Mineral chemistry and crystallization parameters of the A-type Paleoproterozoic Bannach Granite, Carajás Province, Pará, Brazil
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Abstract:
The A-type Paleoproterozoic Bannach Granite belongs to the Jamon Suíte and cross-cut the Archean units of the Rio Maria Domain in the Carajás Province. It comprises eight facies with varied mafic content and texture: even-grained cumulate granite (CG), even coarse-grained biotite-amphibole monzogranite (cBAMz), even coarse-grained amphibole-biotite monzogranite (cABMz), porphyritic biotite monzogranite (pBMz), even coarse-grained leucomonzogranite (cLMz), early even medium-grained leucomonzogranite (EmLMz), late even medium-grained leucomonzogranite (LmLMz) and even fine-grained leucomonzogranite (fLMz). In the less evolved facies, the dominant amphibole is Fe-hornblende passing to Fe-edenite or hastingsite, with associated cummingtonite/grunerite originated from the destabilization of clinopyroxene. Biotite has ferroan composition and approaches annite in the late-emplaced leucomonzogranite. Plagioclase varies from andesine to oligoclase or from oligoclase to albite. Titanite, magnetite, and ilmenite are found in all granite facies showing magmatic origin. The near liquidus temperatures vary between 943ºC and 795ºC and the estimated emplacement pressure is 300 ± 50 MPa (~11.1 ± 1.9 km). Amphibole Fe/(Fe + Mg) ratios together with magmatic magnetite and titanite indicate that these granites crystallized at moderately oxidizing conditions, similar to those admitted for the Jamon granite and magnetite series granites of Laurentia. However, the composition of biotite suggests a more reduced character close to NNO to NNO -0.5. The late leucomonzogranite facies is an exception because it displays high Fe/(Fe + Mg) ratios in biotite and approaches to the reduced granites of Carajás, Laurentia and Fennoscandia in this regard. It derived from a more reduced source than the other facies of Bannach Granite.Keywords:
Amphibole
Titanite
Porphyritic
Hornblende
Allanite
Laurentia
Hornblende from the Lone Grove Pluton, Llano Uplift, Texas, has served as an irradiation reference material in 40 Ar/ 39 Ar studies for decades. In order to evaluate the apparent age bias that currently exists between the U‐Pb and 40 Ar/ 39 Ar systems, zircon and titanite were dated by isotope dilution‐thermal ionisation mass spectrometry ( ID ‐ TIMS ) from the same rock from which the hornblende 40 Ar/ 39 Ar reference material HB 3gr is derived. Zircon U‐Pb data indicate initial crystallisation at 1090.10 ± 0.16 Ma (2 s ), a date that is 1.7% older than the accepted K‐Ar date (1072 ± 14 Ma, 2 s ) for HB 3gr; an offset that exceeds the typical 0.5–1% bias between the two systems, though remaining within uncertainty due to the large uncertainties in the 40 K decay constant. Zircon data are presented using both EARTHTIME tracers ET 535 and ET 2535 and are statistically indistinguishable. Single grain titanite analyses range between 1082 ± 0.75 and 1086 ± 0.81 Ma (2 s ) and are interpreted to record the subsequent cooling following crystallisation at rates between 30 and 50 °C Ma −1 . This is supported by the observation that hornblende 40 Ar/ 39 Ar dates corrected for decay constant bias are resolvably younger than the zircon U‐Pb date and in good agreement with titanite U‐Pb dates, permitting the conclusion that both titanite U‐Pb and hornblende 40 Ar/ 39 Ar systems provide a record of cooling.
Titanite
Hornblende
Isotope dilution
Thermochronology
Isotopes of argon
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Key Points Zircon and titanite from the HB3gr 40Ar/39Ar hornblende reference material were dated by ID-TIMS. Zircon U-Pb data indicate initial crystallization at 1090.10 ± 0.16 Ma, a date 1.7% older than the accepted K-Ar date (1072 ± 11 Ma) for HB3gr. Single grain titanite analyses ranged between 1082 ± 0.75 and 1086 ± 0.81 Ma, and with 40Ar/39Ar hornblende dates are interpreted to record pluton cooling at 30--50 °C Ma-1.
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Hornblende
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Titanite
Allanite
Metamictization
Amphibole
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Crystal size distributions (CSD) and shapes of accessory apatite, titanite and allanite are investigated in three texturally distinct garnet zones (Z1–Z3) and in the matrix (Z4) of a garnet–epidote–biotite gneiss from the Moine Supergroup. Additionally, textural relationships and interactions between the accessory minerals and surrounding rock-forming minerals are considered, results of numerical CSD modelling are presented, and geochronological and geological consequences of the inferred CSD evolutions are discussed. Textures and CSDs indicate that the accessory minerals were in, or near, a stage of nucleation and initial growth immediately prior to garnet Z1 overgrowth, and formed within less than 20 000 years, either by a size-independent or size-dependent growth mechanism. Subsequently, the CSDs were modified by different growth mechanisms, as supported by several parameters including CSDs, grain numbers, grain sizes, specific volumes and others. The apatite CSD evolution from Z1 to Z4 is consistent with open-system LPE (Law of Proportionate Effects) growth accompanied and followed by supply controlled random ripening, whereas transformation of the original titanite CSD is more consistent with Ostwald ripening, temporarily accompanied by positive or negative McCabe growth. The allanite CSDs also point to Ostwald ripening between Z3 and Z4. The textural observations indicate that the growth evolution of the accessory phases was influenced by mineral reactions with surrounding rock-forming minerals, as well as by deformation and matrix coarsening, in a manner similar to that found in more simple ceramic systems. The observed textures require a successive temperature rise throughout the tectono-metamorphic evolution of the investigated rock, in agreement with existing P–T data. Fast nucleation and initial growth of the accessory minerals during Z1 was perhaps initiated by contact metamorphism, whereas subsequent growth and annealing (Z2–Z4) result from regional metamorphic events.
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Titanite
Ostwald ripening
Overprinting
Pseudomorph
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Northern Norrbotten, Sweden is a key part of Baltic Shield and provides a record of magmatic, tectonic and related, superimposed, Fe oxide–apatite and iron oxide–copper–gold (IOCG) mineralization, during the Svecokarelian orogeny. Titanite and allanite from a range of mineral deposits in the area have been analysed for U–Pb isotope systematics and trace element chemistry using laser ablation quadrupole inductively coupled plasma-mass spectrometry (LA-ICP-MS). Analyses of a single sample from the regional scapolite–albite alteration give an age of 1903 ± 8 Ma (2σ) and may be contemporaneous with the early stages of Fe mineralization (1890–1870 Ma). Analyses of titanite and allanite from undeformed IOCG deposits indicate initial alteration at 1862 ± 16 Ma. In many deposits subsequent metamorphic effects reset titanite isotope systematics from 1790 to 1800 Ma, resulting in a spread of U–Pb isotope analyses along concordia. In some instances core regions may record evidence of early thermal events at around 2050 Ma. Titanite and allanite from deformed IOCG deposits on major shear zones record ages from 1785 ± 21 Ma to 1777 ± 20 Ma, corresponding to deformation, metamorphism and secondary hydrothermal alteration as a result of late orogenic movements. The lack of intracrystalline variations in titanite and allanite trace element chemistry suggests that hydrothermal fluid chemistry and metal source were the main controls on mineral trace element chemistry. Titanite from undeformed Fe oxide–apatite and IOCG deposits is typically light rare earth element (LREE) enriched, and shows low U/Th ratios and low Ni in both intermediate to acid and basic volcanic-hosted deposits. This is consistent with a granitic source for metals. Minor variations in trace element patterns are consistent with the influence of aqueous complex formation on relative REE solubility. Deposits related to the Nautanen Deformation Zone have relatively heavy REE (HREE)-enriched titanite, and LREE-depleted allanite, with high U/Th ratios and elevated Ni contents, consistent with leaching of metals from the local basic volcanic rocks. All hydrothermal titanites are high field strength element enriched (Nb, Ta, Zr) indicating their transport as a result of either high salinities or high F contents, or both. The data overall support models of IOCG-type mineralization as a result of regional circulation of saline hydrothermal fluids in association with major crustal structures, with at least some metallic components derived from the granitoid rocks of the area. All the deposits here show evidence of subsequent metamorphism, although penetrative fabrics are restricted to regional-scale deformation zones.
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Allanite
Trace element
Metasomatism
Rare-earth element
Ore genesis
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Allanite
Titanite
Ilmenite
Amphibole
Metamictization
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Abstract Allanite-(La) (containing up to 7.80 wt.% V 2 O 3 and with La/Σ REE and La/Ce atomic ratios up to 0.54 and 1.45, respectively) and allanite-(Ce) (up to 8.46 wt.% V 2 O 3 ) occur in close association with vanadian muscovite, barian tomichite and vanadian titanite in the main ore zone of the Hemlo gold deposit, Ontario, Canada. Allanite-(Ce) generally occurs as a minor constituent in cross-cutting veins or along foliation planes, whereas allanite-(La) invariably occurs in direct contact with titanite. The high V concentrations in the allanites from Hemlo are readily attributable to an adequate local source of this element, and are most likely controlled mainly by a simple substitution of V for Al in octahedral coordination. Vanadian allanite-(La) and vanadian allanite-(Ce), without any systematic differences in other constituents, are clearly distinct in REE composition, in respect to both the relative concentrations of La and Ce and abundances of other REE . The formation of both allanites (Ce- and La-rich) indicates very localised remobilisation and concentration of REE during a late hydrothermal alteration. The unusual REE composition of vanadian allanite-(La) directly reflects partitioning of REE with coexisting titanite, and the formation of this unusual phase may be attributable to replacement of earlier titanite with redistribution of REE in the solid state.
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Titanite
Muscovite
Metamictization
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Titanite
Allanite
Cape
Wolframite
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Allanite-(La) (containing up to 7.80 wt.% V203 and with La/ZREE and La/Ce atomic ratios up to 0.54 and 1.45, respectively) and allanite-(Ce) (up to 8.46 wt.% V203) occur in close association with vanadian muscovite, barian tomichite and vanadian titanite in the main ore zone of the Hemlo gold deposit, Ontario, Canada. Allanite-(Ce) generally occurs as a minor constituent in cross-cutting veins or along foliation planes, whereas allanite-(La) invariably occurs in direct contact with titanite. The high V concentrations in the allanites from Hemlo are readily attributable to an adequate local source of this element, and are most likely controlled mainly by a simple substitution of V for A1 in octahedral coordination. Vanadian allanite-(La) and vanadian allanite-(Ce), without any systematic differences in other constituents, are clearly distinct in REE composition, in respect to both the relative concentrations of La and Ce and abundances of other REE. The formation of both allanites (Ce- and La-rich) indicates very localised remobilisation and concentration of REE during a late hydrothermal alteration. The unusual REE composition of vanadian allanite-(La) directly reflects partitioning of REE with coexisting titanite, and the formation of this unusual phase may be attributable to replacement of earlier titanite with redistribution of REE in the solid state. KEYWOROS: allanite-(La), allanite-(Ce), vanadian allanite, REE mobility, titanite.
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Muscovite
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