Date of Award

5-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor(s)

Suzanne L. Baldwin

Keywords

40Ar/39Ar, gravity, magmatism, Metamorphic core complexes, U/Pb, zircon

Subject Categories

Earth Sciences

Abstract

The footwall of the Catalina MCC located within the Basin and Range Province has been intruded by several magmatic suites. Samples were collected from the Wilderness suite sills, the most voluminous suite. U/Pb data from zircon indicate that the Wilderness suite sills were emplaced during two separate phases of magmatism, the first at ~55 Ma and the second at ~45 Ma with additional evidence of zircon growth at <40 Ma.

40Ar/39Ar data from the Wilderness suite sills indicate that the majority of the older 40Ar/39Ar apparent ages from both potassium feldspar and mica were obtained from the structurally higher sills in the main range, and the younger 40Ar/39Ar apparent ages were obtained on samples from structurally lower sills. The potassium feldspar samples yield 40Ar/39Ar age gradients which may be the result of cooling for ~5 million years or thermal resetting by the Catalina pluton prior to exhumation along the Catalina detachment fault. 40Ar/39Ar lower intercepts from potassium feldspar in the main range suggest that exhumation of the main range occurred ~25 to 23 million years ago. In the forerange, concordant AFT and ZFT data and 40Ar/39Ar potassium feldspar lower age intercepts suggest rapid cooling due to exhumation ~23 to 22 million years ago. The muscovite and biotite samples from the Wilderness suite sills yield relatively flat 40Ar/39Ar age spectra with ages ranging from ~28 to 23 Ma representing recrystallization below the closure temperature for muscovite and biotite.

Forward modeling of aeromagnetic and gravity data from the Catalina MCC region indicates a shallow, felsic to intermediate subsurface pluton in sharp contact with the Wilderness suite sills. The age of the subsurface pluton is unknown. However, on the basis of the gravity and aeromagnetic properties of intrusions in the region, a Tertiary or Mesozoic age subsurface pluton is preferred. The age of the pluton relative to detachment faulting can help distinguish between differing models for MCC formation. A Mesozoic pluton suggests that crustal thickening influenced MCC development, and a preexisting zone of weakness may have controlled the emplacement of this body as well as the Wilderness suite sills. A Tertiary pluton suggests magmatism may have initiated low-angle faulting and MCC formation.

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