Flavors of basalts Flavours of basalts

ü Alkaline ü Sub-alkaline ü Tholeiitic ü Calc-alkaline ü Mid Ocean Ridge basalts (MORBs) ü Ocean Island basalts (OIBs) ü Arc basalts

Figure 16-3. Data compiled by Terry Plank (Plank and Langmuir, 1988) Earth Planet. Sci. Lett., 90, 349-370. Ocean islands in the Atlantic

See mechanisms of magma Differentiation on next lecture…

Figure 14.3. After Wilson (1989) Igneous Petrogenesis. Kluwer. MORBs vs. OIBs

ü Mid-Ocean Ridge vs. Ocean Island Mid-Ocean Ridge System Oceanic Intraplate Volcanism!

MORB vs. OIB

ü Similar major element concentrations ü Difference in trace element abundance

increasing incompatibility Figure 10-13b. Spider diagram for a typical alkaline ocean island basalt (OIB) and tholeiitic mid-ocean ridge basalt (MORB). From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (1989). Calc-alkaline (arc) basalts Crater Lake vs. Skaergaard intrusion

Magma chamber in hot spot-rifting environment

Volcanic Arc Calc-alkaline basalts!

Addition of Fluid-mobile elements AFM diagram Basalts

Tholeiitic – hot spot Divergent margins

Calc-alkaline Subduction zones (arcs) Alkaline basalts – in every tectonic settings

Figure 14.3. After Wilson (1989) Igneous Petrogenesis. Kluwer. Questions

ü Difference between OIBs and MORBs? ü Difference between calc-alkaline basalts (arcs) and MORBs? ü Alkaline basalts? Style of mantle melting

ü CA basalts => Flux melting

ü High water content and higher O concentration (fO2) from slab dehydration ü Early crystallization of oxide phases (low Fe, Ti, Nb, Ta in residual magmas) ü OIBs and MORBs => Decompression melting ü Melting at shallow depths form depleted mantle (previously melted) ü MORB ü Melting deeper from a more enriched mantle ü OIB Alkaline basalts?

ü Low degrees of mantle melting Ø Enrichments in melt-loving elements (incompatible elements) Amount of melting and depth of melting! 1100 1200 1300 1400 1500 (TºC) % melting (and P) solidus determine the 10 Spinel lherzolite 20% composition of 50 (Ol-opx-cpx-sp) 1% the basaltic 20% 20 magma produced 10% Garnet lherzolite 1% (Ol-opx-cpx-gar) 30 P (kbars) P Depth(km) 100

40 Alkaline magmas: Graphite Low degrees of Diamond 50 melting 150

60 Flavors of basalts

OIB = Alkaline magmas or tholeiites From deeper melting of more primitive mantle

MORB Island Arc basalts Tholeiites from shallow Calc-alkaline Continental Arc basalts Melting of depleted (rare) Calc-alkaline From fluxed depleted mantle mantle wedge From fluxed depleted mantle wedge Continental hot spots and rifts: Alkaline magmas or tholeiites