear sense indicators. Geology modified from Foster (1992) and Szumigala et al (2000a); kinematic shear-sense indicators from Hansen and Dusel-Bacon (1998). Areas north and south of 64°latitude are located in the southeastern part of the Eagle quadrangle, and the northeastern part of the Tanacross quadrangle, respectively.…”

Section: Sources Of Data and Analytical Techniques Usedmentioning

confidence: 99%

“…Hornblende from a sample of Qtz monzonite (sample 1) of the Chicken pluton (Szumigala et al 2000a), near the northeastern margin of the Taylor Mountain batholith, gives a pseudoplateau age of 187.0 ± 0.5 Ma (Fig. 5A).…”

Section: Jurassic Plutonic Samplesmentioning

confidence: 99%

“…Sample 3 was collected from the interior of a large batholith, whose map outline (Foster 1976) resembles the shape of a pig's head, and hence we informally refer to it as the "Pig pluton." As with the Chicken pluton, an older Hbl 40 Ar/ 39 Ar plateau age of 194 ± 2 Ma age was determined for the Pig pluton by single-grain laser fusion methods (Szumigala et al 2000a).…”

Section: Jurassic Plutonic Samplesmentioning

confidence: 99%

“…Farther west ( Fig. 3), the Mount Warbelow pluton gives a 40 Ar/ 39 Ar Bt plateau age of 185 ± 1 Ma (Szumigala et al 2000a) and a 191.4 ± 0.4 Ma Zrn U-Pb age (J.K. Mortensen, oral communication, 2001).…”

Section: Jurassic Plutonic Samplesmentioning

confidence: 99%

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Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: ⁴⁰Ar/³⁹Ar data from metamorphic and plutonic rocks

Dusel-Bacon¹,

Lanphere²,

Sharp³

et al. 2002

Can. J. Earth Sci.

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We present new 40Ar/39Ar ages for hornblende, muscovite, and biotite from metamorphic and plutonic rocks from the YukonTanana Upland, Alaska. Integration of our data with published 40Ar/39Ar, kinematic, and metamorphic pressure (P) and temperature (T) data confirms and refines the complex interaction of metamorphism and tectonism proposed for the region. The oldest metamorphic episode(s) postdates Middle Permian magmatism and predates the intrusion of Late Triassic (215212 Ma) granitoids into the Fortymile River assemblage (Taylor Mountain assemblage of previous papers). In the eastern Eagle quadrangle, rapid and widespread Early Jurassic cooling is indicated by ~188186 Ma 40Ar/39Ar plateau ages for hornblende from plutons that intrude the Fortymile River assemblage, and for metamorphic minerals from the Fortymile River assemblage and the structurally underlying Nasina assemblage. We interpret these Early Jurassic ages to represent cooling resulting from northwest-directed contraction that emplaced the Fortymile River assemblage onto the Nasina assemblage to the north as well as the Lake George assemblage to the south. This cooling was the final stage of a continuum of subduction-related contraction that produced crustal thickening, intermediate- to high-P metamorphism within both the Fortymile River assemblage and the structurally underlying Lake George assemblage, and Late Triassic and Early Jurassic plutonism in the Fortymile River and Nasina assemblages. Although a few metamorphic samples from the Lake George assemblage yield Jurassic 40Ar/39Ar cooling ages, most yield Early Cretaceous 40Ar/39Ar ages: hornblende ~135115 Ma, and muscovite and biotite ~110108 Ma. We interpret the Early Cretaceous metamorphic cooling, in most areas, to have resulted from regional extension and exhumation of the lower plate, previously tectonically thickened during Early Jurassic and older convergence.

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Section: Jurassic Plutonic Samplesmentioning

confidence: 97%

Section: Sources Of Data and Analytical Techniques Usedmentioning

confidence: 99%

Section: Jurassic Plutonic Samplesmentioning

confidence: 99%

Section: Jurassic Plutonic Samplesmentioning

confidence: 99%

Section: Jurassic Plutonic Samplesmentioning

confidence: 99%

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Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: ⁴⁰Ar/³⁹Ar data from metamorphic and plutonic rocks

Dusel-Bacon¹,

Lanphere²,

Sharp³

et al. 2002

Can. J. Earth Sci.

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Geochemistry, petrography, and zircon U–Pb geochronology of Paleozoic metaigneous rocks in the Mount Veta area of east-central Alaska: implications for the evolution of the westernmost part of the Yukon–Tanana terrane

2013

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We report the results of new mapping, whole-rock major, minor, and trace-element geochemistry, and petrography for metaigneous rocks from the Mount Veta area in the westernmost part of the allochthonous Yukon–Tanana terrane (YTT) in east-central Alaska. These rocks include tonalitic mylonite gneiss and mafic metaigneous rocks from the Chicken metamorphic complex and the Nasina and Fortymile River assemblages. Whole-rock trace-element data from the tonalitic gneiss, whose igneous protolith was dated by SHRIMP U–Pb zircon geochronology at 332.6 ± 5.6 Ma, indicate derivation from tholeiitic arc basalt. Whole-rock analyses of the mafic rocks suggest that greenschist-facies rocks from the Chicken metamorphic complex, a mafic metavolcanic rock from the Nasina assemblage, and an amphibolite from the Fortymile River assemblage formed as island-arc tholeiite in a back-arc setting; another Nasina assemblage greenschist has MORB geochemical characteristics, and another mafic metaigneous rock from the Fortymile River assemblage has geochemical characteristics of calc-alkaline basalt. Our geochemical results imply derivation in an arc and back-arc spreading region within the allochthonous YTT crustal fragment, as previously proposed for correlative units in other parts of the terrane. We also describe the petrography and geochemistry of a newly discovered tectonic lens of Alpine-type metaharzburgite. The metaharzburgite is interpreted to be a sliver of lithospheric mantle from beneath the Seventymile ocean basin or from sub-continental mantle lithosphere of the allochthonous YTT or the western margin of Laurentia that was tectonically emplaced within crustal rocks during closure of the Seventymile ocean basin and subsequently displaced and fragmented by faults.

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Major oxide, minor oxide, trace element, and geochemical data from rocks collected in a portion of the Fortymile mining district, Alaska, 1999

Cited by 2 publications

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Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: ⁴⁰Ar/³⁹Ar data from metamorphic and plutonic rocks

Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: ⁴⁰Ar/³⁹Ar data from metamorphic and plutonic rocks

Geochemistry, petrography, and zircon U–Pb geochronology of Paleozoic metaigneous rocks in the Mount Veta area of east-central Alaska: implications for the evolution of the westernmost part of the Yukon–Tanana terrane

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Major oxide, minor oxide, trace element, and geochemical data from rocks collected in a portion of the Fortymile mining district, Alaska, 1999

Cited by 2 publications

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Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: 40Ar/39Ar data from metamorphic and plutonic rocks

Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: 40Ar/39Ar data from metamorphic and plutonic rocks

Geochemistry, petrography, and zircon U–Pb geochronology of Paleozoic metaigneous rocks in the Mount Veta area of east-central Alaska: implications for the evolution of the westernmost part of the Yukon–Tanana terrane

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Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: ⁴⁰Ar/³⁹Ar data from metamorphic and plutonic rocks

Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: ⁴⁰Ar/³⁹Ar data from metamorphic and plutonic rocks