1. Enclaves, Schlerien, Autoliths,
Xenoliths And Dikes As Clues To
Structure And Pluton Exposure Level
Of The Great Falls Metagranite On
The Carolina Slate Belt- Charlotte
Belt Boundary
Donald R. Privett, P.G., Ph.D.
2. ENCLAVES, SCHLERIEN, AUTOLITHS, XENOLITHS AND DIKES AS CLUES TO STRUCTURE
AND PLUTON EXPOSURE LEVEL - THE GREAT FALLS METAGRANITE ON THE CAROLINA
SLATE BELT - CHARLOTTE BELT BOUNDARY, SOUTH CAROLINA
PRIVETT, Donald R.,1 Circle St, Great Falls, SC 29055, drprivett@gmail.com
Low-grade felsic and mafic rocks of the Carolina Slate Belt (?) and Charlotte Belt metadiorites and metagranites are intruded by
the Great Falls Metagranite (GFM). The texture of the granite is mostly hypidiomorphic granular with minor porphyritic and aplitic
textures. Quartz veinlets, minor small pegmatites and numerous narrow (0.2-1.5 m. wide) metamorphosed mafic dikes cut the
metagranite.
Larger rock exposures frequently display enclaves, mafic blebs, planar mafic layers, autoliths, xenoliths, aplite dikes and schlerien
layers. Those features provide a record of the magma composition, flow and crystallization history of the older stoped and
disrupted rocks.
Medium-grained magmatic enclaves reveal complex histories and strain as the magma approached solidus. Enclaves are fine-
grained relative to the granite and represent altered co-magmatic, injected material. Enclaves and schlerien are partly resorbed.
Mafic-rich blocks often have fairly rectangular shapes and a sharp, intrusive margin with little alteration, thus are xenoliths,
granite sometimes cuts through a single xenolith. The metagranite stoped and assimilated or partially assimilated smaller mafic
xenoliths, creating wispy ghostly almost indistinct autoliths.
The pluton probably represents the deep-seated portion of an acidic sub-volcanic complex which was possibly a source for rhyolitic
and mafic flows in the Carolina Slate Belt. Larger dikes cutting the granite may have been deep seated feeders for mafic flows of
the slate belt.
Some rock fragments in metagranite are unrelated to the igneous body itself. These xenoliths are located near their original
positions of detachment or those with greater density (mafic) - deeper in the intrusion.
In most exposures, metagranite is deeply eroded and altered to saprolite, outcrops are not sufficient to determine contact or
reliable structural relationships.
Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting (13-16 March 2010)
3. Geologic Setting Map Carolinas
Green is Great Falls metagranite
Yellow shows two near by 300 m.y.o. plutons
4. Mafic dikes cutting metagranite
weathered to gravelly saprolite
in borrow pit.
9. Magmatic enclaves are volumes of rock surrounded by
emplaced host rock of related but distinct composition
and of separated genesis (incomplete magmatic
mixing). Enclaves are distinguished from xenoliths, which
are fragments of metamorphically altered older country
rock that fell into magma and became enveloped within
igneous rock.ref:http://bio-geo-
terms.blogspot.com/2006/06/schlieren.html
10. The origins of schlieren are not always clear; they may be
produced by differential magma flow, or disaggregation of
xenoliths, or by other mechanisms. Magmatic enclaves are
volumes of rock surrounded by emplaced host rock of related
but distinct composition and of separated genesis (incomplete
magmatic mixing).
Enclaves are distinguished from xenoliths, which are
fragments of altered older country rock that fell into magma
and became enveloped within igneous rock.
ref:http://bio-geoterms.blogspot.com/2006/06/schlieren.html
11. Schlieren are usually interpreted as having
arisen by one of four mechanisms:
1. shearing of heterogeneities (enclaves or
xenoliths),
2. crystal sorting during convective flow,
3. crystal sorting during magmatic flow, or
4. crystal settling.
http://bio-geo-terms.blogspot.com/2006/06/schlieren.html
12. Similar geology occurs along the North Carolina-South Carolina
border near Waxhaw, NC, there regional low-grade metavolcanic
volcaniclastic rocks of the Carolina terrane are intruded by the
Waxhaw Granite a 539.4 ± 1.4 Ma crystallization age (U-Pb
zircon, monazite, and xenotime) with greenschist-grade foliation. To
the west, near the Charlotte terrane the Waxhaw Granite contains
amphibolite xenoliths suggusting it is a stitching pluton.
The Waxhaw Granite has been mapped in the footwall of the Gold
Hill fault zone, a steep NW-dipping, dextral-reverse fault system.
Reference
ALLEN, John Stefan MILLER, Brent HIBBARD, James and BOLAND, Irene, 2007, SIGNIFICANCE OF INTRUSIVE ROCKS
ALONG THE CHARLOTTE-CAROLINA TERRANE BOUNDARY: EVIDENCE FOR THE TIMING OF DEFORMATION IN THE
GOLD HILL FAULT ZONE NEAR WAXHAW, NC, GSA, Southeastern Section
14. Enclaves are also distinguished from schlieren,
which are concentrations of mafic material that have
crystallized out of a single magma.
Enclaves may represent the result of mingling of
mafic and felsic magmas.
15. Schlieren are fragile, usually elongate concentrations
of mafic material. A schlieren could be a tabular zone in a
granite with either more or less of some of the minerals in the
surrounding granite, typically the dark (mafic) minerals.
Schlieren may be produced by differential magma flow, or
disaggregation of xenoliths, or by other mechanisms.
34. Schlieren are usually interpreted as having arisen by one of four
mechanisms:
1. shearing of heterogeneities (enclaves or xenoliths),
2. crystal sorting during convective flow,
3. crystal sorting during magmatic flow, or
4. crystal settling.
http://bio-geo-terms.blogspot.com/2006/06/schlieren.html
35. The origins of schlieren are not always clear; they may be produced by
differential magma flow, or disaggregation of xenoliths, or by other
mechanisms.
Ref:http://bio-geo-terms.blogspot.com/2006/06/schlieren.html
