Rb-Sr and oxygen isotopic study of alkalic rocks from the Trans-Pecos magmatic province, Texas: Implications for the petrogenesis and hydrothermal alteration of continental alkalic rocks

Journal Article · Sat Oct 01 00:00:00 EDT 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90293-1· OSTI ID:5180619

Lambert, D D; Malek, D J; Dahl, D A ^[1]

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1. Texas Christian Univ., Fort Worth, TX (USA)

Rb-Sr and O isotopic data for mid-Tertiary alkalic rocks from the Trans-Pecos magmatic province of west Texas demonstrate that hydrothermal alteration and fluid/rock (cation exchange) interactions have affected the isotope geochemistry of these rocks. Strontium and O isotopic data for late-stage minerals in an alkali basalt (hawaiite) still record two episodes of fluid/rock interactions. These data suggest that later meteoric fluids introduced Sr with a Cretaceous marine {sup 87}Sr/{sup 86}Sr ratio into minerals with significant cation exchange capacity. Dilute HCl leaching experiments demonstrate the removal of this labile or exchangeable Sr from the alkali basalt. Rb-Sr isotopic data for the leached alkali basalt and handpicked calcite record a crystallization age of 42 Ma, consistent with K-Ar data for an unaltered alkali basalt (hawaiite) dike from the same area (42.6 {plus minus} 1.3 Ma). Leaching experiments on one phonolite suggest the Sr isotopic variability in unleached phonolite and nepheline trachyte samples may be attributed to Sr in secondary calcite and zeolites, which have an upper Cretaceous marine {sup 87}Sr/{sup 86}Sr ratio. Rb-Sr isotopic data for leached phonolite and sanidine separate yield an age of 36.5 {plus minus} 0.8 Ma, within analytical uncertainty of a K-Ar biotite age (36.0 {plus minus} 1.1 Ma) of another phonolite. These leaching experiments demonstrate that the Rb-Sr isotopic systematics of hydrothermally-altered continental alkalic rocks may be significantly improved, providing more reliable geochronologic and isotopic tracer information necessary in constructing precise models of mantle sources.

• OSTI ID: 5180619
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 52:10; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
BASALT
HYDROTHERMAL ALTERATION
ISOTOPE RATIO
PETROGENESIS
TEXAS
CALCITE
CHEMICAL COMPOSITION
GEOCHEMISTRY
GEOLOGIC HISTORY
ION EXCHANGE
ISOTOPE DATING
LEACHING
MAGMATISM
OXYGEN 18
QUANTITATIVE CHEMICAL ANALYSIS
ROCK-FLUID INTERACTIONS
RUBIDIUM ISOTOPES
STRONTIUM 86
STRONTIUM 87
TERTIARY PERIOD
AGE ESTIMATION
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
BETA DECAY RADIOISOTOPES
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CENOZOIC ERA
CHEMICAL ANALYSIS
CHEMISTRY
DISSOLUTION
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION VI
GEOLOGIC AGES
HOURS LIVING RADIOISOTOPES
IGNEOUS ROCKS
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LIGHT NUCLEI
MINERALS
NORTH AMERICA
NUCLEI
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
RADIOISOTOPES
ROCKS
SEPARATION PROCESSES
STABLE ISOTOPES
STRONTIUM ISOTOPES
USA
VOLCANIC ROCKS
580000* - Geosciences