Amphibole ternary diagram
20, 250–265 (1973)īrady, J.: Coexisting actinolite and hornblende from west-central New Hampshire. 76, 382–403 (1968)īottinga, Y., Javoy, M.: Comments on oxygen isotope geothermometry. 42, 1408–1414 (1970)īence, A.E., Albee, A.L.: Empirical correction factors for the electron microanalysis of silicates and oxides. Usefulness of this exchange equilibrium as a geothermometer is restricted by uncertainties in the calculation of the amphibole formula from a microprobe analysis, especially with regard to Na, M4 in amphibole, to approximately ±50 ° C.Īlbee, A.L., Ray, L.: Correction factors for electron probe microanalysis of silicates, oxides, carbonates, phosphates and sulfates. Temperature dependence of In K D is moderate with Δ ¯H≃35 to 47 kcal at X an=0.25 pressure dependence is small with Δ ¯V≃ −0.24 cal/bar. Changes in both K D and the topology of the ternary reciprocal exchange diagram occur with increasing metamorphic grade. Partitioning is systematic between plagioclase and amphibole in suites collected from single exposures, but the solid solutions are highly non-ideal: values of In K D range from −3.0 at X an=0.30 to −1.0 at X an=0.90 in samples from a single roadcut. The partition coefficient, K D, for the exchange reaction is ( X an/ X ab) plag Finally, the P–T data for both metasedimentary and metaigneous rocks provide new constraints on an accretionary framework, which is responsible for generating metamorphism and partial melting in the Yelapa-Chimo Metamorphic Complex during the Early Cretaceous.The exchange equilibrium between plagioclase and amphibole, 2 albite+tschermakite=2 anorthite+glaucophane, has been calibrated empirically using data from natural amphibolites. Our new data indicate that the Yelapa-Chimo Metamorphic Complex evolved through a metamorphic gradient between ~23–33 ☌ km −1 and the metamorphic rocks formed at depths between ~22 km and ~30 km with a burial rate of ~2.0 km Ma −1. Modelling within a closed system during isobaric heating suggests that melt compositions of metasedimentary and metaigneous units are likely to have direct implications for the petrogenesis of the Puerto Vallarta Batholith. The mode models imply that metasedimentary and metaigneous units can produce up to ~20 vol% and ~10 vol% of melt, respectively. The results for amphibole–orthogneiss and the amphibolite yield P–T peak conditions at ~8.5–10 kbar and ~690–710 ☌. Pseudosections calculated for the two sillimanite–garnet paragneiss samples show P–T peak conditions at ~6–7.5 kbar and ~725–740 ☌.
Amphibole–orthogneiss and amphibolite display a nematoblastic texture with an amphibole + (1) plagioclase + quartz + (1) titanite assemblage and an amphibole + (2) plagioclase + (2) titanite + ilmenite retrograde mineral assemblage. Sillimanite–garnet paragneisses exhibit a lepidoblastic texture with a biotite + sillimanite + kyanite + garnet + quartz + plagioclase + K-feldspar mineral assemblage.
To elucidate metamorphic P–T conditions, phase equilibrium modelling was applied to two sillimanite–garnet paragneisses, one amphibole–orthogneiss, and one amphibolite. However, the pressure–temperature ( P–T) conditions of metamorphism and partial melting remain poorly studied in the region.
The Yelapa-Chimo Metamorphic Complex forms part of the Jalisco Block in western Mexico and exposes a wide range of Early Cretaceous metamorphic rocks such as paragneiss, orthogneiss, amphibolites, and migmatites.