The Middle Fork Plutonic Complex: A plutonic association of coeval peralkaline and metaluminous magmas in the north-central Alaska Range
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
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALASKA
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
MINERALOGY
AGE ESTIMATION
ARGON
BASALT
BIOTITE
CATHODOLUMINESCENCE
DIKES
FLUORINE
GEOLOGIC FORMATIONS
GRANITES
ISOTOPE DATING
ISOTOPE RATIO
MAGMA
MINERALS
MOUNTAINS
PLUTONIC ROCKS
POTASSIUM
RUBIDIUM
STRATIGRAPHY
STRONTIUM
VOLCANIC REGIONS
ALKALI METALS
ALKALINE EARTH METALS
DEVELOPED COUNTRIES
ELEMENTS
FLUIDS
GASES
GEOLOGIC STRUCTURES
GEOLOGY
HALOGENS
IGNEOUS ROCKS
LUMINESCENCE
METALS
MICA
NONMETALS
NORTH AMERICA
RARE GASES
ROCKS
SILICATE MINERALS
USA
VOLCANIC ROCKS
580000* - Geosciences