Igneous Association Flashcards
Suites of rocks that form in response to similar geologic conditions.
Petrotectonic Associations
What are the three classifications of petrotectonic associations?
- Divergent Plate Boundary Magmatism
- Convergent Plate Boundary Magmatism
- Intraplate Magmatism
Primarily driven by the decompression of the asthenosphere in response to lithospheric extension resulting in partial melting of mantle peridotite at divergent margins, producing basic (mafic) melts that rise to solidify and produce oceanic crust
Divergent Plate Boundary Magmatism
A sequence of the ocean lithosphere containing four distinct layers.
Enumerate the four distinct layers.
Ophiolitic sequence
Slices of ocean lithosphere preserved in landmasses.
Ophiolites
Basalts and gabbros that are geochemically distinct which formed from partial melting of lherzolite at ocean spreading centers, and contain plagioclase, augite, hypersthene, pigeonite, diopside and olivine.
-What are its two types?
Mid-Ocean Ridge Basalts (MORB)
Strongly depleted in highly incompatible elements such as large ion lithophile (LIL) elements, high field strength (HFS) elements, and light rare earth elements (LREE), which implies that they represent 20-30% partial melting of a well-mixed, depleted mantle source.
Normal MORB (N-MORB)
Contains higher incompatible element (LREE, HFS, LIL) concentrations compared to N-MORB, representing smaller degrees (~10-15%) of partial melting of residual mantle rock so that the incompatible elements are more highly concentrated in E-MORB magmas.
Enriched MORB (E-MORB)
-Ions that are easily accommodated in the crystal lattice and mineral structure.
-They are left in the ‘early stages’ of the melt. Therefore, it is concentrated in the solid.
Compatible Elements
- Ions that do not fit into the mineral structure of rock- forming minerals at the time of crystallization of the magma, leading to accumulation in the residual magma and concentration in late-stage differentiation.
-They tend to ‘stick’ to the melt instead of the crystallizing portion. Therefore, it is concentrated in the melt.
Incompatible Elements
Small, highly charged incompatible elements (REE, Th, U, Ce, Pb4+, Zr, Hf, Ti, Nb, Ta).
High Field Strength (HFS) Elements
Low field strength incompatible elements that are more mobile, especially in a fluid phase.
Large Ion Lithophile (LIL) Elements
Specific elements that are common but rarely occur in significant amount enough to be economically extractable.
Rare Earth Elements (REE)
Generates chemically diverse igneous assemblages that erupt in the convergent margins widely distributed around the globe, occurs for thousands of kilometers parallel to the trench, and up to 500 km perpendicular to the trench in the direction of the subduction.
Convergent Plate Boundary Magmatism
What are the 5 variables that can diversify magma composition?
- Composition and geometry of the crust.
- Composition of material undergoing anatexis.
- Flux melting
- Diversification processes
- Dip angle of the subduction zone
The calc-alkaline association - signature volcanic rock suite of convergent margins which is one of the most voluminous rock assemblages on Earth.
Basalt, Andesite, Dacite, Rhyolite (BADR)
Develop on the overlying ocean lithosphere plate above the subduction zone.
Island Arcs
(Under island arcs)
Contains calcium plagioclase and quartz, with minor potassium feldspar, biotite, and hornblende.
Tonalite
(Under Island Arcs)
Also called plagiogranite, are granodioritic rocks with half to two- thirds sodium plagioclase for the total feldspar content.
Trondjhemite
Produce low potassium arc tholeiite basalts, as well as relatively rare rocks such as boninites and adakites.
Young Island Arc Systems
Archean associations found in archean subduction zones where adakite formation is linked to.
Tonalite, Trondhjemite and Granodiorite (TTG) associations
Develops behind an arc during lithospheric extension occurring in the overlying plate and can erupt a diverse suite of volcanic rocks.
Back-arc Basins
Mature convergent arcs that involve the subduction of ocean lithosphere beneath thick continental lithosphere, where the subducting lithosphere reacts with the overlying plate, and produces more silicic magmas.
Continental margin arcs
Arcs producing voluminous granodiorite, diorite, granite, and tonalite plutons which can erupt onto the Earth’s surface and produce composite volcanoes.
Ocean-continent convergent margins
Dark-colored, trachyandesites, potassium-rich commonly containing olivine and augite phenocrysts with a groundmass of labradorite plagioclase, alkali feldspar, olivine, augite, and leucite.
Shoshonites
Continent-continent collisions where the lower continental lithosphere does not subduct to great depths, but essentially breaks off and underplates the overlying continental lithosphere plate, producing a doubly thick lithosphere.
Continent collision zones
Fault-bounded, deformed rock sequences that mark the site of present or former convergent margins.
Alpine orogenic complexes
An intensely sheared, heterogenous rock assemblage embedded within a highly deformed mud matrix.
Tectonic mélange
Enumerate the types of granites.
- M-type granite (derived from mantle-derived parental magma)
- I-type granite (generated by melting of igneous protolith)
- S-type granite (produced by melting of sedimentary crustal rocks)
- A-type granite (anorogenic rocks)
Magma generation and igneous rock suites generated within lithospheric plates which may be initiated by hotspot activity, continental rifts, or overthickened continental lithosphere,
Intraplate magmatism
-Greatest manifestations of intraplate magmatism on Earth, encompassing >106 km³ in volume, which occur as both oceanic flood basalts and continental flood basalts, and is generally basaltic in composition.
Large igneous provinces (LIP)
LIPs that are more silicic in composition.
Silicic large igneous provinces (SLIP)
Involves Ocean islands and ocean plateaus that formed above mantle hotspots that erupt anomalously high volumes of tholeiitic and alkalic basaltic lava onto the ocean floor.
Oceanic intraplate Magmatism
Volcanic landforms that rise upward above sea level.
Ocean Islands
Volcanically produced peaks
below sea level.
Seamounts
Broad, flat-topped areas that result from massive outpourings of lava flowing laterally from source vents
Oceanic Plateaus
Geochemically distinct suite of rocks that are more alkalic, less depleted, and may be somewhat enriched with incompatible elements that is interpreted to represent different mantle sources areas.
Ocean Island Basalts (OIB)
Magmatism and volcanism within continental plates that can produce continental flood basalts (CFB), continental rift assemblages, bimodal volcanism, layered basic and ultrabasic intrusions, ultrabasic suites which includes komatiites and kimberlites, and an unusual array of alkaline rocks and anorogenic granites.
Continental Intraplate Magmatism
Huge outpourings of basalts within continental plates.
Continental Flood Basalts (CFB)
A continental feature that produce a wide array of rocks, including alkalic basalt, as well as alkalic and silicic rocks.
Continental Rifts
The widespread occurrence of basalt and rhyolite without significant andesite and occurs at continental rifts and hotspots underlying continental lithosphere.
Bimodal Volcanism
Anorogenic bodies injected into stable continental cratons at moderate depths.
Layered Basic-Ultrabasic Intrusions
Brecciated, magnesium-rich,
ultrabasic rocks that rapidly rise to Earth’s surface via cylindrical diatremes from deep within the mantle and are intimately associated with diamonds
Kimberlites
-Shallow intrusive to volcanic rocks that contain >20% CO3 minerals, and form in stocks, dikes and cylindrical structures primarily at continental rifts.
-Only known active volcano to produce this type of rock?
-Carbonites
-Ol Doinyo Lengai
Magnesium-rich, volatile-rich, porphyritic rocks containing mafic phenocrysts, and are associated with kimberlites and continental rift zones
Lamprophyre
Potassium-rich, peralkaline rocks containing pyroxene and olivine minerals enriched in barium, lanthanum, and zirconium, but relatively poor in CO2, and occur in areas of thickened lithosphere that have experienced earlier plate convergence or rifting episodes.
Lamproite
