scholarly journals Documenting Exhumation in the Central and Northern Menderes Massif (Western Turkey): New Insights from Garnet-Based P-T Estimates and K-Feldspar 40Ar/39Ar Geochronology

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Thomas M. Etzel ◽  
Elizabeth J. Catlos ◽  
Ibrahim Cemen ◽  
Cenk Ozerdem ◽  
Tolga Oyman ◽  
...  
Keyword(s):  
Growth Yield ◽  
Garnet Growth ◽  
Western Turkey ◽  
Chemical Zoning ◽  
Menderes Massif ◽  
Two Samples ◽  
Growth History ◽  
T Path ◽  
Exhumation Model ◽  
Metamorphic Core

Abstract The Menderes Massif (Turkey) is a metamorphic core complex that records Alpine crustal shortening and extension. Here, nine garnet-bearing schist samples in the Central Menderes Massif (CMM) from below the Alaşehir detachment (AD) were studied to reconstruct their growth history. P-T estimates made using a chemical zoning approach, and petrological observations, indicate garnet grew between ~6 kbar and 550°C and 7.5-9 kbar and 625-650°C. Two P-T path shapes from two samples emerged (isobaric and burial), suggesting that either separate garnet-growth events occurred, or different garnet generations from the same metamorphic event were sampled. Despite observable diffusional modification in most garnets, thermobarometric estimates for crystal-rim growth yield P-T estimates similar to those reported elsewhere in the region. Ion microprobe monazite ages, paired with textural observations, from three of the samples time early retrograde metamorphism (~36-28 Ma). To better understand Neogene extension/exhumation, K-feldspar 40Ar/39Ar ages were obtained from two synextensional granites (Salihli and Turgutlu) exposed along the AD and two from the northern Simav detachment (Koyunoba and Eğrigöz). This data suggests the Simav detachment footwall rapidly exhumed at ~20 Ma, whereas the AD experienced two periods of exhumation/cooling (~14 Ma and~5 Ma). AD ages support a pulsed exhumation model for the massif.

scholarly journals Re-Evaluation of the First Metamorphic P-T Path Using QuiG Barometry and Equilibrium Thermodynamics

2021 ◽  
Author(s):  
Sam Couch
Keyword(s):  
Mineral Assemblage ◽  
Nucleation And Growth ◽  
Garnet Growth ◽  
Tauern Window ◽  
Chemical Zoning ◽  
Two Samples ◽  
Growth History ◽  
Mineral Assemblages ◽  
Peak Metamorphism ◽  
T Path

Quartz in garnet (“QuiG”) barometry is a relatively new technique that uses physical properties of minerals to estimate the pressure of garnet nucleation and growth history independent of chemical equilibrium. QuiG barometry was used to determine pressures of garnet growth and compared to thermodynamically calculated P-T conditions for two samples (FH-1M and Z3H) from the Lower Shieferhülle (Formation), Tauern Window, Austria. FH-1M was the first sample for which a P-T path was calculated through inversion of chemical zoning in garnet (Selverstone et al., 1984). Mineral Assemblage Diagrams (MADs) and geothermobarometric techniques were used to determine P-T conditions for garnet nucleation and peak metamorphism. No MAD reproduced either the results of Selvserstone et al. (1984) or petrologic observations such as mineral assemblages and likely P-T conditions as determined using independent thermobarometers. Thermobarometrically calculated rim conditions were consistent between our study and previous work in the Lower Schieferhülle. However, without appropriate inclusion assemblages and compositions, the accuracy of calculated core P-T conditions could not be independently assessed using thermobarometry for either rock. QuiG isomekes from both samples are broadly consistent with growth of garnet during exhumation with heating as originally proposed by Selverstone et al. (1984). However, the QuiG isomekes for Z3H suggest that 90% or more of the Z3H garnet grew over small changes in pressure and temperature or along a QuiG isomeke (heating with a slight increase in pressure). These results support the accuracy of prior P-T paths and their tectonic interpretations. However, inconsistencies between QuiG barometry vs. thermodynamic calculations remain unresolved.

scholarly journals Garnet Chemical Zoning Based Thermobarometry: Method Evaluation and Applications in the Menderes Massif, Western Turkey

Geosciences ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 505
Author(s):  
Thomas M. Etzel ◽  
Elizabeth J. Catlos
Keyword(s):  
Cooling Rate ◽  
Garnet Growth ◽  
Bulk Rock ◽  
Method Evaluation ◽  
Western Turkey ◽  
Chemical Zoning ◽  
Menderes Massif ◽  
High Heating ◽  
The Impact ◽  
And Diffusion

The garnet chemical zoning method (GZM) is a reliable thermodynamic approach for forward modeling pressure-temperature (P-T) paths using observed garnet and bulk rock compositions. However, intracrystalline diffusion is known to compromise the integrity of GZM modeled garnet-growth P-T paths. For this reason, extracting reliable metamorphic estimates from garnet-bearing schists in the Central Menderes Massif (CMM), western Turkey, has been difficult. To evaluate the impact of diffusion on GZM, we simulate garnet growth and diffusion for an average metapelite using the program Theria_G. Modeled garnet compositions from four simulations are used to estimate P-T conditions and paths by GZM, which are compared against Theria_G specified P-T-t trajectories. Factors influencing results are heating/cooling rate, grain size, and peak T. At a maximum T of 610 °C, both undiffused and diffused garnet compositions returned estimates comparable to prescribed conditions regardless of heating/cooling rate. Diffused profiles from simulations reaching a maximum T of 670 °C also reproduced prescribed P-T paths if tectonism occurred at high heating/cooling rates (50 °C/my). From these insights and additional Theria_G simulation-derived observations for CMM garnets, we deduce that metamorphism in the region exceeded 650 °C and achieved a maximum burial P between 8–10 kbar prior to Cenozoic exhumation.

Documenting isobaric cooling in the lower crust using cordierite breakdown textures (Mont Mary nappe, Western Alps)

2021 ◽  
Author(s):  
Michel Ballèvre ◽  
Marc Poujol ◽  
Selim Rousseau ◽  
Paola Manzotti
Keyword(s):  
Western Alps ◽  
Detrital Zircons ◽  
Garnet Growth ◽  
Garnet Porphyroblasts ◽  
Chemical Zoning ◽  
Lower Unit ◽  
The Matrix ◽  
T Path ◽  
The One ◽  
Growth Zoning

<p>Intracrystalline diffusion is an efficient mechanism in high-grade rocks. Therefore, growth zoning in garnet is erased and the evidence for prograde path is lost. However, information recorded by the textures may store significant clues for deciphering part of the P-T path. An example is provided here from the migmatitic paragneisses from the Mont Mary nappe (Western Alps).</p><p>The latter is made of a pre-Alpine basement consisting of an upper and a lower unit. The upper unit is made of paragneisses, marbles and amphibolites similar to those of the Valpelline Unit and of the Ivrea Zone. The lower unit displays granitic orthogneisses, paraschists (with muscovite, biotite, garnet with local occurrences of staurolite, kyanite and andalusite) (Dal Piaz et al. 2015). In this unit, we discovered a hectometre-sized volume with no Alpine overprint, preserving migmatitic paragneisses, the topic of this study.</p><p>The paragneisses display quartzo-feldspathic leucocratic layers interpreted as crystallized melts. The leucosomes are separated by biotite- and sillimanite-rich layers, with conspicuous garnet porphyroblasts. In addition, fresh cordierite crystals are found in these layers. Sillimanite included in garnet rims has the same orientation than the one in the matrix. There, the foliation is defined by the shape fabric of biotite and sillimanite, wrapping both garnet and cordierite crystals.</p><p>Such textures may be used to propose a P-T path. A sequence of prograde reactions, including dehydration-melting of muscovite, then biotite, result in the production of a large amount of sillimanite. Garnet growth was continuing during incongruent melting. However, intracrystalline diffusion has erased the prograde chemical zoning, as well as the distribution and shape of mineral inclusions. The late replacement of garnet and cordierite by biotite and sillimanite indicates near-isobaric cooling, also recorded by chemical zoning along garnet rims.</p><p>Chemical data on coexisting minerals will be used to provide quantitative constraints on the P-T path. In addition, preliminary geochronological data suggest that detrital zircons grains were significantly reset during the HT metamorphism, which could have taken place c. 270 Ma ago. To conclude, the studied paragneisses offer another example of Permian near-isobaric cooling in the middle crust of the Adriatic plate.</p><p>Dal Piaz G.V., Bistacchi A., Gianotti F., Monopoli B., Passeri L., Schiavo A. & collaboratori (2015) – Note illustrative della carta Geologica d’Italia alla scala 1:50.000. Foglio 070, Monte Cervino. ISPRA, Servizio Geologico d’Italia, 070, 1-431.</p>

Evidence for polymetamorphic garnet growth in the Çine (southern Menderes) Massif, Western Turkey

2008 ◽  
Vol 2 ◽  
pp. 012020 ◽  
Author(s):  
C B Baker ◽  
E J Catlos ◽  
S S Sorensen ◽  
I Çemen ◽  
M Hancer
Keyword(s):  
Garnet Growth ◽  
Western Turkey ◽  
Menderes Massif

Chemical zonation and relative timing of growth sections in garnets from eclogites of the Leaota Massif, South Carpathians

2006 ◽  
Vol 70 (6) ◽  
pp. 655-667 ◽  
Author(s):  
G. Săbău ◽  
E. Negulescu ◽  
H.-J. Massonne
Keyword(s):  
Morphological Characteristics ◽  
Garnet Growth ◽  
Growth Stages ◽  
Chemical Zoning ◽  
Metamorphic History ◽  
Growth History ◽  
Mineral Assemblages ◽  
History Of ◽  
Partial Resorption ◽  
Zonation Patterns

AbstractWe have investigated the chemical zoning of garnet in three texturally different eclogite types from the Leaota Massif, Romania, to test the various zonation patterns of Ca, Fe, Mg and Mn as indices of time-lines in porphyroblastic garnets. Mn zonation was found to mark various growth stages very well. It indicates in each of our three case studies a complex growth history dominated by multiple nucleation and coalescence, but also interrupted by partial resorption, as shown by morphological characteristics. Chemical variations of the main elements in garnet during prograde high-pressure metamorphism define time-lines other than those of Mn which decrease, highlighting the stages of porphyroblastic growth. In particular, the Ca/Mn, Mg/Mn and Mg/Fe ratios are useful in late growth stages, when low Mn contents and radial gradients do not allow a satisfactory resolution of Mn time-lines. These ratio-based time-lines further substantiate the potential of Mn time-lines in revealing non-concentric porphyroblastic growth. This is important in order to correctly relate garnet growth stages to stable mineral assemblages, a prerequisite for a reliable derivation of the metamorphic history of the host rock.

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