Mount Pleasant Caldera
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| Mount Pleasant Caldera | |
|---|---|
| Elevation | approx. 248 m (814 ft) |
| Location | New Brunswick, Canada |
| Range | Appalachian Mountains |
| Coordinates | |
| Type | Caldera |
| Age of rock | Late Devonian |
| Listing | List of volcanoes in Canada |
The Mount Pleasant Caldera is a large 17 x 12 km wide eroded Late Devonian caldera complex, located in the northern Appalachian Mountains of southwestern New Brunswick, Canada. It is one of few noticeable pre-Cenozoic calderas and its formation is associated to a period of crustal thinning that followed the Acadian orogeny in the northern Appalachian Mountains.
[edit] Geology
The caldera is divided into Exocaldera, Intracaldera and Late Caldera-Fill series. The Intracaldera Sequence includes four configurations that crop out in a triangular-shaped section and contains: broad pyroclastic flow tuffs, broad sedimentary breccias that dip inward, and stocks of intermediate to felsic composition that intrude the volcanic pile or are confined along caldera-margin faults. The Exocaldera Sequence includes pyroclastic flow tuffs, mafic lavas, sedimentary redbeds and porphyritic felsic lavas that include five formations. The Late Caldera-Fill Sequence includes rocks that are similar to those of the outflow facies and includes two formations and two minor intrusive sections.
Granitic intrusions within the caldera complex include the McDougall Brook Microgranite and the somewhat younger Mount Pleasant Granite. Yielding gold quartz breccias and veins cut the McDougall Brook Microgranite and its volcanic wall-rock, while molybdenum-bismuth-tungsten and later polymetallic mineralization are hereditarily related with the multiphase Mount Pleasant Granite.
The numerous felsic sections are associated by episodes of fractional crystallization in a high-level, zoned magma chamber. Fractionation was continually interrupted by eruption of material from the roof zone such that seven phases of caldera growth have been recognized.
Mount Pleasant lies along the southwestern margin of the caldera complex. Two mineralized zones, termed the Fire Tower Zone and the North Zone, occur within volcanic plugs about 1 km apart. The volcanic necks are defined by magmatic-hydrothermal breccias.
