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Mesozoic igneous activity in the southern Cordillera of North America: Implications for tectonics and magma genesis

Thesis/Dissertation ·
OSTI ID:5598854
A representative section in Santa Rita Mountains is dated using the zircon U-Th-Pb isotopic method. The oldest unit, the lower member of the Mt. Wrightson Formation, is concordantly dated at 210 {plus minus} 3 Ma. Initial basaltic andesite to andesite volcanism was followed by deposition of red beds and associated volcanic rocks that are dated at 200 Ma. Felsic volcanism and eolian sand deposition may have spanned from 190 to 170 Ma. The Piper Gulch Granodiorite, representing the earliest Mesozoic intrusive equivalent, gives concordant dates of 188 {plus minus}2 Ma. A second cycle of andesite and rhyolitic volcanism and sedimentation is dated at 151 {plus minus} 5 Ma using the whole-rock Rb-Sr isotopic method. The Hovatter Volcanics in the Little Harquahala Mountains, southwestern Arizona is dated at 165 Ma. Whole-rock Rb-Sr isotopic method on the same rocks gives a coherent reset isochron of 70 {plus minus} 3 Ma. A new stratigraphic correlation is proposed based on the dating data. This part of the Cordillera was an uplifted arc terrane during the Early Mesozoic and may have provided volcanic detritus to the Late Triassic Chinle Formation in the Colorado Plateau. The second part deals with magma evolution and crust modification during arc magmatism. Rocks in southeastern Arizona have {sub Nd} values of {minus}3.4 to {minus}6.4, while rocks to the west have {sub Nd} values ranging from {minus}8.5 to {minus}9.2. Combined REE and isotopic data indicate that assimilation of lower crust by mantle melts followed by fractional crystallization took place.
Research Organization:
Arizona Univ., Tucson, AZ (USA)
OSTI ID:
5598854
Country of Publication:
United States
Language:
English

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Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
580202 -- Geophysics-- Volcanology-- (1980-1989)
ACTINIDES
AGE ESTIMATION
ALKALI METALS
ALKALINE EARTH METALS
ARIZONA
CRYSTALLIZATION
EARTH CRUST
EARTH MANTLE
ELEMENTS
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC HISTORY
GEOLOGIC MODELS
GEOLOGY
IGNEOUS ROCKS
INTRUSION
ISOTOPE DATING
LEAD
MAGMA
MESOZOIC ERA
METALS
MOUNTAINS
NEODYMIUM
NORTH AMERICA
PHASE TRANSFORMATIONS
RARE EARTHS
ROCKS
RUBIDIUM
SEDIMENTATION
STRATIGRAPHY
STRONTIUM
TECTONICS
THORIUM
URANIUM
USA
VOLCANIC REGIONS
VOLCANIC ROCKS