calcAnomaly {GCDkit}R Documentation

Anomaly on a spiderplot

Description

Calculates a magnitude of an anomaly on a spiderplot, based on concentrations of selected neighboring elements.

Usage

calcAnomaly(which.elem="Eu",dataset=WR,ref="^REE Boynton",left="Sm",
    right="Gd")

Arguments

which.elem

character; which element is being examined?

dataset

character; name of variable holding the whole-rock data.

ref

character; a specification of the normalization scheme.

left

character; a name of element to the left, used for extrapolation.

right

character; a name of element to the right, used for extrapolation.

Details

This is a general function that calculates a magnitude of an anomaly on a spiderplot. For the given element it is a ratio of its normalized contents divided by an extrapolated value (denoted by a star). The extrapolation is performed is from two neighboring elements, one to the left and one to the right, of the examined one. But these two elements used for extrapolation do not need to be immediately adjacent.

The best known and the most commonly used is the Eu anomaly on chondrite-normalized REE plots expressed as:

Eu/Eu* = EuN/SQRT(SmN*GdN)

But this principle can be generalized even for elements that are not immediately adjacent to the anomaly, like on its figure:

AnyAnomaly.png

The spiderplot is selected using the parameter 'ref' which can contain a substring (or a regular expression) specifying the name of the normalizing scheme stored in the file 'spider.data' of the main GCDkit directory. For details and examples, see selectNorm.

Value

A numeric matrix with a single row, containing the calculated values.

Author(s)

Vojtěch Janoušek, vojtech.janousek@geology.cz

References

Boynton WV (1984) Cosmochemistry of the rare earth elements: meteorite studies. In: Henderson P (eds) Rare Earth Element Geochemistry. Elsevier, Amsterdam, pp 63-114

Pearce JA (2014) Immobile element fingerprinting of ophiolites. Elements 10: 101-108 doi: 10.2113/gselements.10.2.101

See Also

selectNorm spider

Examples

    data(blatna)
    accessVar("blatna")
    
    calcAnomaly() # Eu anomaly on chondrite-normalized REE plot after Boynton (1984) 

    # Nb anomaly, Nb/Nb*, based on immobile NMORB spiderplot after Pearce (1984)
    NbNb<-calcAnomaly(which.elem="Nb",dataset=WR,
        ref="^NMORB immobile",left="Th",right="La")     
    WR<-addOn("Nb/Nb*",as.vector(NbNb),where=WR) # Append to the current data set

[Package GCDkit version 6.1 Index]