PRELIMINARY PALEOMAGNETIC RESULTS FROM MAFIC IGNEOUS ROCKS ASSOCIATED WITH THE HOLYOKE BASALT IN MASSACHUSETTS

Hozik (1992) reported on coarse grained gabbros he interpreted as intrusive into one of the flows of the Sander Basalt in the Culpeper Basin of Virginia. In that instance, he noted that the directions of magnetization in the basalt and the gabbro were significantly different: basalt declination and inclination were 18.2° and 2.0°; gabbro declination and inclination were 9.4° and 25.6°. That steepening of inclination was consistent with a similar change in inclination he found in the upper portions of the correlative Preakness Basalt in the Newark Basin of New Jersey.

Recently, we learned that a quarry in the Holyoke basalt exhibited similar field relationships, and we collected samples to see if the same relationship was true in the Hartford Basin. We sampled only the coarse-grained gabbro the quarry at four different sites. Those sites yielded the following results:

Site	# of Cores	Declination	Inclination	α95
1	5	24.3	-5.3	5.3
2	5	22.5	-2.7	13.3
4	5	1.3	8.14	9.6
5	4	8.6	0.57	9.7

For comparison, the Holyoke Basalt typically yields declinations between 16° and 37° and inclinations between -6.8° and 13.7°. In other words, the gabbros do not exhibit magnetic orientations significantly different from the basaltic lava flows. These results could be used to support a conclusion that the gabbros in Massachusetts intruded more nearly concurrently with the lava flow eruption than was the case in the Culpeper Basin.