Abstract
Petrology & geochemistry of the Osborne mafic intrusion, NW Iowa
Abstracts with programs - Geological Society of America, Vol.51(2)
Geological Society of America, Southcentral Section, 53rd annual meeting; Northcentral Section, 53rd annual meeting; Rocky Mountain Section, 71st annual meeting
03/2019
Abstract
Aeromagnetic and gravity surveys have revealed the existence of the North-East Iowa Intrusive Complex (NEIIC), a large ( nearly equal 16,000 km (super 2) ) buried mafic/ultramafic complex that is possibly related to the nearly equal 1.1 Ga Mid-continent rift system, and potentially analogous to the Duluth Complex. An industry core from 1963 drilled the outer 225 m of an inclined NE-trending dike (near Osborne, Clayton Co, Iowa) that is inferred to be related to the main NEIIC complex. Petrographic examination of this core show that it is a layered mafic intrusion, with a nearly equal 110 m olivine-rich outer margin that transitions sharply into troctolite. Fe-Ti oxides are abundant ( nearly equal 30%) throughout the core, and several coarser-grained, plagioclase-rich layers are found sporadically in the lower half of the core. A systematic survey of compositional variations was done using a handheld pXRF, with replicate analyses made on individual cores pieces, at an average sampling interval of 2 m along the core. These data largely confirm the petrographic division into two dominant lithologies (dunite and troctolite). One of the feldspar-rich horizons was significantly enriched in incompatible elements ( nearly equal 500 ppm Zr and nearly equal 3.5% K) compared to the rest of the core (50 ppm Zr and 0.2% K) and likely represents crystallization of the final residual liquid. Electron microprobe X-ray element mapping of large (1' x 3') polished slabs is being carried out to determine phase assemblages and textural relationships in representative core samples of each lithological type. The feldspar-rich residual liquid horizon contains plagioclase + k-feldspar and clinopyroxene, with biotite, ilmenite+ or -magnetite, and apatite, together with trace baddelyite and zirconolite. A systematic survey of mineral compositions through the Osborne intrusion is currently in progress, and preliminary data on a troctolite sample show that the olivine is Fo60 and the plagioclase is An55.
Details
- Title: Subtitle
- Petrology & geochemistry of the Osborne mafic intrusion, NW Iowa
- Creators
- Allison R Kusick - University of Iowa, Department of Earth and Environmental Sciences Iowa City, IA USA United StatesRyan J ClarkL. Kenneth HorkleyDavid W Peate
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.51(2)
- Conference
- Geological Society of America, Southcentral Section, 53rd annual meeting; Northcentral Section, 53rd annual meeting; Rocky Mountain Section, 71st annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, South-Central Section, 53rd annual meeting; Geological Society of America, North-Central Section, 53rd annual meeting; Geological Society of America, Rocky Mountain Section, 71st annual meeting
- Language
- English
- Date published
- 03/2019
- Academic Unit
- Earth and Environmental Sciences; IIHR--Hydroscience and Engineering; Honors Program
- Record Identifier
- 9984240887702771
Metrics
18 Record Views