Progressive mixing of isotopic reservoirs during magma genesis at the Sierrita porphyry copper deposit, Arizona: Inverse solutions

Journal Article · Thu Sep 01 04:00:00 EDT 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90126-3· OSTI ID:5180455

Anthony, E Y; Titley, S R ^[1]

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1. Univ. of Arizona, Tucson (USA)

Trace-element and Sr and Nd isotopic compositions have been determined for a suite of calc-alkaline rocks from southeastern Arizona. The suite consists of andesitic and rhyolitic rocks (67 m.y. old) intruded by granodiorite and granite (62-58 m.y. old). It is situated within Proterozoic basement of 1.7 to 1.65 Ga age. Isotopic composition and chemical evolution are well correlated throughout the suite. The andesite has the least negative {epsilon}{sub Nd} ({epsilon}{sub Nd}(t{sub igneous}) = {minus}4.3) and smallest {sup 87}Sr/{sup 86}Sr{sub o} (0.7069). It is also the oldest and chemically most primitive, having the lowest concentrations of Rb, SiO{sub 2}, and highest concentrations of the transition elements. These parameters change through the system to the youngest unit (granite) which has the most negative {epsilon}{sub Nd}(8-5), the greatest {sup 87}Sr/{sup 86}Sr{sub o} (0.7092), and is most chemically evolved. The authors interpret these trends as resulting from a continuous process of progressive assimilation in which mafic magmas invade and incorporate continental crust. The assimilated continental crust was probably intermediate to mafic in composition and of amphibolite grade. Phase relations among minerals indicate that it was hydrous and oxidizing. Inverse methods have been applied to equations for assimilation and fractional crystallization whose use assumes periodic tapping of a single magma body. Such modeling yields insight into the size and chemistry of the magma system.

• OSTI ID: 5180455
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 52:9; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
ANDESITES
ARIZONA
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CHEMISTRY
CONTINENTAL CRUST
COPPER ORES
CRYSTALLIZATION
EARTH CRUST
EQUILIBRIUM
FEDERAL REGION IX
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC HISTORY
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
MAGMATISM
MINERALIZATION
MIXING
NEODYMIUM ISOTOPES
NORTH AMERICA
ORES
PETROGENESIS
PHASE TRANSFORMATIONS
PRECAMBRIAN ERA
RHYOLITES
ROCKS
STRONTIUM ISOTOPES
TRACE AMOUNTS
USA
VOLCANIC ROCKS