north shore is for lavas

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!