CENTENNIAL HONORS COLLEGE
Western Illinois University
Undergraduate Research Day 2015
Poster Presentation
Mineralogic Trends in the Eastern Region of Mineral Lake Intrusion, Northern Wisconsin
Ramon Glazianne Barbosa Carvalho
Faculty Mentor: Kyle Mayborn
Geology
The Mineral Lake Intrusion (MLI), located in northern Wisconsin, is a 6000m thick mafic intrusion
within the 1.2 billion years old Mellen Igneous Complex which was emplaced at shallow crustal levels
during continental rifting. Subsequent uplift and erosion has exposed a cross-section of the intrusion.
The MLI is primarily composed of homogenous plagioclase rich gabbro with an olivine gabbro base and
an iron rich gabbroic top. The MLI is divided into three zones based on the presence of a thick plagioclase
rich unit in the middle of the intrusion. New data obtained for this study from a traverse in the eastern
region of the intrusion proved to be concordant with data from a previously studied western traverse. The
average composition of plagioclase is An60 throughout the traverse, but the volume of plagioclase
increases after 1000m, reaching 80-90% at 2000m and after 3000m it starts to decrease. Olivine occurs
only in the extremities of the traverse, being totally absent in the middle (1800-3200m), and its
composition ranges between Fo50 to Fo70 near the base and Fo10 to Fo20 near the top. Clinopyroxene is
present throughout the traverse but in the middle its volume decreases. Mineral chemistry data shows that
Fe in plagioclase increases whereas Mg increases in olivine, and clinopyroxene shows an abrupt increase
in Mg at the base of the traverse and decreases after 1000m. These new data support the hypothesis that
the MLI contains a marginal reversal.