laum presen segsa
TRANSCRIPT
F o r m a t io n A n d O c c u r r e n c e s O f L a u m o n t it e A n d R e l a t e dM i n e r a l s In T h e C a r o l in a s A n d V ir g in ia ,
M id d l e M e s o z o ic Z e o l i t e F a c ie s M e t a m o r p h is m , S o u t h e r n A p p a l a c h ia n P ie d mo n t
D o n a l d R . P r iv e t t , P .G . S .T .A . R . E n v ir o n m e n t a l
1 C ir c l e S t r e e t G r e a t F a l l s , S C 2 9 0 5 5
Presentation Time: AM 11:40 AM-12:00 PM
[email protected] Section
60th Annual Meeting (23-25 March 2011) Session No. 4
Piedmont Geology: New Mapping and New Perspectives
Wilmington Convention Center: Room 106
A 175 -195 Ma hydrothermal zeolite grade metamorphic event
altered most pre-Jurassic rocks
Southern Appalachian Piedmont
Central Georgia, South and North Carolina to Virginia
Zeolite grade thermal metamorphismZeolite grade thermal metamorphism
Zeolite facies represents
All mineral, textural and chemical changes resulting
from hot waters, steam or/and gas
crystallization of fracture – filling and replacement
zeolites and prehnite in host rocks
GENERAL GEOLOGY
Area Neoproterozoic and Paleozoic igneous, metamorphic, and Triassic igneous
and sedimentary rocks
altered by period of zeolite grade regional thermal
metamorphism
Event evidenced by the laumontite filling fractures and replacing feldspars in intrusive
and in older metamorphosed diorites and granites.
Laumontite identified from over 100 separate locations
in relatively unweathered outcrops rock exposed in foundations, trenches, quarries, mined caverns and in cores from borings for power plants and cuttings from water wells and exploratory test wells.
LAUMONTITE DISTRIBUTION
(2) veinlets of matted interpenetrating crystal aggregates filling single and multiple narrow fractures and joints
file:///Users/donprivett/Desktop/laumontite/scan0069.jpg
file:///Users/donprivett/Desktop/laumontite/Untitled_003.jpg
Biotite - microline granite porphyry cut by numerous pink
asicular laumontite veinlets.
file:///Users/donprivett/Desktop/laumontite/lau21.tif
(3) replacement of plagioclase forming partial to complete "mosaic pseudomorphs" composed of minute laumontite crystals and albite.
file:///Users/donprivett/Desktop/laumontite/microlaumrpplag.jpg
A. in diffuse plane light laumontized plagioclase displays a mottled texture
file:///Users/donprivett/Desktop/laumontite/lau21.tif
B. polysynthetic twinning of plagioclase is destroyed, partly replaced plagioclase retains its twinning; however, it is mottled top plane light, same cross polars
2
Field exposure in saprolite/partialy weathered quartz monzonite - extensive laumontite
replacement and veins white laumontite leonardite-Compass for scale
ZEOLITE PARAGENESISLaumontite and other zeolites
theoretical and experimental limit determinations and detailed paragenesis studies yield
considerable disparity between theoretical and experimental temperature and pressure limits
and substantially lower temperatures of natural formation.
(Coombs,1952, Thompson, 1971, Frost, 1980 and Loui, 1971) (Boles and Coombs, 1977 and Suranam, 1973).
PARAMETERS THOUGHT TO CONTROL TEMPERATURE AND PRESSURES OF
NATURAL ZEOLITES IN ROCKS
Experimentally determined temperatures are both higher and lower than values obtained under
natural conditionsFluid pressure gradients activities of CO2, pH2Oratio of water and CO2
the permeabilitynucleation and reaction kinetics
oxygen fugacity presence of additional ions all
can alter the temperatures of formation Boles and Coombs (1977)
Laumontite Stability Limits Vary Widely
upper limits of 230º – 325º at 0.5 kb, 250º at 2.75 kb. Thompson (1971) Loui (1971)
lower limit even greater conflict compared 150º - 200º C at 1 kb where p = p (Loui, 1971) lowest recorded temperature of
formation 43º C crystallized at Suspe Hot Springs, California.
In buried sedimentary rocks estimates of 50º C laumontite - 90º C for prehnite (Boles and Coombs, 1977)
75º + 5° C for laumontite in hot springs (Castino and Sparks, 1974, Siki, 1969 )
calcite fluid inclusions in laumontite filled amygdules of lava flows, Iceland 140º - 200º C. Meghan, Robinson and Delaney (1982)
Zeolites occur in
geothermal areas of Iceland a.
in California metamorphic rocks b.
New Zealand thermal areas c.
Southeastern Piedmont U.S.A.
a. (Kristmannedottir and Tomanson,1978), (Mehegan, Robinson and Delaney, 1982) b. (Madsen and Murata, 1970) c. (Barnes, 1977)
Laumontite present in the majority of rock exposed in the Piedmont
gneiss of the Inner Piedmont
metamorphosed and unmetamorphosed igneous rock
metasedimentary rocks of the Charlotte Belt and the
Kings Mountain Belt
metavolcanic and metasedimentary rock Carolina Slate
Belt and in
Buried Triassic - Jurassic sedimentary and igneous rocks
discovery of laumontite in buried Triassic rocks - cored basement below the Triassic of South Carolina and south central Georgia suggest that laumonatization is even more extensive laumontite fills amygdules and replaces plagioclase in a 184 +/- 3 my basalt from Dorchester county, S.C. (Gottfried et.al.,1983)
present in Triassic sedimentary and older igneous rocks from South Central Georgia (Chowns and Williams,1983)
Laumontite imparts a pinkish color to the altered and replaced plagioclase.
appears to be directly proportional to the intensity of laumonatization laumontite and calcite fill vein interiors
x-ray reflections vary with the relative humidity material is best described as laumontite-leonhardite. Laumontite readily dehydrates to leonhardite unless the sample is kept under conditions of 100% relative humidity
Pangea breakup
Tectonic activity about 170 -150 mya - Triassic and Jurassic separation of North
America and Africa
fractured old weaker shears, formed new joints and faults.
ORIGIN
SUMMARYHeated circulating groundwaters mixed with hydrothermal
solutions fluids
reacted with plagioclase prehnite and laumontite.
Excessive calcium reacted with silica to produce the fracture filling laumontite, calcite other lower temperature zeolites.
Two generations of diabase dikes are evident; suggesting that igneous activity persisted as the stress changed.
zeolite grade thermal alteration metamorphism is widespread in rocks of the southern Appalachian rocks.
Immature clastics deposited in subsiding half grabens
generation of basaltic magmas
basalt flows in Triassic sedimentary rock
intrusion of diabase dikes and basaltic to diabase sills.
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