The geology and petrology of the Marble Delta

[摘要] The Marble Delta is an area of approximately 40 sq. km in Natal (30°22' Long., 30°40' Lat.), occupied by Precambrian marble and associated granites. The deeply dissected country was geologically mapped on a scale of I : 6 000. A new lithostratigraphicclassification of the metasediments is proposed.The base of the lowermost Le Joncguet Formation (composed ofdolomitic marble and siliceous beds) is not exposed. This isfollowed by the predominantly ca.lcitic Oribi Formation withinterbedded dolomite and graphitic layers. The marble isunconformably overlain by the Cherrywillingham Formation whichcomprises mainly amphibolite and granulite. The .three formationstogether constitute the Marble Delta Group.The main petrological units are calc-silicate marble,metaquartzite, dolomite marble, cluster serpen~ine marble andce,lcite marble. Graphite layers are considered to have originatedin situ from organic remains; there is occasional evidenceof ionic transfer of carbon from this graphite by magmaticfluids. The common mineral assemblages are diopside +calcite + dolomite, tremolite + calcite + diopside + quartz,calcite + quartz + dolomite, forsterite + calcite + dolomite,plagioclase + cordierite + garnet + quartz, amphibole + clinopyroxene+ plagioclase, hornblende + clinopyroxene + calcite,wollastor~te + calcite + diopside. Other minerals are graphite,antigorite, chrysotile, sphene, spinel, clinohumite, chondrodite,zoisite, clinozoisite, hedenbergite, phlogopite, ilmenite,hercynite, dravite, cummingtonite, talc, apatite, microcline,saponite. The mineral assemblages resulted from regionalmetamorphism and polyphase contact metamorphism.

[发布机构] Stellenbosch University