Transcript Precambrian of Llano Uplift

Aaron Bazzell, Jennifer Beach, Levi
Brown, Jennifer Armitage, Michael
Davis
http://tapestry.usgs.gov/features/02llano.html
This shows what is believed to have
created the Llano Uplift .
Geology.gsapubs.org
Devil’s Watering Hole in Inks Lake State Park

Llano Group



Split into major groups
Valley Spring Gneiss
Packsaddle Group (Schist)
Click Formation (7,800ft)
 Rough Ridge Formation (5,200ft)
 Sandy Formation (2,100ft)
 Honey Formation (7,800ft)


Town Mountain Formation

Lowest Principal
Formation

Rhyolitic

Inks Lake

Marble

Formation is 12,500 ft



Dynamothermal
Preservation
Subdivided into four
formations
Photo: Packsaddle
Schist with marble.
Click Formation
Hornblende schist
Rough Ridge Formation
Quartz Feldspar schist
Biotite gneiss
Sandy Formation
Alternating Quartz feldspar schist, hornblende,
leptite
Honey Formation
Hornblende and Graphite schist, Marble,
Leptite




Part of Packsaddle
Group
Affected by at least two
metamorphic events
Grenville Orogeny
Photo courtesy of last years Precambrian Group
presentation.

Youngest of major
Llano units

Juxtapose domains

Elemental composition
Formation of Llano
Uplift
•
•
•
Based upon Pfiffner’s
models of the Swiss Alps
Llano uplift
characterized by
collisional suture
Compressional
Faults
•
•
•
At time of collision,
tended to form thrust
faults
Ductile Thrust Zone
Mylonite Fabric on the
boundary
S1 & S2 Folds
•
•
Strikes trend NW
Dips trend SW
Differentiated Crenulations
(S3 & S4)
Axial Planar (S5)
Collision of Volcanic Island Arc with Laurentia
Compression
High Angle Upthrust Faults
Overturned Anticlines and Synclines
Up to 5 Recognized Folding Events
NW Trending Strikes
SW Trending Dips
S5 Axial Planar Folds Represent Hinge