|
| << previous |
Journal description
All volumes of the corresponding journal
All issues of the corresponding volume
All articles of the corresponding issues
Details for article 12 of 12 found articles
| Title: |
The St Marys Porphyrite—a Devonian ash-flow tuff and its feeder |
| Author: |
Turner, N. J. Black, L. P. Higgins, N. C. |
| Appeared in: |
Australian journal of earth sciences |
| Paging: | Volume 33 (1986) nr. 2 pages 201-218 |
| Year: |
1986-06 |
| Contents: |
The St Marys Porphyrite crops out in the St Marys district of eastern Tasmania and is a felsic, quartz porphyrite body which contains the only known extrusive rocks associated with the widespread Devonian granitoids of Tasmania. It consists of a thick (1400 m) sheet of predominantly dacitic, welded, ash-flow tuff together with a high-level, vesiculated part of the volcanic feeder. The boundary between these subdivisions is an extension of the eastern boundary of the nearby Catos Creek dyke, a deeper unvesiculated level of the feeder. In the St Marys Porphyrite, the boundary is interpreted as a subsidence fault which threw the extrusive rocks down against their feeder, whilst in the Catos Creek dyke, it was the locus of early magma emplacement as well as of major movement. Ash-flow tuff in the St Marys Porphyrite is particularly rich in crystal fragments (up to 58% by volume). Its matrix becomes progressively more recrystallized with height above the base of the sheet, thus indicating rapid emplacement and cooling as a single unit. This resulted in poor preservation of tuffaceous textures except near the base. Individual ash-flows are generally difficult to identify, but flows or parts of flows are locally defined by variations in the proportions of metasedimentary lithic fragments and strongly recrystallized pumice(?) fragments (schlieren). Rb-Sr isotopic data and major trace and rare earth element chemistry strongly support comagmatism of the St Marys Porphyrite with both Catos Creek dyke and Scamander Tier dyke, which is part of the early I-type phase of magmatism in the Blue Tier Batholith. Thus, the age of emplacement of the porphyrite body (388 ± 1 Ma) precisely limits the age of early magmatism in the Blue Tier Batholith. It also limits the age of earlier deformation in the country rocks (Mathinna Beds). |
| Publisher: |
Taylor & Francis |
| Source file: |
Elektronische Wetenschappelijke Tijdschriften |
Details for article 12 of 12 found articles
| << previous |