Crustal evolution of the New England Avalon Zone as indicated by temporal compositional variations of igneous activity
Changes in magma genesis from Proterozoic Z to Permian time in the New England Avalon Zone can be related to evolving crustal processes and tectonics. In New England, the earliest (620-700Ma.), and least understood, activity is represented by bimodal volcanics and possible oceanic basalt. Better studied igneous activity of calcalkaline affinity occurred at 620Ma during a period of crustal thickening and subduction involving continental crust. From Ordovician to Carboniferous, bimodal mafic and silica-rich alkalic plutonic and volcanic rocks were episodically emplaced. The alkalic rocks differ from coeval igneous rocks in adjacent lithotectonic blocks, indicating that Avalon and adjacent terranes were not assembled until post-Acadian time. Final igneous activity in the Permian is represented by a reversal to hydrous, meta- to peraluminous plutonism in which the zircons contain a strong component of Archean inheritance. The compositional changes in Permian igneous activity, and its inherited zircons, indicate that the crustal source was modified by underplating of SE New England with sediment and crust form Gondwana (.) during the Alleghanian Orogeny. Post-Cambrian components of the New England Avalon exhibit a distinct igneous/tectonic history compared to other Avalon terranes. Throughout much of the Paleozoic, it appears unlikely that the presently recognized Avalon terranes were not originally contiguous components of the same cratonic mass, and perhaps were not even derived from the same craton.
- Research Organization:
- Univ. of Rhode Island, Kingston (USA)
- OSTI ID:
- 6461273
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
FEDERAL REGION I
IGNEOUS ROCKS
PLATE TECTONICS
CHEMICAL COMPOSITION
PETROGENESIS
PETROLOGY
EARTH CRUST
GEOLOGIC HISTORY
MAGMA
MAGMATISM
OROGENESIS
PETROCHEMISTRY
GEOLOGY
NORTH AMERICA
ROCKS
TECTONICS
USA
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)
580201 - Geophysics- Seismology & Tectonics- (1980-1989)