Structural evolution of the Sing Peak pendant: Implications for magma chamber construction and mid-Cretaceous deformation in the central Sierra Nevada, California

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Title: Structural evolution of the Sing Peak pendant: Implications for magma chamber construction and mid-Cretaceous deformation in the central Sierra Nevada, California
Author: Krueger, Ryan
Abstract: Metamorphosed strata of the Sing Peak pendant , central Sierra Nevada , CA , record structures formed during the contemporaneous emplacement of adjacent plutons and regional deformation in the mid -Cretaceous . Host rocks in the Sing Peak pendant consist of deformed metavolcanic rocks of the mid -Cretaceous Minarets Caldera sequence and less common Jurassic metasedimentary rocks . Structures in the Sing Peak pendant include : a ) a penetrative , subvertical , NNW -striking foliation defined by stretched phenocrysts and recrystallized biotite , epidote and amphibole ; and b ) a dextral sense ductile shear zone with a shallow /moderate plunging ( ~40º ) NNW -trending lineation . The shear zone can be traced into the Jackass Lakes pluton along the northeastern and northern margins of the pendant . The Jurassic metasedimentary rocks are locally folded with NNW -striking axial planes and the folds are commonly truncated by the Jackass Lakes pluton . Structures within the Jackass Lakes pluton include a well -developed NNW -striking , steeply west dipping magmatic foliation and a moderately north plunging ( ~40º ) lineation defined by elongated biotite and hornblende phenocrysts . The magmatic structures are continuous across compositional zones within the Jackass Lakes pluton and parallel to the elongated axis of mafic enclaves observed within the pluton . Abundant xenoliths (up to 300 m long ) of metavolcanic rocks appear to be concentrated near the roof pendant but are also found throughout the pluton . Metamorphic foliations observed within the xenoliths are sub -parallel with those in the host rocks and the magmatic foliation of the pluton . Some xenoliths contain dikes of the Jackass Lakes pluton , up to 1 m in width , that have been folded with axial planes striking sub -parallel to the metamorphic foliation in the xenoliths , host rocks and magmatic foliations in the pluton . These observations suggest that the magmatic and metamorphic foliation as well as the folded dikes were formed during chamber construction and most likely due to regional deformation . Based on the lineation data , the deformation in the ductile shear zone and the ~ 98 Ma Jackass Lakes pluton is the result of regional transpression . Previous work has suggested that regional dextral transpression was not initiated until ~ 90 Ma in the central Sierra Nevada . Therefore , the Jackass Lakes pluton – host rock system represents the earliest documented regional dextral transpression in the central Sierra Nevada .
URI: http : / /hdl .handle .net /2346 /1350
Date: 2006-09-05

Citation

Structural evolution of the Sing Peak pendant: Implications for magma chamber construction and mid-Cretaceous deformation in the central Sierra Nevada, California. Master's thesis, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /1350 .

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