The Crystallization History of a Granitic Magma, as Revealed by Trace Element Abundances

1980 ◽  
Vol 88 (2) ◽  
pp. 211-224 ◽  
Author(s):  
T. S. McCarthy ◽  
R. E. P. Fripp
Keyword(s):  
Trace Element ◽  
Granitic Magma ◽  
Element Abundances ◽  
History Of

Geochemical constraints on the differentiation processes that were active in the Sept Iles complex

1986 ◽  
Vol 23 (5) ◽  
pp. 670-681 ◽  
Author(s):  
Michael D. Higgins ◽  
R. Doig
Keyword(s):  
Mass Balance ◽  
Trace Element ◽  
Fractional Crystallization ◽  
Major Element ◽  
Alkali Feldspar ◽  
Granitic Magma ◽  
Trace Element Distribution ◽  
Accessory Mineral ◽  
Quartz Syenite ◽  
Element Abundances

Major- and trace-element abundances in the major units (gabbro, anorthosite, monzonite, syenite, and granite) of the unmetamorphosed Sept Iles complex have been evaluated to determine if these rocks can be related by simple magmatic processes or if it is necessary to invoke separately derived magmas. Major-element mass-balance and trace-element distribution calculations indicate that the diorite and quartz syenite were produced by fractional crystallization of plagioclase and augite, together with minor hypersthene and ilmenite, from a parental gabbroic magma. The Sr depletion of the granite, as compared with the quartz syenite, cannot be developed readily by partial melting and is better explained by fractional crystallization models. Major-element mass-balance solutions indicate that the granite was formed by removal of alkali feldspar, plagioclase, amphibole, and ilmenite from a quartz syenitic magma. Depletion of REE in the granite was probably the result of amphibole or REE-rich accessory mineral fractionation. It is unlikely that an unrelated, independently generated granitic magma could have a composition so related to the remainder of the complex. Therefore, fractional crystallization of a parental gabbroic magma is the dominant process that controlled the diversity of magma in the complex.

A new locality for primary xenolith-bearing nephelinites in northwestern British Columbia

1985 ◽  
Vol 22 (10) ◽  
pp. 1556-1559 ◽  
Author(s):  
Michael D. Higgins ◽  
John M. Allen
Keyword(s):  
British Columbia ◽  
Trace Element ◽  
Volcanic Belt ◽  
Primary Magma ◽  
Similar Composition ◽  
Element Abundances ◽  
Late Tertiary

High Ni abundances (420–500 ppm) and Mg* values (100 × Mg/(Mg + Fe2+) = 69–71) and the presence of mantle-derived xenoliths indicate that a subvolcanic nephelinite intrusion in northwestern British Columbia represents an unmodified primary magma. A separate, closely associated nephelinite intrusion shows evidence of minor olivine fractionation from a similar composition. Only three other occurrences of primary nephelinite have been described. This new occurrence suggests that these magmas may not be so rare as previously supposed. The trace-element abundances closely resemble those of primary nephelinites of similar La content from Freemans Cove, Canada. Such compositions are usually taken as evidence of intraplate rifting and doming. Therefore, these rocks are further evidence of late Tertiary or Quaternary rifting in the Stikine volcanic belt.

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