Lithogeochemistry of Geological Units of the George Lithotectonic Domain
The majority of these samples were analyzed for major oxides, trace elements and base metals. A few selected samples of ultramafic mafic rocks were also analyzed for platinum, palladium and gold. Analyses were performed by various techniques depending on elements, such as plasma-coupled induction mass spectrometry (ICP-MS), coupled induction optical plasma emission spectrometry (ICP-AES) and neutron activation (INAA).
In the tables below, for each geological unit analyzed, the samples’ rare earth element diagrams and ratios, as well as spider diagrams, are mostly represented by 25th to 75th percentile envelopes of the sample population. Such a representation was chosen to simplify visualization of numerous diagrams. Envelopes and ratios presented are therefore indicative. Anomal contents and distinctive trace element ratios, or considered important, are in bold type.
Gneissic rocks
Stratigraphic or Lithodemic Unit | Classification/Rock Type | Mg# | Rare Earth Elements | Spider Diagram |
|---|---|---|---|---|
ApPgss1 and ApPgss1a | Tonalite and quartz diorite (Diagram) | 0.30-0.55 | 16.5 < (La/Yb)N < 26.4 2.8 < (La/Sm)N < 5.2 2.3 < (Gd/Yb)N < 3.3 0.7 < Eu/Eu* < 1.4 (Diagram) | Negative anomalies in: Ta‑Nb; P; Ti (Diagram) |
ApPgss2 | Granodiorite and monzogranite (Diagram) | 0.25-0.43 | 23.0 < (La/Yb)N < 34.6 4.1 < (La/Sm)N < 5.9 2.5 < (Gd/Yb)N < 2.6 0.6 < Eu/Eu* < 1.0 (Diagram) | Negative anomalies in: Ta‑Nb; P; Ti Positive anomalies in: Zr‑Hf; Tb (Diagram) |
Supracrustal Rocks
Stratigraphic or Lithodemic Unit | Classification/Rock Type | Affinity | Tectonic Setting | Mg# | Rare Earth Elements | Spider Diagram | Comments |
|---|---|---|---|---|---|---|---|
Volcanic and Associated Rocks | |||||||
nAtun1 (felsic to intermediate metavolcanics) | Rhyolite/dacite, trachyte, andesite/basaltic andesite and trachyandesite (Diagram) | Calc-alkaline to K-rich calc-alkaline and shoshonitic (Diagram) | 0.18-0.71 | 21.2 < (La/Yb)N < 22.6 4.5 < (La/Sm)N < 6.3 1.9 < (Gd/Yb)N < 2.6 0.8 < Eu/Eu* < 1.1 (Diagram) | Negative anomalies in: Ta‑Nb, P, Ti Positive anomalies in: Th (Diagram) | Zr-Hf anomaly absent or slightly negative | |
nAtun1 (metabasalt) | Andesite, basaltic andesite and basalt (Diagram) | Tholeiitic to calc-alkaline (Diagram) (Diagram) | Plate margin basalt (Diagram) Calc-alkaline volcanic arc basalt (Diagram) | 0.25-0.73 | 3.0 < (La/Yb)N < 6.5 1.7 < (La/Sm)N < 3.0 (Gd/Yb)N ≈ 1.5 0.9 < Eu/Eu* < 1.0 (Diagram) | Negative anomalies in: Th; Ta‑Nb, P, Zr‑Hf (Diagram) | Ti anomaly absent or slightly positive |
nAtun3 | Gabbro (Diagram) | Tholeiitic to calc-alkaline (Diagram) (Diagram) | Plate margin basalt (Diagram) Calc-alkaline volcanic arc basalt, N‑MORB and E‑MORB (Diagram) | 0.27-0.78 | 2.5 < (La/Yb)N < 3.5 1.3 < (La/Sm)N < 2.2 1.2 < (Gd/Yb)N < 1.3 0.9 < Eu/Eu* < 1.0 (Diagram) | Negative anomalies in: Th, Ta‑Nb, P, Zr‑Hf (Diagram) | REE and spider diagrams similar to unit pPtun1 mafic samples, but more primitive |
Sedimentary Rocks | |||||||
nAtun2 | Metawacke (Diagram) | Sedimentary rocks derived from the upper crust (granodioritic to granitic), unrecycled and slightly altered (Diagram) (Diagram) | 0.28-0.49 | ||||
Trace elements of metabasalt and metagabbro samples from the Tunulic Complex (nAtun1 and nAtun3, respectively) suggest a tholeiitic to calc-alkaline arc setting with varying crustal contamination. Paragneiss (nAtun2) of this complex appear to be derived from a felsic protolith (granodioritic to granitic upper crust) and to have undergone low transport or recycling. Extended spider diagrams indicate an increase in Th content (crustal contamination) within the intermediate to felsic metavolcanic and metabasalt unit (nAtun1). The latter also have a negative Ti anomaly, whereas this element is non-anomalous or has a small positive anomaly in metabasalt and metagabbro, possibly suggesting the accumulation of Ti oxides in these samples.
Intrusive Rocks
Stratigraphic or Lithodemic Unit | Classification/Rock Type | Affinity | Tectonic Setting | Mg# | Rare Earth Elements | Spider Diagram | Comments |
|---|---|---|---|---|---|---|---|
Felsic and Intermediate Intrusive Rocks | |||||||
pPdep1 | Tonalite, quartz diorite and quartz monzodiorite (Diagram) | 0.31-0.43 | 46.5 < (La/Yb)N < 47.6 5.4 < (La/Sm)N < 9.4 3.4 < (Gd/Yb)N < 3.9 1.3 < Eu/Eu* < 1.7 (Diagram) | Negative anomalies in: (Ta)‑Nb, P, Zr‑Hf, Sm, Ti Positive anomalies in: Th, (Ta), (Lu) (Diagram) | Slopes (La/Yb)N similar between all pPdep units | ||
pPdep2 (including subunits) | Granite, granodiorite, quartz monzonite and monzonite (Diagram) | Magnesian granitoid, calc-alkaline to alkaline-calcic and metaluminous to peraluminous (Diagrams) | Volcanic arc granite (Diagram) (Diagram) | 0.22-0.50 | 44.9 < (La/Yb)N < 50.3 (La/Sm)N ≈ 5.8 3.8 < (Gd/Yb)N < 4.1 0.9 ≈ Eu/Eu* (Diagram) | Negative anomalies in:Ta‑Nb, P, Zr‑Hf, Ti Positive anomalies in: Th (Diagram) | |
pPdep4 | Granite and granodiorite (Diagram) | Magnesian and ferriferous granitoids, calc-alkaline to alkaline-calcic and generally peraluminous (Diagrams) | Volcanic arc granite (Diagram) (Diagram) | 0.09-0.44 | 42.0 < (La/Yb)N < 45.2 4.9 < (La/Sm)N < 6.3 3.0 < (Gd/Yb)N < 3.9 0.7 < Eu/Eu* < 0.8 (Diagram) | Negative anomalies in: Ta‑Nb, P, Zr‑Hf, Ti Positive anomalies in: Th (Diagram) | Only De Pas unit containing ferriferous granitoids |
pPdep5 | Syenite and quartz monzonite (Diagram) | Magnesian granitoid, alkaline and metaluminous to peraluminous (Diagrams) | Volcanic arc granite (Diagram) (Diagram) | 0.31-0.44 | 42.4 < (La/Yb)N < 58.6 4.2 < (La/Sm)N < 4.8 4.2 < (Gd/Yb)N < 5.9 0.9 < Eu/Eu* < 1.0 (Diagram) | Negative anomalies in: Ta‑Nb, P, Zr‑Hf, Ti Positive anomalies in: Th (Diagram) | |
pPcde1 | Tonalite, quartz diorite, quartz monzodiorite and diorite/gabbro (Diagram) | 0.37-0.55 | 21.3 < (La/Yb)N < 22.3 3.5 < (La/Sm)N < 3.7 2.9 < (Gd/Yb)N < 3.8 0.9 < Eu/Eu* < 1.0 (Diagram) | Negative anomalies in: Th, Ta‑(Nb), P, Nd, Ti Positive anomalies in: (Nb) (Diagram) | |||
pPcde2 | Granodiorite and monzonite (Diagram) | Magnesian granitoid, calc-alkaline to alkaline-calcic and generally metaluminous (Diagrams) | Volcanic arc granite (Diagram) (Diagram) | 0.33-0.50 | 31.3 < (La/Yb)N < 52.2 4.5 < (La/Sm)N < 6.6 3.4 < (Gd/Yb)N < 5.1 1.1 < Eu/Eu* < 1.3 (Diagram) | Negative anomalies in: Ta‑Nb, P, Zr‑Hf, Sm, Ti Positive anomalies in: Th, Nd (Diagram) | |
pPmer | Quartz diorite to monzogabbro (Diagram) | 0.37-0.58 | |||||
Stratigraphic or Lithodemic Unit | Classification | Affinity | Tectonic Setting | Mg# | Rare Earth Elements | Spider Diagram | Comments |
|---|---|---|---|---|---|---|---|
Mafic and Ultramafic Intrusive Rocks | |||||||
pPcde3 | Gabbro, gabbronorite, diorite and monzogabbro (Diagram) | 0.39-0.71 | 9.7 < (La/Yb)N < 20.4 3.5 < (La/Sm)N < 4.3 1.5 < (Gd/Yb)N < 3.1 0.9 < Eu/Eu* < 1.2 (Diagram) | Negative anomalies in: Ta‑Nb, P, Zr‑Hf, Ti Positive anomalies in: Th (Diagram) | |||
pPbon | Gabbro (Diagram) | 0.46-0.68 | 2.6 < (La/Yb)N < 44.5 1.5 < (La/Sm)N < 3.6 1.5 < (Gd/Yb)N < 7.5 0.9 < Eu/Eu* < 1.4 (Diagram) | Negative anomalies in: Ta, Nd, Zr‑Hf, Ti Positive anomalies in: (Th), Nb, P (Diagram) | |||
pPfay | Lamprophyres (vogesite, minette mélanocrate) (Diagram) | 0.42-0.78 | 30.3 < (La/Yb)N < 46.6 2.5 < (La/Sm)N < 3.7 6.2 < (Gd/Yb)N < 6.7 Eu/Eu* ≈ 0.9 (Diagram) Light REE enrichment compared to the average alkaline lamprophyre of Rock (1991) (Diagram) | Negative anomalies in: Ta‑Nb, P, Zr‑Hf, Ti Positive anomalies in: Th (Diagram) Negative anomalies in: Nb, TiO2 Positive anomalies in: Sr, K2O, Rb, Ce, Ba, Sm (Diagram) | REE and spider diagrams similar to those of unit pPdep5 and comparable to that of an average alkaline lamprophyre | ||
The De Pas Supersuite consists of a granitic suite (pPdep) and a charnockitic suite (pPcde). These suites also include the Merville (pPmer) and Bonaventure (pPbon) plutons, respectively. Trace elements of granitoid samples of the De Pas Supersuite suggest a volcanic arc setting, as proposed by Martelain et al. (1998). All granitoids in the supersuite are Type I and generally have affinities ranging from calc-alkaline to alkaline-calcic. With the exception of the pPdep4 granite unit of the De Pas Granitic Suite, which includes magnesian and ferroan granites, De Pas granitoids are generally magnesian. A feature observed in the De Pas Charnockitic Suite samples is the Nd and Sm disturbance on RRE diagrams and, in places, decoupling of the Ta-Nb anomaly is observed on the 25th and 75th percentile envelopes of spider diagrams. In addition, lower Th and Nb contents are observed for the charnockitic suite compared to the granitic suite. Martelain et al. (1998) explain the weak contents of large-ion lithophile elements (LILE) of the De Pas Charnockitic Suite by the primary character of granulitic magmas, as well as by the differential contamination of each suite according to host terrains (the charnockitic suite host, limited to the south of the George Domain, includes granulitic gneiss immediately to the west). Spider diagrams of Fayot Suite (pPfay) samples are similar to syenites of De Pas Granitic Suite (pPdep5); however, P and Ti anomalies are more significant. The Fayot Suite sample profiles are comparable to that of an average alkaline lamprophyre (Rock, 1991), except that the Fayot Suite shows enrichment in light REE, Sr, K2O, Rb, Ce, Ba and Sm, and depletion in Nb and TiO2 (Chartier, 2015).
References
Publications Available Trough SIGEOM Examine
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