Coaxial spinning deformation and non-rotation of porphyroblasts surrounding the Papoose Flat pluton, Inyo Mts. , California
- Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Geological Sciences
A constant angle between planar inclusion trails within cores of dominantly equidimensional andalusite porphyroblasts and lithologic layering is observed within the Harkless schist surrounding the western margin of the Papoose Flat pluton. Porphyroblast-matrix relationships suggest that: (1) the external foliation (S[sub e]) rotated into concordancy with the pluton late in the growth history of the porphyroblasts, (2) the deformation that rotated S[sub e] was coaxial and spinning and, (3) porphyroblasts have not rotated with respect to the foliation. Andalusite porphyroblasts consist of two distinct regions based on differences in inclusion trail density and orientation; (1) a core region with a high density of planar inclusion trails (S[sub i]c) which are at a constant angle to S[sub e], and (2) a rim region with a low density of inclusion trails (S[sub i]r) that continue in orientation from S[sub i]c and curve into parallelism with S[sub e]. The continuous trace of S[sub i]c to S[sub i]r to S[sub e] indicates that late stage growth of porphyroblasts was synchronous with deformation. S[sub i]c from various locations within the pluton aureole are not similar in orientation with respect to geographic coordinates and seemingly indicates that porphyroblasts have rotated. However, unwrapping of S[sub e] from concordancy with the pluton into a planar reference frame unspins S[sub i]c from all locations around the contact into a similar orientation with respect to geographic coordinates while maintaining the constant angle between S[sub i]c and S[sub e]. The constant angle between S[sub i]c and S[sub e] suggests that porphyroblasts have not rotated with respect to the foliation. This relationship suggests that andalusite porphyroblasts initially overgrew a planar foliation that was oblique to the lithologic units while the lithologic units were also still relatively planar- i.e., before the metasedimentary units were deformed into concordancy with the pluton.
- OSTI ID:
- 5769734
- Report Number(s):
- CONF-921058--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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