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奥陶纪Ammouoosuc火山岩及相当的岩石沿着新罕布什尔州北部和康涅狄格州南部之间的BronsonHill复背斜(BHA)分布的OLiverian穹窿出露。在新罕布什尔和相邻佛蒙特和马萨诸塞州,岩系的下部以镁铁质斜长角闪岩为主,上部以长英质变质石英角斑凝灰岩为主。在局部地区两种岩性呈互层,且两者都被奥长花岗岩岩床、岩墙及岩颈侵入。奥长花岗岩还构成若干小穹窿或深成岩体内部的片麻状“核心”。奥长花岗岩高硅(SiO_2=73—81％),低Al_2O_3(11.3—13.5％),一般K_2O<1％,从而类似于某些岛弧或大陆边缘环境的奥长花岗岩。奥长花岗岩和Ammonoosuc火山岩两者化学成分变化基本属于钙—碱性趋势。几个穹窿中的奥长花岗岩的主要元素和微量元素的变化,反映沿Brinson Hill复背斜有些不同的物质来原。可是,从总体上看,奥长花岗岩的主要元素和次要元素组成都很类似于Ammonoosuc石英角斑凝灰岩。由玄武质源岩的部分熔融或分离结晶作用都能够产生这些岩石,但根据该区存在大规模双模式玄武岩-石英角斑岩的Ammonoosuc组合,其中实际上缺少安山岩和其它中性成分的岩石,故部分熔融模式比较合理。正如对纽芬兰的非常相似的奥长花岗岩-角闪岩组合(Twillingate奥长花岗岩,Little Port杂岩)所假定的那样,比较簿的Ammonoosuc剖面似乎排除了奥长花岗岩在目前暴露出的岛弧底部产生。而正如现代板块构造模型所主张的那样,长英质Ammonoosuc岩石的形成更可能发生在BHA以下,沿着向东倾斜的俯冲带的较深部位。硅铝地壳与Ammonoosuc火山岩在时间和空间上紧密并置。可以解释后者的钙-碱趋势,并揭示古构造环境为收敛型的海洋-大陆板块边缘,可能横跨该岛弧有明显的地壳缩短。
Ordovician Ammouoosuc volcanic rocks and equivalent rocks emerge along the OLIVErian dome distributed along the Bronson Hill anticline (BHA) between northern New Hampshire and southern Connecticut. In New Hampshire and adjacent Vermont and Massachusetts, the lower part of the rock series is dominated by mafic amphibolite, and the upper part is dominated by felsic metamorphic quartz hornfly tuff. In some areas, the two lithologies are interbedded, and both are intrusive by the ophiolite granite beds, dikes and rocks. The granite also forms the gnarled “core” of several small vaults or deep plutons. The orthorhombic high silicon (SiO_2 = 73-81%), low Al_2O_3 (11.3-13.5%), generally K_2O <1%, are similar to the orthoclase granites of some island arcs or continental margins. The changes of chemical composition of both Ordovician granite and Ammonoosuc volcanic rock belong to the basic calcium-alkaline trend. Changes in major elements and trace elements of the ophiolitic granulites in several domes reflect some of the different material origins along the Brinson Hill anticlines. However, on the whole, the major elements and minor elements of the opal granite are similar in composition to the Ammonoosuc quartz horn spot tuff. These rocks can be produced by partial melting or fractional crystallization of basaltic source rocks, but according to the Ammonoosuc assemblage of large-scale dual-mode basaltic-quartz porphyries in this area, in which virtually no andesite and other rocks of neutral composition are present, So part of the melting mode is more reasonable. As assumed in the very similar New Orleans granite-amphibolite assemblage (Twillingate Albite, Little Port complex), the comparatively thin Ammonoosuc section appears to exclude the exponential growth of granitoids in the presently exposed island arcs Bottom generated. As suggested by modern plate tectonics models, the formation of the felsic Ammonoosuc rocks is more likely to occur below the BHA, along the deepest part of the subduction zone that is slanted eastward. Silicon-aluminum crust and Ammonoosuc volcanic rocks are closely juxtaposed in time and space. It is possible to explain the latter’s calcium-alkali tendencies and to reveal that the paleo-tectonic setting was convergent at the edge of the marine-continental plate and that there may be significant crustal shortening across the island arc.