Download Carolina Superterrane

v. 1.0 RDH 7-22-13
Carolina Superterrane
The Carolina superterrane in the map area consists of an
assemblage of mafic and felsic metavolcanic rocks along
with several intrusive bodies, mostly gabbros.
In
addition, a traceable body of soapstone occurs here that
appears to be truncated to the southwest by the central
Piedmont suture immediately east of the Ocmulgee River.
There also is a mappable unit of amygdaloidal basalt that
occurs in this area near the northwest edge of the Carolina
superterrane.
Several large gabbro bodies intrude the
volcanic complex.
Hooper (1986) and Hooper and Hatcher
(1989) suggested that this entire assemblage be called the
Berner mafic complex.
Modern SHRIMP age dates on: (1) a
metadiorite body present in the complex and (2) the contact
aureole of the Gladesville Gabbro, indicate that the gabbro
bodies here are Paleozoic (~375 Ma), whereas a 530 Ma age
on the metavolcanic host rocks and the metadiorite clearly
indicates the gabbro bodies are much younger and the
volcanic assemblage that encloses these gabbros is Cambrian
or older.
So, the term “Berner mafic complex” sould be
restricted to either the mid-Paleozoic gabbros or the
Cambrian volcanic assemblage.
Layered Gneisses
Two suites of strongly foliated layered gneiss occur in
the Carolina superterrane in this area: (1) a felsic quartz
biotite feldspar-rich unit, and (2) a mafic gneiss
dominated by hornblende, biotite, and feldspar-bearing
gneisses.
These rocks are not so highly strained that original
volcanic layering has been lost, but most if not all
primary pyroxenes have been converted to hornblende.
Some
of the felsic and mafic rocks are intimately interlayered,
and also grade into each other (Hooper, 1986).
Traceable Ultramafic and Basalt Units
A unit that has been mapped here consists largely of
soapstone, which likely is altered dunite. Individual pods
and layers of altered ultramafic rocks that are not
traceable for long distances also occur in this part of the
Carolina superterrane.
Relict pyroxenes also occur in the
mafic rocks here, and all of these bodies are foliated
(Hooper and Hatcher, 1989).
The layer of amygdaloidal basalt occurs as a narrow almost eastwest-trending belt that is traceable for ~7 km. Its outcrop belt
is subparallel to the Ocmulgee fault (Central Piedmont
suture) and the unit produces abundant exposure consisting
of rounded bounders that appear to not be far out of place
that facilitate tracing it. It consists of basalt containing
vesicles that were filled with quartz, epidote, and
possibly a carbonate mineral.
The amygdules are not highly
strained, although they were deformed into ellipsoids with
K values ~0.30, with the X-Y plane of the ellipsoids lying
in the plane of the foliation.
The matrix of the basalt
consists of hornblende (replacing clinopyroxene?),
plagioclase, and minor biotite and opaque minerals (Hooper,
1986).
Gabbros
Several mappable gabbro bodies intruded the older
volcanic complex during the middle Paleozoic.
These
enclose the Gladesville Gabbro studied in detail by
Matthews (1967), the Rum Creek gabbro, and several smaller
gabbro bodies.
All of the gabbros appear to have well-
developed contact aureoles, although in a few cases they
may not have been mapped (e.g., West, 19XX).
A SHRIMP age
date on the contact aureole of the Gladesville Gabbro is
375 Ma, which likely is the approximate age of intrusion
and cooling of the other gabbro bodies in this area.
While
all of the gabbros here exhibit some alteration,
particularly along fractures that cut the gabbros, the
gabbroic bodies appear to have somewhat the same origin
(Chaumba, 2013).
The Rum Creek gabbro may be more altered
than some of the others, perhaps because of its proximity
to the central Piedmont suture.
Alteration zones within
the gabbros commonly contain chlorite, serpentine
(antigorite), and occasional anthophyllite.
While Matthews
(1967) concluded that the Gladesville gabbro is a layered
body, Hooper (1986) was unable to resolve extensive
layering in either exposure in the field or in drill core.