Understanding the sources of Ordovician magmatic rocks in the broad western Faja Eruptiva Occidental and eastern Faja Eruptiva Oriental magmatic belts in the northern Puna of Argentina and Chile is important to Ordovician geodynamic models for westernGondwana evolution and Gondwana-Laurentian terrane interactions. A critical evaluation of existing chemical and age data, along with new major trace element data, and field observations leads to a working model in which magmatism in the western belt progressively occurred in an active to waning arc to collisional regime, whereas that in the eastern belt occurred in an oblique fault regime transitional to a subduction zone to the south. The model is hampered by data gaps in all areas, and particularly by lack of ages in western and southern regions. The best understood area is the northern Faja Eruptiva Oriental where dacitic and mafic units with published ages of 476-467 Ma occur in linear fault-controlled trends. Their chemistry is consistent with dacitic magma sources being dominated by sedimentary-type protoliths melted in association with emplacement of mantle-derived alkaline mafic magmas. These dacitic units represent lava-dome complexes emplaced contemporaneously with outer shelf and slope basin sedimentation. Farther south where deeper crustal levels are exposed, volcanic/subvolcanic units grade into poorly studied plutonic facies. Trondhjemitic bodies are reported to the east. Contemporaneous units in the Faja Eruptiva Occidental are plutons and mafic to rhyolitic lavas in sequences of volcaniclastic sediments. Chemical signatures in the poorly dated Cordón de Lila lavas and Choschas dioritic to leucogranodioritic pluton in Chile are consistent with emplacement in a magmatic arc on thinned continental or oceanic crust. Mafic volcanic units in volcanic-sedimentary sequences just to the east could represent arc volcanism behind the front. An Arenig-Llanvirn change to bimodal and predominantly silicic magmatism, the emplacement of shoshonitic and mafic andesitic flows with weak arc signatures followed by alkaline dikes in the eastern Faja Eruptiva Occidental, and the formation of the Faja Eruptiva Oriental dacitic-mafic sequences could signal a change to a very oblique subduction regime. This change would be roughly contemporaneous with the arrival of the Laurentia-derived Precordillera terrane to the south. A post-Arenig-Llanvirn compressional regime seems required to explain Ocloyic deformation in the east and late plutons to the west. The nature of the eastern boundary of a periGondwana Arequipa terrane and the existence of a peri-Gondwana Famatina-Puna Oriental terrane remain unclear.
A significant hindrance to reuse of Brownfield properties is the risk associated with redevelopment, specifically the uncertainty associated with environmental cleanup. This paper explores an approach to managing environmental risk through a combination of risk quantification, environmental insurance and the Triad Approach to site sampling and data interpretation. Using the Marsh Peer Review SM risk quantification process that employs statistical techniques and highly experienced technical staff the expected costs of environmental liabilities are estimated. The outputs of the process indicate premiums and attachment points for insurance products, but they also point to "critical uncertainties" that drive the insurance premiums. Insurance premiums are often linked to site delineation deficiencies, such as the magnitude of impacted soil or the size of a groundwater plume. The Triad Approach is an integrated site characterization process developed by the Environmental Protection Agency that combines systematic planning, dynamic or adaptive field decision-making and field analytical methods (FAMs). The real time data produced by FAMs allow for in-field resolution of uncertainty about sample location, which in turn provides more representative delineation of contaminant distribution. The trade-off of using slightly less accurate but substantially lower cost FAMs, is an increase in sampling frequency or density thereby reducing the risk of incomplete detection or delineation while yielding a "data set" that is more powerful than fewer individual data points analyzed through traditional methods. Employing the Triad approach to analyze the "critical uncertainties" identified in the Peer Review Process can impact insurance premiums and allow for better terms of coverage. The combination of using the Triad Approach and environmental insurance products can lead to more predictable and profitable Brownfield transactions.
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