|Title||Compositional evidence for magma recharge and mixing in CFB reservoirs: Evidence from melt inclusions in HALIP basalt|
|Author||Williamson, M C;
Jackson, S E; Yang, Z; Venance, K; Hunt, P|
|Source|| 2017. Open Access|
|Links||Online - En ligne|
|Alt Series||Natural Resources Canada, Contribution Series 20170003|
|Publisher||Geological Association of Canada|
|Meeting||Geological Association of Canada-Mineralogical Association of Canada, Annual Meeting; Kingston; CA; May 14-18, 2017|
|Media||paper; on-line; digital|
|Area||Bunde Fjord; Axel Heiberg|
|Lat/Long WENS|| -92.0000 -91.0000 80.7500 80.5000|
|Subjects||general geology; mineralogy; metallic minerals; trace element analyses; trace element geochemistry; basalts; petrogenesis; inclusions; reservoirs; plagioclase|
Geo-mapping for Energy and Minerals, Western Arctic, High Arctic LIP|
|Abstract||Small pockets of melt trapped as inclusions during crystal growth may provide constraints on the compositional diversity of melts in basaltic magmatic systems, and ultimately shed light on the nature of
their mantle source(s). Melt inclusions preserved in continental flood basalts (CFB) may represent more primitive compositions than the erupted magmas, hence their importance in deepening our understanding of CFB petrogenesis.|
We report the
trace element concentrations of plagioclase-hosted melt inclusions in HALIP flood basalts exposed near Bunde Fiord, northern Axel Heiberg Island. The Arthaber Creek (AC) volcanic succession consists of lava flows with well-defined oxidized flow tops
and an average thickness of ~ 10 m. Whole rock geochemical analyses for 20 samples of basalt yielded compositions typical of continental tholeiites with (e.g.) SiO2 values of 45.7-53.7 wt.%; MgO values of 3.3-6.6 wt.%; and TiO2 values of 1.45-2.89
wt.%. REE patterns show enrichment in LREE (LaN/SmN: 1.66-2.43) and evidence of differentiation within the volcanic succession. The lava flows are characterized by abundant, inclusion-rich plagioclase phenocrysts with disequilibrium textures. A
strong correlation between higher Mg# in the bulk rock and the presence of An-rich cores in phenocrysts suggests that episodic magma recharge and mixing processes operated at depth. Melt inclusions range in size from 100 to 200 µm; glass inclusions
with altered rims (30-50 µm in size) are commonly found in the cores of larger inclusions. Overall, the size and texture of melt inclusions are ideally suited for geochemical analysis by LA-ICP-MS.
The analytical methodology involved the
following steps: (1) detailed textural analysis of melt inclusions using the Scanning Electron Microscope (SEM); (2) selection of targets in four thin sections of basaltic lava; (3) major element analysis of 17 inclusions by Electron Probe
Microanalysis; and (4) LA-ICP-MS spot analyses of melt inclusions using a Teledyne Photon Machines Analyte G2 excimer laser ablation system and an Agilent 7700x ICP-MS.
The experiment demonstrated that melt inclusions ablated without prior
homogenization can yield reliable geochemical data. However, the interpretation of results is critically dependent on the availability of textural information at the micron scale. Our data show a high degree of coherence, particularly for REE and
HFSE. A comparison of REE patterns for bulk rocks and melt inclusions leads us to conclude that some of the glass inclusions represent primitive melts trapped during magma recharge and mixing in shallow reservoirs; and that partial crystallization
modified a significant number of large, plagioclase-hosted melt inclusions.
|Summary||(Plain Language Summary, not published)|
This publication describes the results of bedrock mapping and sampling activities carried out as part of the GEM 2 HALIP Activity. The authors present
the first attempt to resolve the composition of primitive magmas that eventually led to the eruption of HALIP flood basalts. Under favourable conditions, these primitive, Mg-rich magmas have the potential of generating Ni-Cu-PGE deposits hosted in
shallow sills or dykes. The results include major and trace element data for basaltic lava flows sampled from a coastal section of the Strand Fiord Formation located near Bunde Fiord, northern Axel Heiberg Island. The authors interpret the
compositional trends in melt inclusions and host rocks in the context of other HALIP project results. The study carries important implications for the economic potential of the HALIP magmatic system in this region of Nunavut.