Modelling Diverse Processes in the Petrogenesis of a Composite Batholith: the Central Bohemian Pluton, Central European Hercynides

The multiple intrusions making up the Central Bohemian Plutonin the Central European Hercynides have petrographic and geochemicalfeatures consistent with the presence of four main granitoidsuites. Major-element, trace-element and Sr–Nd isotopiccompositions are used to model their petrogenesis. Partial meltingof metabasic rocks or of a CHUR-like mantle source are interpretedto have produced melts parental to the most primitive calc-alkalineSázava suite. Interaction of basic with more acidic magmasfollowed by extensive amphibole–plagioclase-dominatedfractionation accounts for the production of trondhjemites.Alternatively, the trondhjemites correspond to small-degreemelts of a metabasic source. AFC (assimilation–fractionalcrystallization) modelling with a paragneiss as a contaminantand increasing D_Nd values simulates the characteristics of theBlatná suite. Closed-system fractionation of stronglyenriched mantle-derived magmas or their interaction with leucograniticmelts is deduced for the petrogenesis of the shoshonitic     

Metamorphic Segregation Banding in the Loch Kerry Basite Sheet from the Lewisian of Gairloch, Ross-shire, Scotland

The Loch Kerry basite varies from amphibolite through stripedvarieties to strongly banded amphibolite containing many lensesof hornblendite and bands of plagioclasite. The striping andbanding is interpreted as the result of metamorphic segregationwith the complementary development of mafic and felsic types.The geochemical changes are set out and discussed on the basisof thirty-one new rock analyses. Foliation planes acted as pressure minima and differentiationdue to heterogeneous pressure led to the development of finelystriped amphibolite and subsequently to banded amphibolite.With continued deformation, the mafic parts of the banded assemblageacted passively while the felsic material moved along the foliationplanes. By preferential residual enrichment, hornblendite bandsup to 380 metres long and 30 metres across were formed. Theextent to which segregation progressed appears to have beencontrolled by the intensity of deformation in and adjacent toa zone of intense movement between a crystalline basement blockand cover rocks of basite and metasediment.