Preliminary geologic map of the Big Delta quadrangle, Alaska

Weber, Florence R.; Foster, Helen L.; Keith, Terry E.C.; Dusel-Bacon, Cynthia

doi:10.3133/ofr78529a

Cited by 26 publications

(23 citation statements)

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“…4). Carbonaceous quartzite and phyllite and subordinate felsic and mafi c metavolcanic rocks (Nasina assemblage) are overlain by quartzofeldspathic mylonitic rocks of probable hypabyssal origin (unit MDmg) that are, in turn, overlain by phyllite, quartz-feldspar-eye mylonitic semischist, quartzite, marble, and greenstone (Butte assemblage) (Weber et al, 1978). Smith et al (1994) correlated the carbonaceous unit (Nasina assemblage) and the overlying phyllite and semischist unit (Butte assemblage) with the Keevy Peak Formation and the Totatlanika Schist, respectively, of the Alaska Range (Wahrhaftig, 1968(Wahrhaftig, , 1970.…”

Section: Salcha River Area Yukon-tanana Uplandmentioning

confidence: 99%

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U-Pb zircon and geochemical evidence for bimodal mid-Paleozoic magmatism and syngenetic base-metal mineralization in the Yukon-Tanana terrane, Alaska

Dusel-Bacon

Wooden

Hopkins

2004

Geol Soc America Bull

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New SHRIMP (sensitive, high-resolution ion microprobe) U-Pb zircon ages and trace element geochemical data for mafi c and felsic metaigneous rocks of the pericratonic Yukon-Tanana terrane in east-central Alaska help defi ne the tectonic setting of mid-Paleozoic magmatism and syngenetic hydrothermal Zn-Pb-Ag mineralization along the ancient Pacifi c margin of North America. We compare data from similar greenschist-facies sequences of bimodal volcanic and subvolcanic rocks associated with carbonaceous and siliciclastic marine sedimentary rocks, in the Wood River area of the Alaska Range and the Salcha River area of the Yukon-Tanana Upland, and from amphibolite-facies augen gneiss and mafi c gneiss (amphibolite) in the Goodpaster River area of the upland. Allowing for analytical uncertainties, igneous crystallization age ranges of 376-353 Ma, 378-346 Ma, and 374-358 Ma are indicated by 13 new SHRIMP U-Pb dates for the Wood River, Salcha River, and Goodpaster River areas, respectively. Bimodal magmatism is indicated by Late Devonian crystallization ages for both augen gneiss (371 ± 3 and 362 ± 4 Ma) and associated orthoamphibolite (369 ± 3 Ma) in the upland and by stratigraphic interleaving of mafi c and felsic rocks in the Alaska Range. Metabasites in all three study areas have elevated HFSE (high fi eld strength element) and REE (rare earth element) contents indicative of generation in a within-plate (extensional) tectonic setting. Within-plate trace element signatures also are indicated for peralkaline metarhyolites that host the largest volcanogenic massive sulfi de deposits of the Bonnifi eld district in the Wood River area and for metarhyolite tuff interlayered with the carbonaceous Nasina assemblage, which hosts sedimentary exhalative sulfi de occurrences in the Salcha River area. Most of the other felsic metaigneous samples from the Alaska Range and the Yukon-Tanana Upland have geochemical signatures that are similar to those of both average upper continental crust and continental-margin arc rocks generated in thick continental crust. Given the absence in our study areas of intermediate-composition magmatic products generally found in most arcs, and the presence of bimodal magmatism, the alkalic within-plate chemistry of the mafi c rocks and some of the felsic rocks, and the widespread occurrence of interlayered carbonaceous sedimentary rocks indicative of deposition within a restricted marine basin or submerged continental margin, we consider it most likely that this prolonged Late Devonian to Early Mississippian magmatic episode resulted from attenuation of the ancient continental margin of western North America, rather than development of an arc, as proposed by many others.

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Section: Salcha River Area Yukon-tanana Uplandmentioning

confidence: 99%

“…These greenschist-facies rocks structurally and/or depositionally overlie amphibolite-facies metasedimentary and metaigneous tectonites (Weber et al, 1978;Smith et al, 1994). The tectonites crop out in two circular areas (Salcha River gneiss dome and West Point Complex; Fig.…”

Section: Salcha River Area Yukon-tanana Uplandmentioning

confidence: 99%

U-Pb zircon and geochemical evidence for bimodal mid-Paleozoic magmatism and syngenetic base-metal mineralization in the Yukon-Tanana terrane, Alaska

Dusel-Bacon

Wooden

Hopkins

2004

Geol Soc America Bull

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“…The Yukon-Tanana Upland was originally described by Mertie (1937). More recent mapping by Foster and Weber (Foster 1970(Foster , 1976Foster et al 1976Foster et al , 1979Weber et al 1978) and others has recognized the variety of metamorphic rocks in the region and the extent and variety of igneous rocks. Geochronological studies in the terrane have been undertaken on a piecemeal basis starting with early Pb-alpha work by Matzko et al (1958), proceeding to recent U-Th-Pb studies by Aleinikoff et al (1981 a,b), and continuing with K-Ar studies by the authors (Wilson and Shew 1981;this report).…”

Section: Introductionmentioning

confidence: 96%

Review of radiometric data from the Yukon Crystalline Terrane, Alaska and Yukon Territory

Wilson¹,

Smith²,

Shew³

1985

Can. J. Earth Sci.

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The results of more than 20 years of geochronological studies in the Yukon Crystalline Terrane in east-central Alaska and the western Yukon Territory suggest at least six igneous and thermal (metamorphic?) events. Plutonism during Mississippian, Early Jurassic, mid-Cretaceous, Late Cretaceous, and early Tertiary times is indicated. Evidence also indicates that Mississippian, Early Jurassic, late Early Cretaceous, and late Cretaceous thermal (metamorphic?) events have affected parts of the terrane. The western part of the terrane was affected by a significant regional metamorphic event in late Early Cretaceous time, followed by a terrane-wide mid-Cretaceous plutonic event. The pattern of K-Ar ages allows division of the terrane into domains, bounded by northeast-trending lineaments.L'examen des rksultats de plus de 20 annkes d'ktudes gkochronologiques de la plate-forme cristalline du Yukon rkvkle au moins la prCsence de six kvknements ignks et thermiques (mktamorphiques?). Le plutonisme fut actif durant le Mississippien, le Jurassique infkrieur, le Crktack moyen, le Crktack supkrieur et le Tertiaire infkrieur. On observe que des manifestations thermiques (mktamorphiques?) ont affectk des parties de la plate-forme cristalline du Yukon durant le Mississippien, le Jurassique infkrieur, le CrktacC tardi-infkrieur et le Crktace supkrieur. Durant le Crktack tardi-infkrieur est survenu un important kvknement de mktamorphisme regional qui a affectk la partie occidentale de la plate-forme cristalline, lequel fut suivi au CrktacC moyen par un kvknement plutonique englobant toute la largeur de la plate-forme cristalline. Le motif d'ktalement des Lges K-Ar permet de diviser la plate-forme cristalline en domaines, lesquels sont limitks par des lineaments de direction nord-est.[Traduit par le journal]Can.

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“…In the Liese Zone, Rhys et al (2003) mapped several fault generations that consist of early moderately north-northwest dipping normal faults, southsoutheast dipping normal faults, northeast-trending sinistral faults, and rare northwest-trending faults. Low-angle faults of uncertain kinematics are also known in the region (Weber et al 1978).…”

Section: Geology Of the Goodpaster Mining Districtmentioning

confidence: 99%

Cretaceous reduced granitoids in the Goodpaster Mining District, east central Alaska

Dilworth¹,

Mortensen²,

Ebert³

et al. 2007

Can. J. Earth Sci.

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The >5 Moz (1 oz (troy) = 31.103 g) gold veins of the Liese Zone and nearby prospects in the Goodpaster Mining District of east central Alaska are spatially and temporally associated with late-Early to Late Cretaceous reduced granitoids that are divided into a granite suite, tonalite suite, and diorite suite in decreasing age. Synkinematic to postkinematic biotite ± hornblende granite, granodiorite, pegmatite, and two-mica granite with accessory garnet compose the granite suite (109-107 Ma). The tonalite suite (107-103 Ma) forms small to large bodies of postkinematic hornblende-biotite granodiorite to tonalite with rare granite. Intruding the granite and parts of the tonalite suites are aplite and pegmatite that grade through sugary pegmatoidal or aplitic quartz veins and finally into quartz veins along strike. The diorite suite (95.4-93.7 Ma) consists of small stocks of diorite to tonalite that intrude the older suites and are inferred to intrude the shallowly dipping auriferous quartz veins. Limited data indicate granitoid emplacement at 5-9 km depths, consistent with formation of the auriferous quartz veins based upon published fluid inclusion data. The weakly peraluminous granite and tonalite suites are distinguished by variable amounts of monazite and zircon whereas the diorite suite is metaluminous, contains <5% magnetite, and lacks monazite. All suites are subalkalic, calc-alkaline and have low magnetic susceptibilities, high large-ion lithophile element/high field-strength element (LILE/HFSE), and depleted Nb and Ti. The granite suite has higher 206 Pb/ 204 Pb values (19.4-19.6) than the diorite (19.1). Overall the granite and tonalite suites likely represent melts generated late during crustal thickening that intruded along shallowly dipping faults during exhumation, whereas the diorite suite represents postdeformation melts that underwent less interaction with the old silicic crust.Résumé : Les filons aurifères de la zone Liese (>5 Moz) (1 oz (troy) = 31.103 g) et les prospects avoisinants dans le district minier de Goodpaster du centre-est de l'Alaska sont associés dans le temps et l'espace à des granitoïdes du Crétacé précoce à tardif qui ont subi une réduction et qui sont regroupés en une suite granitique, une suite tonalitique et une suite dioritique, selon un âge décroissant. La suite granitique (109 à 107 Ma) est composée de granite syn-à post-cinématique à biotite ± hornblende, de granodiorite, de pegmatite et d'un granite à deux micas avec du grenat accessoire. La suite tonalitique (107 à 103 Ma) forme de petits à de grands amas post-cinématique de granodiorite à hornblend-ebiotite à une tonalite avec, rarement, du granite. Les suites granitiques et certaines parties des suites tonalitiques ont subi l'intrusion d'une aplite et d'une pegmatite qui passent de filons de quartz pegmatoïde finement granulaire ou aplitique à des filons de quartz longeant la direction. La suite dioritique (95,4 à 93,7 Ma) comprend de petits massifs intrusifs, de diorite à tonalite, qui pénètrent les suites plus ancienn...

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Preliminary geologic map of the Big Delta quadrangle, Alaska

Cited by 26 publications

References 0 publications

U-Pb zircon and geochemical evidence for bimodal mid-Paleozoic magmatism and syngenetic base-metal mineralization in the Yukon-Tanana terrane, Alaska

U-Pb zircon and geochemical evidence for bimodal mid-Paleozoic magmatism and syngenetic base-metal mineralization in the Yukon-Tanana terrane, Alaska

Review of radiometric data from the Yukon Crystalline Terrane, Alaska and Yukon Territory

Cretaceous reduced granitoids in the Goodpaster Mining District, east central Alaska

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