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| Titel |
A melt inclusion study of the Sudbury Igneous Complex (Ontario, Canada): preliminary results |
| VerfasserIn |
Kathleen Watts, Jacob Hanley, Daniel Kontak, Doreen Ames |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250084252
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| Zusammenfassung |
| The 1.85 Ga Sudbury Igneous Complex (SIC), Ontario, Canada, is an intrusive complex
representing the crystallized melt sheet that formed within a large impact crater. The SIC has
been extensively studied due to its rich endowment in magmatic sulfide ores (Ni-Cu-PGEs).
The nature and origin of the SIC melt sheet and its subsequent evolution still remain
controversial. In this study, analyses of primary melt inclusions hosted in cumulus apatite
within three mafic units of the SIC (gabbro, norite and sublayer quartz diorite) are used to
decipher the thermometric and chemical characteristics of the evolving melt sheet as it
crystallized.
Apatite-hosted melt inclusions commonly display a negative crystal shape, occur parallel
to the c-axis, and often occur within a central growth zone, which suggest a primary origin.
The compositions of coeval (co-entrapped) melt inclusions are distinct and may represent
either the products of immiscibility (low or high temperature field; c.f. the Skaergaard
Intrusion: Jakobsen et al., Geology, 2005), or a product of early, high-temperature,
impact-generated emulsification (prior to and independent of crystallization of the melt
sheet). The compositions of homogenized (1100-1200oC for 3 hrs) melt inclusions,
determined by SEM-EDS and EMP analyses of opened, homogenized melt inclusions, equate
to two distinct compositions: (1) Type-I are SiO2-rich, ranging from tonalitic to
granodioritic in composition (60-70 wt% SiO2, up to 11 wt% FeO); and (2) Type-II are
Fe-rich with syenogabbroic to essexitic to alkali gabbroic compositions (27-49 wt%
SiO2, 16-44 wt% FeO). Trace element data, obtained by LA-ICPMS analyses of
single inclusions and surrounding host apatite, are used to infer D values between
apatite and the two melt types, and between the coexisting melt types. Apparent
Dap-melt values for both Type-I and Type-II inclusions show that the REE, Sr,
and Y are compatible in apatite, and As is weakly compatible or incompatible in
apatite, whereas the following elements behaved incompatibly (in increasing order of
incompatibility: Cr, Ni, Cu, Zr, Co, Cs, Ag Nb, Hf, Ta, Rb). Apparent D values between
the two coexisting melt phases (DFe-rich-Si-rich) show that most trace elements
were weakly compatible or incompatible in each melt phase, with the exception of
V, Co, Rb, Sr and Cs that show consistent enrichment in the Fe-rich melt phase.
Preliminary melt inclusion analyses suggest that the earliest (and quenched?) melt
phase of the SIC, as represented by sublayer quartz diorite, was enriched in Ni
and Cu, up to an order of magnitude higher than those liquids trapped in the units
stratigraphically higher in the SIC, and may reflect loss of these metals to early sulfide
liquids.
The results of this study have implications for our understanding of layered intrusions
world-wide and may lead to the development of parameters that enhance exploration success
in mafic-ultramafic systems where post-magmatic processes have severely limited the
application of bulk rock chemistry in understanding their petrogenesis. This study provides
the first in-situ determination of actual ore-metal concentrations and partitioning behavior of
ore metals and other trace elements in a differentiated, mafic-ultramafic intrusion. |
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