I. Basaltic associations of the ocean crust.
A. Midocean ridge basalts (MORB, abyssal tholeiites)
represent new crust generated by volcanic eruptions concentrated along ocean ridges of magma
formed in the mantle.
olivine to quartz normative, exceptionally low in K2O (<0.3 wt.%) and TiO2.
also serpentinized peridotites and gabbros (ophiolites) forming the crust.
B. Ocean Island Basalts (OIB; mostly alkali olivine basalts)
mostly formed by hotspot volcanism deep in the mantle
usually silica undersaturated, olivine basalts; can include phonolites and nephelinites; can have a
wide range of chemical compositions due to fractional crystallization.
richer in alkalis and TiO2 compared to MORB’s
II. Continental tholeiitic provinces
A. Flood (plateau) basalts
slightly oversaturated in silica
occur in large provinces:
- Columbia River basalts (141,000 km2, 180,000 km3) [miocene]
- Parana Basin, Brazil [K]
- Karro Province, S. Africa [J]
- Deccan Traps, India [C-Tr boundary]
B. Layered Basic Intrusions (stratiform)
generally found in stable cratonic areas.
differentiated into peridotite, gabbro, "granophyre"
often sources for Pt, Cr, V.
some examples:
- Bushweld, S. Africa (100,000 km3)
- Dufek, Antarctica (>100,100 km3)
- Stillwater, Montana
- Skaergaard, Greenland (500 km3)
III. Continental alkalic mafic magmas from deep mantle sources
A. Alkali basalt and nepheline magmas
examples: East African Rift; Rhine Province, W. Germany; Basin and Range province, U.S.
B. Carbonatites
composed chiefly of carbonates (calcite, dolomite, ankerite)
< 2 km2, probably form by miscibility from nephelinites.
C. Kimberlites
serpetinized, porphyritic, phlogopite peridotites
non-orogenic parts of continental platforms
vertical pipes <0.5 Km2 scattered over a given large area.
originate >100 km in the mantle
often contain diamonds
examples: S. Africa; Siberia; Canada, Australia, U.S. (Arkansas, Kentucky, Tennessee, Kansas,
some in Missouri)
IV. Andesites and associated calc-alkaline series of island arcs and continental margins
alkaline earth and Al-rich
dominantly volcanic
principally andesites with associated basalts and rhyolites
generated above Benioff zones (above subducted oceanic lithosphere) in the mantle wedge
examples: Andes, Cascades of Oregon and Washington, Japan, Phillipines and other circum-Pacific
island arcs
V. Continental Granitic Provinces
A. Suites of isolated granite plutons (e.g., Basin and Range)
B. Granitic batholiths
usually composed of many individual plutons ranging from gabbro to granite but granodiorite
and quartz monzonite predominate.
examples: Sierra Nevada Batholith, Idaho Batholith, Lachlan Fold Belt (Australia), Hercinian belt of
VI. Archean Cratonic Provinces
every continent has them
dominated by calc-alkaline tonalite and granodiorite plutons
greenstone belts (mafic volcanics; perhaps equivalent to MORB’s)
N. American examples: Most of central Canada, Ontario, Quebec, Labrador, Greenland, Wyoming
VII. Anorthosite Provinces
massive anorthosite provinces
may represent tops of very large, deep, sub-continental magma chambers
example: Grenville-age anorthosites of Adirondacks, Quebec, Labrador