Mineralogy of the Steel Mountain Anorthosite Complex, Western Newfoundland Appalachians, Canada: Petrogenesis and Tectonic Affinity
Abstract
:1. Introduction
2. Geological Setting
3. Materials and Methods
4. Petrography
4.1. Anorthosite
4.2. Gabbronorite
4.2.1. Megacrystic Gabbronorite
4.2.2. Gabbronorite with Mafic Layering
4.3. Magnetite-Ilmenite Ore
5. Mineral Chemistry
5.1. Feldspar
5.2. Orthopyroxene
5.3. Clinopyroxene
5.4. Amphibole
6. Lithogeochemistry
7. Geochronology
8. Discussion
8.1. Magmatic Crystallization
8.2. Sub-Solidus Alteration
8.3. Age and Tectonic Affinity of the Steel Mountain Complex
9. Conclusions
- The Steel Mountain complex is a typical Proterozoic anorthosite massif, except for the abundance of amphibole, which indicates more hydrous magmatic conditions than in Laurentian anorthosites in the literature.
- The ferromagnesian megacrysts have exsolution lamellae of Fe-Ti oxides, magnesio–hornblende, and clinopyroxene. The lack of exsolution lamellae of plagioclase is unusual for Proterozoic anorthosites and is a consequence of hydrous conditions in the Steel Mountain anorthosite.
- Sub-solidus exsolution of ilmenite lamellae from orthopyroxene megacrysts was followed by late veins of clinopyroxene, andesine, and almandine garnet, and then by widespread alteration of orthopyroxene to talc and dispersed magnetite. Tschermakitic hornblende was replaced by magnesio–hornblende. Both orthopyroxene and amphibole megacrysts have corona rims of magnesio–hornblende, biotite, and chlorite.
- The magnetite-ilmenite ore, containing minor Fe-sulfides, formed from an immiscible magma that inmixed some siliceous material.
- The Steel Mountain anorthosite massif shows polybaric evolution of a rising mush of plagioclase crystals. The magnetite-ilmenite ore contains inclusions of olivine and of pargasite that equilibrated at >30 km depth. Orthopyroxene megacrysts and groundmass crystallized at 20–25 km and amphibole megacrysts at 15–20 km. The corona rims equilibrated at upper crustal depths.
- Sm-Nd isotopes and Ar-Ar geochronology are more consistent with a peri-Gondwanan than a peri-Laurentian origin of the Steel Mountain complex.
- Zircon is rare or absent in the anorthosite and gabbronorite. Common zircon in this study is found only in a post-tectonic, altered, mafic dyke.
Supplementary Materials
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Rock Type | an | an | an | an | an + | gn | gn | gn | gn |
---|---|---|---|---|---|---|---|---|---|
Sample | 8127 | 8128 | 8150 | 8154 | 8157 | 8129 | 8153 | 8185 | 8187 |
Major oxides (wt%) | |||||||||
SiO2 | 56.09 | 54.85 | 55.3 | 55.47 | 51.19 | 54.90 | 54.45 | 55.75 | 53.20 |
TiO2 | 0.13 | 0.38 | 0.13 | 0.12 | 1.10 | 0.18 | 0.12 | 0.14 | 0.32 |
Al2O3 | 26.88 | 27.49 | 27.04 | 26.49 | 25.01 | 25.62 | 25.98 | 26.92 | 21.08 |
Fe2O3t | 1.26 | 2.32 | 0.61 | 0.58 | 6.65 | 2.30 | 0.64 | 1.28 | 6.83 |
MnO | 0.02 | 0.02 | 0.01 | 0.00 | 0.03 | 0.03 | 0.01 | 0.02 | 0.11 |
MgO | 0.44 | 0.32 | 0.19 | 0.19 | 0.62 | 2.04 | 0.15 | 0.95 | 7.13 |
CaO | 8.21 | 8.84 | 8.14 | 8.18 | 7.55 | 8.21 | 8.53 | 8.61 | 6.85 |
Na2O | 5.67 | 5.43 | 5.87 | 5.67 | 5.19 | 5.32 | 5.63 | 5.5 | 3.73 |
K2O | 1.12 | 0.86 | 1.18 | 1.04 | 0.85 | 0.69 | 1.21 | 0.75 | 0.53 |
P2O5 | 0.04 | 0.03 | 0.04 | 0.03 | 0.03 | 0.03 | 0.04 | 0.03 | 0.03 |
L.O.I. | 0.60 | 0.49 | 0.20 | 0.84 | 0.70 | 1.01 | 1.83 | 0.76 | 0.61 |
Total | 100.46 | 101.03 | 98.71 | 98.61 | 98.92 | 100.33 | 98.59 | 100.71 | 100.42 |
Trace elements (ppm) | |||||||||
Ba | 713 | 515 | 483 | 229 | 359 | 261 | 467 | 432 | 302 |
Rb | 43 | 40 | 47 | 47 | 31 | 40 | 46 | 42 | 29 |
Sr | 1044 | 1007 | 1091 | 1023 | 984 | 923 | 1024 | 996 | 696 |
Y | 7 | 4 | 8 | 6 | 3 | 7 | 7 | 7 | 6 |
Zr | 67 | 65 | 70 | 64 | 67 | 61 | 64 | 64 | 57 |
Nb | 4 | 3 | 4 | 4 | 2 | 3 | 4 | 4 | 3 |
Th | 1 | 2 | 2 | 3 | b.d. | b.d. | 2 | b.d. | b.d. |
Pb | 5 | 4 | 8 | 7 | 4 | 6 | 7 | 7 | 2 |
Ga | 23 | 22 | 23 | 24 | 19 | 22 | 23 | 23 | 18 |
Zn | b.d. | 14 | b.d. | b.d. | 39 | 19 | b.d. | 4 | 61 |
Cu | 20 | 8 | 9 | 11 | 47 | 7 | 8 | 6 | 4 |
Ni | 49 | 27 | 24 | 26 | 104 | 33 | 21 | 24 | 65 |
V | 26 | 51 | 12 | b.d. | 193 | 32 | 10 | b.d. | 75 |
Cr | 8 | 27 | 10 | 7 | 108 | 23 | 8 | 19 | 114 |
Co | b.d. | b.d. | b.d. | b.d. | 22 | 4 | b.d. | b.d. | 34 |
Sc | b.d. | b.d. | 4 | 3 | b.d. | b.d. | b.d. | b.d. | 6 |
La | 19 | 13 | 17 | 14 | 12 | 15 | 12 | 22 | 15 |
Ce | 61 | b.d. | 18 | 52 | 32 | b.d. | 37 | b.d. | 21 |
Nd | 15 | 11 | 9 | 7 | 13 | 5 | 8 | 14 | 10 |
Sample | Lithology | Measured | Calculated | ||||||
---|---|---|---|---|---|---|---|---|---|
Sm ppm | Nd ppm | 147Sm/ 144Nd | 143Nd/ 144Nd | t DM (Ga) | ε0.6 CHUR | ε1.2 CHUR | ε1.5 CHUR | ||
8217 | anorthosite | 0.29 | 2.21 | 0.0802 | 0.511856 | 1.35 | −6.33 | 2.66 | 7.18 |
8131A | anorthosite | 0.25 | 1.84 | 0.0825 | 0.511839 | 1.39 | −6.84 | 1.97 | 6.40 |
8131B | gabbronorite | 0.32 | 2.27 | 0.0848 | 0.511869 | 1.38 | −6.43 | 2.20 | 6.54 |
8187 | gabbronorite | 0.3 | 1.77 | 0.1013 | 0.512006 | 1.40 | −5.02 | 2.34 | 6.04 |
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Pe-Piper, G.; Piper, D.J.W.; Dessureau, G. Mineralogy of the Steel Mountain Anorthosite Complex, Western Newfoundland Appalachians, Canada: Petrogenesis and Tectonic Affinity. Minerals 2024, 14, 81. https://doi.org/10.3390/min14010081
Pe-Piper G, Piper DJW, Dessureau G. Mineralogy of the Steel Mountain Anorthosite Complex, Western Newfoundland Appalachians, Canada: Petrogenesis and Tectonic Affinity. Minerals. 2024; 14(1):81. https://doi.org/10.3390/min14010081
Chicago/Turabian StylePe-Piper, Georgia, David J. W. Piper, and Gilles Dessureau. 2024. "Mineralogy of the Steel Mountain Anorthosite Complex, Western Newfoundland Appalachians, Canada: Petrogenesis and Tectonic Affinity" Minerals 14, no. 1: 81. https://doi.org/10.3390/min14010081
APA StylePe-Piper, G., Piper, D. J. W., & Dessureau, G. (2024). Mineralogy of the Steel Mountain Anorthosite Complex, Western Newfoundland Appalachians, Canada: Petrogenesis and Tectonic Affinity. Minerals, 14(1), 81. https://doi.org/10.3390/min14010081