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The Middle Fork Plutonic Complex: A plutonic association of coeval peralkaline and metaluminous magmas in the north-central Alaska Range

Thesis/Dissertation ·
OSTI ID:7062340
The 57 m.y. Middle Fork Plutonic Complex (MFPC) intrudes Paleozoic metasedimentary rocks south of the Farewell Fault zone in the north-central Alaska Range. Though spatially related to the late Cretaceous - Early Tertiary subduction-related Alaska Range batholith, MFPC is more characteristic of an extensional or anorogenic setting. A swarm of basalt, hawaiite and rhyolite dikes east of the complex intruded, and was intruded by, the plutonic rocks. Approximately 30% of the exposed rock in the 125 km[sup 2] complex is hedenbergite - fayalite syenite, [approx equal]20% is peralkalin arfvedsonite-biotite alkali-feldspar granite (AF granite), and [le]20% is pyroxene-olivine-biotite gabbro. The rest is a mixed unit including clinopyroxene-biotite-amphibole diorite, and hornblende-biotite granite (HB granite). K-Ar and Rb-Sr radiometric dating of rock types shows that they are coeval. Their close spatial and temporal relationships led to complex magmatic interactions. Calculated initial [sup 87]Sr/[sup 86]Sr for gabbro and diorite group is around 0.705 to 0.706. HB granites are heterogeneous, but fall mostly around 0.707 to 0.708. Hypersolvus syenites and AF granites form an isochron with initial [sup 87]Sr/[sup 86]Sr of 0.70965. These groupings suggest that at least three different magmas formed the MFPC; scatter of isotopic data reflects mutual contamination and assimilation. Consanguinous hypersolvus syenite and AF granite mineralogy appears to be controlled by fluorine in the magma chamber. Eruptive stratigraphy, as predicted by intrusive history of MFPC, compares favorably with volcanic stratigraphies of peralkaline volcanic systems worldwide, and MFPC may be modelled as the root zone of a peralkaline volcanic system.
Research Organization:
Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States)
OSTI ID:
7062340
Country of Publication:
United States
Language:
English

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Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
ALASKA
ALKALI METALS
ALKALINE EARTH METALS
ARGON
BASALT
BIOTITE
CATHODOLUMINESCENCE
DEVELOPED COUNTRIES
DIKES
ELEMENTS
FLUIDS
FLUORINE
GASES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
GRANITES
HALOGENS
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPE RATIO
LUMINESCENCE
MAGMA
METALS
MICA
MINERALOGY
MINERALS
MOUNTAINS
NONMETALS
NORTH AMERICA
PLUTONIC ROCKS
POTASSIUM
RARE GASES
ROCKS
RUBIDIUM
SILICATE MINERALS
STRATIGRAPHY
STRONTIUM
USA
VOLCANIC REGIONS
VOLCANIC ROCKS