Implications for Thrust‐Related Shortening Punctuated by Extension From P‐T Paths and Geochronology of Garnet‐Bearing Schists, Southern (Çine) Menderes Massif, SW Turkey
The Menderes Massif, Turkey, is a type locality for deciphering the plate tectonic response from collision‐ to extension‐driven exhumation. Conventional thermobarometry and garnet pressure‐temperature (P‐T) paths from isochemical phase diagrams were calculated across a major fault (Selimiye Shear Zo...
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| Published in: | Tectonics (Washington, D.C.) Vol. 38; no. 6; pp. 1974 - 1998 |
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| Main Authors: | , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Washington
Blackwell Publishing Ltd
01-06-2019
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | The Menderes Massif, Turkey, is a type locality for deciphering the plate tectonic response from collision‐ to extension‐driven exhumation. Conventional thermobarometry and garnet pressure‐temperature (P‐T) paths from isochemical phase diagrams were calculated across a major fault (Selimiye Shear Zone, SSZ) bounding the southern edge of the Menderes Massif. Both approaches yield similar garnet rim temperatures (from 555 to 671 °C), but estimated P differs by between 8 and 15 kbar. Three garnets north of the SSZ reveal N‐shaped P‐T paths, whereas paths from three samples south of the SSZ show a simple increase in P‐T. Monazite and zircon were dated in thin section from the same rocks using Secondary Ion Mass Spectrometry and Laser Ablation Inductively Coupled Plasma‐Mass Spectrometry, respectively. Textural relationships of monazite within garnet appears indicative of post‐garnet growth. The amount of monazite common 204Pb and 137Ba+/Th+ significantly exceeds what is observed for the monazite age standard, suggesting their ages mark fluid‐driven events, loosely constrained to Late Eocene‐Early Miocene. Some zircon ages are consistent with Cambro‐Ordovician ages reported elsewhere in the region, and other ages are Neoproterozoic and Permian‐Triassic, a period not previously recognized in this area. Despite the lack of age constraints for the duration of garnet growth, we present a thermal model to understand the meaning of the N‐shaped path. These paths are best reproduced by thermal models incorporating SSZ thrusting before and after denudation. This paper presents an example of the insight from high‐resolution P‐T paths, and an example of denudation within a prograde metamorphic event.
Plain Language Summary
The Menderes Massif, SW Turkey, is abundant in garnet‐bearing metamorphic rocks formed during an ancient mountain building event. Reconstructing the history of this event has been difficult due to a variety of factors that have altered much of the rocks. Luckily, the mineral garnet largely survived alteration here and retains its original growth chemistry. This chemical information is useful for estimating the pressure and temperature conditions at which the mineral grew. Here we study six garnets and find two growth histories: one suggesting garnet grew as the rock was continuously buried to a depth >20 km and another suggesting garnet experienced fluctuations in burial depth during growth, that is, certain rocks were buried, partially exhumed (<1 km) and then reburied to a maximum depth >20 km. This variation in burial depth is consistent with a model calling on a period of surface erosion during overall mountain building as responsible for partial exhumation.
Key Points
High‐resolution N‐shaped P‐T paths from the S. Menderes Massif (Turkey) are most consistent with a model of burial with intermediate exhumation
Monazite in garnet appears to be secondary based on textural relationships and their high common Pb and 137Ba/Th+ contents
Neoproterozoic and Permian‐Triassic age zircons are reported, a timeframe not yet recognized in the S. Menderes Massif |
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| ISSN: | 0278-7407 1944-9194 |
| DOI: | 10.1029/2018TC005335 |