Observations and controls on the occurrence of inherited zircon in Concord-type granitoids, New Hampshire

Journal Article · Tue Sep 01 04:00:00 EDT 1987 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(87)90305-X· OSTI ID:5064689

Harrison, T M; Aleinikoff, J N; Compston, W

U-Pb analyses of zircons separated from two Concord-type plutons near Sunapee and Dixville Notch, New Hampshire, reveal differences in the pattern and magnitude of zircon inheritance which are related to differences in melt chemistry. The Sunapee pluton contains only slightly more Zr than required to saturate the melt at the peak temperature of 700 +/- 30/sup 0/C. Traces of inherited zircon in this separate are inferred to be present as small, largely resorbed grains. In contrast, the Long Mountain pluton, near Dixville Notch, contains about 240% more Zr than required to saturate the melt. Thus, more than half of the Zr existed as stable, inherited zircon crystals during the partial fusion event, consistent with the observation of substantial inheritance in all grain size fractions. Ion probe intra-grain analyses of zircon from the Long Mountain pluton indicate a complex pattern of inheritance with contributions from at least two Proterozoic terranes and caution against simple interpretations of upper and lower intercepts of chords containing an inherited component. Ion probe analyses of zircons from the Sunapee pluton reveal clear evidence of U loss which results in incorrect apparent conventional U-Pb ages. Ages of crystallization for the Long Mountain and Sunapee pluton are approx. 350 and 354 +/- 5 Ma, respectively. A Sm/Nd measurement for the Long Mountain pluton yields a depleted mantle model age of 1.5 Ga, consistent with the observed inheritance pattern. In contrast, a Sm/Nd model age for the Sunapee pluton is improbably old due to minor monazite fractionation.

• Research Organization: State Univ. of New York, Albany (USA)
• OSTI ID: 5064689
• Journal Information: Geochim. Cosmochim. Acta; (United States), Journal Name: Geochim. Cosmochim. Acta; (United States) Vol. 51:9; ISSN GCACA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
ACTINIDES
AGE ESTIMATION
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
CRYSTALLIZATION
ELEMENTS
FEDERAL REGION I
FRACTIONATION
GEOCHEMISTRY
GEOLOGIC MODELS
IGNEOUS ROCKS
LEAD
MAGMA
METALS
MINERALIZATION
MINERALS
NEODYMIUM
NEW HAMPSHIRE
NORTH AMERICA
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
RARE EARTHS
ROCKS
SAMARIUM
SATURATION
SEPARATION PROCESSES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
URANIUM
USA
ZIRCON
ZIRCONIUM
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES