The White Mountain magma series is a sequence of generally alkalic Mesozoic plutonic and volcanic rocks emplaced mostly into central New Hampshire. The belt of compositionally and time related rocks extends to the SSE into southern New Hampshire to the coast of Maine. and NNW into southernmost Quebec. The Monteregian Hills is a second belt of alkalic intrusives that extends WNW-ESE from the northern end of the White Mountain Magma Series belt. Also included at the end are some photos of rocks in the Cape Ann area, Massachusetts. These rocks represent a complex variety of Paleozoic intrusives, most of which are alkalic also. This photo gallery illustrates some of the rocks and structures associated with this lab.
Nubble Point Gabbro, Maine
This is a photo of the Nubble Point lighthouse, Cape Neddick, Maine. The gabbro body is ~500 m across and has steeply dipping contacts. It is a layered intrusion with the layers nearly vertical. The lighthouse island can be accessed during low tide, and the contact with the country rock is exposed on the ocean side of this island.
This gabbro is a layered intrusion. In this photo, thin layers (~3 cm) that make up thicker layers (1 m) extend away toward the ocean. Samples 4.8.84A, 4.8.84Ca, 4.8.84Cb, and 4.8.84D are samples from near the pluton margin toward its interior.
Trough-and-ridge structures with cross beds that formed on the walls of the intrusion. Layering is vertical.
Prominent trough structures and cross bedding that formed on the intrusion walls. These are indicative of strong currents running down the magma chamber walls, depositing and sometimes eroding modally variable layers.
Composite dike in the Nubble Point gabbro. The outer, earlier margin of the dike has fine-grained basalt ~2 cm thick. Presumably soon after emplacement, the lighter magma was injected. I do not recall what the lighter material is, but I suspect it is a granitic rock.
Cavernous weathering in gabbroic anorthosite.
Moat Volcanics and contact with the Conway Granite, NH
This locality is called "Diana's Baths", on Lucy Brook. Here, the Conway Granite becomes porphyritic near its margin and intrudes the Moat Volcanics overlying it. Porphyritic Conway is NEIGC86-B2-3B; Moat Volcanics is NEIGC86-B2-3A; Osceola Granite was collected from nearby is sample NEIGC86-B2-4.
Conway Granite, Redstone Quarry, NH
Massive Conway Granite, near the contact with a large body of Osceola Granite. Sample NEIGC86-B2-1A.
Belknap intrusive complex, NH
Main ring dike on the SE side of the intrusion. The ring dike is indicated. Sample 4.8.84J is the ring dike rock from this locality.
Main ring dike on the SE side of the intrusion. The ring dike is indicated. This is a different view of the same outcrop above. Sample 4.8.84J is the ring dike rock from this locality.
Faulted muscovite pegmatite dike. Faulting is brittle and late, and may have been associated with formation of the ring dike.
Ring dike on the north side of the intrusion, where the dike is much wider and less altered. These are two fine-grained mafic enclaves (pillows or xenoliths) encased in the alkali granite ring dike host rock. This outcrop has iridescent orthoclase, caused by exsolution of fine-scale albite lamellae in the orthoclase host. Samples 4.8.84L and 4.8.84P are from the interior of the Belknap Complex. Sample NH-2 is of the margin between an enclave and the host felsic rock from the Belknap Complex interior. Sample 4.8.84Q is of a mafic pluton close to the Belknap Complex to the south.
Belknap intrusive complex, New Hampshire Hornblende reaction rim on a quartzite xenolith in the northern ring dike. This feature can also be seen in thin section. Sample 4.8.84K is from this locality.
Marblehead Neck volcanic plug, Marblehead, MA
This plug is made up of fine-grained rhyolite and breccias. The dark parts visible are fine-grained, porphyritic rhyolite. The lighter materials are breccias.
The rock is made up of fine-grained rhyolite and breccias. Marblehead, Massachusetts. Some of the light-colored breccia exposed in this shallowly exposed subvolcanic plug. Clasts mostly include rhyolite and pummice.
Contact between some darker rhyolitic material containing some breccia fragments, and lighter, more clast-rich breccia to the left.
Beverly Syenite, Beverly, MA
Playground dike in Beverly syenite. This is a basaltic dike that intruded the host Beverly syenite. The basalt intruded quickly, fracturing the syenite, which was still partially molten but rheologically brittle on short time scales. After the basalt dike quenched, the syenite flowed somewhat, breaking the dike and separating the broken ends.
Salem gabbro and diorite, Salem MA
The host rock is the Salem gabbro-diorite. It was initially cut by a felsic magma dike, which was closely followed (while the felsic magma was still liquid) by basaltic magma. The result is a composite dike with felsic margins and a central core of basaltic rock that is cut by felsic mini-dikes. The dike was later disrupted by flow of the host gabbro-diorite.
Complex crosscutting and possibly pillow relationships in the Salem gabbro-diorite. Possible pillows are visible to the upper right.
Basalt pillows in alkali granite. While not part of the WMMS, it illustrates some pillow structures, with pillow-shaped enclaves of basalt hosted in alkali granite. Such rounded mafic blobs are found in the interior of the Belknap intrusive complex.
Another photo of the pillows, again not part of the WMMS but illustrative of some features that may be found there. Note that the toping directions of this pillow mass can be determined.