ULTRAMAFIC ROCKS EARTH’S MANTLE IS COMPOSED OF ULTRAMAFIC ROCKS ULTRAMAFICS (ULTRABASIC) ROCKS...
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Transcript of ULTRAMAFIC ROCKS EARTH’S MANTLE IS COMPOSED OF ULTRAMAFIC ROCKS ULTRAMAFICS (ULTRABASIC) ROCKS...
![Page 1: ULTRAMAFIC ROCKS EARTH’S MANTLE IS COMPOSED OF ULTRAMAFIC ROCKS ULTRAMAFICS (ULTRABASIC) ROCKS ARE IGNEOUS & META-IGNEOUS VERY LOW SILICA, LESS THAN.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649e605503460f94b5a522/html5/thumbnails/1.jpg)
ULTRAMAFIC ROCKSEARTH’S MANTLE IS COMPOSED OF ULTRAMAFIC ROCKS• ULTRAMAFICS (ULTRABASIC) ROCKS ARE IGNEOUS & META-IGNEOUS VERY LOW SILICA, LESS THAN 45% GENERALLY >18% MgO, HIGH FeO, LOW POTASSIUM >90% MAFIC MINERALS(DARK COLORED MINERALS, HIGH MAGNESIUM & IRON CONTENT)
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INTRUSIVE ULTRAMAFIC ROCKS
IUGS Classification diagram for intrusive ultramafic rocks based on modal percentages of mafic minerals. Green area represents typical mantle peridotite
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PERIDOTITE HARZBURGITE LHERZOLITE
OSMIUM PYROPE GARNET GARNET-BEARING HARZBURGITE
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PERIDOTITE – DENSE COARSE-GRAINED ULTRAMAFIC(IGNEOUS)ROCK CONSISTING OF OLIVINE & PYROXENE, CONTAINS LESS THAN 45% SILICA; HIGH IN MAGNESIUM-RICH OLIVINE-- OVER 30% WITH APPRECIABLE IRON
• COMPOSITION OF PERIDOTITES VARY RELATIVE TO PROPORTIONS OF PYROXENES, CHROMITE, PLAGIOCLASE, & AMPHIBOLE
• PERIDOTITE NODULES FOUND IN CERTAIN BASALTS & DIAMOND PIPES(KIMBERLITE) ARE OF SPECIAL INTEREST TO PALEOGEOLOGISTS: 1) CLUE TO COMPOSITION OF EARTH’S EARLY MANTLE & COMPLEX PROCESS INVOLVED
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2) P-NODULES PRESERVE ISOTOPE RATIOS OF OSMIUM (Os) [BLUE-GRAY OR BLUE-BLACK HARD BRITTLE VERY HEAVY POLYVALENT METALLIC ELEMENT WITH HIGH MELTING POINT, TRANSITIONAL METAL IN THE PLATINUM FAMILY] & OTHER ELEMENTS THAT RECORD THE PROCESSES OVER 3B YEARS BP.
TYPES OF PERIDOTITE: 1) DUNITE – MORE THAN 90% OLIVINE WITH Mg/Fe RATIO OF ABOUT 9:1 2)WEHRLITE – MOSTLY COMPOSED OF OLIVINE PLUS CLINOPYROXENE 3) HARZBURGITE – MOSTLY COMPOSED OF OLIVINE PLUS ORTHOPYROXENE & LOW PROPORTIONS OF
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INTRUSIVE ULTRAMAFICS – FOUND IN LARGE LAYERED INTRUSIONS WHERE DIFFERENTIATED ROCK TYPES OFTEN OCCUR IN LAYERS
• ULTRAMAFIC INTRUSIVE INCLUDES DUNITES, PERIDOTITES, PYROXENITES & TROCTOLITE (RARE VARIETY HAS GREATER PERCENTAGE OF CALCIC PLAGIOCLASE); THESE GRADE INTO ANORTHOSITES
• GABBRO & NORITE OFTEN OCCUR IN UPPER PORTION OF LAYERED ULTRAMAFIC SEQUENCES; HORNBLENDITE & RARELY PHLOGOPHITE ARE ALSO FOUND
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VOLCANIC ULTRAMAFIC ROCKS • RARE OUTSIDE OF ARCHEAN• ESSENTIALLY RESTRICTED TO NEOPROTEROZOIC
OR EARLIER• BONINITE LAVAS WITHIN BACK-ARC BASINS
( MANUS TROUGH, NEW GUINEA)• SUBVOLCANIC ULTRAMAFIC ROCKS & DYKES
ARE RARE• EXAMPLES OF VOLCANIC ULTRAMAFIC ROCKS:1.KOMATITE – HOST TO ORE DEPOSIT OF NICKEL 2.PICRITIC BASALT
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ULTRAPOTASSIC ULTRAMAFIC ROCKS • ULTRAPOTASSIC ULTRAMAFIC & MELILITIC
ROCKS – TECHNICALLY CONSIDERED SEPARATE GROUP BASED ON MELTING CRITERIA
• HIGHLY SILICA-UNDER-SATURATED ROCKS WITH >18% MgO
• ULTRAPOTASSIC, ULTRAMAFIC IGNEOUS ROCKS SUCH AS LAMPROPHYRE, LAMPROITE & KIMBERLITE OCCUR AS DIKES, DIATREMES, LOPOLITHS OR LACCOLITHS ARE RARELY INTRUSIONS
• KIMBERLITE & LAMPROITE OCCUR AS VOLCANIC
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• DIATREMES & MAARS OCCUR AS SUBVOLCANIC• VENTS OF PROTEROZOIC LAMPROITE (ARGYLE
DIAMOND MINE), CENOZOIC LAMPROITE(GAUSSBERG ANTARCTICA), DEVONIAN LAMPROITE( SCOTLAND)
• KIMBERLITE IN CANADA, SOUTH AFRICA & RUSSIA
• CARBONATITE ARE RARE HIGH-CARBONATE, LOW-SILICA IGNEOUS ROCK
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METAMORPHIC ULTRAMAFIC ROCKS• METAMORPHISM OF ULTRAMAFIC ROCKS IN THE
PRESENCE OF WATER AND/OR CARBON DIOXIDE RESULTS MAIN CLASSES: 1) TALC CARBONATE 2) SERPENTINITE
• SERPENTINIZATION REACTIONS RESULT TO CHLORITE-SERPENTINE-AMPHIBOLE TYPES ASSEMBLAGES WHEN METAMORPHIC FLUIDS IN CONTACT WITH ULTRAMAFIC ROCKS HAVE LESS THAN 10% CO2
• TALC CARBONATION REACTIONS RESULTS TO GRENNSCHIST THRU GRANULITE WHEN METAMORPHIC FLUIDS HAS LESS THAN 10% CO2
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DISTRIBUTION IN SPACE & TIME• MAJORITY OF ULTRAMAFICS ARE EXPOSED IN
OROGENIC BELTS & PREDOMINATE IN ARCHEAN & PROTEROZOIC; ULTRAMAFIC MAGMAS IN PHANEROZOIC ARE RARE & FEW RECOGNIZED
TRUE ULTRAMAFIC LAVAS MANY SURFACE EXPOSURES OF ULTRAMAFICS
OCCUR IN OPHIOLITE COMPLEXES WHERE DEEP MANTLE-DERIVED ROCKS HAVE BEEN OBDUCTED UNTO CONTINENTAL CRUST & {ISLAND ARCS] ALONG & ABOVE SUBDUCTION ZONES
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PLATE TECTONICS
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ULTRAMAFIC ROCKS & REGOLITH• ALKALI-RICH ULTRAMAFIC ROCKS PROVIDE
EXCELLENT BALANCE NUTRIENTS TO THE SOILS; PERIDOTITE & SERPENTINITE HAVE HIGH RATIO OF MAGNESIUM TO CALCIUM BUT DEFICIENT IN POTASSIUM & PHOSPORUS; CONTAIN TOXIC AMOUNTS OF CHROMIUM & NICKEL
• ULTRAMAFIC ROCKS CREATE UNIQUE VEGETATION: ULTRAMAFIC FOREST/VEGETATION IS TYPICALLY STUNTED OR BARREN & HOME TO ENDEMIC SPECIES ADAPTED TO METALLIC SOILS
• WEATHERED ULTRAMAFIC ROCKS FORM LATERITIC NICKEL ORE DEPOSITS