north shore is for lavas
TRANSCRIPT
North Shore is for
Lavas
Lucas Chabela,
University of South Dakota
Jordan Vargas,
University of Minnesota -
Duluth
Zach Younger,
State University of
New York at New Paltz
Steven Noll,
University of Maryland
Tatiana Delledera,
Virginia Tech
Advisor: Sarah Gordee
Research Fellow, NRRI
Objectives
● Assess the volcanic
facies architecture of the
NSVG lower northeast
sequence
● Constrain eruption,
transport and depositional
environment of volcanic
and sedimentary strata
within the succession
Logistics & Methods
● Camped at Judge C.R. Magney State Park
● Traveled daily to Grand Portage Indian Reservation mapping area by van
● Split into two teams
○ Shore crew
○ Road crew
● GPS issues, Brunton triangulation
● Mapped 10 miles of road cuts along Highway 61, 10+ miles of shoreline, and select
outcrops in-between at 1:5000-scale
● Graphically logged strata where exposure afforded detailed analysis
Regional Stratigraphic Correlations
Schematic Regional Geological Cross-
Section
Rock Units Defined
1. Quartz-feldspar-phyric rhyolite
2. Vesicular basalt lava
3. Coarse-grained olivine gabbro
4. Ophitic diabase
5. Basalt dikes and sills
6. Basaltic-andesite
7. Silt/siltstone
Vesicular Basalt Lava● Grey to dark grey to red
● Aphanitic to finely porphyritic
● Locally vesicular/amygdaloidal
● Massive and locally columnar-
jointed
● Locally pyroxene- and/or
plagioclase-phyric
● Amygdules of thomsonite,
quartz, feldspar, calcite
● Locally weakly magnetic
● Local vesicle pods indicate
“clastogenic” (vent-proximal)
origin
● Conchoidal fracturing and
liesegang banding
● Pillowed in the northeast limb
of the NSVG
Quartz-Feldspar-Phyric Rhyolite
● Pink to brick red
● Quartz-feldspar-phyric
● Multiple small-scale
intersecting joint sets
result in characteristic
polygonal pebbly rubble
outcrops, locally massive
and cliff-forming
● Rare fiamme
● Local fracture-controlled
hydrothermal alteration
Quartz-Feldspar-Phyric Rhyolite
Coarse-Grained Olivine Gabbro
● Dark gray (black pyroxene and
translucent plagioclase)
● Coarse- to very coarse-
grained, and locally pegmatitic
● Local flow-alignment of
plagioclase
● Locally sulfide bearing and
weakly magnetic
Coarse-Grained Olivine Gabbro
Ophitic Diabase
● Tan to dark gray, massive and
blocky
● Fine-grained with 2-5 cm-scale
ophitic texture
● Locally olivine-poikilitic texture
● Weakly magnetic
Ophitic Diabase
Basalt Dikes and Sills
● Dark grey
● Very fine grained to
locally plagioclase-
phyric
● Vesicular/
amygdaloidal
● Columnar-jointed
● Vertically emplaced
● Cross-cuts both
basalt and rhyolite
units
Basalt Dikes and Sills
● “Self-Questioning Cove”
● Sheeted dike
● Vertical internal contacts
Basaltic-Andesite
● Tan-grey
● Plagioclase-porphyritic with
fine- to medium-grained
groundmass, to locally medium-
to coarse-grained and near-
equigranular
● Occurs as dikes with vertical
contacts and as intrusions with
no discernible morphology
Siltstone/Sandstone
● Green-red-brown
● Thinly bedded, parallel
laminated
● Siltstone to pebbly sandstone
● Occurs as thin intervals
between thick, massive lavas
● Locally disrupted and
incorporated into the base of
overlying lavas
Basaltic Peperite
● Multi-colored
● Monomictic, globular, clast-
to matrix-supported,
vesicular basalt-clast -
sediment-matrix breccia
● silt/sandstone matrix
● Primary (in situ) volcanic
facies
● Establishes contemporaneity
between lava and
silt/sandstone units, and
constrains environment to
water-saturated sedimentary
substrate
Basaltic Peperite
Graphic Logs
Cross Section
Interpretation
● Grand Portage lavas are oldest of the volcanic succession
● “Esther” lavas overlie the Grand Portage lavas and underly Hovland lavas
● Hovland Lavas are the youngest of the stratified rocks in our study area
● Basalt dikes and sills, and a monzodiorite dike cross-cut the volcanic stratigraphy
● Diabase/gabbro intrude the volcanic succession
Camp Life
Zach Younger“Mountain Goat” Lucas Chabela
“Captain”
Steven Noll
“Cookie Monster”
Jordan Vargas,
The Transporter
“Hey Bear!”
Tatiana Delledera“T-Dogg”
Sarah Sauer
“Deputy”“Commander-in-Chief”
Thank you
Grand Portage Reservation Tribal Council and community for access to land
Sponsors and Contributors:
Thank you for generously continuing to sponsor the PRC Field Camp -
it is an honor to be granted the scholarship each student received
Natural Resources Research Institute (NRRI)
University of Minnesota - Duluth!
Thank you faculty, administrators, and friends for making this Field Camp
absolutely amazing experience!
We would like to personally thank Dr. Jim Miller, Dean Peterson, and George
Hudak for being an exemplary leaders, teachers, mentors and friends in the
field of Geology!