Geochemical
Journal,Vol.
29, pp. 213 to 230, 1995
TetradeffectsandfinestructuresofREEabundancepatterns
ofgraniticandrhyoliticrocks:
ICP-AESdeterminationsof REEand Yin eightGSJreferencerocks
IWAOKAWABE
DepartmentofEarthandPlanetarySciences,SchoolofScience,Nagoya
University,
Chikusa,Nagoya464-01,Japan
(ReceivedNovember 11,1994;AcceptedMarch 27, 1995)
All fourteenREE andY havebeendetermined
for eight GSJ referencerocksincludinggraniticand
. Thetworhyolites(JR-1 and JR-2)andone
rhyoliticsamplesbyICP-AESwith apreconcentrationmethod
-normalizedREEpatterns
granite(JG-2) exhibitconvextetrad effectsofthe M-typeevenin theirchondrite
.
Theirtetradeffects,however,
aremodifiedfromidealones bysome step-likevariationsin theirabundances
fromTm to Lu. Similar step-likeirregularitiesare seencommonlyinchondrite
-normalizedpatternsof
other samples:granodiorites(JG-1, JG-1 a, and JG-3),a freshwaterlake sediment(JLk-1),and an alkali
basalt(JB-1). Wenormalizedthe REE analysesfor JR-1, JR-2, and JG-2 by thosefor JB-1,and then
foundthattheyclearlyindicatequiteregularconvextetradeffectsofthe M-typewithoutapparentirregularitiesin heavy REE. The othersamples,whensimilarlynormalizedby JB-1,alsodisplayanalogousbut
less markedconvextetradeffectsexceptfor JG-3. Ourpresentresultsare strongevidencefor the tetrad
effectinmagmaticprocessesrelevantto graniticandrhyoliticrocksformations
. Thereare commonchemical
characteristics
amongJG-2,JR-1,andJR-2: (1)largenegativeEu anomalies,and (2)ratherhigh Fcontents
and the theoreticalbasisof tetradeffects maysuggest
of about1,000ppm. The chemicalcharacteristics
thatthegraniticandrhyoliticrockswiththe convextetradeffectsofthe M-typeare residualsilicate melts
havingpartitionedREE withfluids in late stages ofdifferentiation
processes
. Thebasalt
-normalization
appearsto be soeffectiveforextractingtetradeffectsofgraniticandrhyoliticrocks. It filtersoffthe REE
characteristics
commoninmagmaticproductslike the step-likeirregularities
inheavyREE abundances
when normalizedby chondrite
. Thismakes it easier to identifylanthanidetetrad effectsinmagmatic
rocks.