Exhumation of the Orlica-Snieznik Dome

EXHUMATION OF THE ORLICA-SNIEZNIK DOME,

NORTHEASTERN BOHEMIAN MASSIF (POLAND AND CZECH REPUBLIC)

A thesis presented to

the faculty of

the College of Arts and Sciences of Ohio University

In partial fulfillment

of the requirements for the degree

Masters of Science

Jacob M. Glascock

November 2004 This thesis entitled

EXHUMATION OF THE ORLICA-SNIEZNIK DOME,

NORTHEASTERN BOHEMIAN MASSIF (POLAND AND CZECH REPUBLIC)

BY

Jacob M. Glascock

has been approved for

the Department of Geological Sciences

and the College of Arts and Sciences by

David Schneider

Assistant Professor of Geological Sciences

Leslie A. Flemming

Dean, College of Arts and Sciences Glascock, Jacob M. M.S. November 2004. Geological Sciences

Exhumation History of the Orlica Snieznik Dome, Northeastern Bohemian Massif

(Poland and Czech Republic) (80 p.)

Director of Thesis: David Schneider

The Orlica-Snieznik Dome (OSD), located in the northeastern Bohemian massif

(Czech Republic and Poland), represents a Variscan massif consisting of widespread

amphibolite-facies gneisses and migmatites enclosing eclogite and granulite crustal-scale

lenses. 40Ar/39Ar thermochronology yielded cooling ages for white mica and biotite between 341 ± 1 Ma to 337 ± 0.6 Ma and 342 ± 1 Ma to 334 ± 0.6 Ma from the Snieznik mountains. One amphibolite-derived hornblende yielded an integrated Ar-Ar age of ca.

400 Ma. The Orlica mountains yielded cooling ages between 338 ± 0.9 Ma to 335 ± 0.5

Ma. U-Th-total Pb monazite geochronology confirms two thermal events, likely commencing at ca. 400 Ma with granulite facies metamorphism. The cooling ages of the gneisses and schists are consistent across the dome and represent rapid wholesale cooling of the OSD, on an order of 50 oC/m.y. indicative of exhumation-related, amphibolite-

facies metamorphism directly following UHP conditions.

Approved: David Schneider

Assistant Professor of Geological Sciences ACKNOWLEDGMENTS

I would like to thank my advisor, David Schneider, for his guidance, support, and friendship, and I am honored to have worked alongside him throughout these last two years. This experience has led to a whole new understanding of my capabilities as a professional and has allowed me to achieve a new level of confidence. I have gained valuable skills and the ability to apply those skills in a variety of settings, but most importantly I have gained a friend.

The last two years were an incredible experience of which I had the privilege of sharing with fellow student and friend, Stephen Zahniser. His camaraderie has helped me through some tough times and will always be greatly appreciated. Along with Dave, the three of us see no evil, hear no evil, and speak no evil. My thanks again to the both of you.

I would also like to thank my committee members, Greg Nadon and Doug Green, as well as Maciej Manecki for their guidance and support throughout my college education.

Their insight, intellect and genuine interest in my graduate work are greatly appreciated.

My gratitude also extends out to Dr. Matt Heizler (NMT) and Dr Robert Tracey (VT).

This project was funded by the National Research Council/National Science Foundation.

I would not have succeeded this far without my family and friends, so I would like to thank my better half; Stephanie Miller, my parents and relatives, my sister and brothers,

Bartek Budzyn, David Patterson, Joey Smith, Brett Laverty, Molly Hart, the Kahns, the

Lyles, the Kristofcos, and Paul Huffer, and anyone else who has helped me along during this adventure. 5 TABLE OF CONTENTS

Page

Abstract…………………………………………………………………………………3

Acknowledgments………………………………………………………………………4

List of Figures…………………………………………………………………………..6

List of Tables………………………………………………………………………….. 7

1. Introduction…………………………………………………………………………..8

2. Tectonic Setting: Variscides………………………………………………………… 10

3. Geologic Setting: Sudetes……………………………………………………………13

4. Previous Geochronology……………………………………………………………..18

5. Petrology and Petrography…………………………………………………………...20

6. 40Ar/39Ar Thermochronology………………………………………………………... 25

6.1. Analytical Procedure……………………………………………………….27

6.2. 40Ar/39Ar Analytical Results………………………………………………. 29

7. U-Th-total Pb Geochronology………………………………………………………. 51

7.1. Analytical Procedure……………………………………………………….52

7.2. U-Th-total Pb Analytical Results…………………………………………..53

8. Discussion……………………………………………………………………………58

9. Conclusions..………………………………………………………………………... 66

10. References…………………………………………………………………………..67

Appendix A: Sample Petrology and Petrography………………………………………73 6 LIST OF FIGURES Figure .Page

1. Modified terrane map of the Bohemian massif and adjacent zones………………… 11

2. Geologic map of the Sudetes, Poland and Czech Republic………………………….14

3. Simplified geologic map of the Orlica-Snieznik Dome and adjacent regions……….15

4. Sample map of collection sites from the Orlica-Snieznik Dome…………………….21

5. Field and petrographic photos of representative rock units………………………….23

6. 40Ar/39Ar age spectra………………………………………………………………… 33

7. Elemental images of monazite grains from szx-10A………………………………...54

8. Distribution of weighted mean monazite total-Pb ages and probability curves of monazite total-Pb age results for szx-10A…………..………………………………….56

9. Distribution of weighted mean monazite total-Pb ages and probability curves of monazite total-Pb age results for szx-10A…………..………………………………….57

10. P-T-t evolution of the Orlica-Snieznik Dome………………………………………63 7

LIST OF TABLES Table Page

1. Analytical 40Ar/39Ar isotopic data…………………………………………………36-50

2. Analytical EMPA monazite U-Th-total Pb elemental data…………………………..55 8 1. Introduction

Ultrahigh pressure (UHP) metamorphic terranes represent crust that has undergone a complex interplay of deep lithospheric and thermal processes, and their subsequent rapid exhumation results in the preservation of the deep-earth petrology. These mineral assemblages, which can lie within the coesite stability field, are typically indicative of conditions exceeding 28 kbar and 700 ºC suggesting deep (~100 km) subduction of continental and/or oceanic crust at major plate margins. The descent phase of these blocks is fairly well understood; however two outstanding enigmatic features of UHP terranes are the mechanism and rate of the ascent phase of deformation. Notably, though, the simple preservation of the UHP assemblages in orogenic belts implies the rocks were rapidly unroofed and exhumed.

Previous models of deep exhumation describe two mechanisms in which preserved continental UHP terranes were rapidly brought to the surface. One such process is the removal of the overburden through surface erosion and normal faulting in which the subsequent extensional collapse of the orogenic belt played the role of the driving mechanism (e.g., Vanderhaeghe et al., 1999). Another widely accepted model is the rapid ascent of UHP eclogites and granulites through the lower and middle lithosphere by means of a density-regulated buoyant crust (e.g., Hacker et al., 1995).

However most UHP rocks are enveloped by an amphibolite-facies metamorphic matrix, which implies multiple stages of exhumation, and likely combines both mechanisms since buoyancy cannot be the only driving force for exhumation and other processes must 9 be acting to allow further ascent of the UHP blocks (Hacker et al., 1995; Qingchen and

Bolin, 2000; Ernst and Liou, 2000).

Detailed exhumation histories of UHP terranes can be revealed through thermochronological and geochronological analyses of the minerals found within the

UHP rocks and surrounding metamorphic matrix, which will allow a quantitative evaluation of the heating and cooling rates associated with ascent. Specifically, this study focuses on the Orlica-Snieznik Dome (OSD) located in the northeastern Bohemian massif of the Czech Republic and Poland. The OSD, a well-known UHP terrane, represents an ideal location for a geochronometric investigation because it can enable a more specific placement of metamorphic and cooling ages into an already existing geologic framework.

The equivocal structure of the dome varies with interpretation but has typically been described as a Neoproterozoic-Early Paleozoic basement-cover sequence consisting of granitic orthogneisses and various paragneisses; a characteristic signature of the widespread Variscan tectonics of Europe (Floyd et al., 1996). Previous thermochronology from the northeastern Bohemian massif are limited, but suggest denudation between ca.

340-310 Ma that is believed to reflect cooling from major Variscan Barrovian metamorphism (Maluski et al., 1995). This study provides new results, which are primarily 40Ar/39Ar thermochronometric and complimentary U-Th-total Pb monazite geochronometric data from enveloping amphibolite-facies metamorphic rocks in order to place timing constraints on the ascent phase (exhumation) of the enclosed eclogites and granulites of the OSD. 10 2. Tectonic Setting: Variscides

The Variscan orogeny has been considered to represent a diachronous obduction- collision zone with a deformational history spanning over 100 m.y. resulting in an oblique dextral collisional regime. The Variscan belt is a collage of arc terranes and microplates that amalgamated within this collisional regime between 480 and 250 Ma

(Matte, 2001). The system, as wide as 1000 km, extended from the present day Caucasus

Mountains of Eurasia through the Mauritanian Belt of Africa to the Alleghenian belt of the Appalachians and the Ouachitas of North America at the end of the Carboniferous.

Collision involved the Armorican Terrane Assemblage (ATM) situated between

Laurentia-Baltica to the northwest and Gondwana to the southeast. The ATM is traditionally comprised of the microplates Moldanubia, Tepla-Barrandia, Saxothuringia,

Armorica, and Iberia within the Rheic seaway, and the main tectonic zones of the

Variscides in Europe are identified as the Rhenohercynian, Saxothuringian, and

Moldanubian zones (Figure 1; Crowley et al., 2000). The Rhenohercynian zone is the northern external fold and thrust belt and consists mainly of Late Paleozoic sedimentary and volcanic successions with Devonian to Carboniferous ophiolite complexes. The

Saxothuringian zone is a low-grade metamorphic terrane consisting of a Neoproterozoic to Carboniferous intrusive and volcano-sedimentary sequence representing northern segments of the Armorican microplate. The Moldanubian zone represents a terrane of

Iberian and Armorican microplate assemblages derived from Gondwana, and is characterized by nappe structures of eclogites, granulites, and high pressure (HP)- ultramafic rock, intruded by post-collisional granites. 11

BALTICA LONIA Berlin AVA

Wroclaw

Dresden SILESIA IA

SAXO- Praha THURING

BOHEMIA

Brno

N MOLDANUBIA 100 km

Southern margin of Laurussia Bohemia & rocks accreted L. Dev.-E. Carb. active margin before 380 Ma Saxo-Thuringia Moldanubia (N. Gondwana?)

Figure 1. Modified terrane map of the Bohemian Massif and adjacent zones (after Franke and Zelanzniewicz, 2000). The box shows the general location of the central Sudete Mountains, Poland, and Czech Republic in Figure 2.

The end of the Silurian was marked by the approach Armorica toward Avalonia and the closure of the Rheic Ocean. The result was a series of tectonic episodes: oblique indentation of the microplates, tectonic underplating, widespread high temperature-low pressure (HT-LP) metamorphism, granite emplacement, and late orogenic extensional collapse (Warr, 2000). The Early to Mid Devonian involved a reverse convergence along the suture zone between Avalonia and Armorica due to transtensional shearing and back- arc spreading above the subduction complex which caused oceanic separation and the formation of the Rhenohercynian Ocean. Orogenic activity commenced again during this 12 time due to the north-directed subduction and collision of Iberia and Armorica resulting in the closure of the Rhenohercynian ocean (Warr, 2000; Matte, 2001).

Avalonia and Armorica reestablished convergence along the suture zone with the

Rhenohercynian oceanic crust subducting southward leading to the formation of a continental arc and ultimate closure. The end of the Devonian also represents transpression and north-directed thrusting as well as lithospheric stretching and thinning of the eastern continental margin of Avalonia. The next tectonic phase occurred during the Early to Mid Carboniferous with a north-northwest foreland-directed thrusting across the Rhenohercynian zone, flexural subsidence, and foreland basin formation, and is thought to have been the result of the Alpine (microassemblage of the ATM) collision

(Franke and Zelanzniewicz, 2000; Warr, 2000). Regional compression led to large-scale crustal thickening and granite intrusions followed by extensional deformation which migrated outwards toward the foreland. The final convergence of Gondwana and its associated microplates in the Late Carboniferous represent the final phase of widespread

(granulite-facies) deformation across the orogenic zone. Crustal stacking was the result of the convergence of the southern margin of Iberia-Armorican microplate and Gondwana as well as large scale oroclinal bending of the orogenic belt (Iberian-Armorican arc) and post-collisional granite intrusion associated with extensional collapse of the orogenic belt

(Warr, 2000). Henk et al. (2000) noted that the greatest magmatic episode of granitic and granodioritic composition occurred between 340 and 325 Ma across a 2000 km corridor.

The magmatism and related HT metamorphism was thought to have been the result of 13 slab break off after closure of the oceanic basins followed immediately by delamination (Henk et al., 2000).

3. Geologic Setting: Sudete Mountains

The Bohemian massif, which consists of several northeast-trending tectonostratigraphic units but most notably the Saxothuringian and Moldanubian zones, forms the easternmost block of the European Variscides and is found exposed in certain areas of Poland and the Czech Republic as well as Austria and Germany (Figure 1). It has been identified as a crystalline basement block amalgamated during the Late Paleozoic portion of the Variscan orogeny as a result of large-scale thrusting and horizontal shear movements (O’Brien, 1997; Marheine et al., 2002). The Sudetes, which make up the northern margin of the Bohemian massif (Figure 2), consists of several dome structures with crustal-scale boudins and large-scale metamorphic complexes comprised of high- and ultrahigh grade metamorphic rocks (Maluski et al., 1995). The Orlica-Snieznik Dome

(OSD) metamorphic complex is one of the largest structural units in the central Sudetes, the easternmost part of the Saxothuringian zone (Figure 3; Steltenpohl et al., 1993). The dome is a well-preserved Precambrian basement-cover complex exposed in a tectonic window through eroded Variscan thrust sheets (Steltenpohl et al., 1993) with the core being described as that of Neoproterozoic to Cambrian rocks intruded by Early Paleozoic granites (Turniak et al., 2000). The autochthonous gneisses of the OSD are interpreted to represent assemblages of a rifted ensialic environment with variable crustal 14 contamination, metamorphosed to amphibolite-facies, and locally granulite facies, conditions (Floyd et al., 2000).

16°E 17°E Poland

A MASSIF IZER

S M F N NOSZE NE RKO GRANITE IS KA F

R ZO GORY SOWIE MASSIF

SHEA

CZA INTRA-SUDETIC BASIN State Border NIEM Czech Repu gneiss

mica schist blic mylonites SNIEZNIK ophiolitic rocks MASSIF

metavolcanics ORLICA MASSIF

phylites & metavolcanics NAPPE Variscan granitoids

Cadomian granitoids KEPRNIK

DESNA DOME metabasites & gneisses 50°N

Stare Mesto & Velke Vbrno Units: amphibolites & mica schists 20 km Undifferentiated gneisses and schists

Figure 2. Geologic map of the Sudetes, Poland and Czech Republic (modified after Turniak et al., 2000). Boxed region represents location of Figure 3. ISF- Intra-Sudetic Fault Zone, SMF-Sudetic Marginal Fault.

The OSD is distinguished by three major lithological units: the Mlynowiec-Stronie

Group, the Snieznik Formation, and the Gieraltow Formation (Lange et al., 2002). The

Mlynowiec-Stronie Group mainly represents the core of the dome, and consists of

plagioclase gneisses with minor mica schists overlain by variegated succession of biotite-

to staurolite-zone mica schists, paragneisses, quartzites, marbles and amphibolites. These 15 schists were intruded by Early Paleozoic granites, which were metamorphosed by subsequent deformation into the Snieznik and Gieraltow gneisses.

STR. GIER T ALOW L U A F Y T U ORLICA BOLESLAWOW O K

MIEDZYGORZE JESENIK T SNIEZNIK FAUL JADLOW RAMZOVA Variscan granitoids MIEDZYLESIE

DESNA metavolcanics DOME

phylites & metavolcanics

tonalite KEPRNIK amphibolite N

mica schist 20 km gneiss

Figure 3. Simplified geologic map of the Orlica-Snieznik Dome and adjacent domes (modified after Maluski et al., 1995 and Turniak et al., 2000) with representative lithologic units and structural features.

U-Pb single zircon and Rb-Sr whole-rock isochron protolith ages for both units are

constrained to between 500 and 400 Ma (Borkowska et al., 1990; Brocker et al., 1997;

Turniak et al., 2000; Lange et al., 2002). Crowley et al. (2000) states that the

emplacement of granitic magmas, which were the result of the recycling of the Late

Proto-Cadomian crustal basement, occurred throughout the Late Cambrian and Early

Ordovician (~480-510 Ma) and were a mafic-dominated and rift-related magmatism.

They further report that the granitic gneisses of the Sudetes display an inherited volcanic

arc signature. The Silurian to Devonian magmatism led to the production of oceanic crust 16 in which the younger, less dense crust was obducted and preserved as ophiolites in the

Sudetes (Crowley et al., 2000).

The orthogneiss core has been subdivided into porphyritic coarse- to medium- grained calc-alkaline metagranites (Snieznik augen gneisses), and laminated, two mica migmatitic alkaline gneisses (Gieraltow gneisses) consisting of lenses of augen gneisses, amphibolites, eclogites, and felsic granulites (Marheine et al., 2002). The eclogites and granulites have been assigned to three subunits within the Snieznik massif as the

Snieznik, Miedzygorze, and Zlote units. The eclogites of the Snieznik and Miedzygorze units are enclosed within the gneisses of the Gieraltow Formation, whereas the eclogites bands (up to 20 cm) of the Zlote unit occur interlayered with intermediate to felsic granulites (Klemd et al., 1995), and have been interpreted to be the result of bimodal volcanism with minor sedimentary contamination (Marheine et al., 2002). The majority of the meta-basic lithologies of the Bohemian massif are recognized by a calc-alkaline volcanic arc signature; however, this signature may be inherited and the result of crustal contamination.

Two main large-scale NNE-SSW faults, the Kouty and Ramzova, transect the northeastern area of the Bohemian massif with the latter being interpreted as an overthrust fault. The Stare Mesto Belt (SMB), which also trends NNE-SSW, separates the East Sudetes from the West Sudetes and has been described as a stack of thrust sheets along the eastern side of the Orlica-Snieznik massif with features found similar to that of a suture zone (Figure 3). The rocks of the SMB are composed of high-grade metasediments, banded felsic amphibolite rock consisting of spinel peridotite lensoids, 17 sheared gabbros, and a syntectonic tonalite intrusion. The protolith emplacement of the

SMB rocks has been suggested to be the result of initial rifting during the Cambro-

Ordovician (Aleksandrowski and Mazur, 2002). The aforementioned metamorphism of the granites into the Snieznik and Gieraltow gneisses was believed to have been the result of deformation associated with regional-scale overthrusting of the West Sudetes (OSD region) over the East Sudetic nappe pile as a result of microcontinent collisions.

Deformation was then followed by anatexis and amalgamation of the UHP blocks

(Turniak et al., 2000).

The East Sudetes contain abundant Neoproterozoic orthogneisses, most notably the Keprnik gneisses (546-584 Ma), the Velke Vrbno gneiss (574 Ma), and the Desna gneiss (685-598 Ma), which are found throughout the East Sudetic nappe pile

(Aleksandrowski and Mazur, 2002; Oberc-Dziedzic et al., 2003). The nappe pile is comprised of the Velke Vbrno Nappe (upper allochthon directly east of the SMB) and the

Keprnik Nappe (lower allochthon directly east of the SMB), which are separated from each other by the NNE-SSW trending Branna Unit (Devonian metasediments; Oberc-

Dziedzic et al., 2003). The Branna Unit, which is found within the Ramzova/Nyznerov tectonic zone, has been noted as providing the best example of regional extension in this area of the Sudetes due to the existence of mylonites derived from mica schists, quartzites, and basal conglomerates. Extensional shearing is also found to the eastern side of the Ramzova within the Keprnik Dome. The Desna Dome makes up the easternmost unit of the eastern Sudetes and is also comprised of Devonian metasediments with overlying Desna gneisses and mylonites (Aleksandrowski and Mazur, 2002). The East 18 Sudetes have been interpreted as being part of the Cadomian (Pan-African) Bruno-

Vistulian microcontinent broken up during Devonian-Carboniferous events (Oberc-

Dziedzic et al., 2003).

In summary, the Orlica Snieznik Dome represents a Variscan UHP terrane consisting of predominantly high-grade, amphibolite-facies gneisses, variegated mica schists, and migmatites enclosing eclogite and granulite crustal-scale lenses. The protolith ages of the orthogneisses are constrained between 500 and 400 Ma, and believed to represent an ensialic rift zone. Granitoid emplacement was followed by metamorphism of the precursors into the orthogneisses (Snieznik and Gieraltow gneisses), which is believed to have been the result of deformation associated with regional-scale overthrusting of the West Sudetes (OSD region) over the East Sudetic nappe pile as a result of microcontinent collisions (Turniak et al., 2000; Lange et al., 2002). These amphibolite-facies grade gneisses surround UHP rocks across the OSD and therefore provide an ideal location for a thermochronological and geochronological investigation.

4. Previous Geochronology

The rocks of the OSD have experienced a complex metamorphic history; attempts to constrain the evolution through the use of various geochronometric techniques have resulted in a scattered range of ages. The Stronie Formation felsic metavolcanics, and the

Gieraltow and Snieznik orthogneisses revealed initial U-Pb crystallization ages of the protolith between 540-500 Ma (Oliver et al., 1993; Kroner et al., 1994; Kroner et al.,

1997; Borkowska & Dorr, 1998; Turniak et al., 2000; Lange et al., 2002). The time of 19 protolith emplacement has been broadly constrained by Rb-Sr and U-Pb methods to between 500-400 Ma (Borkowska et al., 1990; Brocker et al., 1997; Turniak et al., 2000;

Lange et al., 2002). The U-Pb and Rb-Sr geochronology from the gneisses also suggest a possible Devonian metamorphic episode occurring between 370-360 Ma (Borkowska et al., 1990; Brocker et al., 1997). Klemd and Brocker (1999) provided U-Pb zircon ages from a mafic granulite at ca. 369-360 Ma to represent primary crystallization from UHT conditions. Moreover, recent Th-Pb monazite geochronometric data recorded an age of ca. 375 also thought to represent the ultrahigh-grade metamorphism in the Orlica mountains (Gordon et al., 2004), whereas similar ages of ca. 373 Ma from the Snieznik mountains are recorded by U-Pb zircon and Sm-Nd garnet-clinopyroxene-whole rock analyses (Brueckner et al., 1991; Brocker et al., 1997).

U-Pb and Sm-Nd dating methods from the gneisses and eclogites of the OSD revealed Late Devonian to Carboniferous ages of metamorphism. The Sm-Nd whole rock dating of Snieznik eclogites record crystallization ages between 350-330 Ma, whereas a

U-Pb age of 337 ± 3 Ma was reported to represent HP metamorphism (Brueckner et al.,

1991; Brocker et al., 1997). Turniak et al. (2000) reported a U-Pb age of 342 ± 6 Ma from a Gieraltow gneiss, which has been suggested to record the peak of HT-LP metamorphism in the OSD. Bruekner et al. (1991) recorded Sm-Nd garnet- clinopyroxene-whole rock ages of 340-330 Ma for eclogite lenses, and an age of 352 ± 4

Ma for a mafic granulite interpreted as the timing of HT-HP metamorphism. Stipska et al.

(2004) recorded a metamorphic zircon age of 342 ± 5 Ma from a granulite, which was 20 interpreted to reflect growth near peak metamorphism. The combined Sm-Nd and U-

Pb data suggest that HP-HT metamorphism may have lasted 20 m.y.

Although only a few preliminary thermochronometric studies have been undertaken in the OSD, most results tentatively suggest moderate cooling rates.

Metamorphic 40Ar/39Ar cooling ages of the complex were obtained on micas and hornblende from schists, migmatites, and amphibolites in and around the dome, yielding ages between 340 and 320 Ma (Steltenpohl et al., 1993; Maluski et al., 1995; Marheine et al., 2002), which suggest cooling from Variscan amphibolite-facies metamorphism of the complex. Higher-temperature metamorphic cooling ages were also obtained by less reliable Rb-Sr methods, yielding consistent ages between 335-329 Ma on micas from the

Snieznik complex (Borkowska et al., 1990; Brocker et al., 1997). The 40Ar/39Ar method

also revealed a younger muscovite age of 313 ± 3 Ma on an undeformed sample in the

OSD interpreted as system closure and cooling of mineral after a late temperature

increase (Maluski et al., 1995). The geochronometric methods previously utilized to

understand the complex nature of the OSD have led to a dispersed range of ages.

Nevertheless, the combination of geochronometric with thermochronometric techniques

and detailed petrologic and petrographic analysis will help to elucidate the thermal

evolution of this geologic terrane.

5. Petrology & Petrography

In an attempt to characterize the metamorphic history and degree of overprinting

of the massif, detailed petrographic analysis was performed on a total of fifty-three rock 21 samples collected from across the Orlica-Snieznik Dome during the summer of 2002 of which was dictated mainly by outcrop availability (Figure 4).

SZ-3 SZ-1 SZ-2 SZ-15 O-8 SZ-20 O-7 O-6 STR. GIERALOW

O-5 T SZ-4 SZ-21 L O-9 SZ-6 U SZ-22B A F SZ-5 Y O-10 ORLICA BOLESLAWOW T U MIEDZYGORZE O O-12 O-13 SZ-16 K SZ-19 T O-11 SZ-17 JESENIK O-4 O-3 SZ-18 FAUL SZ-26 SNIEZNIK SZ-23A RAMZOVA O-2 JADLOW SZ-24 SZ-25 MIEDZYLESIE SZ-13 SZ-14 O-1 DOME DESNA SZ-9 SZ-14 SZ-7 SZ-11 SZ-27 20 km SZ-8 SZ-10A SZ-28

N KEPRNIK

Figure 4. Sample map of collection sites from the Orlica-Snieznik Dome overlaid on geologic unit boundaries (modified after Maluski et al., 1995 and Turniak et al., 2000). Boxes represent samples processed for Ar-Ar analysis and ellipses represent samples only chosen for petrographic analysis (see Appendix for details).

A total of forty-nine thin sections were processed from these rocks and have been

given a detailed examination (see Appendix), the highlights of which are summarized

below. The majority of the samples collected from the Snieznik mountains are medium-

to coarse-grained foliated gneisses and schists with mineral assemblages typical of those

found within medium to lower amphibolite-facies grade rocks (Figure 5a). The gneisses

consist mainly of a strong foliation of biotite and muscovite as well as some which

exhibit subhedral hornblende altering to chlorite, and poikilitic garnet with fractures

composed of pinite. The typical rock matrix of the gneisses consists of undulatory 22 subhedral quartz, and sericitized and myrmekitic plagioclase. The majority of the accessory minerals for these gneisses include zircons found as inclusions in biotite and titanite. The medium- to coarse-grained micaceous schists consist of a strong foliation of biotite, muscovite, and garnet with fractures composed of pinite. Some of the micas are chloritized (Figure 5b). Minor amounts of kyanite are also present intergrown with micas as well as one sample which consists of porphyroblastic boudin-like structures composed of recrystallized quartz and staurolite. The groundmass is composed of undulatory subhedral quartz, and poikiolitic and sericitized plagioclase. The majority of the accessory minerals for the schists include zircons, found as inclusions in biotite and titanite.

The fine- to coarse-grained foliated amphibolites collected were composed of subhedral/anhedral poikilitic amphiboles, micas and minor garnet and exhibit chlorite alteration. Titanite, zircons, epidote, and apatite are typical accessories. One coarse- grained granulite was collected from the Snieznik mountains with foliation consisting of biotite and poikilitic garnet, with some of the biotite altering to chlorite. The garnet fractures are composed of pinite. The matrix is composed of undulatory subhedral quartz, and sericitized and myrmekitic plagioclase. A coarse-grained micaceous eclogite was also collected and consists of muscovite, biotite, rutile, garnet, and pyroxene (Figure 5c).

The coarse garnet porphyroblasts are intergrown with poikilitic pyroxene. The mica exhibits alteration to chlorite, the garnet is composed of pinite, and the groundmass is made up of subhedral/anhedral undulatory quartz and sericitized plagiclase (Figure 5d).

Overall, the micaceous gneisses and schists collected from across the Snieznik mountains 23 exhibit relatively homogenous petrography. The samples collected from the Orlica mountains are medium- to coarse-grained foliated micaceous gneisses and schists.

A B

C D

Figure 5. (a) Field shot of mylonitic gneiss with boudinage collected from the southeastern region of the Snieznik mountains; pen for scale. (b) Field shot of a garnet- mica schist outcrop; Polish zlote coin for scale. (c) Eclogite lense (Szx-19b) from the OSD, displaying coarse garnet porphyroblasts intergrown with poikiolitic pyroxene. FOV: 2mm. (d) Amphibolite-facies gneiss that comprises the surrounding country rock of the OSD. Photomicrograph of sample O-13, a garnet-tourmaline-mica gneiss, consisting of poikiolitic albite porphyroblasts. FOV: 2mm.

The majority of the gneisses consists of muscovite separated by medium- to coarse-

grained undulatory subhedral quartz and poikilitic plagioclase (some of which have 24 quartz inclusions), sericitic plagioclase, and tourmaline (Figure 5d). There is mica alteration to chlorite, and the accessory minerals allanite and cordierite are present as well as porphyritic/poikilitic albite of which some is partly sericitized.

The Orlica schists are medium- to coarse-grained with foliation consisting of segregations of micas, poikilitic garnet, chlorite, epidote and tourmaline separated by layers of porphritic/poikilitic albite, undulatory sub-anhedral quartz, and sericitized plagioclase. Minor amounts of kyanite are also present intergrown with micas as well as staurolite. The micas are found alternating to chlorite. No eclogites, granulites, or amphibolites were collected from the Orlica mountains. The micaceous gneisses and schists collected from the Orlica mountains exhibit relatively the same homogeneous characteristics as those of the Snieznik mountains, which further demonstrates the nature of widespread amphibolite-facies metamorphism across the massif.

Peak pressures in the Snieznik, Miedzygorze, and Zlote units have been reported to be in excess of 27 kbar at temperatures between 700º and 800ºC for eclogites and 800º-

1000ºC for granulites (Klemd and Brocker, 1999; Stipska et al., 2004). Isothermal decompression and amphibolite-facies retrogression of the ultrahigh-grade rocks followed in the pressure range of 11 to 2 kbars at ~ 600º-650oC (Stipska et al., 2004). The

UHP metamorphism of the OSD eclogites is suggested to be the result of a continent- continent collisional event in which the widespread migmatites and amphibolite-grade overprinting most likely formed during isothermal decompression (cooling from eclogite to amphibolite-facies conditions) and rapid emplacement of the deep crustal blocks

(Marheine et al. 2002). Pressures and temperatures of 550º-600ºC and 4.5 kbars were 25 recently reported for the Snieznik and Gieraltow gneisses through the use of garnet- biotite and muscovite-biotite geothermometers and a muscovite geobarometer in order to constrain amphibolite-facies conditions across the OSD. These estimates are consistent with previously published data and has also been suggested that these rocks were the result of rapid denudation during the Visean times (Budzyn et al., 2004).

6. 40Ar/39Ar Thermochronology

40Ar/39Ar thermochronometry is an effective dating technique through which

thermal histories of geological terranes are obtained in order to provide information on

the timing and rate of geologic events. This technique is based upon the accumulation of

radiogenic Ar over geologic time as a result of the natural decay of the radioactive

isotope 40K to 40Ar. The daughter, which provides the basis for the Ar method, is

continually produced by radioactive decay of K+, but lost from the mineral through

diffusion at high temperatures. The diffusional loss of argon decreases as the mineral

cools through its closure temperature (Tc), which is primarily a function of cooling rate

and grain size (McDougall and Harrison, 1999). Once a mineral cools below its closure

temperature the subsequent decay of radiogenic daughter products are retained within the

mineral along with the parent therefore recording the apparent age of cooling (Zeitler,

1989). Specifically, the apparent age represents the time at which a certain mineral closed

to the diffusion of argon, and an estimated age of a thermal event (reheating or cooling)

may be inferred from this apparent age. The product of the dating technique is an

40Ar/39Ar age spectra which is the result of the incremental release of Ar from a mineral 26 sample through laboratory experiments. The age spectra displays the cumulative 39Ar released in relation to the apparent age (Ma) representing the cooling history of the sampled rock (Zeitler, 1989). Furthermore, the incremental release of 39Ar through the

step-heating process allows for the assessment of the quality of data, including excess Ar

which would yield older ages, and partial resetting, which would yield younger ages. The

plateau ages/preferred ages shown represent the integrated ages calculated for the

relatively flat portion of each age spectrum (using the concentration of 39Ar to weight

both individual ages and errors). This rationale assumes that the steps chosen do not

contain excess 40Ar and have not been highly affected by Ar recoil into alteration phases such as chlorite. The calculated plateau age uncertainties are relatively small because analytical precision in the age of each heating step is high. The K/Ca plots are determined from the Ca-derived 37Ar and K-derived 39Ar, of which the flattest parts of the age spectra generally correspond to relatively constant K/Ca values, whereas the younger apparent ages yield relatively high K/Ca values (Marcoline et al., 1999). The age spectra along with the K/Ca plots for the OSD samples are presented in Figure 6 and the analytical results are in Table 1. Typically amphibole, mica, and potassium-feldspar are the most utilized rock forming minerals for Ar-Ar analysis because they are common in igneous and metamorphic rocks, and contain 5-10 weight percent of K+. Moreover, these minerals are dated because of their high retention of argon under moderate closure temperatures.

Hornblende is exceedingly retentive of radiogenic argon with a high closure temperature at moderate cooling rates of 500 ± 25oC. Thus, the maximum age for cooling through the

closure temperature for argon retention in hornblende is disclosed by the apparent age. 27 Muscovite, which is stable over a wide range of metamorphic conditions, has a closure temperature for moderate cooling rates of 350 ± 25oC, and the biotite Ar-Ar age reflects the time of cooling below a closure temperature of 300 ± 25oC, (McDougall and

Harrison, 1999). However, Tc will vary with cooling rate: a slow cooling rate results in a lower Tc in which the daughter argon is retained, whereas a rapid cooling rate results in a

higher Tc. The combination of ages from these different minerals from the same sample

can provide information on the time and rate of cooling (rapid vs. slow-cooling) of a

geological terrane.

6.1 Analytical Procedure

Hornblende and mica were separated from metamorphic rocks of the Sudete

Mountains for 40Ar/39Ar age spectrum analysis. Size fractions of >150 µm of the target

minerals were obtained using standard crushing, heavy liquids, a Frantz magnetic

separator, and careful handpicking to insure 99% purity. All samples were ultrasonically

cleaned for five to ten minutes, rinsed in acetone, and dried at ~100°C. Mineral separates

were loaded into machined Al discs and irradiated with flux monitor Fish Canyon Tuff

sanidine (27.84 Ma; Deino and Potts, 1990) for 100 hours in the L-67 position at the 2

MW Ford Reactor at the University of Michigan.

Isotopic analyses were conducted at New Mexico Tech using a MAP 215-50 mass

spectrometer on line with automated all-metal extraction system. The flux monitor

crystals were placed in a copper planchet within an ultrahigh vacuum argon extraction

system and fused with a 10W Synrad CO2 continuous laser. Evolved gases were purified 28 for two minutes using a SAES GP-50 getter operated at ~450°C. J-factors were determined to a precision of 0.1% (2
) by analyzing a minimum of four single crystal aliquots from each of 3-4 radial positions around the irradiation sample trays. The unknown minerals were step-heated in a double-vacuum Mo resistance furnace; hornblende was heated for nine minutes and micas were heated for eight minutes. The gas was scrubbed of reactive species during heating with a SAES GP-50 getter for six to eight minutes at 450°C. Following heating, the sample gas was further cleaned with another GP-50 for three minutes for micas and eight minutes for hornblende. Argon isotopic compositions for both the samples and monitors were determined using the MAP

215-50 equipped with an electron multiplier with an overall sensitivity ranging from 2.66 x 10-16 moles/pA.

Extraction system and mass spectrometer blanks and backgrounds were measured

numerous times throughout the course of the analyses. Typical blanks (including mass

spectrometer backgrounds) were 1400, 18, 0.3, 2.7, and 4.8 x 10-17 moles at masses 40,

39, 38, 37, and 36, respectively, for furnace temperatures below 1300°C. Correction

factors for interfering nuclear reactions were determined using K-glass and CaF2 and are

40 39 36 37 as follows: ( Ar/ Ar)K = 0.0256 ± 0.0015; ( Ar/ Ar)Ca = 0.00027 ± 0.00001; and

39 37 ( Ar/ Ar)Ca = 0.00070 ± 0.00005. All errors are reported at the 2
confidence level and the decay constants and isotopic abundance are those suggested by Steiger and Jaeger

(1977). As will be discussed below, complexity of the age spectrum data and the quantity of samples analyzed does not allow standard plateau criteria to be met in all cases. A plateau is defined for this investigation as the part of an age spectrum composed of 29 contiguous increments representing >70% of gas released of which results in concordant ages.

6.2 40Ar/39Ar Analytical Results

For the eastern (Snieznik) side of the dome, four parallel transects were

conducted, each oriented NW to SE across the region (Figure 4). The eclogites do not

contain the appropriate mineral assemblages for thermochronology, however I primarily

sampled the enveloping amphibolite-facies gneisses, schists, and one amphibolite where

the goal was to constrain the ascent phase of the massif. Nine samples [eleven separates]

were chosen for their mineral assemblage and mineral quality for 40Ar/39Ar dating. In

addition, a NW-SE transect was also conducted, which bisected the western (Orlica) side

of the dome (Figure 4). While there are no eclogites documented within this area, four

gneisses and schists were collected from which five mineral separates were chosen for

40Ar/39Ar dating. In total, sixteen mineral separates were chosen for Ar-Ar analysis

because of the abundance and/or quality of the hornblende, white mica, and biotite, which

are being dated because of their high retention of argon under moderate closure

temperatures. Furthermore, petrographic examination showed that these rocks were the

least altered and/or retrograded. The Ar-Ar dates help constrain the timing and rate of

exhumation of gneissic country rock, along with the UHP lenses, to midcrustal depths

during an amphibolite-facies metamorphic event.

The majority of the age spectra were similar in appearance and yielded strikingly

consistent cooling ages for the gneisses and schists across the OSD with the exception of 30 the one amphibole sample (szx-9; Figure 4). The biotite from the mica gneisses and schists of the OSD yielded Ar-Ar plateau ages of 342-333 Ma, with a weighted age for all samples of 336.7 ± 1.9 Ma (MSWD: 17). Muscovite also yielded Ar-Ar plateau ages of

341-334 Ma, with a weighted age of 337.6 ± 3.1 Ma (MSWD: 18), and one sample of

314.4 ± 0.8 Ma (MSWD: 3.63). A hornblende from the southeastern side of the Snieznik massif yielded an integrated (total gas) age of 406 ± 3 Ma.

The nine samples from the Snieznik massif dated by the Ar-Ar technique consisted of six mica gneisses, two mica schists, and one amphibolite (Figure 4). A garnet gneiss (szx-10A) collected from the southeastern area of the Snieznik massif, revealed a somewhat concordant spectrum for a biotite separate with an integrated age of

334.5 ± 0.5 Ma. The 3rd through the 8th increments yield a plateau age of 338.2 ± 0.5 Ma

(MSWD: 3.78). A chlorite retrogressed sample (szx-15) was collected from a mica gneiss unit located in the northern area the Snieznik massif yielding a muscovite integrated age of 347.6 ± 0.7 Ma. The slightly saddle-shaped spectrum increments yield a plateau age of

340.9 ± 0.5 Ma (MSWD: 1.28) over ~90% of the gas released. Analysis of a biotite sample from a (biotite zone) mica augen gneiss (szx-16) revealed a relatively flat spectrum with an integrated age of 332.3 ± 0.4 Ma. The sample was collected just west of

Miedzygorze within the Snieznik massif and yielded a plateau age of 333.9 ± 0.5 Ma

(MSWD: 5.45) with ~98% of the gas, defined by the 2nd through the 11th increments.

Another biotite separate (szx-18) was collected from a (garnet zone) mica gneiss near the same area, and yielded an integrated age of 335.5 ± 0.4 Ma. The 2nd through 11th

increments are mainly concordant with a plateau age of 337.6 ± 0.6 Ma (MSWD: 11.93). 31 Biotite from sample szx-23A was separated from a garnet mica gneiss located in the central western region of the Snieznik massif. The spectrum shape consists of a slightly chaotic display of increments yielding an integrated age 337.8 ± 0.5 Ma; a plateau age of

341.6 ± 1.1 Ma (MSWD: 24.27) is defined by the 2nd through 12th increments. Biotite from a sample of mica gneiss (szx-24) was collected just southeast of szx-23A, and yielded an integrated age of 338 ± 0.5 Ma. The step-like shape of the spectrum reveals a plateau age of 340.9 ± 0.9 Ma (MSWD: 10.74) comprising ~ 98% of the gas released.

Analysis of a coexisting muscovite separate reveals older, early steps that decrease as the

K/Ca ratio increases with an integrated age of 337.5 ± 0.7 Ma, and ~94 % of the cumulative gas released defining a plateau age of 336.9 ± 0.5 Ma (MSWD: 0.87).

Biotite from a sample of garnet-mica schist (szx-6) was collected from the northeastern side of the Snieznik massif and yields an integrated age of 328.4 ± 0.5 Ma.

The shape of the spectrum reveals a dome-shaped pattern of increments in which the 3rd

through the 10th define the plateau and comprise ~70% of the gas with a plateau age of

334.2 ± 0.8 Ma (MSWD: 6.49). Coexisting mica separates were sampled from a garnet-

mica schist collected south of Stary Gieraltow in the northeastern region of the Snieznik

massif. The biotite separate (szx-22B) yielded an integrated age of 338.0 ± 0.5 Ma; the

concordant 3rd through 8th increments yields a plateau age of 339.1 ± 0.6 Ma (MSWD:

2.61) which comprises ~70% of the gas. The muscovite separate (szx-22B) yielded an

integrated age of 333.6 ± 1.1 Ma, and a blocky-shaped spectrum with a similar plateau

age of 334.9 ± 0.9 Ma (MSWD: 0.79), representing close to 100% of the gas released. 32 An amphibolite (szx-9) was collected from the southeastern side of the

Snieznik massif in which the hornblende separate from this sample yields an integrated age of 406 ± 3 Ma. However, three similar flat-lying increments (F, G, and J) revealed an average weighted age of 391.1 ± 3.2 Ma (MSWD: 19). The chaotic nature of the spectrum is likely the result of hornblende contaminated with a fine-grained, relatively high-K non-retentive mineral. The variable amount of degassing of the two or more phases is represented by the complexity of the step-heating increments.

Mineral separates were also collected from the Orlica mountains, which comprises the western dome complex. The four samples from the Orlica massif dated by the Ar-Ar technique consisted of two mica gneisses and two mica schists (Figure 4). A biotite separate from a mica gneiss (O-1) and yielded an integrated age of 332.0 ± 0.4

Ma. The relatively flat spectrum is comprised of 10 increments revealing a plateau age of

334.9 ± 0.4 Ma (MSWD: 4.92) constituting around 96% cumulative gas released. A muscovite separate was analyzed from the same sample (O-1) with an integrated age of

335.1 ± 1.1 Ma and a somewhat discordant spectrum with a plateau age of 335.5 ± 0.8

Ma (MSWD: 0.72). A mica gneiss (O-4) from the west-central side of the Orlica massif in which a muscovite separate was sampled revealing a spectrum that has an integrated age of 339.1 ± 0.5 Ma, with increments 8 through 13 representing ~ 80% of gas released and yielding a plateau age of 337.9 ± 0.7 Ma (MSWD: 3.3).

Biotite from a mica schist (O-3) from the east-central side of the Orlica massif and yielded an integrated age of 332.9 ± 0.5 Ma. The slightly dome-shape of the spectrum is characterized through the 2nd and 10th increments yielding a plateau age of 33 338.2 ± 0.9 Ma (MSWD: 11.18). Sample O-6 is a muscovite separate from a mica schist with an integrated age of 311.9 ± 0.6 Ma, in which increments 8 through 15 represent ~82% of gas and a plateau age of 314.4 ± 0.8 Ma (MSWD: 3.63). 34

100

K/Ca SZX-6 bio SZX-10A bio 4501

400 334.2±0.8 Ma (MSWD = 6.49) 338.2±0.5 Ma (MSWD = 3.78)

350 G D E F G H I D E F HI 300

TGA = 328.4±0.5 Ma TGA = 334.5±0.5 Ma Apparent Age (Ma) 250

100 SZX-15 musc K/Ca SZX-16 bio 4501 340.9±0.5 Ma (MSWD = 1.28) 400 333.9±0.5 Ma (MSWD = 5.45) 350 EF I LM D G H J K B C D E F G H I J 300

TGA = 347.6±0.7 Ma TGA = 332.3±0.4 Ma Apparent Age (Ma) 250

100

K/Ca SZX-18 bio SZX-22B bio 4501

400 339.1±0.6 Ma (MSWD = 2.61) 337.6±0.6 Ma (MSWD = 11.93) 350 B C D E F G H I JK B C D E F G H I 300

TGA = 335.5±0.4 Ma TGA = 338.0±0.5 Ma Apparent Age (Ma) 250

100

K/Ca SZX-22B musc SZX-23A bio 4501

334.9±0.9 Ma (MSWD = 0.79) 400 341.6±1.1 Ma (MSWD = 24.27) 350 B F G Q C D E G H I JK F H I JKLM N OP 300 E R TGA = 333.6±1.1 Ma TGA = 337.8±0.5 Ma Apparent Age (Ma) 250 0 20406080100020406080100

Cumulative 39Ar Released Cumulative 39Ar Released

Figure 6. 40Ar/39Ar age spectra from the Orlica Snieznik Dome. 35

100

K/Ca SZX-24 bio SZX-24 musc 4501 336.9±0.5 Ma (MSWD = 0.87) 400 340.9±0.9 Ma (MSWD = 10.74)

350 B C D E F G H I F G H I K M J L N R 300 P TGA = 338.7±0.5 Ma TGA = 337.5±0.7 Ma Apparent Age (Ma) 250

1

K/Ca SZX-9 hbd O-1 musc 0.01 450 335.5±0.8 Ma (MSWD = 0.72) 400 F J 350 C G E EF G H I J K L M NO 300 B P D Q TGA = 406±3 Ma I TGA = 335.1±1.1 Ma 250

100 O-3 bio O-1 bio K/Ca 4501

400 334.9±0.4 Ma (MSWD = 4.92) 338.2±0.9 Ma (MSWD = 11.18) 350 D E F G B C D E F G HI B C H I J 300 Apparent Age (Ma) Apparent Age (Ma) TGA = 332.0±0.4 Ma TGA = 332.9±0.5 Ma 250

100 O-4 musc O-6 musc K/Ca 4501

400 337.9±0.7 Ma (MSWD = 3.3) 314.4±0.8 Ma (MSWD = 3.63)

350 H I J KL K L 300 H I J M Apparent Age (Ma) TGA = 339.1±0.5 Ma TGA = 311.9±0.6 Ma 250 0 204060801000 20406080100

Cumulative 39Ar Released Cumulative 39Ar Released

Figure 6. Continued. 36 Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

SZX-6 biotite, 0.47 mg, J=0.0162489 A 650 10.74 0.0393 8.123 15.0 13 77.6 3.5 228.7 1.4 B 750 12.37 0.0027 1.151 50.6 188 97.2 15.4 321.6 0.6 C 850 12.54 0.0009 0.445 61.5 595 98.9 29.8 330.6 0.6 D 920 12.70 0.0010 0.334 37.8 488 99.2 38.7 335.3 0.7 E 1000 12.65 0.0012 0.400 55.7 437 99.1 51.8 333.7 0.9 F 1075 12.60 0.0005 0.292 137.4 960 99.3 84.0 333.3 0.5 G 1110 12.71 0.0007 0.247 42.4 712 99.4 94.0 336.4 0.6 H 1180 12.82 0.0020 1.175 16.4 257 97.3 97.8 332.4 1.0 I 1210 12.63 0.0064 1.147 5.0 80 97.3 99.0 327.9 1.5 J 1250 12.87 0.0617 1.716 2.7 8 96.1 99.6 329.9 2.7 K 1300 13.31 -0.0004 3.251 1.6 - 92.8 100 329.2 4.1 Integrated age ± 1
n=11 426.1 K2O=21.43 % 328.4 0.5 Plateau ± 1
steps D-I n=6 MSWD=6.49 334.2 0.8

SZX-9 hornblende, 2.16 mg, J=0.0161262 A 800 119.5 16.67 165.8 0.6 0.031 60.1 1.3 1399.1 14 B 900 25.39 14.56 44.06 0.3 0.035 53.2 2.0 358.7 22 C 1000 16.27 25.78 13.33 1.4 0.020 88.4 4.9 382.1 6.9 D 1030 16.26 39.92 14.91 1.0 0.013 92.5 6.9 401.3 11 E 1060 15.26 27.91 14.58 0.8 0.018 86.3 8.5 353.4 9.8 F 1090 15.68 28.82 10.66 8.5 0.018 94.6 26 393.4 2.8 G 1120 14.63 31.41 10.13 12.8 0.016 96.7 53 377.4 2.8 H 1170 13.86 29.56 21.46 0.5 0.017 71.2 54 271.2 17 I 1200 19.34 30.21 35.73 0.5 0.017 57.8 55 304.6 22 J 1250 16.00 31.33 11.45 19.7 0.016 94.5 96 400.9 2.6 K 1300 22.05 31.09 27.28 1.0 0.016 74.7 98 432.8 10 L 1650 116.6 19.23 360.7 0.8 0.027 9.90 100 311.7 28 Integrated age ± 1
n=12 47.9 K2O=0.53 % 406.2 3 Plateau ± 1
steps A-L n=12 MSWD=461.56 399.6 31.5 37 y tical 40 Ar/ 39 Ar isotopic data Continued. Table 1. Anal 40 39 37 39 36 39 39 40 39 ID Power Ar/ Ar Ar/ Ar Ar/ Ar Ar K K/Ca Ar* Ar Age ±1
(Watts) (x 10 -3 ) (x 10 -15 mol) (%) (%) (Ma) (Ma) O-6 muscovite, 0.22 mg, J=0.015 A 600 15.65 0.1872 28.69 2.6 3 45.9 1.1 184.2 4.2 B 650 12.41 0.0591 3.648 1.6 9 91.3 1.8 282.8 4.8 C 700 13.42 0.0322 3.167 1.6 16 93.0 2.5 309.1 3.6 D 750 13.36 0.0078 1.144 4.1 66 97.5 4.2 321.3 1.8 E 800 13.43 0.0048 1.480 5.6 107 96.7 6.6 320.6 1.6 F 840 13.13 0.0016 0.958 9.5 327 97.8 10.6 317.4 1.2 G 880 12.91 0.0021 0.506 16.0 238 98.8 17.4 315.3 0.8 H 920 12.77 0.0009 0.300 63.1 549 99.3 44.1 313.6 1.2 I 960 12.62 0.0005 0.234 75.4 1118 99.5 76.1 310.7 1.0 J 1000 12.92 0.0009 0.588 24.6 580 98.7 86.5 314.9 0.9 K 1040 12.97 0.0018 0.700 12.5 287 98.4 91.8 315.5 0.7 L 1080 12.96 0.0023 0.326 6.4 219 99.3 94.5 317.7 1.4 M 1120 13.68 0.0116 3.763 3.1 44 91.9 95.8 311.0 2.5 N 1160 13.55 0.0120 2.612 2.0 43 94.3 96.6 315.8 3.5 O 1200 13.49 0.0642 2.027 1.4 8 95.6 97.2 318.4 5.1 P 1250 13.57 0.2113 3.115 1.3 2 93.3 97.7 313.4 5.5 Q 1350 13.50 0.4429 2.207 3.3 1 95.4 99.1 318.3 2.4 IntegratedR 1650 age ± 1 20.39
0.0135 29.25 2.0 38 57.6 100.0 292.3 5.9 Plateau ± 1
n=18 236.1 K2O=27.48 % 311.9 0.6 steps H-O n=8 MSWD=3.63 314.4 0.8 38 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

SZX-15 muscovite, 0.54 mg, J=0.0162816 A 600 13.45 0.0739 18.76 2.1 7 58.8 0.8 218.1 13.5 B 650 14.63 0.0286 7.410 2.1 18 85.0 1.6 332.2 12.6 C 700 14.14 0.0070 5.190 2.4 73 89.1 2.5 336.3 11.1 D 750 13.78 0.0089 3.209 5.1 57 93.1 4.5 341.6 5.6 E 800 13.66 0.0026 2.345 8.8 199 94.9 7.9 345.1 3.3 F 840 13.30 0.0017 1.134 17.1 306 97.5 14.5 344.9 2.3 G 880 13.06 0.0010 0.794 16.5 493 98.2 20.8 341.4 1.9 H 920 12.92 0.0005 0.532 43.9 960 98.8 37.7 340.1 1.0 I 960 12.94 0.0005 0.575 60.0 1089 98.7 60.8 340.3 0.7 J 1000 12.90 0.0003 0.499 45.6 1836 98.9 78.4 339.7 1.5 K 1040 13.16 0.0007 1.206 15.0 779 97.3 84.2 340.9 1.8 L 1080 13.32 0.0012 1.149 13.2 419 97.4 89.3 345.3 2.2 M 1120 13.59 0.0024 1.755 6.8 209 96.2 91.9 347.5 4.1 N 1160 14.58 0.0077 3.016 3.9 66 93.9 93.4 362.3 6.9 O 1200 14.65 0.0078 1.322 2.4 66 97.3 94.4 376.0 10.0 P 1250 19.73 0.0185 2.268 2.1 28 96.6 95.2 487.0 11.4 Q 1350 21.85 0.0168 2.019 5.8 30 97.3 97.4 535.7 4.4 R 1650 19.86 0.0144 19.87 6.7 36 70.4 100.0 369.5 4.4 Integrated age ± 1
n=18 259.7 K2O=11.34 % 347.6 0.7 Plateau ± 1
steps B-M n=12 MSWD=1.28 340.9 0.5 39 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

SZX-16 biotite,1.26 mg, J=0.0162401 A 650 11.17 0.0146 2.589 14.8 35 93.1 2.4 281.0 1.0 B 750 12.63 0.0022 0.316 65.4 230 99.3 12.9 333.6 0.5 C 850 12.45 0.0011 0.114 114.7 474 99.7 31.4 330.6 0.6 D 920 12.62 0.0022 0.202 60.7 228 99.5 41.2 334.2 0.7 E 1000 12.67 0.0039 0.150 58.2 130 99.7 50.5 335.8 0.8 F 1075 12.57 0.0028 0.136 122.3 184 99.7 70.2 333.6 0.6 G 1110 12.57 0.0035 0.163 65.8 144 99.6 80.8 333.4 0.6 H 1180 12.65 0.0107 0.206 53.1 48 99.5 89.4 335.0 0.6 I 1210 12.58 0.0205 0.092 37.3 25 99.8 95.4 334.1 0.6 J 1250 12.69 0.1634 0.310 19.2 3 99.4 98.4 335.6 0.8 K 1300 12.80 0.5062 0.634 9.7 1 98.9 100.0 336.6 1.4 Integrated age ± 1
n=11 621.1 K2O=11.66 % 332.3 0.4 Plateau ± 1
steps B-K n=10 MSWD=5.45 333.9 0.5

SZX-18 biotite, 0.56 mg, J=0.0161578 A 650 7.44 0.1504 6.186 9.9 3 75.5 1.3 156.3 1.7 B 750 13.06 0.0099 0.746 45.2 51 98.3 7.1 339.5 0.6 C 850 12.74 0.0036 0.160 132.3 142 99.6 24.0 336.0 0.6 D 920 12.77 0.0065 0.077 99.3 78 99.8 36.8 337.4 0.6 E 1000 12.85 0.0189 0.162 62.0 27 99.6 44.7 338.6 0.7 F 1075 12.95 0.0131 0.130 115.4 39 99.7 59.5 341.2 0.6 G 1110 12.80 0.0091 0.132 107.2 56 99.7 73.2 337.6 0.6 H 1180 12.76 0.0406 0.251 101.9 13 99.4 86.3 335.8 0.5 I 1210 12.70 0.0931 0.149 61.9 5 99.7 94.2 335.4 0.4 J 1250 12.81 0.2947 0.272 27.9 2 99.6 97.8 337.4 0.8 K 1300 12.98 0.1973 0.511 17.0 3 99.0 100.0 339.6 0.7 Integrated age ± 1
n=11 780.0 K2O=33.11 % 335.5 0.4 Plateau ± 1
steps B-K n=10 MSWD=11.93 337.6 0.6 40 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

SZX-22B biotite, 0.34 mg, J=0.0163397 A 650 12.46 0.0929 9.042 7.0 5 78.6 1.4 267.3 2.1 B 750 12.89 0.0019 0.510 65.8 263 98.8 14.2 340.5 0.5 C 850 12.68 0.0007 0.172 81.0 758 99.6 29.9 337.9 0.7 D 920 12.85 0.0009 0.247 33.0 596 99.4 36.3 341.5 1.3 E 1000 12.77 0.0009 0.209 63.4 598 99.5 48.6 339.8 0.7 F 1075 12.73 0.0004 0.097 131.1 1377 99.8 74.1 339.6 0.6 G 1110 12.65 0.0004 0.249 63.4 1221 99.4 86.4 336.6 1.3 H 1180 12.72 0.0008 0.357 60.7 656 99.2 98.2 337.5 0.8 I 1210 12.84 0.0109 0.602 9.1 47 98.6 100.0 338.6 1.2 Integrated age ± 1
n=9 514.5 K2O=35.57 % 338.0 0.5 Plateau ± 1
steps B-I n=8 MSWD=2.61 339.1 0.6 41 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

SZX-22B muscovite, 0.38 mg, J=0.0162113 A 600 10.13 0.2767 24.26 0.8 2 29.2 0.7 84.4 44.4 B 650 30.59 0.1530 57.37 0.4 3 44.6 1.0 359.9 75.4 C 700 16.01 0.0552 9.744 0.4 9 82.0 1.4 347.7 57.9 D 750 16.44 0.0128 11.25 1.3 40 79.7 2.4 347.1 20.7 E 800 14.48 0.0048 5.803 2.1 106 88.1 4.1 338.8 13.1 F 840 13.75 0.0026 4.558 4.2 193 90.2 7.6 329.9 6.4 G 880 13.00 0.0006 1.018 22.7 807 97.7 26.2 337.2 1.6 H 920 12.61 0.0010 0.544 32.5 517 98.7 52.9 331.1 1.7 I 960 13.54 0.0025 3.040 9.5 201 93.4 60.6 335.6 3.1 J 1000 13.28 0.0015 2.356 4.6 336 94.7 64.4 334.3 5.8 K 1040 13.02 0.0011 0.007 3.6 476 100.0 67.4 344.8 7.3 L 1080 13.31 0.0003 2.532 4.7 1831 94.4 71.3 333.8 5.7 M 1120 13.07 0.0003 1.148 7.1 1535 97.4 77.1 337.9 3.8 N 1160 13.32 0.0008 2.866 8.0 604 93.6 83.7 331.5 3.5 O 1200 13.05 0.0003 1.218 5.9 1952 97.2 88.5 336.9 4.5 P 1250 13.40 0.0015 2.799 4.5 331 93.8 92.2 334.2 5.9 Q 1350 13.27 0.0008 1.863 7.5 659 95.8 98.4 337.6 3.6 R 1650 30.97 0.0018 61.83 2.0 276 41.0 100.0 337.1 14.8 Integrated age ± 1
n=18 121.9 K2O=7.60 % 333.6 1.1 Plateau ± 1
steps E-R n=14 MSWD=0.79 334.9 0.9 42 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

SZX-23A biotite, 0.97 mg, J=0.0161535 A 650 5.640 0.0333 3.655 9.7 15 80.8 2.2 127.6 1.2 B 750 13.31 0.0046 0.341 31.8 110 99.2 9.6 348.2 1.0 C 850 12.85 0.0016 0.182 76.2 319 99.6 27.3 338.4 0.5 D 920 13.05 0.0038 0.293 38.2 134 99.3 36.2 342.5 0.6 E 1000 12.95 0.0103 0.199 35.2 49 99.6 44.4 340.8 0.6 F 1075 13.22 0.0055 0.122 75.3 92 99.7 61.9 347.6 0.6 G 1110 13.07 0.0033 0.130 55.9 156 99.7 74.9 344.1 1.1 H 1180 12.92 0.0074 0.264 46.8 69 99.4 85.8 339.5 0.8 I 1210 12.90 0.0086 0.160 30.2 59 99.6 92.8 339.6 0.7 J 1250 12.89 0.0312 0.299 18.6 16 99.3 97.1 338.6 0.8 K 1300 12.89 0.1021 0.323 6.6 5 99.3 98.6 338.6 1.2 L 1650 14.41 0.0399 5.515 5.9 13 88.7 100.0 338.1 1.7 Integrated age ± 1
n=12 430.4 K2O=10.55 % 337.8 0.5 Plateau ± 1
steps B-K n=10 MSWD=24.27 341.6 1.1 43 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

SZX-24 biotite, 0.49 mg, J=0.0163386 A 650 11.45 0.0517 5.680 14.6 10 85.3 2.8 266.7 1.6 B 750 13.10 0.0052 0.372 74.8 99 99.2 17.4 346.6 1.4 C 850 12.70 0.0016 0.194 121.9 321 99.5 41.1 338.1 0.8 D 920 12.89 0.0038 0.192 45.9 136 99.6 50.1 342.8 0.8 E 1000 12.94 0.0035 0.252 61.4 145 99.4 62.1 343.7 0.6 F 1075 12.71 0.0026 0.195 89.0 194 99.5 79.4 338.5 0.9 G 1110 12.76 0.0042 0.260 44.4 120 99.4 88.0 339.1 0.6 H 1180 12.74 0.0327 0.572 33.9 16 98.7 94.6 336.4 1.1 I 1210 13.01 0.2562 0.961 8.4 2 98.0 96.3 340.8 1.4 J 1250 13.02 0.2630 1.153 8.3 2 97.5 97.9 339.6 1.4 K 1300 13.71 0.1085 2.533 7.8 5 94.6 99.4 346.2 1.4 L 1650 36.59 0.0200 81.26 3.0 25 34.3 100.0 336.6 7.5 Integrated age ± 1
n=12 513.4 K2O=24.63 % 338.7 0.5 Plateau ± 1
steps B-L n=11 MSWD=10.74 340.9 0.9 44 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

SZX-24 muscovite, 0.39 mg, J=0.0162481 A 600 12.93 0.1943 15.17 1.3 3 65.4 0.6 231.8 21.1 B 650 16.65 0.0454 9.189 1.3 11 83.7 1.2 367.8 19.3 C 700 14.09 0.0137 2.701 1.5 37 94.3 1.9 352.2 17.7 D 750 14.18 0.0047 1.794 3.9 109 96.3 3.6 360.7 7.0 E 800 13.36 0.0037 0.798 6.6 138 98.2 6.6 348.2 4.1 F 840 13.06 0.0018 0.743 11.7 284 98.3 11.9 341.2 2.7 G 880 12.94 0.0014 0.632 20.1 356 98.6 21.0 339.1 1.5 H 920 12.81 0.0006 0.452 45.6 826 99.0 41.7 337.2 0.9 I 960 12.73 0.0006 0.327 37.3 925 99.2 58.5 336.2 1.5 J 1000 12.77 0.0006 0.654 20.4 868 98.5 67.8 334.9 1.5 K 1040 12.81 0.0013 0.542 15.1 385 98.7 74.6 336.7 1.9 L 1080 12.73 0.0013 0.495 18.1 381 98.9 82.8 334.9 1.7 M 1120 12.83 0.0008 0.549 19.5 629 98.7 91.6 337.1 1.7 N 1160 13.41 0.0051 2.986 6.3 100 93.4 94.4 333.6 4.1 O 1200 13.60 0.0105 2.003 2.8 48 95.6 95.7 345.2 9.1 P 1250 20.67 0.0575 26.85 1.8 9 61.6 96.5 338.8 14.7 Q 1350 13.46 0.0545 1.763 3.2 9 96.2 98.0 343.7 7.8 R 1650 22.22 0.0120 32.42 4.5 42 56.8 100.0 336.4 7.1 Integrated age ± 1
n=18 221.1 K2O=13.40 % 337.5 0.7 Plateau ± 1
steps F-R n=13 MSWD=0.87 336.9 0.5 45 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

O-1 biotite, 0.32mg, J=0.0161889 A 650 11.77 0.0052 4.870 29.1 97 87.8 4.5 278.5 0.9 B 750 12.81 0.0014 0.449 113.0 360 99.0 22.0 336.1 0.5 C 850 12.64 0.0008 0.212 149.6 669 99.5 45.2 333.8 0.5 D 920 12.72 0.0017 0.231 49.4 308 99.5 52.9 335.6 0.5 E 1000 12.73 0.0017 0.358 62.3 295 99.2 62.6 335.0 0.6 F 1075 12.62 0.0012 0.232 128.1 440 99.5 82.4 333.1 0.7 G 1110 12.67 0.0017 0.315 46.8 301 99.3 89.7 333.6 0.6 H 1180 12.78 0.0044 0.622 32.7 116 98.6 94.7 334.2 0.6 I 1210 12.78 0.0312 0.568 11.6 16 98.7 96.5 334.7 1.0 J 1250 12.84 0.1799 0.468 5.8 3 99.0 97.5 337.2 1.5 K 1300 12.88 0.0056 0.413 16.4 91 99.1 100.0 338.0 0.8 Integrated age ± 1
n=11 644.8 332.0 0.4 Plateau ± 1
steps B-I n=8 MSWD=4.92 334.9 0.4 46 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

O-1 muscovite, 0.30 mg, J=0.0162233 A 600 21.65 0.2570 51.81 0.8 2 29.3 0.6 176.6 35.7 B 650 20.94 0.0464 27.44 0.7 11 61.3 1.2 340.7 40.3 C 700 14.42 0.0097 6.714 0.9 53 86.2 1.8 331.0 32.9 D 750 14.10 0.0073 6.267 2.2 70 86.8 3.5 326.4 12.6 E 800 13.45 0.0034 1.636 4.3 149 96.4 6.7 343.8 6.7 F 840 13.42 0.0019 2.328 6.8 271 94.9 11.9 338.0 4.5 G 880 12.99 0.0017 1.119 12.8 294 97.5 21.6 336.5 2.5 H 920 12.75 0.0009 0.693 26.5 591 98.4 41.7 333.5 1.4 I 960 12.89 0.0004 0.731 12.3 1293 98.3 51.1 336.8 2.4 J 1000 12.74 -0.0003 0.777 9.6 - 98.2 58.4 332.7 3.0 K 1040 12.92 -0.0009 0.431 7.9 - 99.0 64.4 339.6 3.7 L 1080 12.89 0.0006 0.626 11.7 789 98.6 73.3 337.4 2.5 M 1120 12.66 0.0006 0.413 16.7 848 99.0 85.9 333.5 2.0 N 1160 13.09 0.0010 0.898 8.9 525 98.0 92.7 340.3 3.4 O 1200 13.37 0.0025 1.652 4.0 208 96.3 95.7 341.7 7.1 P 1250 13.69 0.0098 4.011 2.2 52 91.3 97.3 332.7 13.2 Q 1350 14.18 -0.0013 5.132 1.3 - 89.3 98.4 336.5 21.2 R 1650 22.50 -0.0025 32.71 2.2 - 57.0 100.0 340.5 14.7 Integrated age ± 1
n=18 131.8 K2O=10.40 % 335.1 1.1 Plateau ± 1
steps B-R n=17 MSWD=0.72 335.5 0.8 47 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

O-3 biotite, 0.30 mg, J=0.0162555 A 650 9.76 0.1808 15.91 6.2 3 51.9 3.0 142.4 2.8 B 750 13.04 0.1100 2.094 12.4 5 95.3 8.9 331.3 1.2 C 850 12.96 0.0425 0.977 18.3 12 97.8 17.7 337.4 0.8 D 920 13.10 0.0804 1.140 13.7 6 97.5 24.3 339.6 0.7 E 1000 13.05 0.0810 0.605 22.3 6 98.7 34.9 342.3 0.9 F 1075 12.90 0.0294 0.314 51.3 17 99.3 59.6 340.7 0.7 G 1110 12.86 0.0379 0.439 30.0 13 99.0 74.0 338.8 0.7 H 1180 12.73 0.0729 0.447 36.9 7 99.0 91.6 335.6 0.6 I 1210 12.75 0.5645 0.620 9.5 1 98.9 96.2 336.0 1.2 J 1250 12.96 0.5567 0.930 5.9 1 98.2 99.0 338.7 1.6 K 1300 13.36 0.1535 1.962 2.1 3 95.7 100.0 340.2 3.3 Integrated age ± 1
n=11 208.5 K2O=16.42 % 332.9 0.5 Plateau ± 1
steps B-K n=10 MSWD=11.18 338.2 0.9 48 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

O-4 muscovite, 0.38 mg, J=0.0163193 A 600 19.76 0.1572 36.21 3.3 3 45.8 1.2 248.4 4.3 B 650 13.85 0.0490 0.102 3.5 10 99.8 2.5 366.3 2.5 C 700 13.99 0.0088 2.219 4.9 58 95.3 4.3 354.7 1.8 D 750 13.49 0.0039 1.074 14.9 130 97.6 9.7 350.8 1.5 E 800 13.09 0.0028 0.681 20.2 185 98.5 17.1 343.9 0.8 F 840 12.92 0.0020 0.466 29.0 257 98.9 27.8 341.2 0.7 G 880 12.82 0.0015 0.321 39.0 351 99.3 42.1 339.7 0.7 H 920 12.62 0.0011 0.134 51.5 455 99.7 61.1 336.2 0.8 I 960 12.70 0.0011 0.315 43.7 473 99.3 77.1 337.0 0.7 J 1000 12.83 0.0010 0.334 31.7 526 99.2 88.8 339.9 0.9 K 1040 12.83 0.0025 0.338 14.8 204 99.2 94.2 339.8 0.9 L 1080 12.86 0.0031 0.816 9.0 164 98.1 97.5 337.2 1.2 M 1120 12.93 0.0086 0.913 4.9 59 97.9 99.4 338.1 1.7 O 1200 12.54 0.0409 0.929 0.8 12 97.8 99.7 328.6 8.2 P 1250 12.85 0.1769 1.935 0.9 3 95.7 100.0 329.2 7.3 Integrated age ± 1
n=15 272.0 K2O=16.85 % 339.1 0.5 Plateau ± 1
steps H-M n=6 MSWD=3.3 337.9 0.7 49 Continued. Table 1. Analytical 40Ar/39Ar isotopic data

ID Power 40 39 37 39 36 39 39 K/Ca 40 39 Age Ar/ Ar Ar/ Ar Ar/ Ar ArK Ar* Ar ±1
(Watts) (x 10-3) (x 10-15 mol) (%) (%) (Ma) (Ma)

O-6 muscovite, 0.22 mg, J=0.015 A 600 15.65 0.1872 28.69 2.6 3 45.9 1.1 184.2 4.2 B 650 12.41 0.0591 3.648 1.6 9 91.3 1.8 282.8 4.8 C 700 13.42 0.0322 3.167 1.6 16 93.0 2.5 309.1 3.6 D 750 13.36 0.0078 1.144 4.1 66 97.5 4.2 321.3 1.8 E 800 13.43 0.0048 1.480 5.6 107 96.7 6.6 320.6 1.6 F 840 13.13 0.0016 0.958 9.5 327 97.8 10.6 317.4 1.2 G 880 12.91 0.0021 0.506 16.0 238 98.8 17.4 315.3 0.8 H 920 12.77 0.0009 0.300 63.1 549 99.3 44.1 313.6 1.2 I 960 12.62 0.0005 0.234 75.4 1118 99.5 76.1 310.7 1.0 J 1000 12.92 0.0009 0.588 24.6 580 98.7 86.5 314.9 0.9 K 1040 12.97 0.0018 0.700 12.5 287 98.4 91.8 315.5 0.7 L 1080 12.96 0.0023 0.326 6.4 219 99.3 94.5 317.7 1.4 M 1120 13.68 0.0116 3.763 3.1 44 91.9 95.8 311.0 2.5 N 1160 13.55 0.0120 2.612 2.0 43 94.3 96.6 315.8 3.5 O 1200 13.49 0.0642 2.027 1.4 8 95.6 97.2 318.4 5.1 P 1250 13.57 0.2113 3.115 1.3 2 93.3 97.7 313.4 5.5 Q 1350 13.50 0.4429 2.207 3.3 1 95.4 99.1 318.3 2.4 R 1650 20.39 0.0135 29.25 2.0 38 57.6 100.0 292.3 5.9 Integrated age ± 1
n=18 236.1 K2O=27.48 % 311.9 0.6 Plateau ± 1
steps H-O n=8 MSWD=3.63 314.4 0.8 50 Continued. Table 1. Analytical 40Ar/39Ar isotopic data Isotopic ratios corrected for blank, radioactive decay, and mass discrimination, not corrected for interferring reactions Ages calculated ralative to FC-1 Fish Canyon Tuff sanidine interlaboratory standard at 27.84 Ma. Errors quoted for individual analyses include analytical error only, without interferring reaction or J uncertainties. Integrated age calculated by recombining isotopic measurements of all steps. Integrated age error calculated by recombining errors of isotopic measurements of all steps. Plateau age is inverse-variance-weighted mean of selected steps. Plateau age error is inverse-variance-weighted mean error (Taylor, 1982) times root MSWD where MSWD>1. Plateau and integrated ages incorporate uncertainties in interferring reaction corrections and J factors. Decay constants and isotopic abundances after Steiger and Jaeger (1977). Discrimination = 1.00484 ± 0.00092 Correction factors: 39 37 ( Ar/ Ar)Ca = 0.0007 ± 5e-05 36 37 ( Ar/ Ar)Ca = 0.00027 ± 1e-05 38 39 ( Ar/ Ar)K = 0.01077 40 39 ( Ar/ Ar)K = 0.02559 ± 0.001487 51 7. U-Th-total Pb Geochronology

U-Th-total Pb geochronology is another reliable dating technique through which the metamorphic evolution of a terrane can be revealed. This technique can be applied to any rock type containing the minerals zircon, monazite, apatite, and sphene. Monazite is a light REE-bearing phosphate mineral, which contains relatively large amounts of U and

Th that radioactively decay to Pb (U238, 235Pb206, 207, Th232Pb208), and is ideal for dating metamorphic events due to its notably high closure temperature for Pb diffusion >800oC, which can help elucidate higher-grade metamorphic episodes (Cherniak et al., 2004;

Catlos et al., 2002). Monazite can also grow as discrete mineral domains on existing crystals during subsequent thermal episodes at temperatures as low as ~400ºC, which assists in constraining the timing of younger thermal events (Catlos et al., 2002).

The electron microprobe analyzer (EMPA) is an in situ microanalytical technique,

which has the ability to rapidly identify and analyze minerals, and has recently come into

use as a geochronology instrument. EMPA analysis of monazite provides high-resolution

elemental compositional maps of individual grains as small as 10
m in thin section that

can reveal U, Th, and Pb zoning patterns within the crystal. This zoning is typically a

result of multiple growth events representing discrete thermal pulses, and allows for a

means of interpreting the age significance of compositional domains. More than one age

domain can be obtained from a single crystal of monazite representing different stages of

metamorphic events (Williams and Jercinovic, 2002). Zoning patterns found within

single monazite grains from the OSD may imply multiple thermal events, and therefore 52 can be used to facilitate the thermal evolution of the OSD through the use of U-Th- total Pb geochronology.

7.1 Analytical Procedure

To further constrain the thermal evolution of the OSD, the chemical U-Th-total

Pb dating technique was employed on monazites using the electron microprobe analyzer

(EMPA; Suzuki and Adachi 1991; Montel et al., 1996; Cocherie et al., 1998; Williams et al., 1999; Cocherie and Albarede, 2001). This EMPA geochronology investigation involved two techniques: high-resolution compositional mapping to aid in the identification of intracrystalline age domains, and quantitative chemical analyses of Y,

Th, U, and Pb (Williams and Jercinovic, 2002). Analyses were carried out on a Cameca

SX-50 electron microprobe at Virginia Tech. Matrix corrections were done using the

PAP method of Pouchou and Pichoir (1984, 1985); images were collected using high sample current (>200 nA) and small step sizes (~0.5 µm), while rastering the electron beam with the stage fixed. X-ray maps of Y, U, Th, and Pb were obtained from individual sample monazite grains, and subsequently showed distinct chemical domains. Analyses were carried out in two steps. Major elements of the samples were determined first, and were then hand entered for trace-element analysis using the Cameca trace-element routine. Note that a representative single major-element analysis was used for multiple age determinations for individual samples. Background intensities were acquired using high-resolution wavelength scans around the peaks of interest, allowing selection of wavelength regions to use in curve fitting, using appropriate polynomial or exponential 53 models, and calculation of the net intensity to be subtracted from the peak.

Quantitative trace-element analysis was done using a beam current of 150 to 200 nA at

15 kV accelerating voltage with a counting time of 700 to 900 seconds. Once concentrations of U, Th, and Pb were obtained, the age equation of Montel et al. (1996) was solved by iteration. Lead concentration was corrected for Y interference on the Pb

M-alpha line by estimation using the empirical approach of Amlie and Griffen (1975), in

this case based on analysis of Pb-free Y3Al5O12 garnet (YAG) to determine the magnitude of the interference. This estimate was then modified based on the major compositional differences between YAG and monazite to estimate the shift in relative line intensities due to matrix properties. Similarly, U concentrations were corrected based on empirical overlap of Th M-gamma on U M-beta, as suggested by Scherrer et al. (2000). Ages and errors presented may only reflect analytical precision (analyses are grouped by identified domains) and were calculated using the equation for standard error of the mean based on the number of analyses for each domain. Weighted-mean ages were calculated using the standard error from individual analyses of similar age domains and presented graphically as probability curves.

7.2 U-Th-total Pb Analytical Results

This U-Th-Pb geochronometry study utilized the EMPA technique, and in combination with Ar-Ar thermochronometry, allows for a more comprehensive and systematic means of unraveling the metamorphic and cooling history of the OSD.

Monazite grains selected from two of the OSD rock samples (szx-10A and O-1; Figure 4 54 and Figure 7) were analyzed via EMPA methods. The analytical results are presented in Table 2. Sample szx-10A is from the eastern half of the OSD bordering the Keprnik dome and is a well-foliated garnet-zone gneiss containing minor poikilitic garnet with fractures composed of pinite. This sample contained two monazite grains (MON 4 and

MON 5) the size and shape (>75 µm) of which allowed for three transects across the surface of each grain. The images showed that the majority of the monazites are found along broken foliation planes between major metamorphic minerals (i.e., garnet) and the mica matrix. Furthermore, many of the imaged monazite grains reveal crystals that are apparently cracked, possibly creating conduits for fluid infiltration or Pb diffusion.

A B

szx-10A Monazite 4 20 µm szx-10A Monazite 5 20 µm

Figure 7. Yitrium elemental image of an individual monazite grains from szx-10A, collected from the eastern half of the OSD. (a) Sample sz-10A monazite 4 displays two apparent zones: one defining the majority of the crystal core and the other as a thin heterogeneous rim. (b) Sample sz-10A monazite 5 displays no real distinguishable zonation. 55 Table 2. U-Th-total-Pb elemental data Snieznik-10AAnalysis (ppm) Age (Ma) Snieznik-10A Analysis (ppm) Age (Ma) Orlica-1 Analysis (ppm) Age (Ma) Spot Th U Pb Y Spot Th U Pb Y Spot Th U Pb Y Transect 1 Transect 1 Mon 1-7(9)-1 42266 5777 1976 12329 705 Mon 4-1-1 36735 4032 766 910 344 Mon 5-1-1 25230 8269 1204 21794 497 Mon 1-7(9)-2 45011 2915 1014 13189 406 Mon 4-1-2 35816 4881 823 1019 356 Mon 5-1-2 24558 7531 1047 21849 458 Mon 1-7(9)-3 50703 4640 1597 13050 532 Mon 4-1-3 35104 5295 773 1099 331 Mon 5-1-3 26074 9268 1032 21499 395 Mon 1-7(9)-4 36582 3396 907 11777 415 Mon 4-1-4 30580 5168 831 1065 391 Mon 5-1-4 25381 11577 1092 21396 375 Mon 1-7(9)-5 47562 4348 1252 12760 444 Mon 4-1-5 34997 5273 791 1092 339 Mon 5-1-5 25570 11754 1116 21427 378 Mon 1-7(9)-6 48085 3604 1324 12371 485 Mon 4-1-6 35550 5448 838 1133 352 Mon 5-1-6 25006 11398 1196 21280 417 Mon 1-7(6)-1 43479 6039 1189 10593 414 Mon 4-1-7 35162 5402 860 1149 364 Mon 5-1-7 24567 9907 1131 20349 430 Mon 1-7(6)-2 52297 5292 1427 12453 451 Mon 4-1-8 34103 5162 789 994 346 Mon 5-1-8 25091 11088 1135 21067 401 Mon 1-7(6)-3 44825 8917 1581 8677 472 Mon 4-1-9 36791 4635 837 835 360 Mon 5-1-9 25673 11428 1111 20592 383 Mon 1-3A(11)-1 41954 2659 860 13523 369 Mon 4-1-10 37870 4970 834 915 345 Mon 5-1-10 25937 11946 1208 21387 404 Mon 1-3A(11)-2 40778 2776 781 12728 341 Mon 4-1-11 38757 5042 915 1064 370 Mon 5-1-11 25795 11147 1177 21046 410 Mon 1-3A(11)-3 43906 4623 1388 12901 515 Mon 4-1-12 37514 4272 827 2383 358 Mon 5-1-12 26012 11720 1232 21143 416 Mon 1-7A(12)-4 46263 4121 989 12361 363 Mon 4-1-13 32712 6431 1113 11575 454 Mon 5-1-13 25657 12311 1475 20860 487 Mon 4-1-14 28872 5647 813 11247 376 Mon 5-1-14 26556 11934 1272 20908 422 Transect 2 Mon 5-1-15 26092 11325 1261 19898 435 Mon 4-2-15 24723 2420 29 3299 15 Mon 5-1-16 26093 11326 1262 19899 436 Mon 4-2-16 34218 3969 751 817 356 Transect 2 Mon 4-2-17 34581 5166 839 948 365 Mon 5-2-17 24666 9236 1027 20849 404 Mon 4-2-18 35010 5065 795 1019 345 Mon 5-2-18 23310 9979 1017 19149 395 Mon 4-2-19 34897 5141 775 1004 336 Mon 5-2-19 31066 9000 1108 15135 401 Mon 4-2-20 35536 5341 800 1047 338 Mon 5-2-20 28951 11104 1196 17346 401 Mon 4-2-21 35266 5296 822 1055 350 Mon 5-2-21 29641 12399 1314 18650 409 Mon 4-2-22 35143 5290 836 1062 357 Mon 5-2-22 40718 9924 1341 16082 402 Mon 4-2-23 34184 5084 788 1017 347 Mon 5-2-23 36449 8091 1089 15883 378 Mon 4-2-24 35161 5357 818 1057 348 Mon 5-2-24 28095 11861 1217 20289 396 Mon 4-2-25 39124 4294 793 773 334 Mon 5-2-25 28472 11305 1277 21317 424 Mon 4-2-26 37139 3740 780 447 354 Mon 5-2-26 31512 9845 1145 20483 390 Mon 4-2-27 30198 5923 1017 8517 452 Mon 5-2-27 29093 4121 726 11943 371 Mon 4-2-28 1162 4739 121 85 167 Mon 5-2-28 26066 7839 792 15692 333 Transect 3 Mon 5-2-29 29811 10076 1169 16414 407 Mon 4-3-29 38920 5197 809 1098 324 Mon 5-2-30 30646 17141 1137 18047 289 Mon 4-3-30 37457 5636 910 1058 364 Transect 3 Mon 4-3-31 37259 5606 913 977 367 Mon 5-3-31 24165 10888 1118 19561 407 Mon 4-3-32 33527 5054 783 940 350 Mon 5-3-32 28329 10224 1120 17466 396 Mon 4-3-33 37304 5371 826 989 337 Mon 5-3-33 28470 10568 1064 17396 369 Mon 4-3-34 40558 4476 850 819 345 Mon 5-3-34 29854 11531 1171 17125 379 Mon 4-3-35 38281 4177 815 695 351 Mon 5-3-35 30030 12420 1250 18076 387 Mon 4-3-36 37980 3988 799 707 351 Mon 5-3-36 28888 12076 1155 18241 369 Mon 4-3-37 35552 4218 828 2875 374 Mon 5-3-37 26360 11410 1162 20672 397 Mon 4-3-38 27025 6541 905 12947 408 Mon 5-3-38 26563 11595 1191 21007 401 Mon 5-3-39 25861 11667 1168 20587 397 Mon 5-3-40 25596 11905 1219 21229 411 Mon 5-3-41 25037 9830 1159 20838 439 Mon 5-3-42 17977 3876 409 10911 286 56 Sample szx-10A-MON 4 (85 x 85 µm) consisted of three transects: 1) a northern SW-NE section line containing fourteen spot analyses, 2) a middle W-E section line containing fourteen spot analyses, and 3) a southern SW-NE section line containing ten spot analyses. The Y, Th and U elemental maps for this monazite did not display any complex zoning, although two zones are apparent: one defining the majority of the crystal core and the other as a thin heterogeneous rim (Figure 7a). The combined three transects revealed a weighted-mean spot-age average of 349.5 ± 4.2 Ma (MSWD: 1.3; Figure

8a,b). Despite heterogeneous elemental map, all spot ages across the grain are relatively concordant.

MON 4 MON 5 A n: 38 n: 43 szx-10A 350 ± 4 398 ± 6 Relative Probability

250 300 350 400 450 500 550

480 520 B 500 C 460 szx-10A Mean = 350 ± 4 Ma 480 szx-10A garnet-zone gneiss 440 MSWD = 1.3 garnet-zone gneiss 460 440 420 420 400 400

380 380

Total-Pb Age (Ma) Total-Pb 360

360 Age (Ma) Total-Pb 340

340 320 300 Mean = 398 ± 6 Ma 320 MSWD = 2.6 280 300 260

Figure 8. (a-c). Cumulative probability curves from monazite total-Pb age results and distribution of weighted mean monazite total-Pb ages from sample szx-10A. (a) Cumulative probability graph of sample szx-10a MON 4 and MON 5 comprised of a total of 81 spot age analyses from 6 transects (three across each grain). (b,c) Mean ages are given at 1
error. Horizontal gray boxes show the distribution of this error around the calculated average age domain. The dashed lines represent spots not included in the determination of the mean ages. See Table 2 for analytical details. 57 Sample szx-10A-MON 5 (70 x 85 µm) also consisted of three transects: 1) an

eastern NW-SE section line containing seventeen spot analyses, 2) a western NW-SE

containing fourteen spot analyses, and 3) a middle SW-NE section line containing twelve

spot analyses. The Y, Th and U elemental maps for MON 5 of szx-10A also did not

display any complex zoning (Figure 7b). The three transects combined revealed a

weighted-mean average age of 397.6 ± 5.7 Ma (MSWD: 2.6; Figure 8a,c).

A O-1 600 n: 13 B

550 O-1 garnet-zone gneiss 500

450

Total-Pb Age (Ma) Total-Pb 400 Mean = 455 ± 57 Ma Relative Probability MSWD = 90 350

300

250 300 350 400 450 500 550 U-Th-total Pb ages (Ma)

Figure 9. (a) Cumulative probability graph of sample O-1 comprised of 13 single spot age analyses. (b) Distribution of weighted mean monazite total-Pb ages from sample O-1. Mean ages are given at 1
error. Horizontal gray boxes show the distribution of this error around the calculated average age domain. The dashed lines represent spots not included in the determination of the mean ages. See Table 2 for analytical details.

Sample O-1 was collected from the Orlica massif and is a medium- to coarse- grained foliated garnet-mica augen gneiss with a matrix consisting of medium- to coarse- grained undulatory subhedral quartz, and sericitized and myrmekitic plagioclase. The majority of the O-1 monazite grains were small (<15 µm), narrow, and typically located on edges of larger major rock-forming minerals (quartz, potassium-feldspar) and where the mica matrix is fractured (likely along foliation planes); therefore, applying transects 58 across the surface of the grains was not feasible. Thirteen individual spot analyses were performed on four crystals all of which were less than 20 µm in size yielding a range of total-Pb dates from 363 to 532 Ma, and the combined date resulted in a weighted average age of 455 ± 57 Ma (MSWD: 90; Figure 9a,b).

8. Discussion

The new Ar-Ar thermochronometric and the total-Pb geochronometric data which

I report here provide insight into the thermal evolution of the Orlica Snieznik Dome and assist in placing constraints on the timing of exhumation of the ultrahigh-grade assemblages found within this Variscan terrane. Specifically, these combined data allow the timing of thermal events to be documented within a ~500 oC window and suggest wholesale cooling of the OSD through amphibolite-facies metamorphism shortly following UHP conditions. The investigation resulted in 1) documentation of two metamorphic events at ca. 400 Ma and 350 Ma as revealed through total-Pb monazite geochronology, as well as an Ar-Ar hornblende event at ca. 400 Ma 2) timing constraints of mid-crustal exhumation between 340-330 Ma as revealed through Ar-Ar cooling age data, which was preceded by a HT-MP (amphibolite-facies) thermal event ca. 345-330

Ma, 3) cooling rates on the order of 100 – 50 oC/m.y., and 4) a clockwise P-T-t path of

the OSD from peak HT-HP eclogite-facies metamorphism through exhumation-related

HT-MP amphibolite-facies metamorphism.

Previous workers suggested protolith emplacement was broadly constrained to ca.

500 Ma (Borkowska et al., 1990; Oliver et al., 1993; Kroner et al., 1994; Brocker et al., 59 1997; Kroner et al., 1997; Borkowska and Dorr, 1998; Turniak et al., 2000) with subsequent UHP metamorphism (700-800 oC and >27 kbar) of the OSD reported to have

occurred at ca. 375-360 Ma (Brueckner et al., 1991; Brocker et al., 1997; Klemd and

Brocker, 1999; Gordon et al., 2004). The UHP-HT event was followed by a metamorphic

episode (~600 oC and 10-4 kbar) associated with Variscan crustal thickening at ca. 345-

330 Ma (Brocker and Klemd, 1996; Kozlowski and Bakun-Czubarow, 1997; Gordon et al., 2004); rapid cooling is constrained to between 340-330 Ma (Maluski et al., 1995;

Steltenpohl et al., 1993; Marheine et al., 2002; this study).

Total-Pb monazite dates from sample O-1, a garnet-mica augen gneiss, revealed a

mean age of age of 455 ± 57 Ma, which represents a combined date from 13 individual

spot analyses. The age falls within the range of events occurring throughout the Variscan

orogeny, but is considered ambiguous due to the nature of the grains analyzed, which

were few, fractured and small in size (<15 µm). Total-Pb monazite data from the sample

szx-10A revealed two metamorphic events at 398 ± 6 and 350 ± 4 Ma. The ca. 400 Ma

monazite age from a garnet-zone gneiss is similar to ages found in the adjacent Gory

Sowie Block (GSB), located 50 km to the north in which granulites were produced during

an Early Devonian HP/HT metamorphic event, however both the OSD and the GSB are

fault-bounded terranes, which makes the comparison of metamorphic evolution difficult

(O’Brien et al., 1997). Nonetheless, the ca. 400 Ma age most likely represents an early

Variscan HT localized episode possibly attributed to the widespread, batholithic-scale,

granitoid intrusion which occurred throughout the Sudetes as well as the Variscan belt

(Oliver et al., 1993; Turniak et al., 2000). 60 The 350 Ma total-Pb monazite age (szx-10A MON 4) from the garnet-zone gneiss is found to be similar to previous Sm-Nd garnet-clinopyroxene whole rock age of ca. 352 Ma from a Snieznik eclogite of the high pressure Zlote region located in the northeastern OSD (Brueckner et al., 1991). Gordon et al. (2004) reported an ion microprobe Th-Pb monazite age of ca. 350 Ma from a biotite schist (southeast OSD), interpreted to reflect an analytical mixed age between the 375 Ma and 345 Ma thermal events. However, I suggest the 350 Ma total-Pb age provides further documentation for a discrete Late Devonian/Early Carboniferous metamorphic event believed to have occurred during commencement of isothermal decompression under amphibolite-facies conditions.

The 40Ar/39Ar data obtained in this study reveal cooling between 340-330 Ma following amphibolite-facies metamorphism of the massif. These ages are remarkably consistent across the dome and in conjunction with previous thermochronological results, further constrain the timing and rate of exhumation of country rock gneisses and schists, along with UHP/UHT lenses, to midcrustal depths during an amphibolite-facies metamorphic event. These Ar-Ar cooling ages are interpreted to be the result of rapid exhumation and isothermal decompression during a E to NE directed thrusting event which continued through the Early Carboniferous as documented by Ar-Ar and Rb-Sr cooling ages of 335-328 Ma (Borkowska et al., 1990; Steltenpohl et al., 1993; Maluski et al., 1995; Brocker et al., 1997; Lange et al., 2002; Marheine et al., 2002). Similar

Variscan ages of 340-320 Ma were also recorded from the Ar-Ar and Rb-Sr dating of micas and hornblendes in gneisses and schists throughout the Erzgebirge Dome located at 61 the northwest margin of the Bohemian massif (Kroner and Willner, 1998). Marheine et al. (2002) compared Ar-Ar cooling ages of 344-333 Ma from the Krkonose-Izera Terrane

(to the west of the study area; Figure 2) and the OSD to represent coeval exhumation and isothermal decompression across the Sudetes. The timing of exhumation relates to late

Variscan orogenic events in which the rapid nature is characteristic of orogenic collapse.

A mica schist (O-6) from the Orlica mountains yielded a younger Ar-Ar muscovite age of 314 ± 0.8. Similarly young Th-Pb monazite dates of 315 ± 4 Ma and

295 ± 4 Ma were also reported from the OSD (Gordon et al., 2004), all of which are described as the result of a weak, localized heating episode. An Ar-Ar muscovite age of

313 ± 3 Ma was reported from the southern OSD by Maluski et al. (1995) and localized

Ar-Ar cooling ages between 314-312 Ma were recorded from the Krkonose-Izera Terrane by Marheine et al. (2002), interpreted to represent cooling under static conditions after a late increase in temperature. A U-Pb zircon age of 318 ± 1 Ma was reported from the

Blansky Les granulite massif located in southern Bohemia and was interpreted as a Late

Carboniferous event involving granite intrusions deforming into granulite gneisses

(Svojtka et al., 2002).

The results of this study suggest cooling rates on an order of 500-50 oC/m.y. with

100-50 oC/m.y. being the preferred rate of cooling of the OSD, consistent with similar

Variscan structures across the orogen. This further suggests rapid exhumation of the

eclogites to shallow crustal levels, probably near isothermal decompression conditions as

indicated by sillimanite-kyanite intergrowth mineral assemblages found within this

portion of the Bohemian massif (O’Brien et al., 1997; Platt and Whitehouse, 1999; Kryza 62 and Pin, 2002). Steltenpohl et al. (1993) first reported exhumation rates in the OSD of

~5 km/m.y., whereas recently Stipska et al. (2004) suggested localized initial cooling and exhumation rates of a granulite belt from the Rychleby and Zlote mountains (northern

OSD) on an order of 100-20 oC/m.y. and 15-3 km/m.y. during compression-driven vertical extrusion (70 km to 35 km) followed by late exhumation rates of 40-24 km/m.y. during subsequent uplift (35 km to 30 km). Furthermore, they reported the cooling rate of the HP granulite belt to have decreased to 25-30 oC/m.y. during a lateral spreading stage.

Kroner and Willner (1998) suggest similarly rapid cooling and uplift rates to be in excess of 50 oC/m.y. and 4 km/m.y. based on Ar-Ar and Pb-Pb ages from core gneisses and mica schists of the Erzgebirge Dome located at the northwest margin of the Bohemian massif.

A P-T-t diagram was constructed in order to provide insight into a two-stage exhumation path of the eclogites, granulites, and country rock gneisses of the OSD

(Figure 10). The clockwise P-T path represents initial peak eclogite facies metamorphism

(700-800 oC, >27 kbar; Klemd and Brocker, 1999), which was attained at ca. 375-360

Ma, followed by isothermal decompression and subsequent rapid exhumation. The descent phase is marked by the preservation of these ultrahigh-grade rocks which preserve UHP mineral assemblages typically indicative of conditions exceeding 100 km depths, and is the key to the implication of a rapid exhumation. Amphibolite rimmed eclogite lenses have been found on an outcrop scale, providing evidence that the ultrahigh-grade units underwent successive thermal heating (Brocker and Klemd, 1996) following the deep subduction (~100 km) of continental and/or oceanic crust.

Furthermore, Brocker and Klemd (1996) report the eclogite contains a symplectic texture 63 with intergrown omphacite, garnet, and phengite of which are representative of HT-HP conditions.

e 30 tag Peak eclogite facies metamorphism S nt (700-800°C, >27 kbar) e sc e 375-360 Ma 25 D Midcrustal ascent and exhumation- related amphibolite facies metamorphism (~600°C, 10-4 kbar) 4 20 00 M a ? Post-peak metamorphic cooling 15 following isothermal decompression ca. 340-330 Ma on an order of 50°C/m.y. e g Pressure (kbars) ta 10 t S en Asc 330-340 Ma 5 midcrustal cooling

300 400 500 600 700 800 900 Temperature (°C)

Figure 10. Clockwise P-T-t path of the OSD from peak eclogite-facies metamorphism (700-800 oC, >27 kbar) through midcrustal ascent and exhumation-related amphibolite facies metamorphism (~600 oC, 10-4 kbar). Post-peak metamorphic cooling following isothermal decompression ca. 340-330 Ma on an order of 50 oC/m.y. The ca. 400 Ma metamorphic event most likely represents a Caledonian HT episode. This diagram was constructed in order to provide insight into the exhumation path of the eclogites, granulites, and country rock gneisses of the OSD. The ellipses were generated using published thermobarometric data and the results of this study (Lange et al., 2002; Marheine et al., 2002; Brocker and Klemd, 1999; Kryza and Pin, 2002; Maluski et al., 1995; Steltenpohl et al., 1993; Bakun-Czubarow, 1991). The three intersecting black lines represent the aluminosilicate triple point junction. 64 The UHP metamorphism was followed by a metamorphic event dated ca. 350

Ma, in which previous workers have interpreted this age to represent HT-HP metamorphism or an analytical mixed aged between the 375 Ma and 345 Ma thermal events (Brueckner et al., 1991; Gordon et al., 2004). Nevertheless, this ambiguous age has been difficult to resolve as to whether it represents a late UHP metamorphic event, a separate thermal event occurring during the onset of isothermal decompression, or ascent of the ultrahigh-grade rocks. This midcrustal ascent and exhumation-related amphibolite- facies metamorphism occurred ca. 345-330 Ma (~600 oC, 10-4 kbar) with post-peak

metamorphic cooling following isothermal decompression ca. 340-330 Ma on an order of

100-50 oC/m.y. The timing of exhumation is broadly coeval with the onset of major

Variscan magmatism, characteristic of orogenic collapse, although no crustal scale

extensional detachment has been reliably documented so it is unlikely that the OSD is a

metamorphic core complex, a hallmark of crustal extension (Henke et al., 2000).

The structure of the OSD is complex and poorly understood, however it is widely

accepted that it represents a fault-bounded gneissic dome consisting of antiforms and

synforms preserving micaceous gneisses and schists (Marheine et al., 2002). The OSD is

stacked in an E to NE direction on the Moravo-Silesian nappe-pile and is believed to be

the result of foreland overthrusting due to microcontinent collisions in the West Sudetes

(Marheine et al., 2002). The ascent phase of the ultrahigh-grade rocks through the lower

and middle lithosphere likely occurred by means of a density-regulated buoyant crust;

however, the UHP rocks are enveloped by an migmatitic matrix, therefore, buoyancy is

not the only driving force for exhumation and different processes are acting to allow 65 further ascent of the UHP terrane. A HP granulite belt in the OSD (Rychleby mountains, eastern Czech Republic) was recently reported to have been exhumed by lateral viscous spreading at mid-crustal levels (35 km, 10 kbar), which was attributed to the indentation of a rigid continental ramp (Stipska et al., 2004). Ductile thinning and/or erosion may have assisted the exhumation process to shallow crustal levels (Hacker et al.,

1995; Qingchen and Bolin, 2000; Ernst and Liou, 2000). More recently, Gordon et al.

(2004) has interpreted the wholesale exhumation of the OSD to be the result of erosional denudation of a crustal-scale pop-up structure. The OSD appears to be extraordinarily simple: a relatively homogenous massif of gneisses, migmatites, and schists enveloping localized UHP lenses. The monotonous petrology of the OSD suggests widespread migmatization and metamorphism; thermochronometry is similar in that cooling across the massif is remarkably concordant and suggests rapid exhumation. Nevertheless, the structural interpretation of the OSD is somewhat elusive and awaits further research. 66 9. Conclusions

The results of this investigation into the tectometamorphic evolution of the OSD can be summarized as follows:

1) The U-Th-total Pb monazite analyses reported in this study are broadly consistent

with previously published data from the OSD that may be used to document a

separate metamorphic event of ca. 400 Ma most likely representing a Caledonian

HT episode possibly attributed to granitoid intrusion throughout the orogen, and a

ca. 350 Ma age to further constrain a separate Late Devonian/Early Carboniferous

metamorphic event believed to have occurred during isothermal decompression

under conditions.

2) The OSD underwent a multi-stage exhumation with HT-HP eclogite-facies

metamorphism at ca. 375-360 Ma. (marking descent) which was followed by an

metamorphic event ca 345-330 Ma (marking ascent).

3) The Ar-Ar analyses reported here compliments preliminary work of Maluski et

al. (1995) and Marenheine et al. (2002) with similar cooling ages of the OSD ca.

340-330 Ma which further constrains the ascent phase (exhumation) of the

enclosed eclogites and granulites of the OSD to midcrustal depths during an

metamorphic event.

4) A clockwise P-T-t path is consistent with a two-stage evolution with cooling rates

on an order of 100o-50 oC/m.y. further suggesting rapid exhumation of the

ultrahigh-grade rocks to shallow crustal levels, probably near isothermal

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Note: [number] refers to the petrologic unit in Sawicki, 1997, Mapa Geologiczna Regionu Dolnoslaskiego Z Przyleglymi Obszarami Czech I Niemiec, 1:100,000, Podstawy Litostratygraficzne I Kodyfikacja Wydzielen, Warszawa.

Note: Hill and number (i.e. Hill 943) refers to elevation in meters above sea level.

Snieznik Mountains

szx-1: Coarse-grained foliated gneiss (mylonite?) with heterogeneous mica banding. Foliation consists of muscovite and biotite. Groundmass consists of undulatory subhedral quartz and seresitic plagioclase. Muscovite occurs as spindle-like growths on the plagioclase grains. Accessory minerals consist of zircons occur as halos in biotite, titanite. Location: Poland; 5.31 km south of Zloty Stok, area of Lysy Garb [252]. szx-2: Coarse-grained, foliated micaceous gneiss. Foliation consists of biotite and muscovite with subhedral hornblende; some of which is altering to chlorite. Groundmass consists of undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase. Location: 1.9 km SW of Lysy Garb in Droszkov [253]. szx-3: Coarse-grained, foliated micaceous gneiss. No sample collected. Location: Poland; ~1 km NW of szx-2 in Droszkov [344]. szx-4: Medium- to coarse-grained foliated micaceous augen gneiss. Foliation consists of biotite and white mica. Groundmass consists of undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase, myrmekitic plagioclase. Location: Poland; due west of Biala Woda and near L. Marcinkow; along stream [256]. szx-5: Medium- to coarse-grained foliated micaceous augen gneiss. Foliation consists of biotite, white mica, and fragments of anhedral garnet. Groundmass consists of undulatory subhedral quartz and poikilitic, serecitized, and myrmekitic plagioclase. Location: Poland; top area of Czarna Gora, the Black Mountain (1205 m.), SW of Sienna [256]. szx-6: Medium- to coarse-grained micaceous schist consisting of a strong foliation of micas appearing to “wrap” around subhedral poikilitic garnet. The garnet fractures are composed of pinite. There is some chloritization of the micas with a groundmass of subhedral undulatory quartz and plagioclase. Accessory minerals consist of zircons as halos in biotite. Location: Poland; the bend in road in the SE direction from Sienna; limited access road (no vehicles) [256]. 74 szx-7: Coarse-grained foliated micaceous gneiss. Foliation consists of biotite, white mica, and garnet. Garnet fractures appear to be composed of chloritoid. Mica is altering to chlorite. Groundmass consists of undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase, myrmekitic plagioclase. Accessory minerals consist of zircon and titanite. Location: Czech Republic; 1.9 km west of szx-8; area of Mala Morava [256]. szx-8: Coarse-grained foliated micaceous schist. Foliation consists of biotite, white mica, and garnet intergrown with quartz. Minor amounts of kyanite are also present intergrown with the micas. The garnet fractures appear to be composed of pinite with a groundmass of subhedral undulatory quartz. Location: Czech Republic; ~1 km south of Vjtiskov [268]. szx-9: Fine- to coarse-grained foliated amphibolite. Foliation due to subhedral poikilitic hornblende and anhedral amphiboles; chlorite alteration. Hornblende is intergrown with undulatory quartz and poikilitic plagioclase; some serecitized plagioclase; cordierite. Accessory mineral titanite is also present. Location: Czech Republic; along same road heading east as szx-8; ~2.06 km from Szx-8 [273]. szx-10: Medium- to coarse-grained foliated gneiss. Foliation consists of biotite and muscovite with poikilitic garnet with fractures composed of pinite. Micas are intergrown with subhedral quartz and poikilitic and serecitized plagioclase; mica alteration to chlorite; cordierite. Accessory minerals consist of zircons occur as halos in biotite. Location: Czech Republic; along the same road heading east as szx-9; 0.63 km from szx- 9 [265/375]. szx-11: Medium- to coarse-grained foliated gneiss (migmatite). Foliation due to subhedral poikilitic hornblende and anhedral amphiboles; “denim blue” chlorite alteration. Hornblende has distinct cleavage and is intergrown with undulatory quartz and poikilitic plagioclase; some serecitized plagioclase. Minor garnet with amphibole, and micas intergrown with subhedral quartz and plagioclase; microcline. Accessory mineral zircon. epidote, apatite. szx-11T: Medium- to coarse-grained foliated amphibolite. Foliation due to subhedral poikilitic hornblende and anhedral amphiboles; “denim blue” chlorite alteration. Hornblende/amphiboles are intergrown with undulatory quartz and poikilitic plagioclase; some serecitized plagioclase. Minor garnet with amphibole, and micas intergrown with subhedral quartz and plagioclase. Accessory mineral zircon. epidote, apatite. Location: Czech Republic; 1.73 km east from szx-10 along the right arm of the fork in the road; quarry [273]. 75 szx-12A/B: Medium- to coarse-grained foliated gneiss. Foliation consists of muscovite intergrown with quartz; some alternating to chlorite; chloritoid. Garnet is also present. Groundmass consists of undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase. Accessory minerals consist of zircon; titanite. Location: Czech Republic; Hill 943/ Kunzicka Hora; 3 km NW from hill 943 [269]. szx-13: Medium-grained well-foliated augen-gneiss (mylonite?). Foliation consists of segregation of fine-grained muscovite and biotite separated by layers of fine quartz, porphyritic quartz, and some undulatory sub-anhedral quartz. Some mica is altering to chlorite. Accessory minerals consist of zircon; titanite. szx-13T: Medium- to coarse-grained well foliated augen-gneiss (mylonite?). Foliation consists of segregation of fine-grained muscovite and biotite separated by layers of fine quartz, porphyritic quartz, and some undulatory sub-anhedral quartz. Location: Czech Republic; town of Branna; large outcrop at corner of church [275]. szx-14: Coarse-grained foliated micaceous schist. Foliation consists of muscovite and biotite with some mica altering to chlorite. The micas are intergrown with the quartz. Porphyroblastic boudin-like structures consist of recrystalized coarser-grained undulatory quartz and staurolite. Accessory minerals consist of zircon; titanite. Location: Czech Republic; Branna train station around back on opposite side of tracks near shed [275]. szx-15: Medium- to coarse-grained foliated gneiss. Foliation consists of muscovite intergrown with quartz; some alternating to chlorite. Groundmass consists of undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase; cordierite. Accessory minerals consist of zircon, titanite. Location: Poland; 2 km NE of Radochow; logging road [255]. szx-16: Medium- to coarse-grained well foliated micaceous augen gneiss. Foliation consists of biotite and muscovite intergrown with quartz. Mica altering to chlorite. Groundmass consists of undulatory subhedral quartz and poikilitic, serecitized, and myrmekitic plagioclase. Accessory minerals consist of zircon halos on biotite. Location: Poland; same area as szx-15; top of dam [256]. szx-17: Coarse-grained foliated micaceous gneiss (mylonite?). Foliation consists of muscovite, biotite, and garnet with some mica altering to chlorite. The micas and garnet are intergrown with the quartz, with the garnet cracks composed of pinite. Groundmass consists of undulatory subhedral quartz and poikilitic, serecitized, and myrmekitic plagioclase. Accessory minerals consist of zircon; titanite. Location: Poland; same area as szx-16/17; near dam [255]. 76 szx-18: Medium- to coarse-grained well-foliated micaceous gneiss. Foliation consists of biotite and muscovite intergrown with quartz. Garnet fragments are found throughout. Mica altering to chlorite. Groundmass consists of undulatory subhedral quartz and poikilitic, serecitized, and myrmekitic plagioclase. Accessory minerals consist of zircon halos on biotite. Location: Poland; 4.3 km SE of Miedzygorze by river on left and across from martyr/prayer site [246]. szx-19A: Fine- to coarse-grained foliated peroxinite. Foliation due to biotite, some subhedral hornblende and abundant anhedral amphiboles; chlorite alteration. Hornblende/amphiboles are intergrown with micas, undulatory quartz and poikilitic plagioclase; some serecitized plagioclase. szx-19B: Coarse-grained micaceous eclogite. Groundmass consists of muscovite, biotite, rutile, garnet and pyroxene. Mica alteration to chlorite. Coarse garnet porphyroblasts are intergrown with poikilitic pyroxene as well as sub- anhedral undulatory quartz and plagioclase; some serecitized. The garnet fractures are composed of pinite. Location: Poland; Miedzygorze in forest 250 meters from bridge between two roads [256]. szx-20: Coarse-grained granulite. Foliation consists of biotite, and poikilitic garnet with some biotite altering to chlorite. The garnet fractures are composed of pinite. Groundmass consists of undulatory subhedral quartz and some seresitic plagioclase. Location: Poland; ~3.7 km NE of Goszow in Str. Gieraltow [256]. szx-21: Coarse-grained foliated micaceous gneiss. Foliation consists of muscovite and biotite. Some altering to chlorite. Groundmass consists of undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase, myrmekitic plagioclase. Location: Poland; 0.94 km from szx-20 [256]. szx-22A: Coarse-grained foliated micaceous gneiss. Foliation consists of muscovite, biotite, and fragmented garnet. Some micas altering to chlorite. Groundmass consists of undulatory subhedral quartz and plagioclase as well as serecitized plagioclase. Accessory minerals occur as zircon halos on biotite; titanite. szx-22B: Medium- to coarser-grained foliated micaceous schist. Foliation consists of muscovite, biotite, and garnet. Garnet fractures composed of prenite. Groundmass consists of undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase. Accessory minerals occur as zircon halos on biotite. Location: Poland; ~0.62 miles from szx-21 in Nova Gieraltow along river by road and across log bridge across from house [255]. 77 szx-23A: Medium- to coarse-grained foliated gneiss. Foliation consists of large subhedral muscovite and biotite; some alternating to chlorite (anomalous blue). Garnet is also present with fractures composed of prenite. Groundmass consists of medium- to coarse-grained undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase. Accessory minerals occur as zircon halos on micas. szx-23B: Medium- to coarse-grained foliated gneiss. Foliation consists of large subhedral muscovite, biotite, and garnet; some alternating to chlorite. Groundmass consists of medium- to coarse-grained undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase. Accessory minerals occur as zircon halos on micas. szx-23C: Medium- to coarse-grained foliated gneiss. Foliation consists of large subhedral muscovite and biotite; some alternating to chlorite. Groundmass consists of medium grained undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase. Accessory minerals occur as zircon halos on micas; titanite. Location: Czech Republic; ~ 1.6 km SE from NW Weis; logging road [255]. szx-24: Medium- to coarse-grained foliated gneiss. Foliation consists of large subhedral muscovite and biotite; some alternating to chlorite. Groundmass consists of medium- to coarse-grained undulatory subhedral quartz and poikilitic plagioclase. Location: Czech Republic; ~ 4.82 km N of Yelka at quarry off of logging road [256]. szx-25A: Medium- to coarse-grained foliated gneiss. Foliation consists of large subhedral muscovite, biotite and garnet; some alternating to chlorite. Garnet fractures composed of prenite. Groundmass consists of medium- to coarse-grained undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase. szx-25B: Medium- to coarse-grained foliated gneiss. Foliation consists of muscovite, biotite and garnet; some alternating to chlorite. Garnet fractures composed of anomalous blue chlorite. Groundmass consists of medium- to coarse-grained undulatory subhedral quartz and poikilitic plagioclase as well as serecitized plagioclase. Location: Czech Republic; Stare Mesto [256/275]. szx-26: Medium- to coarse-grained foliated micaceous schist. Foliation consists of segregation of fine-grained muscovite, biotite, and garnet separated by layers quartz, porphyritic quartz, and some undulatory sub-anhedral quartz. Serecitized and porphyritic plagioclase are present as well as porphyritic garnet. Accessory minerals occur as zircon halos on biotite. szx-26T: Medium- to coarse-grained foliated micaceous schist. Foliation consists of muscovite, biotite, porphyritic amphibole/amphibole, porphyritic garnet, and kyanite intergrown with layers of quartz and plagioclase. Groundmass consists of undulatory subhedral quartz and seresitic plagioclase; opaques. 78 Location: Czech Republic; ~ 2.89 km N by NW of szx-25 on rt. Side of road at Novy Runburk [268]. szx-27: Medium- to coarse-grained foliated augen gneiss with heterogeneous mica banding. Foliation consists of muscovite, biotite, amphibole/amphibole, and minor kyanite; mica altering to chlorite. Groundmass consists of undulatory subhedral quartz, seresitic/porphyritic/myrmekitic plagioclase; microcline. Accesory minerals occur as zircon halos on biotite; albite, allanite. Location: Czech Republic; ~1.44 km SW of Puste Zlbricovice [285]. szx-28: Medium- to coarse-grained foliated micaceous schist. Foliation consists of segregation of fine-grained muscovite and biotite separated by layers of undulatory sub- anhedral quartz; serecitized plagioclase. Location: Czech Republic; ~0.64 km N of Puste Zlbricovice [275].

Orlica Mountains

O-1: Medium- to coarse-grained foliated garnet-mica gneiss. Foliation consists of biotite and muscovite. Groundmass consists of medium- to coarse-grained undulatory subhedral quartz, and serecitized and myrmekitic plagioclase. Chlorite alteration of the micas is also present. Fragmented garnet also appears throughout as an accessory mineral. Location: Czech Republic; ~1.44 km W of Lichkov [256].

O-4: Medium- to coarse-grained foliated mica gneiss. Foliation consists of muscovite separated by medium- to coarse-grained undulatory subhedral quartz and poikilitic plagioclase (some of which has quartz inclusions); seresitic plagioclase mica alteration to chlorite. Accessory mineral cordierite is present as well as porphyritic/poikilitic albite of which some is partly serecitized; opaques. Location: Czech Republic; ~0.64 km W of Ricky [256].

O-6: Medium- to coarse-grained foliated muscovite schist. Foliation consists of muscovite separated by medium- to coarse-grained undulatory subhedral quartz and poikilitic plagioclase (some of which has quartz inclusions); seresitic plagioclase; mica alteration to chlorite. Accessory mineral cordierite is present as well as porphyritic/poikilitic albite; opaques. Location: Czech Republic; ~4.3 km SW of Zieleniec [256].

O-7: Medium- to coarse-grained foliated micaceous schist. Foliation consists of segregation of muscovite and biotite separated by layers of medium- to coarse-grained undulatory subhedral quartz; small scale folding of schistocity; serecitized plagioclase. Micas altering to chlorite. Accessory minerals consist of tourmaline which is found with trigonal cross-sectional shapes in minor amounts with zoning of the absorption colors; porphyritic/pokilitic garnet; opaques, cordierite? Location: Czech Republic; ~2.25 km N of Destne Orl. H. [246]. 79 O-8: Medium- to coarse-grained foliated micaceous schist. Foliation consists of segregation of muscovite, biotite and tourmaline separated by layers of porphritic/poikilitic albite and undulatory sub-anhedral quartz; serecitized plagioclase; s- fold porphyroblast indicators; micas alternating to chlorite. Tourmaline is found in minor amounts throughout with greenish/yellow gray “lath” as well as trigonal cross-sectional shaping. Accessory minerals consist of porphyritic/pokilitic garnet; opaques, cordierite? Location: Czech Republic; ~0.64 km N of 0-7 [246].

O-9: Medium- to coarse-grained foliated micaceous schist. Foliation consists of muscovite separated by layers of medium- to coarse-grained undulatory subhedral quartz and serecitic porphyritic albite; small scale folding of schistocity; serecitized plagioclase. Accessory minerals consist of minor anhedral garnet. Location: Czech Republic; ~2.09 km SE of O-6 [246].

O-10: Medium- to coarse-grained foliated micaceous schist. Foliation consists of muscovite separated by layers of medium-grained undulatory subhedral quartz; small scale folding of schistocity. Location: Czech Republic; ~0.8 km S of O-5 [246].

O-11: Medium- to coarse-grained foliated micaceous schist. Foliation consists of a segregation of muscovite and garnet separated by layers of porphritic/poikilitic albite (partly serecitized) and medium- to coarse-grained undulatory subhedral quartz; small scale folding of schistocity. Micas seem to “bend” around garnet as microfolds in the schistocity. Location: Czech Republic; 2.09 km S of Velke [256].

O-12A: Medium- to coarse-grained foliated micaceous gneiss. Foliation consists of a segregation of muscovite, biotite, and serecitized poikilitic garnet separated by layers of medium- to coarse-grained undulatory subhedral quartz; small scale folding of schistocity. Some micas altering to chlorite intergrown with garnet. Accessory minerals consist of minor amounts of allanite and opaques.

O-12B: Medium- to coarse-grained foliated micaceous gneiss. Foliation consists of muscovite separated by layers of medium- to coarse-grained undulatory subhedral quartz; small scale folding of schistocity. Accessory minerals consist of poikilitic garnet (partly serecitized); cordierite? Location: Czech Republic; 0.96 km S of Velke [256].

O-13A: Medium- to coarse-grained foliated micaceous schist. Foliation consists of segregation of muscovite and tourmaline separated by layers of porphritic/poikilitic albite and undulatory sub-anhedral quartz; serecitized plagioclase. Albite porphyroblast are composed of s-fold indicators; micas alternating to chlorite. Tourmaline is found throughout with greenish/yellow gray “lath” as well as trigonal cross-sectional shaping. 80 O-13B: Medium- to coarse-grained foliated micaceous schist. Foliation consists of segregation of muscovite, garnet, anhedral amphibole, and tourmaline separated by layers of porphritic/poikilitic albite and undulatory sub-anhedral quartz; serecitized plagioclase; s-fold porphyroblast indicators; micas alternating to chlorite. Tourmaline is found throughout with greenish/yellow gray “lath” as well as trigonal cross-sectional shaping.

O-13C: Medium- to coarse-grained foliated micaceous schist. Foliation consists of segregation of muscovite and tourmaline separated by layers of porphritic/poikilitic albite and undulatory sub-anhedral quartz; serecitized albite is composed of z-fold porphyroblast indicators. Tourmaline is found in minor amounts throughout with greenish/yellow gray “lath” as well as trigonal cross-sectional shaping. Location: Czech Republic; ~ 1.6 km N of O-3 [246].