HIGH NI IN ARCHEAN THOLEIITES

被引:47
作者
ARNDT, NT [1 ]
机构
[1] MAX PLANCK INST CHEM,W-6500 MAINZ,GERMANY
关键词
D O I
10.1016/0040-1951(91)90479-C
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Archean tholeiites generally have higher Ni, Co, Cr and Fe than most younger tholeiites with similar MgO contents. These characteristics cannot be attributed to high T or P batch melting in the Archean mantle, because, although such melts are enriched in siderophile elements, they have higher MgO than normal tholeiites. As primary melts fractionate to lower MgO, they lose Ni, Co and Cr. Nor can the differences between Archean and younger tholeiites be attributed to secular variation in mantle compositions because Archean komatiites have Ni, Co, Cr contents similar to modern (Gorgona) komatiites. It is suggested that the high siderophile element content of Archean tholeiites results from mixing of either komatiitic with basaltic magmas, as might occur in an ascending, melting mantle plume or column, or of komatiite and more evolved rocks, as may take place when komatiite encounters and assimilates crustal rocks.
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页码:411 / 419
页数:9
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