Tying Together Textures, Temperatures, and Timing in the Western Tatra Mountains, Slovakia

TYING TOGETHER TEXTURES, TEMPERATURES, AND TIMING IN THE WESTERN TATRA MOUNTAINS, SLOVAKIA

A thesis submitted to the Kent State University Graduate College in partial fulfillment of the requirements for the degree of Master of Science

Jenna C. Hojnowski

December, 2010

Thesis written by

Jenna C. Hojnowski

B.A. State University of New York at Geneseo, 2008

M.S. Kent State University, 2010

Approved by

, Advisor Daniel Holm

, Chair, Department of Geology Daniel Holm

, Dean, College of Arts and Sciences John R.D. Stalvey

Table of Contents

List of Figures ...... vii

List of Tables, Equations, and Appendices………………………………………..…..viii

Acknowledgments ...... x

Abstract ...... 1

1. Introduction ...... 3

Tectonic Background of the Western Tatra Mountains...... 5

Structural Features……………………………………………………………….10

P-T-t Paths……………………...... …….11

Geochronology Data…………………………………………………………....13

2. Petrographic Fabrics...... 14

Optical Methodology...... 17

Mica Schists...... 19

Migmatites……………………………………………………………………….25

Granite…………………………………………………………………………...29

Kinematice Indicators…………………………………………………………...30

Implications…………………………………………..………………….……...30

3. Titanium-in-Quartz Thermometry……...... 32

Methodology...... 35 iv

Titanium-in-Quartz Results...... 37

Titanium-in-Zircon Results …...... 41

Implications...... 44

4. EMPA Monazite Geochronology……...... 46

Methodology...... 47

Results...... 52

Implications...... 53

5. Electron Backscatter Diffraction (EBSD) of Quartz …...... 55

Methodology...... 56

Results...... 60

Implications...... 64

6. Summary and Discussion……………………………..…………………………..…71

Summary...... 71

Discussion...... 74

References…………………………………………….………………..………………80

Appendices……………………………………………...….……………………………84

List of Figures

1. Geologic maps of Eastern Europe and Western Tatra Mountains……………..6

2. Tectonostratigrahpic column of the Tatric Unit……………………………….7

3. Variscan tectonics……………………………………………………………...9

4. P-T-t paths of upper and lower units…...... 12

5. Geologic map and sample locations…………………………………….……15

6. Baranec Peak cross-section……………………………………...... 16

7. Rock fabrics in the field………………………………………………………16

8. Stereonet of lineations…………………………………………………….….18

9. Mica schist sample ZT-14-08…………………………………………….…..21

10. Protomylonitic mica schist sample ZT-15-08…………………………....….22

11. Mylonitic mica schist sample ZT-24-08………………………………….…23

12. Ultramylonitic mica schist sample ZT-16A-08……………………………..24

13. Migmatite sample ZT-18-08………………………………………………...25

14. Protomylonitic migmatite sample ZT-7A-08……………………………..…27

15. Mylonitic migmatite sample ZT-9-08…………………………………….....28

16. Protomylonitic granite sample ZT-5-09………………...... 29

17. Titanium-in-quartz histograms...... 39

18. Optical and BSE images of TitaniQ spot analysis………………...………..40

19. BSE images of detrital zircon……………………………………………….43

20. BSE images of zircon ……………………………………………………….43

21. BSE images of sample ZT-4-08 for monazite dating…………………....….47

22. BSE images of sample ZT-24-08 for monazite dating…………………...... 49

23. BSE images of sample ZT-14-08 and ZT-15-08 for monazite dating…...…50

24. Relative probability plot for monazite dating results……………………….52

25. Crystal orientation maps for sample ZT-24-08…………………………...... 58

26. Crystal orientation maps for sample ZT-15-08………………...... 59

27. Flinn diagram with CPO and girdle patterns………………………………..61

28. Quartz slip systems………………………………………………………….62

29. Deformation and temperature influencing slip systems…………………….62

30. EBSD results ……………………………………………...... 65

31. Revised Variscan tectonics……………………………………………….…76

32. Enhanced Baranec Peak cross-section………………………………………78

vii

List of Tables

1. Previous P-T work...... 37

2. Titanium-in-quartz results…………………………………………………….38

3. Titanium-in-zircon results………………………………………………….…41

4. Summary of temperatures, textures, and timing……………………………...72

List of Equations

1. Titanium-in-quartz thermometry with pressure effect...... 33

2. Titanium-in-zircon thermometry …………………………………………….34

3. Zirconium-in-rutile thermometry…………………………………...………..34

List of Appendices

1. Sample table…………...... 85

2. Original titanium-in-quartz and titanium-in-zircon data………………..…….86

3. Electron microprobe chemical data and monazite ages……………………...91

viii

Acknowledgements

I owe much of my appreciation to Daniel Holm for his guidance and wisdom from the very beginning of this research. Much gratitude goes to Dave Scneider for support during fieldwork and additional advisement throughout the progression of this work.

I am very grateful to the following for their time, expertise, and instruction during my visits to conduct lab work. This allowed me to establish a set of data sufficient for analysis and interpretation: Nelia Dunbar and Lynn Heizler at the New Mexico Institute of Mining and Technology for analyses of monazite for geochronological purposes;

Nicholas Seaton at the University of Minnesota for Electron Backscatter Diffraction and constructive reviews; John Price in using titanium as a thermometer and providing useful comments.

Many other additional thanks go to Yves Moussallam for assistance in the field and proceeding dialogues regarding our samples. Jaroslaw Majka (Jarek) for constructive discussions regarding geochronology in the Tatra Mountains. To Donald Palmer for comments during the proposal and defense phases of this thesis work and Dave Waugh during sample characterization.

Of course I would not have completed this work without the love and support from family and friends. To my family, your encouragement was vital to this completion. To my friends, thank you for times of mental relief.

Funding for this research was provided by grants from: Geological Society of

America; Gamma Zeta Chapter (Kent State) of Sigma Gamma Epsilon; Kent State‟s

Geology Alumni, Graduate Student Senate, and University Research Council. Parts of this work were carried out in the Institute of Technology Characterization Facility,

University of Minnesota, a member of the NSF-funded Materials Research Facilities

Network (www.mrfn.org).

Abstract

In the Western Tatra Mountains, the Variscan-age (~340 Ma) exhumed shear zone, reveals high-grade metamorphic rocks thrust over medium-grade metamorphic rocks, creating an unusual macroscopic rock geometry known as an inverted metamorphic sequence. Polyphase petrographic fabrics record the formation of the inverted metamorphic sequence, making it ideal for characterizing mid-crustal deformation mechanisms of large-scale tectonic processes. A combination of microstructural (optical petrography) and microanalytical (monazite EMPA, Titanium thermometry, Electron backscatter diffraction-EBSD fabric analysis) techniques reveal the dynamic processes involved in the evolution of this major crustal-scale discontinuity.

The timing of the Early Variscan continent-continent collision was measured by

U/Pb monazite dating at c. 370 Ma in the mica schists, with titanium-in-zircon temperatures of ~ 880 °C in the migmatite. These data reflect the peak metamorphic conditions of Early Variscan deformation. During or following exhumation of the high- grade rocks into the mid-crust, titanium-in-quartz data suggests the newly formed inverted metamorphics coexisted at temperatures of approximately 540 °C. The age of

Variscan SE thrusting (~ 340 Ma) and its kinematic indicators are lacking in the mica schists. Instead, additional monazite ages from mica schists correlate to younger (c. 315

Ma) plutonism/uplift? and microstructural and analytical results reflect kinematics in a E-

W orientation.

Collectively, data on the textures, temperatures, and timing within the Tatra tectonic zone do not support the „hot iron‟ model of inverted metamorphic formation.

Rather, simultaneous or closely related exhumation of the high-grade metamorphics with orogen parallel extension.

1. Introduction

Crustal sections commonly exhibit an increase in metamorphic grade with increasing structural depth. In some cases however, tectonic crustal shuffling has resulted in reversed metamorphic zonation with higher grade metamorphic rocks structurally above lower grade rocks (Jamieson et al., 1996). Inverted metamorphism may occur when tectonic thrust stacking juxtaposes high grade metamorphic rocks above lower grade rocks, resulting in transient inversion of isotherms with a transfer of heat downward during thrusting. This „hot iron‟ model requires rapid rates of displacement during mass transfer, and results in metamorphism that is closely linked in time to deformation. Alternatively, pre-existing „normal‟ metamorphic layering can become overturned into a recumbent nappe. In this case the metamorphism predates deformation and isograds are commonly sheared and attenuated (Hubbard, 1996).

Considerable research has developed more sophisticated models and concepts to explain the development of inverted metamorphics. Recent work supports channel flow, which involves a lateral flow bounded on each side by rigid bodies and subjected to lithostatic pressures. Models support simultaneous channel flow and thrusting of the viscous fluid with erosion as an alternative generation of an inverted metamorphic sequence (Godin et al., 2006; Jones et al., 2006).

Field and petrological studies in the Western Tatra Mountains, Slovakia, reveal the upper and lower units of an exposed crystalline complex are an inverted metamorphic sequence. The terms “upper” and “lower” define the structural relationship of the layers.

The contact between the upper and lower units is a major deformation zone that formed during Variscan tectonism (i.e. 380-330 Ma). Results of P-T-t reconstructions in the

Western Tatras (Janak, 1994) favor the „hot iron‟ model for inverted metamorphism formation. Variscan thrusting was followed by a later phase of deformation, the Alpine orogeny, which uplifted the basement to expose the inverted metamorphic section (Janak,

1994). Structures and microfabrics in the Western Tatra Mountains are the result of both pre-Alpine and Alpine deformations, distinguishable via their different P-T conditions of formation (Fritz et al., 1992).

The purpose of this study is to assess the conditions of deformation preserved in the metamorphic sequence using the latest techniques in microstructural research.

Analyzing the understudied and seemingly monotonous unit of mica schists has provided a comparison to the better characterized higher grade portion of the inverted metamorphic sequence. A quantitative approach tying together results from thermometry, geochronology, and textural analyses of the crystalline basement rocks provides important information on the metamorphic and kinematic history of the Western Tatra

Mountains. Qualitative inferences of the (re)crystallization temperatures via textural associations to quartz regimes are compared against temperatures measured via chemical analyses. A quantitative measurement of (re)crystallization temperatures will allow for a

comparison to previous P-T studies and additional assessment of quartz deformation mechanisms. Results from this study warrant new interpretations of the dynamics for metamorphic inversion in the Western Tatras. Additionally, data from an ancient inverted metamorphic sequence will allow for comparisons with the well-studied young

Himalayan inverted metamorphic sequence specifically, as well as enhance our knowledge of mid-crustal orogenic processes in general.

Tectonic Background of the Western Tatra Mountains

The Tatra Mountains are located on the border between southern Poland and northern Slovakia and are the northern-most section of the Western Carpathian

Mountains (Fig. 1A). The lower elevation Western Tatra Mountains are geomorphically distinct from the dramatic peaks of the High Tatra Mountains to the east. More easily eroded gneisses and schists are exposed in the Western Tatras, in contrast to the eastern

High Tatras which exposes primarily Variscan-age plutonic rocks (Fig. 1B).

The Tatric unit contains dominantly pre-Mesozoic rocks, deformed under medium to high grade metamorphic conditions (Fritz et al., 1992; Janak, 1994). The Tatric basement complex is divided into two units: 1) a lower unit consisting of medium-grade mica schists, and 2) an upper unit consisting of granites, migmatites, gneisses, and amphibolites with boudins of relict eclogites (Fig. 2). The lower unit is subdivided into a staurolite-kyanite zone and a kyanite-fibrolite zone, which lie beneath the kyanite zone of the upper unit followed by sillimanite zonation. The Variscan low-angle thrust fault,

A.)

B.)

Figure 1: A) Map of the tectonic provinces of Eastern Europe. The Tatra Mountains lie within the Western Carpathians. The Western Tatras are on the border between Poland and Slovakia, south of Krakow in the outlined area (from Struzik et al., 2002). B) Simplified geology of the Western Tatra Mountains. The Variscan thrust fault separates the upper and lower units (Fig. 2). Plotted are Fritz et al. (1992) kinematic results: D1) Variscan thrusting of the upper unit to the SE over the lower unit, D2) a sense of dextral shearing towards the east causing lineation in the E-W direction at higher levels of the upper unit, consequently overprinting previous compressional deformation, D3) Late Cretaceous brittle deformation shown by shearing to the NW associated with the transpression and nappe displacement during Alpine orogeny (from Ludhova & Janak, 1999).

separating the upper and lower units of the basement rock in the Western Tatras, represents a major mid-crustal tectonic discontinuity. Ductile deformation is evident in all of the rock units, with limited brittle deformation. This crystalline basement is overlain by mildly tilted Mesozoic and Cenozoic sedimentary layers (Janak, 1994; Janak et al., 1999).

younger

Figure 2: Tectonostratigraphic column of the basement complex of the Western Tatra

Mountains, illustrating the inverted metamorphic sequence. The Variscan thrust fault separates the high grade upper unit from the medium grade lower unit. Black pods depict relict eclogite boudins (modified from Janak et al., 1996).

The lower unit mica schists originated as a thick sequence of flysch deposits that may have been a part of Laurasia‟s accretionary wedge (Poller et al., 2000). Detrital zircon ages of 500 - 490 Ma from the lower unit mica schists are interpreted to represent the youngest igneous protolith of the mica schists or the latest age for sedimentation

(Kohut et al., 2008).

The crystalline basement complex was primarily developed during the collision of

Laurasia and Gondwana (Jurewicz, 2005). A proposed progression of tectonic events that shaped the Western Tatra Mountains, during the Paleozoic, is depicted in Figure 3.

At c. 420-400 Ma, subduction of oceanic lithosphere beneath Gondwana resulted in the formation of the now deformed older granites (ortho and paragneisses) (Pollwer et al.,

2000).

Continent-continent collision beginning in the Late Devonian contributed to the dominant tectonic imprint preserved in the Tatra Mountains crystalline rocks.

Transformation of the „older‟ granites into gneisses occurred around 365 Ma (Poller et al., 2000) followed by subsequent generation of felsic magmatism at 360-350 Ma.

Emplacement of the upper unit above the lower unit occurred during rapid exhumation; thrusting of the upper unit to the SE led to the formation of the inverted metamorphic sequence (Janak, 1994).

1. Late Silurian/ Early Devonian

2. Middle to Late Devonian

3. Late Devonian to Early Carboniferous

(Laurasia)

Figure 3: Variscan tectonics of the Western Tatra Mountains showing the different stages of deformation, metamorphism, and plutonism recorded in the Tatric unit. Note this diagram depicts the lower unit as the downgoing slab during Late Devonian to Early Carboniferous/Variscan thrusting (modified from Poller et al., 2000).

Structural Features

The Tatra Mountains preserve deformational features associated with both the ductile Variscan and brittle Alpine events. Fritz et al. (1992) suggested there are four distinguishable periods in the deformational history of the Tatra Mountains, mainly determined from mesoscopic field and microscopic fabric studies of the crystalline basement (Fig. 1B). The two early stages (D1 and D2) were associated with high temperature deformation, whereas the proceeding deformations (D3 and D4) formed under much lower P-T conditions during Alpine collision (Fritz et al., 1992).

Early intense shearing (D1) is indicated by the presence of a NW-SE mineral and stretching lineation that formed within the stability field of sillimanite and shear sense indicators suggest Variscan overthrusting to the SE resulting in the juxtaposition of the upper and lower units (Janak et al., 2001). Top-to-the east shearing (D2) overprinted the initial fabric under greenschist facies contitions (Janak, 1994). The top-to-the east kinematics are preserved at shallow levels of the upper unit, and within the Tatra younger granites. Fabrics D1 and D2 are interpreted to be a result of mid-crustal thrusting during pre-Carboniferous times, likely during the Variscan age (Fritz et al., 1992; Janak et al.,

1999; 2001).

Following the Variscan orogeny, NW-directed (D3) Alpine convergence resulted in a semi-brittle fabric; low temperature plasticity is evident from the deformation of quartz during shearing. Alpine deformation occurred under hydrous fluids during nappe transport (Fritz et al., 1992). D4 involves large scale refolding with km-size open SSE- plunging folds deforming previous foliation (Fritz et al., 1992; Janak, 1994). Apatite

fission track data suggest the Tatras were recently uplifted 10-15 Ma (Janak et al., 2001) via E-W trending wrench zones coupled with normal faulting in a N-S to NW-SE direction (Janak et al., 1999). Deep seismic profiles may indicate that Alpine tectonics detached and relocated the basement complex during deformation (Janak, 1994).

P-T-t Paths

Reconstruction of metamorphic conditions and the evolution for both the upper and lower units show typical clockwise P-T paths characteristic of continent-continent collisions (Fig. 4). Thermobarometic results recorded in the migmatitic upper unit indicate peak metamorphic conditions of 700-800 °C at pressures of 10-14 kbar in the kyanite zone. Following peak metamorphic conditions the upper unit preserves moderate grade metamorphism with temperatures of 650-750 °C and pressures of 4-6 kbar in the sillimanite zone (Janak, 1994). The mid-crustal younger metamorphism was interpreted by Janak (1994) as coincident with recrystallization of the older granites during Variscan high temperatures and partial melting at c. 365 Ma. The lower unit preserves increasing metamorphic conditions from the box parameters of 550 - 600 °C at 5-6 kbar to peak metamorphic conditions of 650 °C at 7 kbar in the later box. In general, these paths formed in association with collision and juxtaposition of the upper and lower units during

Variscan overthrusting.

Figure 4: Schematic P-T paths representing the metamorphic evolution of the upper and lower units. The parameters of the boxes are based on geothermometry and geobarometry (from Janak, 1994).

Additional P-T work by Moussallam (2010) shows that relict eclogite facies assemblages yield post-peak conditions of 16-18 kbar and 750-800 °C, indicating possible tectonic interleaving with the migmatites (which host the eclogite boudins).

Alternatively, the eclogites and migmatites may have followed the same P-T path, with only the migmatites re-equilibrating during rapid decompression to moderate pressure conditions.

Geochronology Data

A c. 405 protolith age of the upper unit gneisses obtained from U-Pb zircon analyses suggest an intrusion age associated with Late Silurian to Early Devonian subduction (Poller et al., 2000). Formation of the gneisses during peak metamorphic conditions is coeval with a phase of younger granitic magmatism recorded by zircons from 370-345 Ma (Kohut et al., 2001; Moussallam, 2010). High-pressure metamorphism, forming the high grade crystalline basement, appear likely to have occurred at 365-360 Ma (Poller et al., 2000), concurrent with melting.

Moussallam (2010) obtained a robust c. 340 age from multiple geochronometers interpreted as dating the widespread metamorphism and exhumation of the upper unit during Variscan thrusting. A second phase of younger magmatism, resulted in the generation of the High Tatra diorites and granites from 340 – 310 Ma, which may have formed from rapid decompression at c. 340 Ma (Kohut et al., 2001). Biotite Ar/Ar ages in the High Tatras and muscovite Ar/Ar ages from the Western Tatras record cooling from 330-300 Ma (Janak, 1994; Moussallam, 2010). Recent uplift of the Tatra

Mountains, captured via apatite fission track data occurred at 10-15 Ma (Janak et al.,

2001).

2. Petrographic Fabrics

The major thrust fault in the Western Tatras is defined by an approximately 200-

300 m thick deformation zone surrounding the contact between the upper and lower units.

Thirty-two samples of mica schist (lower unit) and migmatites, amphibolites, and granites (upper unit) were collected by transecting the contact (Figs. 5 & 6). The dominant foliation of the lower unit mica schists is deformed, producing inconsistent attitude measurements (Fig. 6 & Appendix 1). The Tatras are heavily forested, making for limited exposure below the tree line. Additionally, limited access to outcrops via designated foot trails prevented ideal transects of the fault. Oriented samples were taken at a range of distances from the contact measuring lineation and foliation attitudes

(Appendix 1). Lineations consisted of dominantly stretched quartz grains but were not identifiable at every locality. Other meso-textures and structures such as foliation, sigma structures, and boudins characterize the deformed granitiods and metamorphic rocks (Fig.

7).

This study makes use of the latest microstructural methods for a quantitative textural analysis, which is beneficial in making interpretations concerning the nature of the strain in the samples collected from the thrust zone. Although new instruments rapidly collect a significant amount of microstructural data, it is important to combine laboratory analyses with observations made in concert with the petrographic microscope

(Trimby & Prior, 1999). 14

sectionfigure. following the in -

cross in map the represented of center the in

Generalized geologic map of the Western Tatra Mountains including Mountains from locations Western the both geologic sample the of map Generalized Tatra

Figure 5: Figure exposed lower lower in unit both portions Unlike units. Tatric and and Tatras, are the of upper the upper High the al., Nemcok & 1996 al., et Tatras et from Janak separated (modified Variscan the by fault thrust and Western the Peak Baranec Note 1994).

Figure 6: Cross-sectional of Baranec Peak, Western Tatras with the upper and lower unit contact and rock types from corresponding cross section showing elevation in meters (modified from Janak et al., 1999). Samples were collected from within the deformation zone, above and below the contact. Dominant mica schist foliations are deformed (kinked lines), as displayed in the diagram.

a. b.

10 cm

Figure 7: Rock fabrics from deformed outcrops of the upper and lower units: a) Sigma structure in a micaschist, b) lineation in a micaschist, and c) boudin in an amphibolite with distinct foliation.

The microfabrics were first characterized petrographically, in order to select those most appropriate for quantitative analyses. Deformation mechanisms involving quartz crystals have been well studied in controlled experiments and in various tectonic settings

(e.g. Hirth & Tullis, 1992). Experimental studies deforming quartz resulted in three broadly defined deformation regimes involving dislocation creep and tested their dependency on temperature, strain rate, and water content. The three regimes defined by

Hirth and Tullis (1992) are based on the temperature and strain rate, which produces distinguishing microstructural textures:

regime 1) low temperatures and a fast strain rate produce patchy undulose

extinction and migratory grain boundaries that diffuse into one another,

regime 2) high temperatures and lower strain rate form sweeping undulose

extinction, high-angle grain boundaries, and subgrains possibly forming

core-mantle structures, and

regime 3) defines the highest temperatures and lowest strain rate, resulting

in high-angle grain boundaries with nearly 100 % recrystallization and

larger subgrains with core-mantle structures.

Optical Methodology

For analysis of the fabrics, oriented samples were cut perpendicular to foliation and parallel to lineation. The lineations were based on field measurements where present, which was predominantly in an E-W orientation (Fig. 8). For samples without visible lineations, the oriented samples were cut in a NW-SE orientation. Reasoning for

the NW-SE orientation stems from the fabric analysis of Fritz et al. (1992) (Fig. 1B), and the proximity of the samples to the Variscan thrust fault. The SE trend is known to be the fabric developed during D1 Variscan thrusting and measured by quartz c-axes. The E-W orientation, observed in the field, is the subsequent D2 fabric. Additionally, the NW trend, measured by quartz c-axes, is the direction of motion recorded during lower temperature Alpine tectonics (Fritz et al., 1992). Since samples were collected along the thrust fault, it is assumed the NW-SE trend (D1 and D2) would be the dominant fabric preserving kinematic indicators, hence being designated the orientation to cut samples without visible lineations.

Figure 8: Stereonet with pole plots of the 11 lineations measured in the field (Appendix 1). Most of the lineations have a trend of approximately 080 to 105. The E-W orientations, D2, correspond to work by Fritz et al. (1992), along with the NW- SE orientation of D1.

Beyond their standard lithologic names the mica schists, migmatites, and mildy deformed granite were characterized based on their percentages of matrix to porphyroclasts from Passchier and Trouw (1996); protomylonites have a matrix of 10-

50%, 50-90% for the mylonites, and greater than 90% for ultramylonites. The matrix in all three rock types consists of quartz and lesser micas, differentiated from quartz and feldspathic porphyroclasts. Sample descriptions begin with the lithologic characteristics, followed by the kinematics suggested by their deformation textures.

Mica Schists

The thick sequence of mica schists occupying the structurally lower unit exhibit variable microfabrics from undeformed to strongly deformed. Lineation is defined by the alignment of muscovite, biotite and stretched quartz with porphyroclasts of sericitic feldspars (2-4 mm) (Fig. 9A). In select samples the altered feldspars are poikioblastic with mica and quartz inclusions (Fig. 9B). The dynamically recrystallized quartz has patchy and sweeping undulose extinction and often quartz veins oriented parallel to the dominant fabric. Most of the samples (deformed and undeformed) contain primary metamorphic and secondary/alteration minerals such as chlorite, talc, sillimanite, staurolite, and garnet.

The protomylonitic to mylonitic schists contain quartz grains ranging in size less than 2 mm down to barely visible subgrains. At sample location ZT-15 the lineation was measured on the coarser stretched quartz grains (Fig. 10A). Quartz grains exhibit patchy undulose extinction with migrating grain boundaries developing into subgrains and

incipient of core-mantle structures (Fig. 10C). Boudins of quartz and feldspar flasers and augens also dominate this protomylonitic schist (Fig. 10D). The micas are often altered to chlorite. The quartz in the mylonitic schists differ from the protomylonitic schists by exhibiting more grain size reduction and higher angle grain boundaries (Fig. 11A). The quartz ribbons in the mylonitic samples help to define the strong fabric and core-mantle structures are fully developed (Fig. 11B). The micas are often bent and kinked and in some instances form a crenulation cleavage. The patchy to sweeping undulose extinction, migrating grain boundaries, subgrains and core-mantle structures of the significantly recrystallized quartz place the mylonites in the high temperature and low strain rate regimes (2-3).

A majority of the samples studied were mildly to moderately deformed.

However, one outcrop (ZT-16A) exhibited ultramylonitic textures with > 90% grain size reduction and few relict porphyroclasts (≤ 0.5 mm) of quartz and sericitic feldspars (Fig.

12). The porphyroclasts form core-mantle structures and pressure shadows. Opaque minerals make up approximately 10% of the section. This highly sheared rock is characteristic of quartz regime 3 with its highly flattened and very fine subgrains and nearly 100% recrystallization.

NW SE

A. A.

B. B.

Figure 9: Mica schist sample ZT-14-08: A) Photomicrograph of the entire section under polarized light. The lineation is defined by the micas and quartz ribbons. B) A portion of the thin section, focusing on the poikioblastic texture of the feldspars.

B. W

C. D.

Figure 10: Protomylonitic mica schist (ZT-15-08): A) Field photo of the resistant quartz defining the lineation parallel to the pen, B) photomicrograph of full thin section, C) example of migratory boundaries and subgrains seen throughout the sample with micas, chlorite, and talc and D) quartz boudins surrounded by micas.

W E 5 mm 5 mm

A.A.

C-M C-M East

C‟

Figure 11: Mylonitic mica schist (ZT-24-08): A) Photomicrograph of a thin section, B) example of core-mantle structures and crenulation cleavage that developed into a S-C‟ fabric suggesting top-to-the east motion, and C) mica fish with top-to-the east shear sense.

East

D. C. W

Figure 12: Ultramylonitic mica schist (ZT-16A-08): A) Photograph of the outcrop in the eastern portion of the Western Tatras, B) pen oriented parallel to the lineation, C) photomicrograph of full thin section with the very fine black minerals being opaque minerals, and D) delta porphyroclast of feldspar showing top-to-the east motion.

Migmatites

Mesoscopic textures and foliations of upper unit migmatites were also measured in the field (Fig. 13A). The migmatites consist dominantly of quartz, feldspars, and biotite with lesser amounts of muscovite (Fig. 13B). The quartz and feldspars are up to 6 mm in size and the feldspars commonly exhibit alteration to sericite and contain quartz inclusions. The micas are folded and often kinked, also folding and crenulation cleavage is observed in most sections. A protomylonitic migmatite contained notable garnets that

NW SE

C . D. Figure 13: Migmatite sample ZT-18-08: A) Leucosomes and mesosomes observed in the field, B) photomicrograph of entire section, C) and D) folded and kinked micas, altered to chlorite (D).

are fractured with biotite grains wrapping around them, aligned with the surrounding lineation (Fig. 14D). There is a lack of the strongly organized fabrics in the migmatites, as compared to the discrete lineations defined by the quartz and micas in the lower unit schists. Another difference from the schists, is the greater amount of chlorite alteration evident in migmatites (Fig. 13D).

The protomylonitic migmatites have quartz grain boundaries that are straight to curved. Other quartz crystals display migrating boundaries and vary with the angle at which grains meet (Fig. 14C). The picture of the whole section (Fig. 14B) is an example a large feldspar (center) with quartz inclusions. Figure 14C is an example of specific concentrations of the smallest subgrains and accessory/altered minerals (chlorite) adjacent to one another (also note dislocation in plagioclase twinning). The correlation between accessory minerals and higher quartz regime characteristics exist in a majority of the migmatite samples, as well as a limited number of schists. With a difference in the amount and degree of grain size reduction, there is a transition from the protomylonitic to mylonitic type migmatites. The mylonitic migmatite has a greater number of quartz subgrains developed at the migrating boundaries during recovery (Fig. 15C-D).

Protomylonitic to mylonitic migmatites have undergone a considerable amount of recrystallization with seriate subgrains forming core-mantle structures with cores ≤ 4 mm. The quartz characteristics place these migmatites in regimes 2-3 with regime 3 being distinguished by larger subgrains and extensive grain boundary migration with high angle grain boundaries and sweeping undulose extinction. Both samples have a weathered appearance under plain light (iron staining?).

SW NE

D. C. Figure 14: Protomylonitic migmatite sample ZT- 7A-08: A) Weathered surface of outcrop showing folding of fabric, B) Photomicrograph of the entire section, crenulation cleavage, and feldspars with quartz inclusions C) varying sizes of quartz with micas altering to chlorite, and D) sample ZT-12-08 containing garnets that have biotite bending around the crystals.

B. A.

C. Figure 15: Mylonitic migmatite (ZT-9-08): A) and B) Outcrop photographs near Baranec Peak, C) polarized view the crenulated sample, and D) dynamically recrystallized quartz.

Granite

One sample was collected of a granitic intrusion of the upper unit. The granite is much coarser than the schists and migmatites, with porphyroclasts of seritic feldspars ≤

20 mm. The quartz matrix has been recrystallized and reduced to subgrains (Fig. 16).

The quartz in this deformed granite is characteristic of regimes 2-3 due to its high degree of recrystallization, grain size reduction, sweeping undulatory extinction, and migratory boundaries at high angles to one another. Micas scattered throughout the sample (< 10%) are altered to chlorite. The feldspars are fractured and have been filled in with quartz.

A. B.

Figure 16: Protomylonitic granite (ZT-5-09): A) Standard section in plane light with larger grains than the preceding samples, B) and C) quartz subgrains amongst feldspar porphyroclasts and micas, altered to chlorite.

Kinematic Indicators

As evident by the microstructures, most of the sampled Tatra rocks are mylonitic and appear to have undergone a considerable amount of strain under high temperatures, and suggest polyphase deformation. Mica fish are the most frequent shear sense indicator

(Fig. 11C). Unfortunately, the mica fish have conflicting kinematics amongst samples, and can even show opposing shear sense within samples. In some instances, different microstructures in a sample agree with one another. For example, in sample ZT-24 (Fig.

11) the S-C‟ fabric suggests top-to-the east kinematics, and the mica fish indicates top-to- the east motion. A top-to-the west shear sense was noted in a different mica schist (ZT-

25) based on mica fish and imbricated micas. The highly sheared ultramylonite contained numerous core-mantle porphyroclasts, which developed into δ (delta) – objects with a top-to-the east motion (Fig. 12D). The identical poikioblastic textures in two samples from separate locations preserves an earlier deformation with inclusions of micas and elongated quartz, all aligned in the same fashion (Fig. 9). Their original orientation is unclear but this does suggest multiple phases of deformation.

Implications

Specific textural characteristics are attributed to varying deformation mechanisms associated with the three quartz regimes. As a whole, most of the Tatric samples displayed characteristics of regimes 2 and 3 in thin section. Under regimes 2 and 3 the flow stress is reduced and dislocation climb occurs at a fast rate, with recrystallization beginning at the grain boundaries. Recrystallization occurs mainly as subgrain rotation in

regime 2 and both subgrain rotation and grain boundary migration for regime 3. The higher temperature of regime 3 further reduces the flow stress from regime 2, increasing the size of subgrain growth during grain boundary migration. A limited number of mica schists and migmatites were classified as regime 1 (Appendix 1), where recovery occurs as grain boundary migration, as opposed to dislocation climb, with no formation of subgrains. Preliminary work indicates that in select samples both regimes 2 and 3 are distinctly visible in different portions of the thin section (Fig. 14C). A greater number of subgrains correspond to highly altered veins suggesting an influx of fluids, which reportedly increases the temperature, reducing flow stress and locally enhancing to creep regime 3 (Hirth & Tullis, 1992).

The array of microstructures and textures are indicative of pure and simple shearing recorded during the polyphase tectonics of the Tatra Mountains. Cross-cutting relationships reveal multiple episodes of deformation in numerous samples (Appendix 1).

For instance, a consistent poikioblastic texture in sample ZT-14 (Fig. 9) and other samples may preserve an earlier fabric than the current E-W lineation. Also, the frequency of crenulation cleavage (Fig. 11, Fig. 14, Fig. 15) implies more than one period of deformation. The most frequent record of deformation in these Tatric samples is in the orientation of the previously noted E-W extension, D2 (Fritz et al., 1992). Shear sense varies from top-to-the east and top-to-the west.

3. Titanium-in-Quartz Thermometry

Microstructures in quartz-feldspar rich rocks can now be used to learn about deformation processes and conditions that occurred in exhumed ancient shear zones.

Laboratory experiments, as well as natural studies suggest that microstructures, especially in quartz, are mostly a function of temperature during deformation (Hirth & Tullis, 1992;

Wark & Watson, 2006). In the previous chapter I used a qualitative approach to optically characterize the microstructures for a relative inference of the deformation temperatures, based on the quartz regimes of Hirth and Tullis (1992). Improved analytical techniques coupled with novel assessments of trace-element incorporation in rock-forming minerals permit us to determine the temperature of crystallization. We can begin to unravel the complicated nature of deformation when this information is coupled with a detailed investigation of microstructures and other textural features.

Experimental work indicates a strong temperature dependence on titanium substitution in quartz; titanium is a trace element that substitutes for silicon in quartz.

Electron microprobe measurements of titanium in quartz serve as a proxy to determine the quartz crystallization temperature, indicating the temperature at which the rock crystallized (for igneous rocks) or at which quartz recrystallized in the sub-solid state

(Wark & Watson, 2006). High titanium concentrations equates to high temperatures with low titanium concentrations indicating low temperatures. The relation between 32

temperature and Ti solubility in quartz, shown in Equation 1, suggests that pressure plays a role when using titanium as a thermometer in quartz (Thomas et al., 2010).

a  cP T(°C)qtz   273.15 (1) b  Rln X qtz  Rln a  TiO2 TiO2

Where: a, b, c = empirical parameters for the temperature dependence of ln X qtz , TiO2 qtz P = pressure (kbar), R = gas constant (8.3145 J/K), X TiO = mole fraction of TiO2 2 in quartz, and a = TiO2 activity during quartz (re)crystallization. TiO2

This study utilized Eq. 1 to determine TitaniQ temperatures. Temperatures have been corrected based on known pressures, determined by previous studies using various geobarometers within the Tatric unit at this studies locality (Janak, 1994).

Titanium-in-quartz thermometry is a quantitative tool used on igneous and metamorphic rocks, for determining specific and precise temperatures of polystage

(re)crystallization. Kohn & Northrup (2009) applied TitaniQ to highly deformed metamorphic rocks as a means to use deformation temperature to make inferences regarding strain rates and viscosity in various tectonic areas. Their results indicate that the titanium content does vary directly with the temperature, both precisely and accurately (±2° C to ±10° C). Additionally, they were able to measure temperature differences preserved in one single grain, which indicates multiple exposures to heat and/or pressure.

Equation 2 was applied to titanium concentrations measured in zircon developed by Watson et al. (2006). This equation does not incorporate the potential effects of pressure; further analyses are needed to determine the relationship between pressure and the solubility of titanium in zircon.

5080  30 T(°C)zircon   273.15 (2) (6.01  0.03)  log(Ti)

For Zr concentrations in rutile and titanite/sphene we applied Eq. 3. The equation for this thermometer was also developed by Watson et al. (2006). Their work indicates the rutile thermometer is not affected by pressure.

4470 120 T(°C)rutile   273.15 (3) (7.36  0.1)  log( Zr)

Methodology

Oriented microprobe sections of selected samples were carbon coated (to a thickness of 200 Å) in preparation for thermometry analyses at Rensselaer Polytechnic

Institute‟s electron microprobe laboratory. Although analyses of Ti and Zr contents in these common minerals may be carried out on any instrument of sufficient sensitivity to detect concentrations at the ppm level, the EMP at Rensselaer was the same instrument used to construct the trace-element thermometers used in this work. Grains were chosen from backscattered electron (BSE) and cathodoluminscence (CL) images taken with a scanning electron microscope (SEM) on a Cameca SX100 and an attached Gatan‟s monoCL3 spectrometer and photomultiplier. Prior to wavelength dispersive spectroscopy the Cameca SX 100 electron microprobe was standardized using

Smithsonian, Stony Brook, and RPI quartz, zircon, titantite, and rutile crystals with known Ti or Zr concentrations. Analyses were conducted with a 15 kV accelerating potential and beam current of 200 nA. Counting procedures, quantification, and analysis techniques followed those within Watson et al. (2006), Wark and Watson (2006) and

Thomas et al. (2010).

A range of quartz grain sizes were selected for spot or transect measurements, using CL and BSE images. Concentrations of Ti-in-quartz were measured for 15 min per spot and Ti-in-zircon concentrations were measured for 30 min per spot. Before temperatures were calculated, I assessed each analysis point in terms of measurable Ti elemental weight fraction and total weight % detected by the electron microprobe; based on the Ti lower limit of detection (7 ppm) and the standard deviation of the weight

fraction (6 ppm), both assessed from the counting statistics of the SX100. Ti concentrations less than 13 ppm were not included in the final dataset. With the presence

of rutile in the samples a titanium activity of 1(aTi O2 = 1) and the appropriate pressure was entered into Equation 1, yielding a quartz crystallization temperature. For the crystallization temperature of zircon the Ti-in-zircon equation was utilized from Watson et al. (2006) (Eq. 2); with a Ti lower limit detection of 6 ppm and 5 ppm for the standard deviation of the weight fraction equating to an acceptable Ti value greater than 11 ppm.

An attempt was made to measure the Zr concentrations in rutile and titanite/sphene but low Zr concentrations did not provide fruitful results; all analyses fell below the detection limits.

Watson et al. (2006) discuss the influence of pressure on Zr-in-rutile; these same authors have made adjustments in the Ti-in-quartz calculations to include the effects of pressure (Eq. 1). In a study area where the pressure of a terrane is well documented, the pressure should be factored into the equation for a more accurate determination of the crystallization temperatures. In the Western Tatra Mountains, the mica schists of the lower unit reached pressures of 5-7 kbar within the staurolite-kyanite and kyanite to sillimanite metamorphic zones, whereas high-T migmatization occurred at pressures of

12 kbar (kyanite) and at 6 kbar (sillimanite) during decompression melting associated with the granite intrusion into the upper unit (Table 1; Janak, 1994).

Tectonic Unit Metamorphic zone P (kbar) ± stdev T (°C) ± stdev Lower unit staurolite-kyanite 5.7 ± 0.9 571 ± 17 Lower unit kyanite-fibrolite 6.7 ± 0.8 638 ± 20

Upper unit kyanite 12.0 ± 2.2 754 ± 68 Upper unit sillimanite 5.0 ± 0.6 706 ± 68 Table 1: Pressures and temperatures in metamorphic zones within the lower and upper unit of the Western Tatra Mountains. Values were calculated using thermobarometers and estimates from metamorphic mineral compositions. These pressures were used for correction TitaniQ calculations (modified from Janak, 1994).

Originally 12 kbar was believed to be the appropriate pressure for migmatite (ZT-

18) genesis, based on geothermobarometry from the same collection of samples

(Moussalam, 2010). A second-look revealed that kyanite did not appear to be present in the migmatite (ZT-18) thin section but rather prismatic sillimanite. This indicates the migmatite sample, from the upper unit in the eastern portion of the Western Tatras, coincides with previous P-T work, which places the sillimanite zone to the east with a pressure of 6 kbars (Fig. 1; Table 1) (Janak et al., 1999). Therefore, results reported in the following tables for the upper and lower tectonic units are corrected to a pressure of 6 kbars.

Titanium-in-Quartz Results

A total of 99 spots on four samples were analyzed for TitaniQ. Of the 99 spots,

60 points contained minimum acceptable Ti values (≥13 ppm) (Appendix 2). Average and range temperatures from each lithology are reported in Table 2, with the values obtained prior to pressure calculations; pressure corrected values lowered temperatures

Sample Lithology Original P Corrected ± error T ºC T ºC ºC Lower Unit ZT14-08 Schist Avg 603 541 33 ZT14-08 Schist Range 550-688 494-613 19-53 Upper Unit ZT18-08 Migmatite Avg 598 536 35 ZT18-08 Migmatite Range 556-742 499-659 20-50 ZT5-09 Granite Avg 612 547 31 ZT5-09 Granite Range 548-650 491-580 26-55 Table 2: Summary of TitaniQ thermometry results for three different

samples and lithologies from the upper and lower units. Pressure corrected temperatures are based on pressure estimates in Table 1; 6 kbars was used for

all corrected data.

~ 50-80 °C from the original TitaniQ data. The quartz thermometry in the schist ranged from 495-615 °C; the upper unit migmatite varied from 500 – 660 °C and the granite provided temperatures of 490-580 °C. These ranges and the complete dataset (Appendix

2) give a sense of the fairly narrow differences (~ 90-160 °C) within a sample. Two temperatures from the mica schist were excluded because their probe points were too close to the quartz grain boundary (< 5 μm), posing a risk of sampling elemental concentrations from bordering minerals and explaining their anomalously high titanium concentrations.

All of the quartz thermometry data summarized in Table 2 are plotted in Figure

17. The upper unit temperature with the highest measured frequency is around 540 °C with a recurrent temperature of 520 °C in the lower unit. The spread of the data in both units appears to be very homogenous to one another ranging from 500 °C to approximately 620 °C.

Figure 17: Histograms of the pressure corrected titanium-in-quartz thermometry data from the upper and lower units.

Pressure corrected temperatures are marked on the photomicrographs (Fig. 18) based on the x and y coordinates of the probe points and through visual inspection of the

BSE images taken at the microprobe lab. The photomicrographs display the highly recrystallized nature of the samples, as observed throughout the Tatric unit (Fig. 18).

Most of the data was collected in transects in hopes to attain a range of temperatures from in a single grain with different episodes of recrystallization. Note the quartz in migmatite sample ZT-18 (Fig. 18) exhibits a steady increase in temperatures towards the center of the quartz grain, a similar occurrence was also observed in the mica schist. Sample ZT-

24 exhibited the highest degree of recrystallization and grain size reduction.

Sample ZT-24 was analyzed for Ti but none of the points in this sample produced Ti concentrations high enough to be accepted (see sample ZT-24 in Appendix 2).

Mica Schist (ZT-14-08)

Polarized Photomicrograph BSE Image Migmatite (ZT-18-08)

Polarized Photomicrograph BSE Image Granite (ZT-5-09) Mica Schist (ZT-24-08)

Figure 18: Images of the mica schist, migmatite, and granite samples measured for titanium- in-quartz with the temperature associated with each point. The migmatite transect is an example of the increase in temperature measured with increasing distance from the rim to the core of the quartz. Mica schist sample ZT-24 lacked titanium concentrations sufficient for TitaniQ calculations, suggesting that recrystallization occurred at lower temperatures within this rock. Note the highly recrystallized nature and reduction in grain size surrounding the vertical quartz grain.

Titanium-in-Zircon Results

A limited number of zircons were present in the Tatric samples; six of the seven measured grains produced acceptable Ti concentrations to calculate temperatures. As anticipated the Ti-in-zircon temperatures are higher than the Ti-in-quartz (Table 3). Ti- in-zircon analysis was taken to be reasonably accurate based on comparable temperatures between the two points measured from single grains in ZT-14, as well as the T conditions previously estimated for the upper unit (Table 1).

Sample Lithology T ± error ºC ºC Lower Unit ZT14-08-F Schist 826 36

ZT14-08-F Schist 821 38 ZT14-08-G Schist 915 27 ZT14-08-G Schist 923 27 ZT14-08-H Schist 873 30 ZT14-08-H Schist 891 29 Upper Unit ZT18-08 Migmatite 834 35 ZT18-08 Migmatite 811 39 ZT18-08 Migmatite 978 25 ZT5-09 Granite 801 42 Table 3: Titanium in zircon temperatures from the same samples measured for titanium in quartz. Zircons F, G, and H from the mica schist were large enough for two spot analyses; the similarity in results indicates the accuracy of the thermometer.

The zircons from the mica schists are rounded and fractured, varying in length from 50 – 100 μm (Fig. 19). In general, the three zircons from the lower unit (ZT-14) had consistent temperatures per grain, with individual temperatures of approximately 825 °C,

880 °C, and 920 °C. Based on the appearance and different temperatures between zircons F, G, and H, meaning possibly different magmatic sources, these zircons are most likely from detitral sources, indicating protolith temperatures to the sedimentary rocks superseded by tectonism to form the mica schists. Because of the protolith origin, a pressure effect was not added to the temperatures of the lower unit zircons, as well as the limited research related to the influence of pressure on titanium-in-zircon.

The pristine zircons in the migmatite and granite of the upper unit are euhedral and zoned, but too small to successfully measure core and rim temperatures (Fig. 20). In the CL image A containing three zircons, the top-most zircon was the only grain whose

Ti values fell below the acceptable limit, but adjacent zircons provided temperatures of

810 °C, 830 °C, and 980 °C (Table 3). Only one sizable zircon was found in the granite, with titanium concentrations producing a temperature of 800 °C. Unlike the detrital zircons of the lower unit mica schists, this temperature may record peak thermal conditions of the upper unit during Variscan tectonic events.

G H

Figure 19: BSE images of zircons F, G, and H from sample ZT-14-08. These rounded and fractured zircons appear to be detrital.

20 μm

Figure 20: Pristine zircons from the upper unit, possibly a record of peak thermal conditions during Variscan orogenesis: A) CL image of zoned zircons from the migmatite, and B) BSE images of the granitic zircon.

Implications

Generalizing the TitaniQ temperatures from the mica schist and the migmatite allows for a comparison to temperatures calculated based on metamorphic mineral assemblages by Janak (1994) (Table 1). Peak metamorphic temperatures for the lower unit schists are on the order of 600 °C, whereas peak temperatures for the higher grade upper unit are 700-750 °C (Janak, 1994). In contrast, quartz temperatures for both upper and lower units are remarkably uniform at ~ 540 °C (Fig. 17). Therefore, the previously suggested temperatures may be interpreted as peak metamorphism and the pressure corrected TitaniQ temperatures reported herein are associated with subsequent

(re)crystallization in the lower and upper units. This is further supported by low Zr concentrations in rutile and titanite/sphene, indicating recrystallization at lower temperatures. There were two quartz grains which measured higher temperatures that decrease towards the grain boundary (Fig. 18). This preservation of a spread of temperatures, measured in both the migmatite and the mica schist, is consistent with recrystallization during rapid exhumation of the upper and lower unit.

A majority of the unacceptable points came from sample ZT-24 (Fig. 18), which did not provide any spots with acceptable Ti concentrations; this likely indicates that concentrations were below the detectable limits of the electron microprobe because dynamic recrystallization of this sample occurred at lower temperatures. Future work with an ion microprobe would determine whether such finely recrystallized samples contain low Ti concentrations hence lower temperatures.

I interpret the zircons measured in the mica schist to be detrital, therefore these temperatures are not associated with the P-T events in this study. Furthermore, zircon grains from the upper unit appear to be magmatic and not reworked suggesting they formed during high P-T Variscan conditions and preserve temperatures that for the most part were not retained by the quartz during lower P-T events.

Application of TitaniQ on coarsely recrystallized quartz from different lithologies of both upper and lower units reveal a consistent average temperature of 540-545 °C.

These data indicate that metamorphic recrystallization of quartz continued well after peak metamorphic temperatures were reached. Minimum temperature values of 490 °C likely represent the analytical detection limit. Peak temperature values differ according to peak metamorphic grade. For instance, the migmatite records a maximum value of 660 °C whereas the schist records a maximum value of only 610 °C.

4. EMPA Monazite Geochronology

Monazite is a REE phosphate mineral used for geochronology because of its low diffusivity, (hence high retentivity) and relative abundance in igneous and metamorphic rocks. Chemical analysis on deformed monazite is complimentary to a fabric analysis, as the simultaneous dating and mapping allows for examination of metamorphic and deformation age domains. Distinct chemical domains within monazite may reflect multiple periods of growth during polyphase deformation. This technique is particularly valuable for analyzing the tectonic history of metamorphic rocks subjected to multiple periods of deformation (i.e. Tatra tectonites), especially high temperature events, as monazite remains a closed system during high grade resetting and secondary monazite growth. High resolution measurements are needed for analysis of elemental concentrations within each growth domain. To achieve such high resolution, analysis is often conducted using an electron microprobe (Williams et al., 1999; Williams &

Jercinovic, 2002).

Previous dating in the Western Tatra Mountains has provided ages used to parse out tectonic events and develop P-T-t diagrams (Fig. 4). The purpose of collecting a set of ages in this study, is to better constrain the timing of deformation and metamorphism of the lower unit. In an attempt to determine absolute timing of deformation along the thrust zone, I performed electron microbe chemical dating of monazite from variably mylonitized mica schists. 46

Methodology

Four of the deformed mica schists were analyzed to determine the timing of monazite growth. The samples used for monazite geochronology were taken from the lower unit, close to the contact with the upper unit, and within the zone of Variscan shearing. Mica schists were selected with the strongest deformation fabrics, described in the optical petrography chapter, with the least alterations and an abundance of micaceous minerals (Fig. 21).

Figure 21: Example of the mica schist

Mica deformation texture in sample ZT-4, as viewed through BSE image (top), with the metamorphic overprint Mica Monazite surrounding the grain. The monazite in the center of the top image is featured in the lower BSE image. The monazite image was taken following trace analysis, and the calculated ages (Md) are shown on their analytical 324 pits.

344

300

316

383

Image analyses shows that the samples have undergone metamorphic overprint.

In Figure 11 the corona-like appearance of the monazite grain may be attributed to retrogression or a later metamorphic event. A closer look at the BSE images of the monazite grains (Fig. 21; Fig. 22, Fig. 23) displays their cuspate edges.

Electron microprobe work was done on the Cameca SX 100 at New Mexico

Institute of Mining and Technology with Dr. Nelia Dunbar and Lynn Heizler. The samples were made into probe sections and then carbon coated (simultaneously with the standard) to create a conductive surface for the electron beam. Both the major and trace elemental analyses were run with a 200 nA beam current. Large scale elemental maps were made of Ce, Y, and Fe to determine if the samples contained monazite. After locating sizable monazites, BSE images were taken of the monazites and Th, Y, and U maps were created of each of the selected grains. These elemental maps (Fig. 22; Fig.

23) were utilized in selecting areas to conduct major elemental analyses, as differing degrees of brightness on the Th maps suggests high versus low elemental concentrations and potential growth domains; separate chemical domains are important to measure as they may result from different periods of monazite growth and may therefore be important for distinguishing between multiple tectonic events (Williams & Jercinovic,

2002).

464

377 358 487

454

479

307 302

400 352

407 310 359

330

Figure 22: Monazite grains of sample ZT-24-08 with embayed edges. Thorium maps (left) with brighter zones represent higher concentrations and corresponding post- analysis BSE images (right) with calculated ages (Md).

383 555

480

479

616

401 403 425 405

407

Figure 23: Monazite grains of sample ZT-14-08 (top) and ZT-15-08 (bottom) as examples of grains with rejected ages, due to sampling from more than one comp ositional domain. Thorium maps (left) and corresponding post-analysis BSE images (right) with calculated ages (Md).

The monazites analyzed are typically 40 μm x 20 μm, large enough for selecting multiple probe points; two to ten spots per grain were measured for Th, Y, Pb, and U

(amongst other elements). Spot analysis for major elements was done on each grain.

Probe points were chosen using the Th maps to measure different chemical domains, and

BSE images were used to avoid grain edges, fractures, and holes to minimize trace element mass transfer. Next, background scans were run, as recommended by Jercinovic and Williams (2005), to eliminate background concentrations and ensure the measurement of only trace concentrations. To determine the appropriate background levels for Th, Y, Pb, and U the data were processed in BKGII (BackgroundII), a program developed by Mike Jercinovic that performs a regression analysis to determine background concentrations.

Many trace element analysis points were chosen close to the points where major element data were collected and used to calculate the background concentrations.

Picking trace points close to the majors ensures trace concentrations were collected for

Th, U, Pb, and Y using the appropriate procedural calibrations for the different chemical domains. These trace concentrations were entered into the age dating equation. Before ages were accepted in the final dataset the trace element analysis points, seen in the final

BSE images, were compared to the trace concentrations and ages to eliminate any disputable data. Five data points were rejected either due to their proximity to fractures or holes in the monazite, or due to their questionable elemental concentrations in comparison to nearby data points. The questionable concentrations may have resulted from the sampling of two different chemical domains at their boundaries (Fig. 23).

Results

Four samples were analyzed with four to eight grains per sample resulting in a total data collection of 100+ ages (Appendix 3). The final dataset shows 1 sigma errors of ± 15 Ma. Although the monazites did not produce results with visible neoblastic domains, suggestive of monazite growth during proceeding deformation events, plotting the data from each sample generates age peaks corresponding to known tectonic events in the Western Tatra Mountains (Fig. 24). Collectively, the four samples produced three dominant age peaks at c. 480 Ma, c. 420 Ma, c. 370 Ma, and a subordinate age peak c.

315 Ma.

Lower Unit Monazite Geochronology Caledonian/Early Variscan ZT-15

Early Variscan Protolith ZT-4 ZT-14

ZT-24

Relative probability Relative Late Variscan

250 300 350 400 450 500 550 600 650 700 Total-Pb Age (Ma) Figure 24: Relative probability plot for the Total-Pb ages of monazite analyses from mica schists of the lower unit (ZT-4, ZT-14, ZT-15, and ZT-24). Peaks are labeled with corresponding tectonic events for the Tatra Mountains, as discussed in this chapter.

Implications

The total-Pb age data displayed in Figure 24 are interpreted here in light of previous knowledge of documented tectonic events in the region, and with consideration of new monazite geochronology (Moussallam, 2010) recently obtained from the upper unit of the inverted metamorphic sequence. Total-Pb age clusters around 420 Ma, 370

Ma, and 315 Ma (Fig. 24) are similar to total-Pb age data reported by Janak et al. (2004) in a pilot study of three samples from the upper and lower units

Monazites from sample ZT-14 reveal a strong age population c. 480 Ma, with similar but smaller age population obtained from samples ZT-4 and ZT-24. Linking the

U-Pb ages that result in two age population from samples ZT-4 and ZT-24 to their spot analyses does not reveal two distinct age domains in a single grain. The top monazite grain from sample ZT-24 in Figure 22 was the only analysis where the interior of the grain measured an older, c. 480 age, and the exterior of the grain measured a younger, c.

370 age. The rest of the total-Pb ages from samples ZT-4 and ZT-24 represent a homogenous age population or contain multiple peak ages in no clear domains. Based on the roundness of the grains and previous geochronology, the peaks at c. 480 Ma mirror protolith ages (detrital monazite) similar to some detrital zircons in the lower unit measured by Kohut et al. (2008), which produced 2.0 - 1.8 Ga, 491 +/- 11 Ma, and 495

+/- 4 Ma detrital zircon ages. The 480 - 500 Ma U-Pb ages are interpreted to be either the youngest igneous protolith of the lower unit or to reflect the age of the latest sedimentation (Kohut et al., 2008).

Mica schist sample ZT-15, from the eastern portion of the study area, yielded a single age population of c. 420 Ma. This is inferred to be a record of the Late Silurian to

Early Devonian subduction to the NW, and debated whether associated with Caledonian or Early Variscan tectonics (Buchart, 1968; Poller et al., 2000). The U-Pb zircon analyses by Poller et al. (2000) resulted in an age of 405 Ma, similar to the 420 Ma total-

Pb age, from the granitic protolith of the orthogneisses of the upper unit, suggesting an intrusion age associated with Late Silurian to Early Devonian subduction.

Evidence for early Variscan metamorphism at c. 370 Ma is represented by dominant age peaks for samples ZT-4 and ZT-24, and a subordinate overprinting in ZT-

14. This c. 370 Ma coincides with what has been previously determined as the onset of the Varsican continental collision, as determined by U-Pb zircon ages of c. 365 Ma exhibiting zircon growth during peak metamorphic conditions of early Variscan crustal thickening and partial melting (Poller et al., 2000). Also, a recent U-Pb monazite age of

380 Ma from a migmatite of the upper unit further supports a period of intense Mid-

Devonian metamorphism (Moussallam, 2010).

Surprisingly, there is no evidence in the EMPA geochronologic data for middle

Variscan (340 Ma) metamorphism so prevalent in the high-grade upper unit rocks.

Instead, a weak metamorphic overprinting at c. 315 Ma is evident in two samples and coincides with the end of the widespread Carboniferous magmatism in the High Tatras.

Additionally, Ar/Ar mineral analyses of granitoid and metamorphic rocks in the High

Tatras record cooling and uplift from 330-300 Ma (Janak et al., 2001).

5. Electron Backscatter Diffraction (EBSD) of Quartz

A focus of this research is to characterize the tectonic fabric recorded in the crystalline basement complex to provide greater insight into the extent, style and nature associated with formation of the inverted metamorphic sequence. This study utilizes the advancements in EBSD and its ability to produce a large dataset in a short period of time.

EBSD is a powerful method that has several applications to crystallographic work and that allows for the measurement of crystallographic characteristics of individual rock- forming minerals ≥ 1μm. Deformational textures are measured through EBSD, which is performed using a scanning electron microscope (SEM) whose electron beam supplies a source of scattered electrons within a sample. Scattered electrons are diffracted off the lattice planes of the target grain to form a diffraction pattern that is imaged on a phosphor screen.

I applied EBSD to obtain crystallographic preferred orientation (CPO) data on ductiley deformed quartz in the Tatra Mountains. In relating the CPO to a samples‟ kinematic reference frame (foliation, lineation, and shear sense) one can interpret a relationship between the dominant CPO and the geographic kinematics for a region (Prior et al., 1999). Recent microstructural studies from the adjacent Veporic unit in the

Carpathians (Jerabek et al., 2007) and highly sheared rocks along the young Alpine fault,

New Zealand (Toy et al., 2008) indicates the power and potential of EBSD. These 55

studies demonstrate the capabilities of EBSD to provide evidence of shear zone evolution, in a measurable direction of motion, with varying quartz slip systems and temperatures. Such measurements allow for analysis of small-scale (quartz deformation) and large-scale (tectonic) processes in ancient systems/terranes.

Methodology

Seven mica schist samples displaying a strong lineation and one lesser deformed migmatite sample, all abundant in quartz, were chosen for quantitative EBSD analysis.

Microprobe sections were prepared parallel to lineation and perpendicular to foliation to ensure stereographic projections of the CPO data reflect the kinematics. The geographic orientation of lineation was based on field measurements. Similar to optical analysis, lineations undeterminable in the field were assigned a NW-SE plane (ZT-6, ZT-14, ZT-

18).

EBSD analysis of the fabrics was conducted on an SEM at the College of Science and Engineering, University of Minnesota, Minneapolis. The thin sections were polished using colloidal silica for about an hour to remove the damaged surface from previous polishing and then carbon coated. The SEM (JOEL 6500F) has a NordlysS Detector camera system attached for making EBSD measurements that were indexed using the

Oxford Channel 5 software; specifically the HKL Flamenco for acquisition, Mambo for pole figures, and Tango for the crystal orientation maps. The step size varied from 3 – 25

μm, based on the grain size and amount of quartz in each sample. Samples were tilted at

70° with a 20 kV accelerating voltage, beam current of 50 nA, and a working distance of

25 mm.

With a range in size of quartz grains (Figs. 25 & 26) a smaller step size was needed to measure the fine grained quartz. This resulted in the coarser grains being sampled multiple times. Therefore with a greater number of data points collected on the larger grains, they had a stronger presence on the pole diagrams. For a more equal representation of the CPO for each grain, the features of Tango maps were utilized to reduce the noise of the data. For example, in the initial orientation map for ZT24 (Fig

25A) the grains are not as distinguished as Figure 25B; Figure 25B is a product of interpolating the point data to fill in each grain. This step reduces the data to one point per grain, which is plotted on a pole diagram.

A. B

eft, eft,

for of and purpose the

s distinguishes quartz grains grains quartz distinguishes

the the interpolation

orientation different t grain

in map map in

he original map with a large quartz ribbon on ribbon quartz with map original l the he large a

24. Colors 24. represen -

grains. istinguishseparate

ZT orientation Crystal for maps

Figure 25 Figure d colors thiscomparison finer whereas quartz, of indistinct by boundaries surrounded the of and reduction equaldata grains. representation for

Figure 26: Crystal orientation maps for ZT-15 with gray areas being non-quartz grains. A) The original map for ZT-15a. The coarse (orange-pink) quartz was predominantly basal < a > slip with the fine (blue-green) quartz representing the prism < c > slip. B) The interpolated map for ZT-15b (see pole diagrams).

Once the stereonets of the quartz CPO data were plotted the patterns could be analyzed to determine the type of strain and dominant slip system. With coaxial deformation, most often patterns are small circle girdles. In the case of plane strain a

Type I cross girdle develops, which has a central girdle to connect the smaller girdes

(Fig. 27). Type II cross girdles develop during constrictional strain, with a CPO pattern reflecting the letter X (Passchier & Trouw, 1996). With non-coaxial or simple shearing patterns have an asymmetrical appearance, as compared in Figure 28.

Figure 28 also depicts the different slip systems that occur along the a-axes and c- axes, with either pure shear or simple shear. The axial plane or slip plane on which the dislocation occurs is dependent on orientation, the degree of stress, and temperature conditions surrounding the crystal. Additionally, Figure 29 illustrates the slip systems that result from low to high temperatures during shearing. For these reasons, dependence of the dominant slip system lies in the metamorphic and deformational conditions

(Passchier & Trouw, 1996). Application of the quartz slip systems to CPO results will allow for inferences in regards to temperature and strain conditions.

Results

The data collection for each analysis was reduced before the final construction of stereonet plots. Note the point data in the pole diagrams for ZT-15a&b and ZT-25 (Fig.

30). These pole diagrams are examples of the number of points collected before data reduction. In these cases the data reduction did not change the contour plots so the original point data was an equal representation of each grain.

Plane

Constrictional

Flattening

Figure 27: Example of Flinn diagram containing the CPO and girdle patterns with their associated strain (constrictional, plane, and flattening). Girdle type I and II are depicted as point, skeletal, and contour plots with c-axes and a-axes (from Twiss & Moores, 1992).

A. Pure Shear

B. Simple Shear

Figure 28: Diagrams of the quartz slip systems seen with pure shear (A) and simple shear (B). Girdle patterns result from the associated schematic of quartz crystals with labeled < a > -axes and basal, rhomb, or prism slip planes. Slip in the direction of the c-axis is shown in the bottom right (from Passchier & Trouw, 1996).

Figure 29: Pole diagrams showing the difference in quartz c-axes (solid) and a-axes (striped) with increasing temperature during deformation. Most of the Tatra samples fall under the low T category, with high T being the c-prism slip of ZT-15a (from Passchier & Trouw, 1996).

There is no consistent slip system for the deformed quartz analyzed in this study; the CPO shows basal < a > (ZT-15a), basal to rhomb < a > (ZT-15b, ZT-15a&b, ZT-24), basal to prism < a > (ZT-14), prism < a > (ZT-6), or prism < c > (ZT-15a) (Fig. 20).

Samples ZT-4, ZT-16A, and ZT-18 did not have a CPO or had a CPO that was questionable to fit to a slip system. Sample ZT-15 was analyzed twice due to the presence of both basal < a > and prism < c >. These two slip systems correspond to a specific grain size (Fig. 26). The map of ZT-15a displays two grain sizes with the coarser grains ( ≥ 500 μm) having basal < a > slip and the finer quartz with prism < c > slip. The second area measured for EBSD on section ZT-15(b) did not have prism < c > slip, but rather more basal to rhomb < a >. The map for measurement ZT-15b (Fig. 26B) also displays coarser and finer quartz, with grains at least twice the size (≥ 1000 μm) of those in ZT-15a and material as fine as in measurement ZT-15a. A stereograph combining these two datasets displays the basal to rhomb < a > slip as the predominant slip system for ZT-15.

The CPO patterns of the deformed mica schists display both single and cross girdles (Fig. 30). Five of the samples have cross girdles with only one being a type II girdle and four others of type I; one of the samples is a single girdle. The asymmetrical girdle for ZT-6 records sinistral movement, top-to-the NW. Three of the asymmetrical cross girdles indicate a dextral sense of motion and one sinistral, within the E-W geographic plane. This suggests a more dominant top-to-the east kinematics from samples spaced throughout the study area. In deciphering the type of strain in these samples, there is constrictional, plane, and flattening strain. With a majority of the

samples being cross girdles most of the strain is plane, and a limited number of the samples exhibit constrictional or flattening strain.

Implications

The results of the EBSD analysis on the tectonites did not produce the strong pole figures anticipated from optical work, especially the absence of a CPO in the ultramylonite (ZT-16A). This fabric analysis does show the strain recorded by the Tatra metamorphic rocks, but it is possible that the CPO was weakened during a later phase of recrystallization. Verification of internal deformation was made with the large grain at the bottom of the sampled area for ZT-15a (Fig. 26A), which had a misorientation angle consistently ~ 30° across the grain (~ 500 μm), suggesting dynamic recrystallization in the form of subgrain rotation and a large amount of internal deformation. Half of the samples measured recorded plain strain. This is the type of strain expected within the deformation zone surrounding the thrust fault. Beyond recognition of crystallographic deformation, the CPO data and resulting EBSD patterns may suggest certain temperatures and kinematics.

Crystallographic slip systems can be used to infer the temperature conditions during deformation. Since most of the samples have a-axes slip systems, this suggests deformation at temperatures < 650° C. Deformation along the c-axis (ZT-15a) is less common and suggests the presence of higher temperatures (> 650° C) (Fig. 30).

ism

the NW the

08 08

- -

/330 to

/330

4 14

- -

15/080 -

255, 71 S 71 255, NE 42 128, NE 19 318,

- - -

- – -

- - -

ZT S L ZT slip > Prisma < Cross Girdle I Type Strain Plane S L Top ZT to Pr Basal slip > a < Cross I Type Girdle Strain Plane S L

the E the W the E the

- - -

to to to

15a 15b 15a&b

45/100 - 45/100 - 45/100 -

075, 57 SE 57 075, SE 57 075, SE 57 075,

- - -

– – –

- - -

Basal < a > > a < Basal slip > Prismc < SingleGirdle S L Top ZT to Rhomb Basal slip > a < Cross I Type Girdle Strain Plane S L Top ZT to Rhomb Basal slip > a < Cross I Type Girdle Strain Plane S L Top ZT

the E the

08 08

- -

/330 to

16A 18 24

26/090 - 31/082 -

004, 3 004,

276, 84 NW 84 276, E 37 025,

- - -

– – –

- - –

S S L ZT S L ZT to Rhomb Basal slip > a < Cross II Type Girdle Constrictional Strain S L Top ZT

(right) quartz the of

axes pole diagrams diagrams axespole -

(middle) c with axes -

axes (left) and (left) and a axes

c Contourplots the of

: :

axes plots. axes contour

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Flattening

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Figure 30 Figure strain sample‟s slip lithologies. samples and type, system, Each girdle different two and CPOdifferent eight in to reported is sense reported Shear are shearing, left. the where of applicable, direction and orientations with abov

Basal < a > slip > a < Basal Cross Girdle I Type Plane Strain S L Top ZT

Additionally, the girdle patterns of the CPO data either compliment the higher and lower temperatures or they support an increase in strain rate as well as temperatures. The samples with a cross girdles suggest formation under lower temperatures than a single girdle pattern and lower strain rates (Passchier & Trouw, 1996). The cross girdle patterns, seen in all of the samples except ZT-15a, point towards formation under medium to lower temperatures. Tying the slip system and girdle pattern results together, all of the cross girdle patterns have slip systems (basal to rhomb < a > slip) indicating medium to lower temperatures. Also, ZT-15a is the only sample with a single girdle, as well as the only high temperature and/or high strain rate prism < c > slip. Therefore, the difference in girdle type coincides with the temperatures inferred from the quartz slip systems. Furthermore, the variance in CPO patterns may suggest deformation under different temperatures and strain rates.

Previous petrologic analyses found top-to-the east shearing (D2), which overprinted the initial Variscan thrust fabric to the SE (Janak, 1994); D2 developed at lower temperatures and shallower levels of the upper unit and along the pluton margins

(Fritz et al., 1992; Janak et al., 1999). The D2 fabric is a result of E-W Variscan extension; the lack of Variscan normal faults is attributed to denudation or Alpine reactivation (Janak et al., 1999). Here, field measurements on these lower unit mica schists were made within the fault zone with lineations trending in the E-W plane. EBSD analysis indicates a dextral, top-to-the east, shearing within the lineation fabric. This extends the previous observations of E-W Variscan extension (D2) being limited to the upper unit, and defined by the biotite and sillimanite (Janak et al., 2001). Fabric analyses

indicate D2 is present in both the upper and lower units, as indicated by quartz CPOs to the east.

Alpine thrusting during the collision of Africa into Europe has been previously noted as a top-to-the NW sense of motion in the Western Tatra Mountains. The same top-to-the NW kinematics is seen in ZT-6, greater support for the resetting of the fabric to record this later kinematic event is ZT-6‟s proximity to the Alpine fault along the southern border of the Western Tatras (Fig. 5). Therefore, I support Alpine faulting as occurring at higher temperatures, from what was originally thought to be mainly brittle deformation.

6. Summary and Discussion

This integrative study has focused on assessing temperatures, textures, and timing of the deformed metamorphic and igneous rocks exposed in the Western Tatra Mountains of Slovakia. The results provide a test of models of formation for an inverted metamorphic sequence and yield quantitative information on mid-crustal tectonic processes. The thermometric, microstructural, and geochronologic results obtained on nine targeted samples from the Tatra upper and lower units are summarized in Table 4.

Summary

Thirty-two samples were characterized petrographically and subdivided texturally based on degree of grain size reduction as a proxy for strain. A suite of nine samples were selected (based on varying degrees of deformation) for further quantitative analyses.

Deformed mica schists, migmatites, and granite samples are dominantly protomylonitic to mylonitic. A strong E-W lineation defined by ribbon quartz, aligned micas, and distinct microstructures are most common. Quartz deformation textures indicate moderately high temperatures and/or lower strain rates of regimes 2-3 from both the upper and lower units.

(Re)crystallization temperatures were obtained using titanium concentrations in quartz from a mica schist, migmatite, and granite. Lithologies yield a range of 71

Timing

Temperatures

nalyses. From left to right: kinematic indicators from from indicators to right: From kinematic left nalyses.

Textures

temperature, and timing texture, the a Summaryof

Table 4: Table4: lastly geochronology. and by titanium then followed monazite the thermometry work EBSD optical analyses,

temperatures from 500 °C (detection limit) up to 650 °C. Strikingly, these medium to high grade metamorphic and igneous rocks produced uniform average temperatures around 540 ± 30 °C. The mica schist and migmatite preserve higher relict temperatures from select microprobe transects. Very low Ti concentrations (below detection limits) from a mylonitic mica schist sample suggest ductile deformation below 500 °C. In addition, titanium-in-zircon analyses yielded magmatic temperatures of ~ 800 – 900 °C in the granite and migmatite samples.

EMPA monazite geochronology on four variably deformed mica schists resulted in three major age populations at c. 480 Ma, 420 Ma, 370 Ma, and a minor age population c. 315 Ma. The weathered appearance of the monazite grains suggests the 480

Ma ages were obtained from detrital monazite grains. The c. 420 Ma age population was obtained solely from a single protomylonitic mica schist sample that did not yield any other age domains. Ages of c. 480 Ma and c. 370 Ma were obtained from three samples, two of which yielded minor age populations of c. 315 Ma.

Lastly, samples with thermometry and geochronology data were chosen for fabric analyses. The quartz CPOs analyzed via EBSD varied from a basal to prism < a > slip system with a subordinate prism < c > slip. The higher frequency of quartz a-axes slip systems indicates deformational temperatures below 650° C. Asymmetrical CPO girdle patterns in the mica schists suggest primarily plane strain with a top-to-the east shear sense and a less frequent top-to-the northwest shearing that was scarcely noted in optical analyses. Such variations in shear sense reflect the complex polyphase deformational and metamorphic history of the Tatras.

Discussion

Medium grade rocks of the lower unit, exposed in the lower reaches of the

Western Tatra Mountains, lie beneath Variscan high grade metamorphic rocks and granites. Much geologic research in the Western Tatras has focused on the high grade and better exposed upper unit; less attention has been given to the seemingly monotonous kilometer thick package of mica schists making up the lower unit. However, detailed study of the mica schists show that they are heterogeneously deformed, polymetamorphosed, and preserve a variety of microtextures that reveal important new information regarding the geodynamic evolution responsible for formation of the inverted metamorphic sequence (Poller et al. 2000).

Direct evidence of Early Silurian metamorphism coincident with generation of the strongly deformed older granites (ca. 405 Ma, Poller et al. 2000) has been difficult to document. The oldest preserved metamorphic ages collected from the high grade upper unit in recent years cluster around 380-360 Ma (Burda, 2007; Burda & Gaweda, 2009;

Moussallam, 2010). The monazite age of c. 420 Ma reported here is problematic in that it was obtained solely from a single mica schist sample that preserves none of the metamorphic ages recorded in the other dated mica schist samples. Interestingly, this sample is also anomalous in that it is the sole sample that produced quartz c-axis slip indicating high temperature deformation (> 650 °C). However, similarly old monazite ages (415-395 Ma) were reported in a pilot study of monazite dating by Janak et al.

(2004) from two separate Western Tatra samples (a migmatite and a mica schist). I interpret the 420 Ma age as geologically meaningful and temporally, but not spatially

associated with the generation of the older granites during Caledonian or Early Variscan collision (Fig. 31A). The subsequent moderate (lower unit) and strong (upper unit) metamorphic overprinting of the Western Tatra rocks is likely responsible for the lack of preservation of Late Silurian/Early Devonian metamorphic ages (Buchart, 1968; Poller et al. 2000).

The dominant metamorphic imprint of the lower unit, as measured in three of the mica schist samples, is c. 370 Ma. This coincides with peak metamorphic conditions and the onset of younger plutonism in the upper unit from 370-350 Ma (Poller et al., 2000;

Kohut et al., 2001; Moussallam, 2010), likely associated with initial collision. The similar peak metamorphic ages from both the upper and lower units suggests the formation of an initial mid to deep „normal‟ metamorphic gradient at c. 370 Ma (Fig.

31B). Not surprisingly, crustal thickening during collision was associated with a second generation of granites in the lower crust (the „younger‟ granites of Poller et al. 2000).

Today, these younger Variscan granites occur throughout the High Tatras to the east and intrude the upper unit rocks just above the Tatra shear zone, but not the lower unit rocks

(Fig. 2).

Variscan magmatism and exhumation of the upper unit rocks are intimately linked as suggested by the occurrence of granites solely within the overthrust unit (Janak et al.,

2001). Rapid deep-crustal overthrusting contributed to continued magmatism (via decompression melting?) and to post-peak metamorphism of the upper unit, but had little effect on the lower unit (Fig. 31C). Initial metamorphic studies of the Western Tatras

Older magmatism 420 – 405 Ma

Metamorphism from subduction related events A )

Lower

Onset of younger 380 – 360 Ma magmatism Upper Metamorphic overprint of older granites B )

Continued younger magmatism (Laurasia?) Upper 340 Ma Exhumation and Lower metamorphic inversion Metamorphism of the upper unit during thrusting C )

Figure 31. Revised progression of Variscan tectonics in the Western Tatra Mountains from the original Poller et al. (2000) geodynamic evolution (Fig. 3). Events A-C are displayed with a key and age of tectonism, with an additional event c. 315 Ma (see Fig. 32). Upper and lower units are defined, with plutonism restricted to the upper unit. Diagrams B to C depict the dynamics associated with the inversion of metamorphics.

interpreted the inverted metamorphism as forming syn-tectonically via the „hot iron‟ model. This model predicts that thrust zone petrofabrics developed at high temperatures and simultaneously with metamorphism of the footwall and hanging wall. The absence of 340 Ma metamorphic ages from the lower unit strongly argues against the „hot iron‟ model for metamorphic inversion. Moreover, the lack of a strong petrofrabric in the direction of the previously determined top-to-the SE thrusting (Fritz et al., 1992; Janak

1994) in the CPO data from the lower unit does not agree with the „hot iron‟ model.

The new footwall monazite age results instead suggest the inversion of a pre- existing „normal‟ metamorphic gradient at 340 Ma during overthrusting of a deep-seated thrust nappe above mid-crustal footwall rocks without downward transfer of heat into the footwall (Fig. 31C). The lack of footwall thermal overprinting during rapid hanging wall exhumation suggests that rapid erosional or extensional unroofing of the upper unit occurred during thrusting with little to no consequent burial of the footwall.

Following metamorphic inversion, both the upper and lower units were weakly metamorphosed at 315 Ma. This moderate metamorphic event coincides with the end of

Variscan younger magmatism at 320-310 Ma and is interpreted to be associated with uplift and collapse of this part of the Variscan orogen. Late Variscan ductile structures, including the E-W oriented lineations, are interpreted to have formed at a high angle to earlier 370-340 Ma convergence (Fig. 32).

Figure 32. Figure 6 enhanced to display the collapse structures developed during orogenic parallel spreading at c. 315 Ma. The lithology of the cross section shows the deformed dominant foliation (kinked lines) and the proceeding fabric developed during orogenic collapse (straight lines). The collapse structures are reported as forming at temperatures of ~ 540 °C or lower (modified from Janak et al., 1999).

The E-W oriented textures (high-angle to orogenic collision) occur in both the

lower unit and the base of the upper unit, consistent with their forming after

migmatization of the upper unit and at moderate temperatures. Specifically, lower unit

quartz CPO data indicate a dominant top-to-the east stretching fabric. Additionally,

thermometry of the same samples suggests the quartz in both the upper and lower units

was recrystallized at temperatures ~ 540 °C, with deformation continuing at lower

temperatures (below 500 °C). With quartz deformation mechanisms largely controlled by

temperature (Hirth & Tullis, 1992), I propose that the quartz CPO data formed at 500 °C

temperatures during orogen subparallel collapse. Considering both the temperatures and

fabrics occurred post-thrusting (340 Ma) it seems reasonable to interpret the E-W

collapse structures to have formed at c. 315 Ma age.

Orogen parallel stretching or lateral escape is commonly associated with continental collisions. Convergence and mid-crustal extension occur simultaneously and are characterized by ductile fabrics. A study of the nearby Veporic unit indicates large scale processes developed fabrics linked to mid-crustal collapse (Jerabek et al., 2007), similar to the Tatric unit and further supporting the inclusion of E-W collapse in the tectonic history of the Western Tatra Mountains.

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Williams, M.L, and Jercinovic, M.J., 2002, Microprobe monazite geochronology: putting absolute time into microstructural analysis: Journal of Structural Geology, v. 24, p. 1013-1028.

Appendices

Site Rock Type Foliation Lineation Qtz Regime Periods of Def'm Shear Top-to-the Accessories ZT1-08 Mica Schist 260, 00 29, 310 None Chlorite ZT2-08 Protomylonitic Mica Schist 2-3 2 Pure ZT3-08 Mica Schist 105, 21 NE 1 3 Pure Sillimanite, chlorite, garnet ZT4-08 Mylonitic Mica Schist 255, 71 S 15, 080 3 2 Pure E Chlorite, garnet ZT5-08 Amphibolite 015, 47 SE 1 1 Pure ZT6-08 Protomylonitic Migmatite 128, 42 NE 3 2 Simple NW & SE ZT7A-08 Protomylonitic Migmatite 2/3 2 Simple ZT8-08 Migmatite 322, 22 S 1 1 Pure Chlorite, zircon ZT9-08 Mylonitic Migmatite 2-3 2 Simple SE Chlorite ZT10-08 Amphibolite 1 1 Pure ZT11-08 Protomylonitic Migmatite 050, 6 NW 2-3 2 Simple W ZT12-08 Protomylonitic Migmatite 030, 6 SE 6, 120 1 1 Pure ZT13-08 Migmatite 033, 58 NW 2 1 None Chlorite, opaques ZT13A-08 Migmatite 038, 53 NW 2-3 None Chlorite, opaques ZT14-08 Mica Schist 318, 19 NE 2-3 3 Simple SE Sillimanite, chlorite, zircon ZT15-08 Protomylonitic Mica Schist 075, 57 SE 45, 100 2-3 2 Simple W Chlorite ZT16-08 Amphibolite 068, 70 SE None ZT16A-08 Ultramylonitic Mica Schist 276, 84 NW 26, 090 3 1 Simple E ZT17-08 Amphibolite 226, 55 SE None ZT18-08 Migmatite 025, 37 E 1 2 Pure Sillimanite(prismatic) ZT19-08 Protomylonitic Migmatite 343, 30 E 2-3 2 Simple SE Garnet, zircon, chlorite ZT20-08 Mica Schist 35, 80-100 2-3 1 Pure ZT21-08 Protomylonitic Mica Schist 35, 80-101 2-3 1 Pure ZT22-08 Protomylonitic Mica Schist 36, 080 3 1 Pure ZT23-08 Protomylonitic Mica Schist N/A, 105 3 1 Simple W Chlorite ZT24-08 Mylonitic Mica Schist 004, 31 E 31, 082 3 1 Simple E Garnet ZT25-08 Mylonitic Mica Schist 7, 096 3 2 Simple W Staurolite ZT26-08 Protomylonitic Mica Schist 335, 29 2-3 1 Simple SW ZT4-09 Mica Schist 2-3 1 Simple N & S ZT5-09 Protomylonitic Granite 2-3 1 None ZT6-09 Migmatite 2-3 1 Simple E ZT7-09 Mica Schist 2-3 1 Simple SW Appendix 1: Table of the thirty-two samples collected from the Western Tatra Mountains with field measurements and corresponding observations and conclusions made from optical work.

Si Ti std* O Total Ti Ti std TitaniQ err+ err- Distance Sample Lithology DataSet/Pt wt.% wt.% wt.% wt.% wt.% ppm ppm ºC ºC ºC (um) Date ZT14-08 Q-M Sch. 1 / 1 . 46.7 0.0015 0.0006 53.2 99.9 15 6 561 37 48 0 1/8/10 5:17 PM ZT14-08 Q-M Sch. 2 / 1 . 46.7 0.0038 0.0006 53.2 99.9 38 6 643 25 26 0 1/8/10 5:32 PM ZT14-08 Q-M Sch. 4 / 1 . 46.5 0.0042 0.0006 53.0 99.6 42 6 654 24 25 0 1/8/10 6:02 PM ZT14-08 Q-M Sch. 5 / 1 . 46.2 0.0054 0.0006 52.7 99.0 54 6 679 22 23 0 1/8/10 6:17 PM ZT14-08 Q-M Sch. 8 / 1 . 46.2 0.0025 0.0006 52.6 98.8 25 6 605 29 33 0 1/8/10 7:02 PM ZT14-08 Q-M Sch. 9 / 1 . 46.7 0.0106 0.0006 53.2 100.0 106 6 - - - 0 1/8/10 7:16 PM ZT14-08 Q-M Sch. 10 / 1 . 46.7 0.0059 0.0006 53.3 100.0 59 6 688 22 22 0 1/8/10 7:31 PM ZT14-08 Q-M Sch. 11 / 1 . 46.8 0.0028 0.0006 53.3 100.2 28 6 616 28 31 0 1/8/10 7:46 PM ZT14-08 Q-M Sch. 12 / 1 . 46.8 0.0039 0.0006 53.3 100.1 39 6 644 25 26 0 1/8/10 8:02 PM ZT14-08 Q-M Sch. 13 / 1 . 47.0 0.0067 0.0006 53.5 100.5 67 6 - - - 0 1/8/10 8:17 PM ZT14-08 Q-M Sch. 14 / 1 . 46.4 0.0052 0.0006 52.9 99.4 52 6 674 23 23 0 1/8/10 8:32 PM ZT14-08 Q-M Sch. 1 / 5 . 46.9 0.0029 0.0006 53.5 100.4 29 6 619 28 30 0.0 1/9/10 6:24 PM ZT14-08 Q-M Sch. 1 / 15 . 46.7 0.0050 0.0006 53.2 100.0 50 6 669 23 23 1794.4 1/9/10 8:53 PM ZT14-08 Q-M Sch. 1 / 19 . 47.0 0.0013 0.0006 53.6 100.6 13 6 550 40 53 2512.1 1/9/10 9:52 PM ZT14-08 Q-M Sch. 1 / 20 . 46.9 0.0019 0.0006 53.4 100.3 19 6 581 33 39 2691.6 1/9/10 10:07 PM ZT14-08 Q-M Sch. 2 / 1 . 47.0 0.0014 0.0006 53.5 100.5 14 6 555 39 50 0.0 1/9/10 10:22 PM ZT14-08 Q-M Sch. 2 / 2 . 47.0 0.0020 0.0006 53.5 100.5 20 6 583 33 39 49.3 1/9/10 10:37 PM ZT14-08 Q-M Sch. 2 / 3 . 46.9 0.0015 0.0006 53.4 100.3 15 6 563 37 46 2171.9 1/9/10 10:52 PM ZT14-08 Q-M Sch. 2 / 4 . 47.0 0.0013 0.0006 53.5 100.5 13 6 551 40 53 2125.6 1/9/10 11:07 PM ZT14-08 Q-M Sch. 2 / 7 . 46.9 0.0016 0.0006 53.5 100.4 16 6 564 37 46 1994.5 1/9/10 11:51 PM ZT14-08 Q-M Sch. 2 / 9 . 46.9 0.0016 0.0006 53.5 100.4 16 6 567 36 45 1914.8 1/10/10 12:21 AM ZT14-08 Q-M Sch. 3 / 5 . 47.0 0.0016 0.0006 53.5 100.5 16 6 565 37 46 0.0 1/10/10 1:50 AM ZT14-08 Q-M Sch. 3 / 8 . 46.7 0.0017 0.0006 53.2 99.8 17 6 571 35 43 125.7 1/10/10 2:35 AM ZT14-08 Q-M Sch. 4 / 1 . 47.0 0.0025 0.0006 53.6 100.6 25 6 604 30 33 0.0 1/10/10 2:49 AM ZT14-08 Q-M Sch. 4 / 2 . 46.9 0.0020 0.0006 53.5 100.4 20 6 586 32 38 34.6 1/10/10 3:05 AM ZT14-08 Q-M Sch. 4 / 3 . 47.1 0.0019 0.0006 53.6 100.7 19 6 579 34 40 69.2 1/10/10 3:19 AM ZT14-08 Q-M Sch. 4 / 4 . 47.1 0.0022 0.0006 53.6 100.7 22 6 594 31 35 103.9 1/10/10 3:34 AM ZT14-08 Q-M Sch. 4 / 5 . 47.0 0.0030 0.0006 53.5 100.5 30 6 621 27 30 138.4 1/10/10 3:49 AM ZT14-08 Q-M Sch. 4 / 6 . 47.0 0.0018 0.0006 53.5 100.5 18 6 575 34 42 173.0 1/10/10 4:04 AM ZT14-08 Q-M Sch. 4 / 7 . 47.1 0.0023 0.0006 53.7 100.8 23 6 596 31 35 207.6 1/10/10 4:19 AM ZT14-08 Q-M Sch. 4 / 8 . 47.1 0.0033 0.0006 53.7 100.7 33 6 630 26 28 242.3 1/10/10 4:33 AM AVG 603 33 RANGE 550-688 19-53 Appendix 2: Original thermometry (titanium -in-quartz) data prior to pressure corrections. Void temperatures were eliminated from the final dataset (see text). „Distance‟ represents the distances between points in transects.

Si Ti std* O Total Ti Ti std TitaniQ err+ err- Distance Sample Lithology DataSet/Pt wt.% wt.% wt.% wt.% wt.% ppm ppm ºC ºC ºC (um) Date ZT18-08 Migmatite 15 / 1 . 46.7 0.0018 0.0006 53.3 100.0 18 6 575 34 41 0.0 1/8/10 8:46 PM ZT18-08 Migmatite 15 / 2 . 46.7 0.0014 0.0006 53.2 100.0 14 6 556 39 50 18.7 1/8/10 9:02 PM ZT18-08 Migmatite 15 / 3 . 46.7 0.0016 0.0006 53.2 99.9 16 6 564 37 46 37.4 1/8/10 9:17 PM ZT18-08 Migmatite 15 / 4 . 46.8 0.0016 0.0006 53.3 100.1 16 6 565 37 46 56.1 1/8/10 9:31 PM ZT18-08 Migmatite 15 / 5 . 46.3 0.0020 0.0006 52.7 99.0 20 6 583 33 39 75.0 1/8/10 9:46 PM ZT18-08 Migmatite 15 / 6 . 46.8 0.0024 0.0006 53.3 100.1 24 6 599 30 34 93.7 1/8/10 10:01 PM ZT18-08 Migmatite 15 / 7 . 46.9 0.0035 0.0006 53.4 100.3 35 6 636 26 27 112.4 1/8/10 10:16 PM ZT18-08 Migmatite 15 / 8 . 46.9 0.0072 0.0006 53.4 100.3 72 6 709 21 21 131.1 1/8/10 10:31 PM ZT18-08 Migmatite 16 / 1 . 46.6 0.0021 0.0006 53.1 99.6 21 6 588 32 37 0.0 1/8/10 10:46 PM ZT18-08 Migmatite 16 / 2 . 46.6 0.0021 0.0006 53.1 99.8 21 6 590 32 37 23.7 1/8/10 11:01 PM ZT18-08 Migmatite 16 / 4 . 46.5 0.0018 0.0006 53.0 99.6 18 6 574 35 42 71.0 1/8/10 11:31 PM ZT18-08 Migmatite 17 / 1 . 46.3 0.0014 0.0006 52.8 99.1 14 6 557 38 49 0.0 1/8/10 11:46 PM ZT18-08 Migmatite 17 / 2 . 46.3 0.0017 0.0006 52.7 99.0 17 6 569 36 44 56.7 1/9/10 12:01 AM ZT18-08 Migmatite 17 / 3 . 46.5 0.0021 0.0006 53.0 99.4 21 6 588 32 37 113.3 1/9/10 12:16 AM ZT18-08 Migmatite 17 / 4 . 46.5 0.0019 0.0006 53.0 99.5 19 6 581 33 39 170.0 1/9/10 12:31 AM ZT18-08 Migmatite 15 / 1 . 46.4 0.0019 0.0007 52.8 99.2 19 7 581 35 43 0.0 12/12/2009 2:43 ZT18-08 Migmatite 16 / 1 . 46.1 0.0095 0.0007 52.5 98.7 95 7 742 20 20 360.0 12/12/2009 2:58 AVG 598 35

RANGE 556-742 20-50 Appendix 2: Original thermometry (titanium - in-quartz) data prior to pressure corrections. „Distance‟ represents the distances between points in transects.

Ti Si Ti std* O Total Ti std TitaniQ err+ err- Distance Sample Lithology DataSet/Pt wt.% wt.% wt.% wt.% wt.% ppm ppm ºC ºC ºC (um) Date ZT24-08 Q-M Sch. 20 / 1 . 45.4 -2E-04 0.0006 51.7 97.09 -2 6 - - - 0.0 1/9/2010 3:31 ZT24-08 Q-M Sch. 20 / 2 . 44.7 -6E-05 0.0006 50.9 95.65 -1 6 - - - 60.2 1/9/2010 3:46 ZT24-08 Q-M Sch. 20 / 3 . 45.4 0.0004 0.0006 51.7 97.12 4 6 - - - 120.4 1/9/2010 4:01 ZT24-08 Q-M Sch. 20 / 4 . 45 0.0019 0.0006 51.2 96.18 19 6 - - - 180.6 1/9/2010 4:16 ZT24-08 Q-M Sch. 20 / 5 . 45.4 -1E-04 0.0006 51.7 97.13 -1 6 - - - 240.8 1/9/2010 4:31 ZT24-08 Q-M Sch. 20 / 6 . 45.3 0.0002 0.0006 51.6 96.89 2 6 - - - 301.0 1/9/2010 4:46 ZT24-08 Q-M Sch. 21 / 1 . 46.4 -2E-04 0.0006 52.9 99.3 -2 6 - - - 0.0 1/9/2010 5:01 ZT24-08 Q-M Sch. 21 / 2 . 46.6 0.0011 0.0006 53.1 99.67 11 6 - - - 176.0 1/9/2010 5:16 ZT24-08 Q-M Sch. 21 / 3 . 46.6 -3E-04 0.0006 53.1 99.62 -3 6 - - - 352.0 1/9/2010 5:31 ZT24-08 Q-M Sch. 21 / 4 . 46.5 8E-05 0.0006 53 99.58 1 6 - - - 528.0 1/9/2010 5:46 ZT24-08 Q-M Sch. 21 / 5 . 46.7 -4E-05 0.0006 53.2 99.85 0 6 - - - 704.0 1/9/2010 6:01 ZT24-08 Q-M Sch. 21 / 6 . 46.4 6E-05 0.0006 52.9 99.34 1 6 - - - 880.0 1/9/2010 6:16 Appendix 2: Original thermometry (titanium-in-quartz) data prior to pressure corrections. Void temperatures were eliminated from the final dataset (see text). „Distance‟ represents the distances between points in transects.

8 88

Si Ti std* O Total Ti Ti std TitaniQ err+ err- Distance Sample Lithology DataSet/Pt wt.% wt.% wt.% wt.% wt.% ppm ppm ºC ºC ºC (um) Date

ZT5-09 Granite 18 / 1 . 46.4 0.0033 0.0006 52.8 99.2 33 6 629 26 28 0.0 1/9/10 12:46 AM ZT5 -09 Granite 18 / 2 . 46.4 0.0023 0.0006 52.9 99.3 23 6 596 31 35 76.3 1/9/10 1:01 AM ZT5-09 Granite 18 / 4 . 46.6 0.0027 0.0006 53.1 99.7 27 6 609 29 32 229.0 1/9/10 1:31 AM ZT5 -09 Granite 19 / 1 . 46.8 0.0032 0.0006 53.3 100.0 32 6 628 27 28 0.0 1/9/10 1:46 AM ZT5-09 Granite 19 / 2 . 47.0 0.0028 0.0006 53.6 100.6 28 6 613 28 31 186.1 1/9/10 2:01 AM

ZT5-09 Granite 19 / 3 . 47.0 0.0025 0.0006 53.6 100.6 25 6 603 30 33 372.2 1/9/10 2:16 AM ZT5 -09 Granite 19 / 4 . 47.1 0.0013 0.0006 53.7 100.8 13 6 548 41 55 558.3 1/9/10 2:31 AM ZT5-09 Granite 19 / 5 . 47.1 0.0032 0.0006 53.7 100.8 32 6 626 27 29 744.4 1/9/10 2:46 AM ZT5 -09 Granite 19 / 6 . 46.9 0.0027 0.0006 53.5 100.4 27 6 610 29 32 930.5 1/9/10 3:01 AM ZT5-09 Granite 19 / 7 . 47.4 0.0027 0.0006 54.0 101.3 27 6 612 28 31 1116.6 1/9/10 3:16 AM ZT5 -09 Granite 11 / 1 . 46.4 0.0041 0.0007 52.9 99.3 41 7 650 26 27 0.0 12/12/2009 1:42 ZT5 -09 Granite 12 / 1 . 46.7 0.0029 0.0007 53.2 99.9 29 7 616 30 33 134.2 12/12/2009 1:57 AVG 612 31

RANGE 548-650 26-55 Appendix 2: Original thermometry (titanium - in-quartz) data prior to pressure corrections. „Distance‟ represents the distances between points in transects.

Ti Si Zr Ti std* Hf O Total Ti std TiZr err+ err- Distance Sample Lithology DataSet/Pt wt.% wt.% wt.% wt.% wt.% wt.% wt.% ppm ppm ºC ºC ºC (um) Date 1/11/10 ZT18-8 Migmatite 3 / 1 . 15.1 50.3 0.003 0.0005 1.0 35 101.6 26.3 5.3 834 34 36 27.07 6:46 PM 1/11/10 ZT18-8 Migmatite 4 / 1 . 15.1 49.6 0.002 0.0005 0.7 35 100.2 21.1 5.4 811 37 41 215.62 7:15 PM 1/11/10 ZT18-8 Migmatite 3 / 1 . 15.1 50.0 0.009 0.0005 1.1 35 101.2 89.0 5.4 978 25 25 1919.39 4:45 PM

1/11/10 ZT14-8 Mylonite 4 / 1 . 15.0 49.8 0.002 0.0005 1.1 35 100.6 24.6 5.4 826 35 38 42388.64 5:13 PM 1/11/10 ZT14-8 Mylonite 5 / 1 . 15.1 49.9 0.002 0.0005 1.1 35 101.0 23.4 5.3 821 36 39 42395.92 7:43 PM 1/11/10 ZT14-8 Mylonite 6 / 1 . 15.1 49.9 0.005 0.0005 1.0 35 100.9 54.1 5.4 915 27 28 40061.02 8:11 PM 1/11/10 ZT14-8 Mylonite 7 / 1 . 15.1 49.5 0.006 0.0005 1.0 35 100.4 58.1 5.4 923 27 27 40096.55 8:39 PM 1/11/10 ZT14-8 Mylonite 8 / 1 . 15.1 50.0 0.004 0.0005 0.9 35 100.9 37.8 5.4 873 30 31 38969.39 9:08 PM 1/11/10 ZT14-8 Mylonite 9 / 1 . 15.2 50.2 0.004 0.0005 0.9 35 101.3 44.3 5.4 891 29 29 39014.22 9:36 PM

1/11/10 ZT5-9 Granite 10 / 1 . 15.1 49.9 0.002 0.0005 0.7 35 100.7 19.1 5.4 801 39 44 29596.93 10:04 PM

Appendix 2: Original thermometry (titanium-in-zircon) data prior to pressure corrections. „Distance‟ represents the distances between points in transects.

Age Sample-spot# Y Th U Pb (my) Error (+/-) ZT-4-trace-01 8220 34010 8050 1030 383 15 ZT-4-trace-02 7860 35300 7070 820 316 15 ZT-4-trace-03 6340 29410 6420 670 300 15 ZT-4-trace-04 7910 43500 11900 1260 344 15 ZT-4-trace-05 7570 43780 10430 1120 324 15 ZT-4-trace-06 5300 34910 7600 1060 398 15 ZT-4-trace-07 5850 48150 10250 1320 363 15 ZT-4-trace-08 5600 34720 7930 1060 392 15 ZT-4-trace-09 7200 44950 9850 1080 344 15 ZT-4-trace-10 7110 34600 7980 1040 384 15 ZT-4-trace-11 17690 39740 8260 1110 373 15 ZT-4-trace-12 14590 39210 8120 1090 372 15 ZT-4-trace-13 8180 50060 11270 2070 530 15 ZT-4-trace-14 7820 53030 11820 2140 520 15 ZT-4-trace-15 7000 26220 7610 720 318 15 ZT-4-trace-16 8560 42170 11440 1410 397 15 ZT-4-trace-17 9670 61290 16390 2470 480 15 ZT-4-trace-18 8640 63880 14950 2520 498 15 ZT-4-trace-19 8660 60450 13770 2330 493 15 ZT-4-trace-20 11380 39060 10990 1930 571 15 ZT-4-trace-21 5260 33460 7810 1050 399 15 ZT-4-trace-22 5100 34940 7460 1070 404 15 ZT-4-trace-23 14810 36260 4600 770 337 15 ZT-4-trace-24 7930 37430 11370 1220 367 15 ZT-4-trace-25 7150 31300 8590 990 374 15 ZT14-trace-01 10840 34100 7070 1190 464 15 ZT14-trace-02 10300 33910 7220 950 371 15 ZT14-trace-03 14090 30760 6070 1150 506 15 ZT14-trace-04 15640 37740 6310 1180 451 15 ZT14-trace-05 11440 44100 0 0 0 15 ZT14-trace-06 10970 53020 9380 1430 383 15 ZT14-trace-07 15230 28760 9400 1280 480 15 ZT14-trace-08 11380 23140 6390 1100 555 15 ZT14-trace-09 16730 36040 7210 1280 479 15 ZT14-trace-10 15840 15580 12200 1250 502 15 ZT14-trace-11 17110 30590 7170 1200 495 15 ZT14-trace-12 17910 31120 8060 1260 489 15 ZT14-trace-13 17660 35300 7700 1300 480 15 ZT14-trace-14 13030 36880 7010 1080 404 15 ZT14-trace-15 12790 29620 7290 1080 452 15 ZT14-trace-16 17130 32790 7180 1230 487 15 ZT14-trace-17 14870 36290 7410 1270 468 15 ZT14-trace-18 16880 33770 6890 1200 475 15

Appendix 3: Electron microprobe chemical data and ages of monazites from the lower unit mica schists. Ages have a 1 sigma error and ages that are not highlighted were eliminated from the final dataset (see text).

Age Sample-spot# Y Th U Pb (my) Error (+/-) ZT-15-trace-1 18140 29420 6410 1010 448 15 ZT-15-trace-2 13180 40550 8110 1260 420 15 ZT-15-trace-3 10750 21410 2330 520 401 15 ZT-15-trace-4 19120 20720 5380 790 460 15 ZT-15-trace-5 18040 21280 6430 830 439 15 ZT-15-trace-6 20250 22010 5910 840 454 15 ZT-15-trace-7 19320 29670 7250 1000 420 15 ZT-15-trace-8 19810 22820 5640 850 460 15 ZT-15-trace-9 17790 24820 3720 470 286 15 ZT-15-trace-10 22520 16140 5150 730 493 15 ZT-15-trace-11 12010 56200 8110 1450 392 15 ZT-15-trace-12 16250 43410 7740 1260 410 15 ZT-15-trace-13 16190 47750 8010 1310 397 15 ZT-15-trace-14 13220 43270 7060 1280 431 15 ZT-15-trace-15 15890 40100 6630 1210 438 15 ZT-15-trace-16 19540 40620 7600 1220 417 15 ZT-15-trace-17 23290 27920 7680 980 414 15 ZT-15-trace-18 22200 38830 7880 1180 409 15 ZT-15-trace-19 27720 28750 7160 970 417 15 ZT-15-trace-20 21770 23950 4270 750 442 15 ZT-15-trace-21 18290 16420 4060 580 437 15 ZT-15-trace-22 18070 25510 8830 1030 424 15 ZT-15-trace-23 17590 36230 7880 1140 412 15 ZT-15-trace-24 15410 40220 7610 1200 413 15 ZT-15-trace-25 12510 32070 8540 1150 429 15 ZT-15-trace-26 16750 21120 7210 930 465 15 ZT-15-trace-27 17270 26350 7100 910 411 15 ZT-15-trace-28 4180 9020 540 300 616 15 ZT-15-trace-29 17500 38990 8110 1190 407 15 ZT-15-trace-30 18400 45990 7500 1270 403 15 ZT-15-trace-31 18610 55070 7560 1430 401 15 ZT-15-trace-32 18740 40320 6920 1140 405 15 ZT-15-trace-33 19270 39340 6330 1140 425 15 ZT-15-trace-34 19490 36280 6670 1120 431 15 ZT-15-trace-35 19830 56900 9860 1570 395 15 ZT-15-trace-36 20410 39290 7140 1180 421 15 ZT-15-trace-37 19670 42830 9240 1360 417 15 ZT-15-trace-38 18500 41010 8360 1310 429 15 ZT-15-trace-39 21760 40220 9310 1310 415 15 ZT-15-trace-40 23060 42700 9480 1360 413 15 ZT-15-trace-41 22490 46250 11140 1510 409 15 ZT-15-trace-42 18830 44590 7890 1350 429 15 ZT-15-trace-43 5960 20380 1590 490 428 15

Age Sample-spot# Y Th U Pb (my) Error (+/-) ZT24-trace-01 17450 62670 5540 1340 372 15 ZT24-trace-02 17360 44300 9850 1340 393 15 ZT24-trace-03 15560 43820 9830 1250 369 15 ZT24-trace-04 15620 46400 6170 1090 367 15 ZT24-trace-05 11700 65380 3900 1080 310 15 ZT24-trace-06 14360 54010 4680 1190 352 15 ZT24-trace-07 19790 58100 6610 1450 407 15 ZT24-trace-08 19110 65500 6630 1560 400 15 ZT24-trace-09 23040 114850 4410 2140 370 15 ZT24-trace-10 18370 88840 3670 1650 366 15 ZT24-trace-11 19860 159010 5470 2820 357 15 ZT24-trace-12 16190 102660 5240 2030 379 15 ZT24-trace-13 23320 82070 12160 2050 377 15 ZT24-trace-14 17450 38070 6890 1300 479 15 ZT24-trace-15 17130 38510 6020 1270 487 15 ZT24-trace-16 18360 48290 6870 1470 464 15 ZT24-trace-17 21420 40160 6540 1030 375 15 ZT24-trace-18 16510 67620 7860 1430 344 15 ZT24-trace-19 19880 52370 6770 1180 355 15 ZT24-trace-20 10760 61030 3960 1090 330 15 ZT24-trace-21 13040 104440 6260 2000 359 15 ZT24-trace-22 12550 102770 5860 1670 307 15 ZT24-trace-23 13260 83030 5530 1360 302 15 ZT24-trace-24 16970 34790 6230 1120 454 15 ZT24-trace-25 23220 81350 12310 1940 358 15