| Abstract: | These volcanic rocks consist of a lower, mainly mafic unit of hornblende-plagioclase amphibolite and an upper, mainly felsic metamorphosed quartz keratophyre tuff. They are intruded by sills, dykes and plugs of trondhjemite; which is highly silicic (SiO2, 73-81%), low in Al2O3 (11.3-13.5%) and generally contains <1% K2O. Both trondhjemite and volcanics are calc-alkaline. The major- and minor-element geochemistry of the trondhjemites is closely similar to that of the quartz keratophyre tuff. These rocks were probably produced by partial melting of basaltic source rocks, rather than by fractional crystallization, in view of the virtually bimodal nature of the Ammonoosuc assemblage. The generation of the felsic rocks occurred at deeper levels along a subduction zone dipping eastward.-L.C.H. |
| Genre: | Article |
| ProdID: | 70012997 |
| Citation Author: | Leo, G. W. |
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| Citation End Page: | 1507 |
| Citation Issue: | 12 |
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| Citation Language: | English |
| Citation Larger Work Title: | Geological Society of America Bulletin |
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| Citation Number Of Pages: | 15 |
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| Citation Search Results Text: | Trondhjemite and metamorphosed quartz keratophyre tuff of the Ammonoosuc volcanics (Ordovician), western New Hampshire and adjacent Vermont and Massachusetts.; 1985; Article; Journal; Geological Society of America Bulletin; Leo, G. W. |
| Citation Start Page: | 1493 |
| Citation Volume: | 96 |
| Citation Year: | 1985 |
| Type: | citation/reference |
| Text: | Trondhjemite and metamorphosed quartz keratophyre tuff of the Ammonoosuc volcanics (Ordovician), western New Hampshire and adjacent Vermont and Massachusetts.; 1985; Article; Journal; Geological Society of America Bulletin; Leo, G. W. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Tue, 1 Jan 1985 00:00 -0600 |
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