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dc.creatorChattopadhyay, Indrani
dc.date.available2011-02-18T21:10:20Z
dc.date.issued2003-08
dc.identifier.urihttp://hdl.handle.net/2346/15611en_US
dc.description.abstractThe mid-crustal xenoliths from Potrillo maar record a petrologic and geochemical history that has until now been unknown from the Potrillo volcanic field. The igneous and meta-igneous xenoliths are samples of one or more plutonic bodies that crystallized at depths from 7-14 km (middle to upper crust). The rock unit ranges in composition from hornblende biotite diorite to quartz monzonite and monzogranite; it is broadly alkalicalcic The initial Sr87Sr86 suggests that the source region is heterogeneous or that the parental magmas were contaminated by crustal material. At least three geochemical groups can be identified, primarily on the basis of silica content. There is considerable overlap between groups 1 and 2, and the boundary between these two groups cannot be distinguished graphically. The third group is granitic and is geochemically distinct from groups 1 and 2. A dioritic composition is thought to represent mafic parental magma. Its calculated liquidus temperature at 2% H2O and 4 Mpa pressure is 1172°C. The presence of fossiliferous limestone xenoliths indicates that the Potrillo maar eruption sampled rocks of late Paleozoic age. However, the age of marble and quartzite xenoliths are not known. The quartzite xenoliths are relatively undeformed, but isoclinal folding in some of the marble xenoliths suggests subsurface deformation that has not been observed in local surface exposures of metasedimentary rocks. One model proposed for the crust under the southern Rio Grande rift assumes that the marble is late Paleozoic in age. The fossiliferous limestones are late Paleozoic in age and are older than the plutonic rocks. The relative age of the deformed marbles in this model is not clear, it can be deformed with the plutonic rocks or due to an earlier regional extensional event. In the second model, marble is proposed to result from contact metamorphism in the aureole of a plutonic rock body at a depth of 7-14 km. The presence of marble and calc-silicate xenoliths in dioritic blocks is consistent with a correlation of the marble with surface exposures of the Castner Marble in the Franklin Mountains
dc.format.mimetypeapplication/pdf
dc.language.isoeng
dc.publisherTexas Tech Universityen_US
dc.subjectStructuralen_US
dc.subjectGeologyen_US
dc.subjectRio Grandeen_US
dc.subjectStratigraphicen_US
dc.subjectGeologyen_US
dc.subjectPetrologyen_US
dc.subjectWesten_US
dc.subjectGeology -- Texasen_US
dc.subjectGeochemistryen_US
dc.subjectEarth -- Crusten_US
dc.titleCrustal xenoliths from Potrillo Maar: Implications for evolution of continental crust beneath the southern Rio Grande rift
dc.typeThesis
thesis.degree.nameM.S.
thesis.degree.levelMasters
thesis.degree.grantorTexas Tech University
thesis.degree.departmentGeoscience
dc.rights.availabilityUnrestricted.


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