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Abstract

The Shap Granite in the Lake District of northern England intruded the surrounding host rocks as a magma that released hydrothermal fluids as it crystallized and cooled. These hot fluids in turn produced an atypically wide contact metamorphic and metasomatic aureole around the intrusion. There is no evidence at the boundary for tectonic emplacement of a primordial cold granite body. This study documents an abundance of Po radiohalos in the Shap Granite. These Po radiohalos had to have been produced in the granite after the hydrothermal fluids released in the granite had assisted in the formation of the granite’s distinctive orthoclase feldspar megacrysts, and after the crystallized granite had subsequently cooled below the 150 °C annealing temperature of radiohalos. The abundance of Po radiohalos is consistent with the hydrothermal fluid transport model for Po radiohalo formation and with catastrophically rapid granite formation. These features imply that the Shap Granite formed in 6–10 days and its Po radiohalos within hours to days once the granite cooled below 150 °C. Hydraulic fracturing of the host rocks overlying the pluton facilitated rapid unroofing of the granite. Continued rapid erosion then deposited granite pebbles in the basal conglomerate of the overlying limestone. It is, therefore, conceivable that the Shap Granite formed, was unroofed, and the basal conglomerate with granite pebbles was deposited, all within 2–3 weeks during the early-middle part of the Flood year. The Po radiohalos and other evidence associated with this granite thus remove objections to Flood geology and any need to place the Flood/post-Flood boundary in the lower Carboniferous.

Keywords

Shap Granite, Northern England, Contact metamorphic aureole, Hydrothermal fluids, Po radiohalos, Orthoclase feldspar megacrysts, Catastrophic granite formation, Hydraulic fracturing, Rapid unroofing, Overlying basal conglomerate, Flood/post Flood boundary

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Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

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