Geochemistry and zircon geochronology of Late Proterozoic leucogranites north of Boston, eastern Massachusetts

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5640118

Markus, R; Hon, R ^[1]; Dunning, G ^[2]

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1. Boston Coll., Chestnut Hill, MA (United States). Geology and Geophysics
2. Memorial Univ., St. Johns, Newfoundland (Canada). Dept. of Earth Sciences

An igneous sequence that includes Late Precambrian volcanics (Lynn Volcanics) and granites, granodiorites, tonalites, plus diorites of the Dedham North suite, is located in a tectonic block bounded by the Walden Pond and Northern Boundary Faults north of the Boston Basin. Within the block between the rhyolites and granodiorites is a several hundred foot wide zone of leucogranites that contains frequent roof pendants in various stages of partial melting. The migmatitic nature of the pendants suggests that the leucogranites were locally derived by melt extraction from the partially melted pendant xenoliths. U-Pb zircon ages were obtained from samples of the leucogranite, granodiorite and diorite. Their crystallization ages are: leucogranite 609 [+-] 4 Ma, granodiorite 607 [+-] 4 Ma, and diorite 606 [+-] 3 Ma. All three samples yield ages that are identical within their statistical error limits and all three samples contain inherited component with average mid-Proterozoic ages. Major and trace element geochemistry of 43 samples of all representative types show that the predominantly pelitic'' layers underwent extensive partial melting and that the leucogranites represent a minimum granite melt at 0.5 to 2.0 kb of P(H2O). Geochemical modeling also supports the origin by partial melting of the pendant inclusions. Once formed, the leucogranite melts were then mixed with mafic magmas which must have also been the provider of the necessary heat to sustain the partial melting process. The data indicate that the Dedham North plutonic suite was formed at shallow crustal levels and that its compositional range is a result of magma mixing of varying proportions between the leucogranite and mafic melts.

• OSTI ID: 5640118
• Report Number(s): CONF-9303211--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:2
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTINIDE ISOTOPES
AGE ESTIMATION
CHEMISTRY
DEVELOPED COUNTRIES
DIORITES
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGY
GRANITES
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPES
LEAD ISOTOPES
MASSACHUSETTS
MINERALS
NORTH AMERICA
PETROGENESIS
PETROLOGY
PLUTONIC ROCKS
PRECAMBRIAN ERA
ROCKS
SILICATE MINERALS
URANIUM ISOTOPES
USA
ZIRCON