TECTONICS OF THE LANTERN HILL FAULT, 
SOUTHEASTERN CONNECTICUT:  EVIDENCE FOR THE 
EMBRYONIC OPENING OF THE ATLANTIC OCEAN
	ALTAMURA, R.J.1, Department of Geosciences, The 	
		Pennsylvania State University, University Park, PA  
		16802

The Lantern Hill fault (LHF) is a 10-mile long, N-S trending 
hypersilicified breccia zone that transgresses meta-igneous and meta-
sedimentary units of the Proterozoic Z Avalonian terrane in 
southeastern Connecticut.  The fault zone is massively silicified along 
its trace, especially at its northern end, at the intersection with the 
Honey Hill fault, the terrane boundary between Avalonian and Gander 
terranes.  
	An analysis of stress and motion-sense indicators as recorded 
by faults and quartz-filled fractures indicates an extensional tectonic 
regime with a subvertical sigma 1 and sigma 3 = approximately 
00/105.  Analysis of bore-hole data of the U.S. Silica Company 
suggests that the main silcified zone strikes NNE and dips 50o west 
and is comprised of steeply-dipping one-meter thick parallel quartz-
filled fractures.  These quartz veins strike 15o clockwise to the LHF 
and represent evidence for oblique slip along a pre-existing regional 
fault.  Main-stage fracturing and mineralization in the LHF occurred 
during the Middle Triassic (Altamura and Lux, 1994).  Deposition of 
redbeds exposed 30 miles to the west in the Hartford basin began 20 
Ma later during the Late Triassic.  The tectonic setting and regional 
stress field from which this failed-rift basin (de Boer and Clifford, 
1988) was the same as that from which formed the LHF.  
Hypersilicified breccia zones similar to the LH occur in the footwall 
of the eastern border fault (EBF) of the Hartford basin and elsewhere 
in southern New England and may be correlative.  In the proposed 
model, regional WNW-ESE extension was accompanied by 
hypersilicifiaction and brecciation during the embryonic opening of 
the Atlantic Ocean during the Middle Triassic (approximately 238 
Ma:  Anisian) - some 20 Ma prior to deposition of graben-fill 
sediments and tholeiitic basalts in the rifts.  Whereas establishment of 
the Hartford rift marked the end of significant extensional tectonics 
along the LHF, the establishment of the Mid-Atlantic Ocean spreading 
center during the Jurassic marked an end to extensional tectonics 
along the EBF.  At this point the regional stress configuration was 
dominated by approximately E-W compression due to ridge push.

Altamura, R.J. and Lux, D.R., 1994, 40Ar/39Ar and K-Ar ages for 
muscovite from a giant quartz lode and alaskite host rocks, 
Avalonian terrane, southern New England:  Geological Society 
of America Abstracts with Programs, 26, 7, p. 529.

1Present Address: Dept. of Geology & Planetary Sciences, University 
of Pittsburg, Johnstown, PA  15904