ULTRAMAFIC ROCKS EARTH’S MANTLE IS COMPOSED OF ULTRAMAFIC ROCKS ULTRAMAFICS (ULTRABASIC) ROCKS...

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)

INTRUSIVE ULTRAMAFIC ROCKS

IUGS Classification diagram for intrusive ultramafic rocks based on modal percentages of mafic minerals. Green area represents typical mantle peridotite

PERIDOTITE HARZBURGITE LHERZOLITE

OSMIUM PYROPE GARNET GARNET-BEARING HARZBURGITE

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

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

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

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

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

• 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

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

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

PLATE TECTONICS

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