Editing Flood basalt (section)

=== Geochemistry ===
[[File:Parana traps.JPG|thumb|Parana traps]]
Flood basalts show a considerable degree of chemical uniformity across geologic time,{{sfn|Philpotts|Ague|2009|p=380}} being mostly iron-rich tholeiitic basalts. Their major element chemistry is similar to mid-ocean ridge basalts (MORBs), while their trace element chemistry, particularly of the [[rare earth elements]], resembles that of [[ocean island basalt]].<ref name=Wilson2007>{{cite book |last1=Wilson |first1=Marjorie |title=Igneous Petrogenesis |chapter=Continental tholeiitic flood basalt provinces |date=2007 |pages=287–323 |doi=10.1007/978-94-010-9388-0_10|isbn=978-0-412-75080-9 }}</ref> They typically have a silica content of around 52%. The magnesium number (the [[mol%]] of magnesium out of the total iron and magnesium content) is around 55,{{sfn|Philpotts|Ague|2009|p=383}} versus 60 for a typical MORB.{{sfn|Philpotts|Ague|2009|p=367}} The [[rare earth elements]] show abundance patterns suggesting that the original (primitive) magma formed from rock of the [[Earth's mantle]] that was nearly ''undepleted''; that is, it was mantle rock rich in [[garnet]] and from which little magma had previously been extracted. The chemistry of plagioclase and olivine in flood basalts suggests that the magma was only slightly contaminated with melted rock of the [[Earth's crust]], but some high-temperature minerals had already crystallized out of the rock before it reached the surface.{{sfn|Philpotts|Ague|2009|p=382}} In other words, the flood basalt is moderately [[Magma differentiation|evolved]].<ref name=Wilson2007/> However, only small amounts of plagioclase appear to have crystallized out of the melt.{{sfn|Philpotts|Ague|2009|p=382}}

Though regarded as forming a chemically homogeneous group, flood basalts sometimes show significant chemical diversity even with in a single province. For example, the flood basalts of the [[Parana Basin]] can be divided into a low phosphorus and titanium group (LPT) and a high phosphorus and titanium group (HPT). The difference has been attributed to inhomogeneity in the upper mantle,<ref>{{cite journal |last1=Hawkesworth |first1=C. J. |last2=Mantovani |first2=M. S. M. |last3=Taylor |first3=P. N. |last4=Palacz |first4=Z. |title=Evidence from the Parana of south Brazil for a continental contribution to Dupal basalts |journal=Nature |date=July 1986 |volume=322 |issue=6077 |pages=356–359 |doi=10.1038/322356a0|bibcode=1986Natur.322..356H |s2cid=4261508 }}</ref> but [[strontium isotope]] ratios suggest the difference may arise from the LPT magma being contaminated with a greater amount of melted crust.<ref>{{cite journal |last1=Mantovani |first1=M. S. M. |last2=Marques |first2=L. S. |last3=De Sousa |first3=M. A. |last4=Civetta |first4=L. |last5=Atalla |first5=L. |last6=Innocenti |first6=F. |title=Trace Element and Strontium Isotope Constraints on the Origin and Evolution of Paran Continental Flood Basalts of Santa Catarina State (Southern Brazil) |journal=Journal of Petrology |date=1 February 1985 |volume=26 |issue=1 |pages=187–209 |doi=10.1093/petrology/26.1.187}}</ref>