Petrogenesis of the Lower Zone cumulates beneath the Platreef and their correlation with recognised occurrences in the Bushveld Complex
Until recently,there was a general concept that the Lower Zone is absent in the layered sequence beneath the Platreef north of the Planknek fault occurring only as satellite bodies or offshoots in country rocks.Here we describe new Lower Zone occurrences beneath the Platreef that show both the remarkable similarity to the recognized occurrences but with distinct local variations that suggest tongues of magma were emplaced in the northern limb during Lower and Critical Zone times.Stratigraphy of the new Lower Zone sections indicates a major break and magmatic discontinuity between the Lower Zone and the Platreef sequences.Differing whole-rock sulfur contents and distinct geochemical signatures of olivine and orthopyroxene from adjacent sites substantiating emplacement of discrete magmatic pulses in separate magmatic compartments that were defined partly by the geometry of the floor contours and possibly by faulting during magma loading.A character of cyclicity and reversals through the ultramafic sequence also support a mechanism of repeated emplacement of fresh mafic melt into a fractionating column with a subsequent mixing between liquids and crystal mush.New data on the most chemically primitive compositions of olivine and orthopyroxene give constrains on a more primitive composition of parental magma for the Lower Zone sequence than was previously accepted.
M.Yudovskaya J.A.Kinnaird A.Sobolev D.Kuzmin A.Wilson
EGRI,University of the Witwatersrand,Wits 2050,South Africa IGEM RAS,Staromonetny 35 Moscow 119017 R EGRI,University of the Witwatersrand,Wits 2050,South Africa Max Planck Institute(MPI)for Chemistry,Post Office Box 3060,55020 Mainz,Germany
国际会议
贵阳
英文
77-80
2012-06-16（万方平台首次上网日期，不代表论文的发表时间）