Isotope Geochemistry of Proterozoic Talc Occurrences in Archean Marbles of the Ruby Mountains, Southwest Montana, U.S.A

Talc occurs as massive, economic deposits in upper amphibolite facies marbles of Archean age in southwestern Montana. Previous workers have demonstrated that the talc is a replacement of the marble that resulted from interaction with a large volume of fluid. δ18O (SMOW) values for dolomite and calcite range from 20-25‰ for the unaltered Archean marbles to as little as 8-10‰ in the talc deposits, suggesting that the metasomatic fluids had low δ18O values. In contrast, δ13C values for calcite and dolomite are similar for all samples (-2 to +2‰ PDB). Therefore, it is likely that the metasomatic fluids were oxygen-rich and carbon-poor, namely water-rich and CO2-poor. A CO2-poor fluid is also indicated by Δ13C (calcite-graphite) values (3.6-5.3‰), which appear little altered from values expected for upper amphibolite facies marbles, and by the occurrence of the mineral assemblage talc+calcite, 40Ar/39Ar age spectra for hornblende, phlogopite, and biotite record cooling at 1.72 Ga from a regional thermal event. 40Ar/39Ar age spectra of fine-grained muscovite associated with the talc date talc formation at 1.36 Ga. The Ar data limit the temperature of talc crystallization to below ∼350 DEGC, the biotite closure temperature for Ar diffusion. If the metasomatic fluid was seawater (0‰), then the carbonate oxygen data require a minimum temperature of 270 DEGC for talc formation. Oxygen (δ18O = 4.7 to 8.8‰) and hydrogen (D/H = -49.9 to -57.6 SMOW) isotope data for the talc are consistent with a 200-300 DEGC metasomatic fluid derived from seawater, based on theoretical models of the fractionation of oxygen and hydrogen between talc and water. Regional, northwest-trending faults associated with the extension that formed the Belt Basin in the Middle Proterozoic may have provided channels for seawater to circulate in continental crust and to react with marble, forming talc at depths of 5-10 km

\u3csup\u3e40\u3c/sup\u3eAr/ \u3csup\u3e39\u3c/sup\u3eAr Ages of Metamorphic Rocks from the Tobacco Root Mountains Region, Montana

Measurements of 60 single-grain, UV laser microprobe 40Ar/39Ar total gas ages for hornblende from metamorphic rocks of the Tobacco Root Mountains in southwest Montana yield a mean age of 1.71 ± 0.02 Ga. Measurements of 40Ar/39Ar step-heating plateau ages of three bulk hornblende samples from the Tobacco Root Mountains metamorphic rocks average 1.70 ± 0.02 Ga. We believe that these and the K/Ar or 40Ar/39Ar ages reported by previous workers are cooling ages from a 1.78 to 1.72 Ga, upper-amphibolite to granulite facies, regional metamorphism (Big Sky orogeny) that affected the northwestern portion of the Wyoming province, including the Tobacco Root Mountains and adjacent ranges. Based on the 40Ar/39Ar data, this 1.78–1.72 Ga metamorphism must have achieved temperatures greater than ~500 °C to reset the hornblende 40Ar/39Ar ages of samples from the Indian Creek Metamorphic Suite, which was previously metamorphosed at 2.45 Ga, and of the crosscutting metamorphosed mafic dikes and sills (MMDS), which were intruded at 2.06 Ga. Biotite and hornblende from the Tobacco Root Mountains appear to give the same 40Ar/39Ar or K/Ar age (within uncertainty), indicating that the rocks cooled rapidly through the interval from 500 to 300 °C. This is consistent with a model of the Big Sky orogeny that includes late-stage tectonic denudation that leads to decompression and rapid cooling. A similar cooling history is suggested by our data for the Ruby Range. Three biotite samples from the Ruby Range yield 40Ar/39Ar step-heating plateau ages with a mean of 1.73 ± 0.02 Ga, identical to the best-estimate (near-plateau) age for a hornblende from the same rocks. Two samples of the orthoamphibole, gedrite, from the Tobacco Root Mountains were studied, but did not have enough K to yield a reliable 40Ar/39Ar age. Several biotite and three hornblende samples from the region yield 40Ar/39Ar dates significantly younger than 1.7 Ga. We believe these samples were partially reset during contact metamorphism by Cretaceous (75 Ma) intrusive rocks. Hydrothermal alteration associated with ca. 1.4 Ga rifting led to growth of muscovite with that age in the Ruby Range, but this alteration was apparently not hot enough to reset biotite and hornblende ages there

Ar ages of metamorphic rocks from the Tobacco Root Mountains region, Montana

Ar dates signifi cantly younger than 1.7 Ga. We believe these samples were partially reset during contact metamorphism by Cretaceous (75 Ma) intrusive rocks. Hydrothermal alteration associated with ca. 1.4 Ga rifting led to growth of muscovite with that age in the Ruby Range, but this alteration was apparently not hot enough to reset biotite and hornblende ages there

Extragenital Endometriosis

Parietal, appendiceal, pleuropulmonary and diaphragmatic endometriosis represent 5% of endometriosis cases. Diagnosis and management of these extra-genital localisations are described according to the literature. Parietal endometriosis usually requires large resection of the tumor. Appendiceal endometriosis is frequently observed in cases of digestive endometriosis. Induration or rigidity of the appendix due to the presence of deep infiltrating endometriosis justifies appendicectomy. Thoracic and diaphragmatic endometriosis is characterized by the presence of typical symptoms during the perimenstrual periode. Medical treatment obtaining therapeutic amenorrhea is firstly administered and surgery is indicated in cases of symptoms recurrence