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Derivation of the monzodioritic rocks of the Mooselookmeguntic igneous complex most likely occurred by melting of Bronson Hill belt crust of mafic to intermediate composition. The Mooselookmeguntic igneous complex granites show limited correlation of isotopic variations with elemental concentrations, precluding any significant presence of mafic source components. Given overlap of initial Nd and Pb isotopic compositions with data for Central Maine belt metasedimentary rocks, the isotopic heterogeneity of the granites may have been produced by melting of rocks in this crustal package or through a mixture of metasedimentary rocks with magmas derived from Bronson Hill belt crust.
New data from other granites in western Maine include Pb isotope data for the Phillips pluton, which permit a previous interpretation that leucogranites were derived from melting heterogeneous metasedimentary rocks of the Central Maine belt, but suggest that granodiorites were extracted from sources more similar to Bronson Hill belt crust. Data for the Redington pluton are best satisfied by generation from sources in either the Bronson Hill belt or Laurentian basement. Based on these data, we infer that Bronson Hill belt crust was more extensive beneath the Central Maine belt than previously recognized and that mafic melts from the mantle were not important to genesis of Devonian granite magma. 相似文献
The mineral water of Vilajuïga village in Alt Empordà (NE Catalonia, Spain) owes its uniqueness to an emanation of geogenic CO2 that modifies groundwater hydrochemistry to produce a differentiated HCO3–Na- and CO2-rich groundwater among the usual Ca–HCO3 type found in this region. A hydrogeological conceptual model attributes its occurrence to the intersection of two faults: La Valleta and Garriguella-Roses. The former provides a thrust of metamorphic over igneous rocks, formed during the Paleozoic, over a layer of ampelitic shale that, from a hydrogeological perspective, acts as a confining layer. The Garriguella-Roses normal fault, which originated during the Neogene, permits the degassing of geogenic CO2 that is attributed to volcanic activity occurring in the Neogene. Groundwater mixing from the metamorphic and igneous rock units plus the local occurrence of CO2 creates a HCO3–Na water that still holds free-CO2 in solution. Interaction with the gas phase is restricted at the intersection of the two faults. Radiocarbon dating, after correcting for geogenic dead carbon, estimates an age of 8,000 years BP. The low tritium content (0.7 TU) indicates that Vilajuïga water is a mix of “older” groundwater recharged in the metamorphic rocks of the Albera range and “younger” groundwater from the igneous rocks of the Rodes range, over a recharge area of 45 km2 and a maximum elevation of 600 m. Given its origin as rare groundwater in the southern slope of the Eastern Pyrenees, purposeful monitoring is necessary to evaluate the groundwater vulnerability and anticipate impacts from nearby wells and climate-change effects.
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