Evidence for the compaction of feldspar-rich cumulates in the Pleasant Bay layered intrusion, coastal Maine
- Franklin and Marshall College, Lancaster, PA (United States)
The Pleasant Bay intrusion is roughly 12 km by 20 km. It consists of prominent rhythmic layers, up to 100 m thick, that grade from chilled gabbro on the base, to coarse-grained gabbroic, dioritic, or granitic rocks on the top. These layers were formed by multiple injections of basalt into a large chamber of silicic magma. The focus of this study is on one layer that is about 100 m thick, and is overlain by another basally chilled gabbroic layer at least 50 m thick. Silicic pipes and veins extend upward into the overlying gabbroic chill. The lower part of the layer has dominant calcic plagioclase, An60, augite, and olivine, with subordinate hornblende and biotite. The uppermost part has dominant sodic plagioclase, An20, and two pyroxenes with subordinate quartz, K-feldspar and hornblende. SiO[sub 2] and MgO vary from 49% and 5% at the base to 58% and 1% at the top, respectively. The top 7 m of this layer are characterized by variably deformed minerals. The deformation grades from bent biotite and plagioclase near the bottom to sutured plagioclase at the top. Pockets of undeformed quartz and K-feldspar in the uppermost rocks demonstrate that interstitial liquid was present during a after compaction. The pipes and veins probably represent trapped liquid and some crystals that were expelled into the overlying gabbroic chill.
- OSTI ID:
- 5723217
- Report Number(s):
- CONF-9303211-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:2; Conference: 28. annual Geological Society of America (GSA) Northeastern Section meeting, Burlington, VT (United States), 22-24 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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