Jim River and Hodzana plutons, Alaska: the role of assimilation in the petrogenesis of syenite and granite

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6595425

Blum, J D; Blum, A E; Dillon, J T

Early Cretaceous plutonic rocks in central Alaska intrude both Devonian to Jurassic oceanic rocks of the Angayuchum terrane (AT) and early Paleozoic to Precambrian continental metasediments of the Ruby terrane (RT). Most plutons intrude only the RT and are biotite and two-mice granite. The Hodzana pluton intrudes both fault-bounded terranes, constraining movement between them to the emplacement age of about 110 million years, and is mainly biotite-amphibole granite with some monzodiorite. Modal and chemical data from the Jim River and Hodzana plutons define two distinct compositional trends. One trend is monzonitic to syenitic while the other is mostly granitic. The two suites are the same age, yet cannot be related by simple differentiation due to a pronounced chemical discontinuity. Rb-Sr whole-rock isochrons yield an age of 112 million years and (87Sr/86Sr)o of .7078 for the syenitic suite, and an age of 108 million years and (87Sr/86Sr)o of .7079 for the granitic suite. The authors suggest that the monzonite represents a primary magma that formed in the lower crust or mantle and initiated upper crustal melting as it intruded the AT and RT. Assimilation of continental crust could have allowed the portion of the magma that intruded the RT to evolve from a monzonite to a granite. Fractionation of these two parent magmas may have resulted in the contemporaneous syenitic and granitic suites. The two suites may reflect the contrasting composition of assimilated wallrock across the AT-RT boundary. Isotopic studies of the wallrocks are in progress and may help to constrain the amount and composition of crust that was assimilated where the magma intruded the AT versus the RT.

• Research Organization: Alaska Division of Geological and Geophysical Survey, Fairbanks (USA)
• OSTI ID: 6595425
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100 -- Geology & Hydrology-- (-1989)
580400* -- Geochemistry-- (-1989)
AGE ESTIMATION
ALASKA
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
CHEMICAL COMPOSITION
CRETACEOUS PERIOD
FEDERAL REGION X
FRACTIONATION
GEOLOGIC AGES
GEOLOGIC MODELS
GRANITES
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
MAGMA
MAGMATISM
MESOZOIC ERA
NORTH AMERICA
PETROCHEMISTRY
PETROGENESIS
PLUTONIC ROCKS
ROCKS
RUBIDIUM ISOTOPES
SEPARATION PROCESSES
STRONTIUM ISOTOPES
SYENITES
USA