Along-Strike Variations in the Mediterranean Tethyan Orogen

Transcription

1 Field Guide 23 - THl GLOLOGICAL SOCIETY - OF AMERICA Along-Strike Variations in the Mediterranean Tethyan Orogen By Klaus Gessner, Uwe Ring, and Talip GUngo r

2 Field Guide to Samos and the Menderes Massif: Along-Strike Variations in the Mediterranean Tethyan Orogen by Klaus Gessner Western Australian Geothermal Centre of Excellence and Centre for Exploration Targeting School of Earth and Environment The University of Western Australia M Stirling Highway Crawley WA 6008 Australia Uwe Ring Department of Geological Sciences University of Canterbury Private Bag 4800 Christchurch, New Zealand Talip Güngör Department of Geological Engineering Dokuz Eylül University Tinaztepe Campus Buca Izmir, Turkey Field Guide Penrose Place, P.O. Box 9140 Boulder, Colorado , USA 2011

3 Copyright 2011, The Geological Society of America (GSA), Inc. All rights reserved. GSA grants permission to individual scientists to make unlimited photocopies of one or more items from this volume for noncommercial purposes advancing science or education, including classroom use. In addition, an author has the right to use his or her article or a portion of the article in a thesis or dissertation without requesting permission from GSA, provided the bibliographic citation and the GSA copyright credit line are given on the appropriate pages. For permission to make photocopies of any item in this volume for other noncommercial, nonprofit purposes, contact The Geological Society of America. Written permission is required from GSA for all other forms of capture or reproduction of any item in the volume including, but not limited to, all types of electronic or digital scanning or other digital or manual transformation of articles or any portion thereof, such as abstracts, into computer-readable and/or transmittable form for personal or corporate use, either noncommercial or commercial, for-profit or otherwise. Send permission requests to GSA Copyright Permissions, 3300 Penrose Place, P.O. Box 9140, Boulder, Colorado , USA. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, sexual orientation, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Copyright is not claimed on any material prepared wholly by government employees within the scope of their employment. Published by The Geological Society of America, Inc Penrose Place, P.O. Box 9140, Boulder, Colorado , USA Printed in U.S.A. GSA Books Science Editors: Marion E. Bickford and Donald I. Siegel Library of Congress Cataloging-in-Publication Data Glessner, Klaus, Field guide to Samos and the Menderes massif : along-strike variations in the Mediterranean Tethyan orogen / by Klaus Gessner, Uwe Ring, Talip Güngör. p. cm. (Field guide ; 23) Includes bibliographical references. ISBN (pbk.) 1. Orogeny Greece Samos Island. 2. Orogeny Turkey. 3. Geology, Stratigraphic Miocene. 4. Tethys (Paleogeography) 5. Geology Fieldwork. I. Ring, Uwe. II. Güngör, Talip. III. Title. QE621.5.G8f dc Cover: Panoramic view of the Kerketas Massif in the southwest part of Samos Island, Greece (Locality 1.1 of this field guide). Outcrops of monotonous dolomite of Kerketas Nappe form the Mount Kerkis ridge in the background and variegated sequence of schists, quartzite, marble, and amphibolite make up the lower ground of the Ampelos Nappe in the foreground. The mylonitic foliation in the quartzite of the Ampelos Nappe is dipping to the SE and contains an ESE-trending stretching lineation associated with top-ese shear sense indicators. View is toward the southwest. Photo courtesy of Klaus Gessner, 17 May

4 Contents Abstract Introduction Geology of the Eastern Mediterranean Paleogeography Regional Structure Important Tectonic Contacts Metamorphic History Basal Unit Cycladic Blueschist Unit Menderes Nappes Eocene Oligocene Crustal Thickening Miocene to Holocene Extension Summary Part A. Samos Island, Greece Geology of Samos General Architecture of Samos Island and Important Tectonic Contacts Structural History and Deformation-Metamorphism Relationships Day 1 Localities 1.1 to Locality 1.1. Ridge East of Mount Kerkis Locality 1.2. Glaucophane Schist at Road Intersection North of Neochori Locality 1.3. Breccia of Basal Conglomerate Formation Locality 1.4. Limestone of Pythagorion Formation Locality 1.5. Hora Formation Locality 1.6. Conglomerate of Mytilini Formation Day 2 High-Pressure Assemblages along the Northern Coast (Localities 2.1 to 2.3) Locality 2.1. Around Agios Konstandinos Locality 2.2. West of Avlakia and East of Turnoff to Vourliotes Locality 2.3. Gankou Beach Part B. The Menderes Massif Some Remarks about Controversies on Menderes Massif Tectonics Architecture of the Menderes Massif Miocene to Holocene Extension in the Central Menderes Region Alpine Nappe Tectonics The Menderes Nappes The Cycladic Blueschist Unit The Cyclades-Menderes Thrust Interpretation of Deformation-Metamorphism-Timing Relationships Menderes Massif Field Trips iii

5 iv Contents Day 3 Around Selçuk (Localities 3.1 to 3.5) Overview Locality 3.1. Selçuk-Aydın Road Cut Locality 3.2. Ephesus Fault Locality 3.3. Metaconglomerates and Metapelites of the Dilek Nappe Locality 3.4. Yavansu Fault near Kuşadası Locality 3.5. Dilek Nappe Outcrops along the Coast Road Day 4 Section across the Bozdağ and Aydın Mountains Overview Bozdağ Mountains (Localities 4.1 to 4.6) Locality 4.1. Kuzey Detachment at Çakaldoğan Locality 4.2. Kuzey Detachment Surface Locality 4.3. Bayındır Nappe Locality 4.4. Bozdağ Nappe Locality 4.5. Küçük Menderes Graben Locality 4.6. Çine Nappe Garnet-Bearing Augen Gneiss Ödemiş Area and Aydın Mountains (Localities ) Locality 4.7. Çine Nappe Granitic Augen Gneiss Locality 4.8. Çine Nappe Augen Gneiss near Halıköy, Mercury Mine Locality 4.9. Migmatite Gneiss at Adaküre (Adagide) Village Locality Çine Nappe Granites and Gneisses Locality Metabasic Lenses in Çine Nappe Day 5 Western Aydın Mountains: Cyclades-Menderes Thrust and Güney Detachment (Localities 5.1 to 5.4) Overview Locality 5.1. Bozdağ Nappe North of Ortaköy Locality 5.2. Bozdağ Nappe North of Yemişler Locality 5.3. Crossing the Cyclades Menderes Thrust Locality 5.4. Kuzey Detachment North of Meşeli Day 6 Southern Menderes Massif: The Selimiye Shear Zone and the Lake Bafa Area (Localities 6.1 to 6.7) Overview Locality 6.1. Foliation Boudinage in Çine Nappe Orthogneiss Locality 6.2. Çine Nappe Orthogneiss on the Edge of Selimiye Shear Zone Locality 6.3. Selimiye Shear Zone Locality 6.4. Intrusive Contacts within the Çine Nappe Locality 6.5. Platform Carbonates of the Dilek Nappe Locality 6.6. Folding in Lycian Nappes Locality 6.7. Carpholite in Lycian Nappes Acknowledgments References Cited

6 The Geological Society of America Field Guide Field Guide to Samos and the Menderes Massif: Along-Strike Variations in the Mediterranean Tethyan Orogen Klaus Gessner* Western Australian Geothermal Centre of Excellence and Centre for Exploration Targeting, School of Earth and Environment, The University of Western Australia M006, 35 Stirling Highway, Crawley WA 6008, Australia Uwe Ring* Department of Geological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand Talip Güngör* Department of Geological Engineering, Dokuz Eylül University, Tinaztepe Campus, Buca 35160, Izmir, Turkey ABSTRACT In this field-trip guide we explore the tectonics of Samos and the Menderes Massif, two fascinating areas within the eastern Mediterranean section of the Tethyan orogen. We include detailed outcrop descriptions, maps, and diagrams to explore along-strike variations in the Hellenide-Anatolide orogen, including the architecture of the Early Tertiary Alpine nappe stack and its strong Miocene extensional overprint. The suggested itinerary is based on the 2010 Geological Society of America Field Forum Significance of Along-Strike Variations for the 3-D Architecture of Orogens: The Hellenides and Anatolides in the Eastern Mediterranean. We start the outcrop descriptions with Day 1 in Samos, where, untypically for the N-S stretched Aegean region, Miocene extension is E W. We describe a section in western Samos, where the Cycladic Blueschist Unit is in contact with the underlying External Hellenides along a large-scale thrust, reactivated as a Miocene top-east extensional shear zone. The focus of Day 2 is on high-pressure assemblages in northern Samos. The following three days explore the Anatolide Belt in western Turkey where the Menderes nappes also known as the Menderes Massif form the tectonic footwall below the Cycladic Blueschist Unit. The outcrops in western Anatolia include the Cycladic Blueschist Unit in the area around Selçuk (Day 3) and sections across the Bozdağ and Aydın Mountains including the Kuzey and Güney detachment faults and the Cycladic Menderes Thrust (Days 4 and 5). Outcrops on Day 6 showcase structures along the southern margin of the Menderes Massif in the Milas Selimiye area. *klaus.gessner@uwa.edu.au; uwe.ring@canterbury.ac.nz; talip.gungor@deu.edu.tr. Gessner, K., Ring, U., and Güngör, T., 2011, Field Guide to Samos and the Menderes Massif: Along-Strike Variations in the Mediterranean Tethyan Orogen: Geological Society of America Field Guide 23, 52 p., doi: / For permission to copy, contact editing@geosociety.org The Geological Society of America. All rights reserved. 1

7 2 Gessner et al. INTRODUCTION Much of the conceptual understanding of the development of orogens is still largely based on assuming cylindricity, i.e., the premise of structural continuity along strike. However, lithospheric architecture and strain in orogens usually vary substantially, both across and along strike. Consequently, along-strike variations have been described from a number of orogens, including the European Alps, the North American Cordillera, the Andes, and the Hellenide-Anatolide orogen of southeastern Europe. The causes for along-strike variations might be different, but pre-orogenic paleogeography, continental architecture, lateral changes in the nature of the downgoing (subducting) lithosphere, and kinematic-geometric variations at the lithospheric scale potentially play an important role. Along-strike changes in orogens have a profound impact on how major orogenic processes proceed in time and space. Here we present an example of along-strike variations in the Hellenide-Anatolide orogen in the eastern Mediterranean. This field guide has evolved from an informal document handed out to the participants of the Geological Society of America Field Forum, Significance of Along-Strike Variations for the 3-D Architecture of Orogens: The Hellenides and Anatolides in the Eastern Mediterranean, which the authors organized together with Nikos Skarpelis, Dov Avigad, and Olivier Vanderhaeghe from 16 to 22 May The field forum itself was borne of trans-disciplinary field-based studies pointing out major along-strike variations in the Hellenide-Anatolide orogen (Gessner et al., 1998, 2001c; Ring et al., 1999a) that bear strongly on future research directions. These studies have shown that differences in pre-orogenic paleogeography caused the Hellenide orogen of eastern Greece and the Anatolide Belt of western Turkey to evolve in sharply different ways. We believe that better identification and understanding of those differences will potentially clarify how eastern Mediterranean subduction zones evolved, how pre-orogenic architecture controls crustal thickening and the subsequent exhumation of high-pressure rocks, and how large-scale continental extension evolves. These studies also bear on a number of new and innovative methods for interpretation of geochronologic data for direct dating of deformation and metamorphism (Glodny et al., 2002, 2008). Deciphering temporal aspects of orogenic processes is an important objective in tectonics. The key to successful dating of orogenic processes directly depends on appropriate sampling in the field; therefore, it is crucial that this aspect be discussed thoroughly in the field. The spatial and temporal evolution of the Hellenide- Anatolide orogen is also significant economically because of its key importance to understanding spatial controls on faults and basins for hydrocarbon generation, metallogeny, and geothermal resources. GEOLOGY OF THE EASTERN MEDITERRANEAN Paleogeography The relative motion of the Adriatic plate (here referred to as Adria) controls the late Mesozoic to Holocene orogenic development of the Mediterranean region to a large degree. Adria is a small tectonic plate (microplate) that broke away from the African plate in the Cretaceous and is thought to still move independently of the Eurasian plate. In the eastern Mediterranean, Adria pinches out. Figure 1 shows a schematic paleogeographic reconstruction of the area. In the eastern Mediterranean, little is known Eurasia Adria Northern Neotethys Pelagonia Pindos s Rift Tripolitza platform Ionian n Rift Southern Neotethys Cycladic - Dilek platform Lycian platform Afyon / Ören Sakarya Tavşanli Vardar-Izmir-Ankara ocean Selçuk ocean Anatolia Figure 1. Simplified and speculative reconstruction of the Cretaceous (ca. 70 Ma) paleogeography in the eastern Mediterranean, based on Şengör and Yilmaz (1981), Gessner et al. (2001c), and van Hinsbergen et al. (2010). Dashed lines refer to contentious interpretations, such as the link between Adria and Anatolia (Dürr et al., 1978; Şengör and Yilmaz, 1981) versus the existence of a small backarc Selçuk ocean (Ring et al., 1999a, 2007a; Gessner et al., 2001c). The Cyclades-Dilek platform provided the protolith for metasediments in the Dilek Nappe, which constitutes the lower part of the Cycladic Blueschist Unit. Africa

8 Field Guide to Samos and the Menderes Massif 3 about the Mesozoic to early Tertiary paleogeography of the Adriatic plate. In the Greek transect, Adria is characterized by ribbons of normal-thickness continental crust and intervening parts of highly stretched and thinned crust that may or may not have been partly oceanic (Jacobshagen, 1986; Robertson et al., 1991). Stretching and possible generation of oceanic crust resulted from Mesozoic rifting during and prior to the Cretaceous, when Adria was the northern part of the African plate. These rifting processes ultimately separated Adria from Africa. Farther east, Neotethys broadened (Robertson et al., 1991; Stampfli et al., 2001), and a number of continental blocks that rifted off Gondwana in the Jurassic and Cretaceous drifted northward toward subduction zones at the northern margin of Neotethys. In the eastern Mediterranean the continent directly east of Adria was Anatolia (Gessner et al., 2001c). Regional Structure The Hellenide orogen of Greece and the Anatolide Belt of western Turkey form an arcuate orogen to the north of the present-day active Hellenic margin, which marks the site of northeastward underthrusting of the African plate underneath Europe (Fig. 2). Both regions consist of stacked nappes that are limited to the north by the Late Cretaceous to Paleogene Vardar-Izmir- Ankara Suture Zone. The Hellenides can be subdivided from top (north) to bottom (south) into (1) an internal zone, consisting of the Rhodope-Sakarya-Strandja Block, (2) the Vardar-Izmir- Ankara Oceanic Unit, (3) the Pelagonian-Lycian Unit, (4) the Pindos Unit (including the Cycladic Blueschist Unit), (5) the External Hellenides, comprising the Gavrovo-Tripolitza Block and the underlying Ionian Block, and (6) the Mediterranean Ridge Accretionary Complex (Fig. 2). The main aspect of this field guide concerns the lowest tectonic units of the Anatolide and Hellenide nappe stacks. In the Anatolides the Pindos Unit overlies the Menderes nappes, which are part of Anatolia, whereas in the Aegean region the Pindos Unit overlies the Basal Unit, which is part of the Gavrovo-Tripolitza Block (External Hellenides) (Dürr et al., 1978; Robertson et al., 1991; van Hinsbergen et al., 2005). The major differences between the Menderes nappes and the Basal Unit are that the nappe piles have distinct architectures (Gessner et al., 1998; Ring et al., 1999a). What we summarize as the Vardar-Izmir-Ankara Oceanic Unit represents the remnants of a Triassic to early Paleocene ocean that were subducted below Eurasia or Sakarya since the Cretaceous. In western Turkey we include Cretaceous to Paleogene subduction-accretion complexes in the footwall of the actual Izmir-Ankara-Erzincan suture, including the Tavşanlı zone, and the Bornova Flysch zone (sensu Okay and Tüysüz, 1999; Okay, 2011). In southern Bulgaria a volcanic arc related to the subduction of the Vardar-Izmir-Ankara Oceanic Unit was initiated at ca. 90 Ma (von Quadt et al., 2005). The Pelagonian-Lycian Unit, in which we include the Ören- Afyon zone rocks (Okay and Tüysüz, 1999; Pourteau et al., 2010), occurs structurally below the Vardar-Izmir-Ankara Oceanic Unit. Parts of the Vardar-Izmir-Ankara Oceanic Unit and of the Pelagonian-Lycian Unit were metamorphosed under blueschist-facies conditions between ca. 125 and 85 Ma (Lips et al., 1999; Sherlock et al., 1999; Ring and Layer, 2003; Ring et al., 2003a; Pourteau et al., 2010). Above the southern edge of the Pelagonian-Lycian Unit, the Meso-Hellenic and Thrace Basins formed in a forearc position at the beginning of the Eocene (Vamvaka et al., 2006; Huvaz et al., 2007). The units to the south, i.e., in the footwall of the Pelagonian- Lycian Unit, do not have a Cretaceous orogenic history. They became involved in subduction-accretion and associated highpressure metamorphism at least 20 m.y. later than the Pelagonian-Lycian Unit and the Vardar-Izmir-Ankara Oceanic Unit (Ring et al., 2010). The Pindos Unit (Fig. 2) is a heterogeneous paleogeographic domain that mainly includes normal-thickness, continental basement cover sequences. Also, the Pindos Unit contains thick radiolarite sequences, indicating that it was either underlain by oceanic crust or by thinned continental crust (Pe-Piper and Piper, 1984; Robertson et al., 1991). In the Cyclades the uppermost unit of the Pindos Unit is the highly attenuated ophiolitic Selçuk Mélange (Okrusch and Bröcker, 1990; Ring et al., 1999a; Katzir et al., 2000), which now traces the suture between the Pindos Unit and the overlying Pelagonian-Lycian Unit (Ring and Layer, 2003). Slivers of oceanic crust (gabbro, plagiogranite, basalt) that formed at ca Ma (Keay, 1998) formed blocks with a serpentinitic matrix of the Selçuk Mélange. Below the Selçuk Mélange the continental rocks of the Cycladic Blueschist Unit constitute the most deeply exhumed parts of the Hellenides. This unit comprises a Carboniferous basement of schist and orthogneiss, and a late- to post-carboniferous passive-margin sequence of marble, metapelite, and volcanics (Dürr et al., 1978). The passive-margin sequence is unconformably overlain in southwestern Turkey by middle to upper Paleocene flysch (Özer et al., 2001). Initial flysch deposition slightly predates the beginning of sedimentation in the Meso-Hellenic and Thrace forearc basins. The flysch and forearc basin sediments were deposited in response to the inception of subduction of the Pindos Unit (Ring et al., 2010). The different elements of the Pindos Unit are part of an accretionary complex that formed between ca. 55 and 30 Ma (Ring et al., 2003a, 2010; Jolivet and Brun, 2010). The Gavrovo-Tripolitza Block represents a continental platform unit of Triassic to Eocene age and is partly overlain by late Eocene to early Oligocene flysch (Jacobshagen, 1986). Underthrusting of the Gavrovo-Tripolitza Block commenced at ca Ma (Thomson et al., 1998; Sotiropoulos et al., 2003). In the Cyclades, high-pressure rocks of the Gavrovo-Tripolitza Block are usually referred to as the Basal Unit, which is locally exposed in tectonic windows through the overlying Cycladic Blueschist Unit (Godfriaux, 1968; Shaked et al., 2000), including in Samos (Ring et al., 2001b). Farther south in the Peloponnese and in Crete the rocks of the Gavrovo-Tripolitza Block and the Pindos Unit are only weakly metamorphosed. The Ionian block

9 4 Gessner et al. Quaternary Rhodope-Sakarya- Strandja Block Vardar-Izmir-Ankara Oceanic Unit Unit Pindos Unit (including Cycladic Blueschist Unit) Menderes Nappes Gavrovo-Tripolitza Block ca. ca. ca. Figure 2. Simplified tectonic map of the Aegean region, showing the main tectonic zones above the Hellenic subduction zone (modified from Jolivet and Brun, 2010). The Mediterranean Ridge represents the modern accretionary wedge that is bounded to the north by a major backthrust system. Red line-patterns indicate the positions of subduction-related magmatic-arc rocks from ca. 38 Ma to the Holocene (Fytikas et al., 1984; Barr et al., 1999; Pe-Piper and Piper, 2002). The migration of this magmatic arc in the overriding plate mimics the retreat of the Hellenic slab. Also shown in the north is a volcanic arc related to the subduction of the Vardar-Izmir-Ankara Oceanic Unit at ca. 90 Ma.

10 Field Guide to Samos and the Menderes Massif 5 comprises Late Carboniferous to possibly Triassic rocks overlain by limestone and late Eocene to Miocene flysch (Jacobshagen, 1986). Rocks of both the Gavrovo-Tripolitza and Ionian Blocks do not crop out in western Turkey (Fig. 2). The southernmost and most outboard tectonic domain of the Hellenides is the Mediterranean Ridge Accretionary Complex (Fig. 2) (Kopf et al., 2003). The onset of accretion occurred at ca. 19 Ma during ongoing subduction of Triassic oceanic crust of the eastern Mediterranean Ocean (van Hinsbergen et al., 2005). Along the central Mediterranean Ridge this oceanic crust of the eastern Mediterranean Ocean has been completely consumed, and the leading edge of the African passive continental margin is currently entering the subduction zone. The overall structure of the Anatolide Belt consists of the Lycian nappes as part of the Lycian-Pelagonian Unit. Recently the Lycian nappes have been subdivided into the high-pressure Ören-Afyon Zone and the unmetamorphosed Lycian nappes sensu stricto (Pourteau et al., 2010). The Lycian nappes rest on the Cycladic Blueschist Unit, the latter of which have been thrust along the Cyclades-Menderes Thrust onto the Menderes nappes (Gessner et al., 2001c). The Menderes nappes comprise four main tectonic units that we interpret as nappes (Ring et al., 1999a; Gessner et al., 2001c; Régnier et al., 2003). From top to bottom these are (1) the Selimiye Nappe, (2) the Çine Nappe, (3) the Bozdağ Nappe, and (4) the Bayındır Nappe. The Çine and Bozdağ Nappes have a polyorogenic history, which extends back into the Neoproterozoic Cambrian (Candan et al., 2001; Gessner et al., 2001a, 2004; Ring et al., 2001b). The Selimiye Nappe at the top of the nappe pile contains Paleozoic metapelite, metabasite, and marble (Schuiling, 1962; Çağlayan et al., 1980; Loos and Reischmann, 1999b; Régnier et al., 2003; Gessner et al., 2004). The Eocene Selimiye Shear Zone separates the Selimiye Nappe from the underlying Çine Nappe (Régnier et al., 2003). Most of the Çine Nappe consists of deformed orthogneiss, largely undeformed metagranite, and minor pelitic gneiss, eclogite, and amphibolite. Protoliths of much of the orthogneiss-metagranite intruded at ca Ma (Loos and Reischmann, 1999b; Gessner et al., 2001a, 2004). The underlying Bozdağ Nappe is made up of metapelite with intercalated amphibolite, eclogite, and marble lenses. Protolith ages of all rock types of the Bozdağ Nappe are unknown, but geologic constraints (Candan et al., 2001; Gessner et al., 2001a) suggest a Precambrian age for at least parts of these rocks. The Bozdağ Nappe was intruded by granitoids at Ma (Dannat and Reischmann, 1999; Koralay et al., 2001). The Bayındır Nappe contains phyllite, quartzite, marble, and greenschist of inferred Permo-Carboniferous to Mesozoic age (Özer and Sozbilir, 2003). The rocks were affected by a single Eocene greenschist-facies metamorphism (Catlos and Çemen, 2005; Çemen et al., 2006). The analysis of regional structures and metamorphism shows that the tectonic units below the Cycladic Blueschist Unit are different in Greece from those in western Turkey. The oldest known basement rocks in the Phyllite-Quartzite Unit are ca. 510 Ma (Romano et al., 2004), whereas there is evidence for a Pan-African orogenic cycle in parts of the Menderes nappes (Oberhänsli et al., 1997; Gessner et al., 2001c, 2004; Ring et al., 2004). The Late Triassic to Eocene platform sequence of the Gavrovo-Tripolitza Block has no equivalent in the Menderes nappes of western Turkey. The orogenic history of both tectonic units was also different: The Gavrovo-Tripolitza Block did not enter the subduction zone until ca Ma, whereas the Menderes nappes were already underthrust by that time. Important Tectonic Contacts Critical for understanding the local geological architecture are the nappes of the Gavrovo-Tripolitza Block (the Basal Unit on Samos), the Cycladic Blueschist Unit (Selçuk, Ampelos and its mainland equivalent Dilek, and Agios Nikolaos Nappes both on Samos and in western Turkey), and the Menderes nappes of western Turkey (Fig. 3). In the following we describe the tectonic contacts between these units from top to bottom. On top of the succession in both Samos and western Turkey is the Selçuk Ophiolitic Mélange, which is separated from the underlying Ampelos-Dilek and Agios Nikolaos Nappes by the Selçuk Normal Shear Zone (Gessner et al., 2001c; Ring et al., 2007b). This shear zone must have been a thrust during early Eocene subduction and accretion. However, the present kinematics in the Selçuk Normal Shear Zone are top-to-the NE, and it resulted from normal faulting between 42 and 32 Ma (Ring et al., 2007b). As mentioned above, the Ampelos-Dilek and Agios Nikolaos Nappes rest on different units. In Samos, both nappes have been placed atop the Basal Unit along the Pythagoras Thrust (Ring et al., 1999b), whereas in western Turkey both nappes have been put on top of several of the Menderes nappes along the Cyclades- Menderes Thrust (Gessner et al., 2001c), including the Selimiye Nappe. The Pythagoras Thrust is supposed to have been reactivated as a top-to-the-e extensional fault associated with mid- Tertiary basin development in Samos (Ring et al., 1999b). The Cyclades-Menderes Thrust has top-to-the-s kinematics (Gessner et al., 2001a) and operated coevally with the Selçuk Normal Shear Zone (Ring et al., 2007b). The Menderes nappes beneath the Cyclades-Menderes Thrust were imbricated by top-to-the-s movement on the thrusts between the various nappes. The thrust zone relevant for this field-trip guide is the Eocene Selimiye Shear Zone, which separates the Selimiye and the Çine Nappes. Metamorphic History In this section critical rock types of the Basal Unit (on Samos), the Cycladic Blueschist Unit (Selçuk, Ampelos, and Agios Nikolaos Nappes both on Samos and in western Turkey), and the Menderes nappes of western Turkey will be described, followed by estimates of pressure-temperature (P-T) conditions of metamorphic events. Details of the metamorphic history have

11 6 Gessner et al. S Cyclades and western Anatolia N Vardar-Izmir-Ankara Oceanic Unit Pelagonian - Lycian Unit B Unit Crete Pindos (Cyclades- Dilek platform) Basement Selçuk Oceanic Unit Gavrovo-Tripolitza Ionian Zone Gavrovo-Tripolitza (Basal Unit) Anatolia Lycian Nappes Lycian Nappes Ampelos / Dilek Nappe M M Agios Nikolaos Kerketas Nappe Dilek Nappe Menderes Nappes Cyclades Menderes Figure 3. Schematic architecture of tectonic units in the Aegean Sea region and western Anatolia (cf. Figs. 1 and 2). Modified from Ring and Layer (2003). been extensively discussed elsewhere (Mposkos, 1978; Will et al., 1998; Ring et al., 2001b, 2007b; Whitney and Bozkurt, 2002; Régnier et al., 2003). Basal Unit There are hardly any diagnostic metamorphic minerals in the various marbles of the Kerketas Nappe on Samos. Most of the marbles contain phengitic white mica, talc, and chlorite. The metabauxite deposits on the western flank of the Kerketas Massif show early diaspore that has been transformed to corundum, and corundum then reacted back to diaspore (Mposkos, 1978). The correlative Almyropotamos Nappe on Evia in the western Aegean shows similar parageneses as the Kerketas Nappe on Samos (Shaked et al., 2000). However, sporadic glaucophane has been found in the Almyropotamos Nappe. P-T conditions of 8 10 kbar and ~400 C have consistently been reported for the Basal Unit in the central Aegean (Ring et al., 1999b; Shaked et al., 2000). This weak high-pressure overprint occurred at Ma (Ring et al., 2001a, 2003b; Ring and Reischmann, 2002). At a later stage, probably during regional extension, the Kerketas Nappe heated slightly to >420 C as indicated by the transformation of diaspore to corundum (Mposkos, 1978). Cycladic Blueschist Unit The P-T conditions inferred for high-pressure metamorphism in the Agios Nikolaos Nappe of the Cycladic Blueschist Unit have shown to be ~18 19 kbar and ~ C (Will et al., 1998). Age data for the Cycladic Blueschist Unit for a number of islands (e.g., Sifnos, Naxos, Ios, Syros, Tinos, Ikaria) across the entire Aegean are interpreted to date the peak of high-pressure metamorphism from 55 to 30 Ma (Wijbrans et al., 1990; Tomaschek et al., 2003; Ring et al., 2010). 40 Ar/ 39 Ar dating of phengite showed that ages of >45 Ma have to be envisaged for the peak of high-pressure metamorphism in the Cycladic Blueschist Unit on Samos (Ring et al., 2003b). The temperatures inferred for the strongly foliated chloritoid kyanite white mica schists from the Ampelos-Dilek Nappe are C, but with pressures ranging from ~5 to 15 kbar. A possible interpretation of these data is that the rocks underwent a near isothermal decompression from eclogite to epidote-amphibolite and greenschist-facies conditions related to tectonic extrusion of the Ampelos Nappe between 42 and 32 Ma (Ring et al., 2007a). In metagabbro from the basal Selçuk Nappe in western Turkey, calculations were carried out on mineral assemblages containing

12 Field Guide to Samos and the Menderes Massif 7 barroisitic hornblende, epidote-zoisite, plagioclase, chlorite and ± quartz. Clearly, this is an assemblage transitional between the middle to upper greenschist and lower blueschist facies. Furthermore, the jadeite barometer was used for the omphacite-bearing massive metagabbros. A garnet-amphibolite from the Selçuk Nappe in western Turkey yielded well-constrained P-T conditions of 550 ± 18 C and 12.4 ± 1.2 kbar, which is considered to reflect maximum P-T in the Selçuk nappe. The conditions inferred correspond with estimates on undeformed metagabbros from Samos: 8 12 kbar and C and are transitional between epidote-amphibolite and eclogite facies conditions. In contrast, strongly foliated, mylonitized Selçuk Nappe metagabbros in the Selçuk Normal Shear Zone consistently yielded P-T values of 4 ± 1.5 kbar and 450 ± 40 C. Similar greenschist-facies P-T estimates of ~3 4 kbar and C were also obtained for Selçuk Nappe metagabbros that occur as lenses in the underlying Ampelos Nappe (Ring et al., 2007a). Evidence for high-pressure metamorphism in the Selçuk Nappe is preserved only in the unfoliated samples but is no longer present in the mylonitized metagabbros from the Selçuk Normal Shear Zone. Presumably, this is the case, because fluid ingress hydrated the mylonitic metagabbros in the Selçuk Shear Zone and caused retrogression of the rocks under greenschist-facies conditions of 3 5 kbar. This deformation-related greenschistfacies overprint in the Selçuk Nappe apparently occurred before 32 Ma (Ring et al., 2007a). The Eocene eclogite-facies metamorphism (10 12 kbar) of the Selçuk Nappe was followed by a shearing-related greenschist facies overprint at 3 4 kbar. These data imply that the Selçuk Nappe must have been exhumed by ~20 30 km between the high-pressure metamorphism and the end of the mylonitization event. This decompression was accompanied by only slight to moderate cooling from 500 C to C and is ascribed to Eocene normal shearing in the Selçuk Normal Shear Zone (Ring et al., 2007b). The P-T data reveal a pronounced metamorphic break (up to 10 kbar) toward higher pressures and temperatures between the Kerketas and Agios Nikolaos Nappes. An inverse break in metamorphic pressure of ~3 5 kbar occurs above the Agios Nikolaos Nappe. Menderes Nappes High-grade metamorphism in the Çine and Bozdağ Nappes occurred before the intrusion of granites at ca. 550 Ma (Gessner et al., 2001a, 2004); this topic will be addressed in a later section. Reliable P-T estimates for the Tertiary tectonometamorphic evolution exist only for the uppermost nappe of the Menderes nappe pile, the Selimiye Nappe (Whitney and Bozkurt, 2002; Régnier et al., 2003). Metasediments from the Selimiye Nappe have maximum P-T conditions of <6 kbar and ~500 C near the base of the nappe. Metamorphism in the Selimiye Nappe decreases structurally upward as indicated by mineral isograds defining the garnet-chlorite zone at the base, the chloritoid-biotite zone, and the biotite-chlorite zone at the top of the nappe (Régnier et al., 2003). The mineral isograds in the Selimiye Nappe run parallel to the regional foliation and parallel to the Selimiye Shear Zone and suggest that the Selimiye Shear Zone formed during this prograde greenschist to lower amphibolite facies metamorphic event. No reliable P-T estimates exist for the strongly chloritized mylonite at the Cyclades-Menderes Thrust. However, biotite is not stable in the mylonite anymore, and the pressures of 4 6 kbar in the rocks of the Selimiye Nappe below the thrust suggest P-T conditions of <4 6 kbar and <400 C in the mylonite. These P-T estimates are largely similar to those from the mylonitic metagabbros at the base of the Selçuk Nappe (Ring et al., 2007a). Eocene Oligocene Crustal Thickening The subduction of the Vardar-Izmir-Ankara ocean that fringed Adria and Anatolia on its northern sides caused highpressure metamorphism in these oceanic units in the Late Cretaceous (e.g., Sherlock et al., 1999). At ca. 60 Ma the northern edge of the Pindos Unit was underthrust, causing high-pressure metamorphism in large parts of the Cycladic Blueschist Unit in the central Aegean Sea region (Cyclades islands) and westernmost Anatolia. Well-constrained ages for high-pressure metamorphism range from 53 to 30 Ma (Ring et al., 2003b, 2007a, 2011; Tomaschek et al., 2003; Putlitz et al., 2005). High-pressure metamorphism occurred in the External Hellenides in Crete and the Peloponnesus in the latest Oligocene at Ma (Seidel et al., 1982; Jolivet, et al., 1996). Recent reviews on the progression of high-pressure metamorphism (Jolivet and Brun, 2010; Ring et al., 2010) showed that this metamorphism becomes younger in a southerly direction. The major along-strike variations in the Hellenide-Anatolide orogen arose when the Anatolian microcontinent arrived in the subduction zone in the eastern part of the eastern Mediterranean region in the Eocene (Gessner et al., 2001c). During incipient underthrusting of the leading edge of Anatolia the high-pressure metamorphosed Cycladic Blueschist Unit was thrust onto the Menderes nappes; this thrusting can be constrained between 42 and 32 Ma (Ring et al., 2007b). The important point is that, in contrast to the Aegean Sea region, high-pressure metamorphism did not progress downward toward structurally deeper units. All quantitative data from the Menderes nappes available so far show no evidence for Tertiary high-pressure metamorphism in the Menderes nappes (Candan et al., 2001; Ring et al., 2001b, 2004; Whitney and Bozkurt, 2002; Régnier et al., 2003; Catlos and Çemen, 2005; Baker et al., 2008b). Tertiary metamorphism in the Bayındır Nappe, the structurally deepest nappe in the pile (Gessner et al., 1998, 2001a, 2001c; Ring et al., 1999a), reached 4 6 kbar at a maximum of C (Ring et al., 2007b). Available age data indicate ages of Ma for greenschist-facies metamorphism in the Menderes nappes (Hetzel and Reischmann, 1996; Catlos and Çemen, 2005; Baker et al., 2008b). The Menderes nappes, together with the Cycladic Blueschist Unit and the Lycian nappes above them, formed a southward-propagating

13 8 Gessner et al. thrust-and-fold belt in the late Eocene and Oligocene (e.g., Collins and Robertson, 1997, 1998; Rimmelé et al., 2001; Gessner et al., 2001c). The review of thrust deformation and high-pressure versus greenschist-facies metamorphism reveals that the underthrusting of Anatolia caused a greenschist-facies thrust-and-fold belt in western Turkey, whereas in the Aegean Sea transect, ongoing deep subduction caused an orogenic wedge characterized by sustained high-pressure metamorphism. Miocene to Holocene Extension Despite the fact that extension commenced in both the Aegean Sea region and in the Anatolide Belt of western Turkey at the same time, the extension-related cooling patterns are strikingly different in both regions. Contoured maps for apatite and zircon fission-track (AFT and ZFT) cooling ages for the central and southern Aegean Sea region show similar overall age patterns (Ring et al., 2010). For apatite (Fig. 4), with a closure temperature of ~110 C (Reiners and Brandon, 2006), the contouring reveals old ages (>20 Ma) on the islands of Donoussa and Amorgos in the east-central Aegean, and Crete, for which Figure 5 shows a distinct westward-younging age pattern. In the latter islands the old AFT ages are all from the hanging-wall areas of detachment faults for which they provide a maximum age. The youngest AFT ages (<8 Ma) occur on Ikaria, Mykonos, Naxos, and Serifos in the footwalls of major detachments in the central Aegean. For zircon, with a closure temperature of C (Reiners and Brandon, 2006), the regional distribution of cooling ages is similar. Exceptions are Crete, where extensional deformation along large-displacement, low-angle normal faults above which sedimentary basins formed commenced at ca. 23 Ma (Jolivet and Brun, 2010; Ring et al., 2010), and the Anatolide Belt of western Turkey, probably slightly earlier at ca. 24 Ma (Ring et al., 2003a; Thomson and Ring, 2006). For the Anatolide Belt of western Turkey, AFT and ZFT cooling patterns reveal a two-stage cooling history (Fig. 6). Three crustal segments differing in structure and cooling history have been identified. The Central Menderes Metamorphic Core Complex represents an inner axial segment of the Anatolide Belt and exposes the lowest structural levels of the nappe pile, whereas the two outer submassifs, the Gördes submassif to the north and the Çine submassif to the south, represent higher levels of the nappe pile. A regionally significant phase of cooling in the latest Oligocene and early Miocene affected the outer two submassifs and the upper structural levels of the Central Menderes Metamorphic Core Complex (Fig. 6). In the northern 24 E Apatite fission-track ages 50 km Evia Serifos Syros Sifnos Mykonos Naxos Paros Ios Amorgos Cretan Sea Ikaria Tinos Donoussa Samos Current magmatic arc 0-8Ma 8-12Ma Ma Ma Figure 4. Contouring of 249 apatite fissiontrack (AFT) ages from the central Aegean, western Turkey, and Crete (Thomson et al., 1998, 1999; Brix et al., 2002; Hejl et al., 2002; Ring et al., 2003a, 2007a, 2007b, 2009; Kumerics et al., 2005; Brichau et al., 2008, 2010; S.N. Thomson, unpublished data). The contouring reveals old ages (>20 Ma) in western Turkey, on the islands of Donoussa and Amorgos, and in rocks above the Cretan detachment on Crete. The youngest AFT ages (<8 Ma) occur on islands that are almost adjacent to the islands with old ages, e.g., on Ikaria and Naxos next to the westernmost Turkey- Donoussa area. The white sample dots indicate areas from which we have data, and question marks indicate islands for which no data exist Ma >30 Ma Crete Low-angle normal fault High-angle normal fault

14 Field Guide to Samos and the Menderes Massif 9 part of the Gördes submassif, cooling was related to top-nne movement on the Simav Detachment, as the AFT ages show a northward-younging trend in the direction of movement on this detachment. In the Çine submassif, relatively rapid cooling in the late Oligocene and early Miocene may have been related to top-s extensional reactivation of the basal thrust of the overlying Lycian nappes. The second phase of cooling in the Anatolide Belt is related to Pliocene to Holocene extension, resulting in the formation of the Central Menderes Metamorphic Core Complex in the inner part of the Anatolide Belt. Core-complex development caused the formation of supra-detachment basins, which document the ongoing separation of the Central Menderes Metamorphic Core Complex from the outer submassifs. The difference in extension between the Aegean and western Turkey is considerable. Gautier et al. (1999) estimated ca. 350 km for the Aegean, and van Hinsbergen (2010), ca. 150 km across the Menderes. The difference in extension is also documented in the topographic development of both regions. The Aegean is largely submerged, and the Cycladic archipelago represents a general horst structure between the more highly extended northern Aegean Sea and the Cretan Sea. The highest peaks in the Cyclades reach ~1 km elevation; only in Samos the Kerkis Mountain reaches more than 1400 m. Western Turkey is characterized by thicker crust than the Aegean (Makris and Stobbe, 1984), and this is manifested also in peak elevation exceeding 2 km. The E-W oriented grabens in western Turkey bend to the south and curve into a NE orientation in the vicinity of the Aegean Sea. It appears as if NE structures accommodate a gradient in extension between the Aegean and western Turkey (e.g., Ring et al., 1999a; Özkaymak and Sözbilir, 2008; Uzel and Sözbilir, 2008). Summary The lowermost tectonic units in the Hellenides (Gavrovo- Tripolitza and Ionian Blocks) and the Anatolides (Menderes nappes) show significant geological-structural dissimilarities, which are caused by tectonic differences of both areas since the Eocene. In the Anatolides the collision of the Anatolian microcontinent caused a cessation of deep underthrusting and highpressure metamorphism, whereas farther west the subduction zone retreated southward and caused a Miocene high-pressure belt in the External Hellenides. 24 E 50 km Zircon fission-track ages Evia Serifos Syros Sifnos Ios Mykonos Naxos Paros Tinos Cretan Sea Ikaria Amorgos Samos 0-10Ma Ma Ma Ma Figure 5. Contouring of 167 zircon fissiontrack (ZFT) ages from the central Aegean, western Turkey, and Crete. The trends are fairly similar to those of the AFT ages. A surprising and not well-understood feature is the east-to-west younging of ZFT ages on Crete. We have no ZFT ages for Donoussa (for location, see Fig. 4), but these ages must be older than the AFT ages of ca. 25 Ma. Data are from (Thomson et al., 1998, 1999; Brix et al., 2002; Hejl et al., 2002; Ring et al., 2003a, 2007a, 2007b, 2009; Kumerics et al., 2005; Brichau et al., 2008, 2010; Thomson et al., 2009; S.N. Thomson, unpublished data). Crete Ma >50 Ma Low-angle normal fault High-angle normal fault

15 10 Gessner et al. gm cmcc çsm KMD BMD SSZ Figure 6. Time slices from 28 Ma to 2 Ma imposed on a general outline of Menderes nappes with major detachments; the map for 28 Ma shows locations of 34 samples used to construct the maps. Cooling below ~130 C commenced in the southern Gördes submassif (gm) at ca. 28 Ma but did not progress northward until Ma. Cooling in the northern Çine submassif (çsm) started at 25 Ma and progressed southward toward the base of the Lycian nappes (south of the Selimiye Shear Zone, SSZ). The downfaulted block in the central Central Menderes Metamorphic Core Complex (cmcc) started to cool at 22 Ma. The footwall of the Kuzey Detachment (KMD) at the northern end of the Central Menderes Metamorphic Core Complex remained at elevated temperatures >~130 C until 5 Ma; the footwall of the Güney Detachment (BMD) started to cool below ~130 C at 14 Ma, but final cooling occurred only after 2 Ma (Ring et al., 2003a).

16 Field Guide to Samos and the Menderes Massif 11 PART A. SAMOS ISLAND, GREECE Samos is not one of the typical Aegean turtle-back shaped core-complex type islands like Ios or Mykonos, for example. The general structure of Samos is dominated by steep faults, and the overall architecture of the islands is best described as a horst. The topography of Samos is rugged and dominated by the sheer cliffs of 1433-m-high Mount Kerkis in the western part of the island (Fig. 7). The geology of Samos consists of a number of metamorphosed nappes, one non-metamorphosed nappe, and a Miocene graben. The island offers a look at an exceptionally complete nappe stack of the Central Hellenides, ranging from the highpressure metamorphosed Basal Unit (as part of the External Hellenides), all the way up to the ophiolitic Selçuk Nappe and the non-metamorphosed Cycladic Ophiolite Nappe. This field guide is concerned with the two structurally lowest units, the Basal Unit and the overlying Cycladic Blueschist Unit, as well as the Tertiary sediments. Geology of Samos A simplified geological map of Samos Island is shown on a map (Fig. 8) and two cross sections (Fig. 9). The nappe pile and the Neogene basins are summarized schematically in Figure 10. The nappe stack consists of six major tectonic units, which are described in descending order: 1. The Kallithea Nappe is part of the Cycladic Ophiolite Nappe, which probably belongs to the Vardar-Izmir-Ankara Oceanic Unit. The Kallithea Nappe consists of peridotite, basalt, Triassic-Jurassic limestone, radiolarite, and sandstone (Theodoropoulos, 1979). The Katavasis Complex, consisting of amphibolite-facies schist, marble, and amphibolite, forms a tectonic block in the Kallithea Nappe (Ring et al., 1999b). 2. The Selçuk Nappe is the uppermost nappe of the Cycladic Blueschist Unit and is exposed only in a few patches. It is far more extensively exposed on the westernmost Turkish mainland some km east of Samos (Gessner et al., 2001c; Ring et al., 2007b). The Selçuk Nappe is essentially an ophiolitic mélange and contains metagabbro, in part in primary contact with serpentinized peridotite and mica schist. 3. The Ampelos Nappe is composed of the shelf sequence of the Cycladic Blueschist Unit and contains marble (with metabauxite lenses), metapelite (including conspicuous chloritoidkyanite schist), quartzite, glaucophane-epidote schist, and greenschist. Detailed work showed that the Ampelos Nappe is correlative with the Dilek Nappe of adjacent western Turkey (Candan et al., 1997; Ring et al., 1999a, 1999b; Gessner et al., 2001c). 4. The Agios Nikolaos Nappe at the base of the Cycladic Blueschist Unit is, like the Selçuk Nappe, exposed only in a few outcrops at the northern coast between the church of Agios Nikolaos and Konstandinos. It forms part of the Carboniferous basement of the Cycladic Blueschist Unit and consists of metagranitic gneiss, garnet-mica schist, and dolomitic marble. 5. The Kerketas Nappe of the Basal Unit is made up of a succession of monotonous dolomitic marble at least 1000 m thick, the base of which is not exposed. The Basal Unit is generally correlated with the Gavrovo-Tripolitza Block of the External Hellenides (Godfriaux, 1968). 6. Molasse-type sediments were deposited in the Miocene and Pliocene in N-, NE-, and WNW-oriented Karlovasi, Pyrgos, and Mytilini Grabens, which are filled with fluviatile and lacustrine sediments (Figs. 9 and 10). Above the Basal Conglomerate Formation are the Pythagorion and Hora Formations, which laterally interfinger. The sediments of the Hora Formation are thought to have formed in a deeper basin than the limestone of the Pythagorion Formation (Weidmann et al., 1984). A major angular unconformity is present at the top of the Hora Formation. Lacustrine sedimentation is succeeded by fluviatile conglomerate of the basal Mytilini Formation. Weidmann et al. (1984) showed that in some places the unconformity occurs on top of the Old Mill beds, whereas in other places it occurs below these beds. This difference might indicate that the unconformity did not occur at the same time in all parts of the basin, or it might indicate that the Old Mill beds are time-transgressive. General Architecture of Samos Island and Important Tectonic Contacts Figure 7. View of Samos from the NE, showing the Kerketas Massif, which is part of the lowest tectonic unit in Samos, the Basal Unit. The island of Samos in the Aegean Sea exposes highpressure metamorphic rocks of the Cycladic Blueschist Unit, which are sandwiched between the mildly blueschist-facies Kerketas Nappe below and the overlying non-metamorphic Kallithea Nappe. The general architecture of the island is depicted in two generalized cross sections in Figure 9. Overall the nappe pile dips to the east.

17 12 Gessner et al. Figure 8. Simplified geological map, showing major rock units, thrusts, and and representative measurments of Samos (modified from Theodoropoulos, 1979). Lower series of graben fill comprise Basal Conglomerate and Pythagorion and Hora Formations. Upper series of graben fill include Mytilini and Kokkarion Formations (see also Figs. 9 and 10). The D 1 Ampelos and Selçuk Thrusts are the basal thrusts of the Ampelos and Selçuk Nappes, respectively. The D 2 Pythagoras thrust put the Cycladic Blueschist Unit on top of the Kerketas Nappe. The Kallithea Detachment is a late-d 3 low-angle normal fault. Middle to late Miocene volcanic and volcanoclastic rocks occur at the eastern and northeastern margins of the Karlovasi and Pyrgos Grabens and at the western side of the Mytilini Basin. Numerous reverse (D 4 ) and normal (D 5 ) faults overprinted all earlier ductile contacts. We interpret the curved D 5 high-angle normal faults to have a listric geometry. Figure 9. Serial cross sections A A and B B through Samos Island, showing general architecture of the island (refer to Fig. 6 for transect positions). The trace of the main foliation illustrates the generally E-dipping structure.

18 Field Guide to Samos and the Menderes Massif 13 Figure 10. Idealized comparative tectono-stratigraphic column of the nappe pile on Samos Island. Notice that the dashed line between the Hora and Mytilini Formations is an unconformity. The base of the Kerketas Nappe is not exposed. At the northern end of the island the dolomite of this nappe can be followed from the top of Kerkis Mountain down to the sea. The contact of the Kerketas Nappe with the Agios Nikolaos Nappe has been excised, either by Eocene out-of-sequence thrusting and/or subsequent Eocene normal shearing, or by Miocene extensional shearing (see Structural History and Deformation-Metamorphism Relationships section). What is well exposed is the Pythagoras Thrust, separating the Kerketas Nappe from the overlying Ampelos Nappe (see Locality 1.1 descriptions). 40 Ar/ 39 Ar phengite ages of ca Ma have been interpreted to date shear-related phengite recrystallization during thrusting of the Cycladic Blueschist Unit onto the Kerketas Nappe (Ring and Layer, 2003). The Pythagoras Thrust was then reactivated as a top-e extensional fault in the middle Miocene, probably associated with the formation of the middle Miocene basins. The base of the Agios Nikolaos Nappe is nowhere exposed. The upper contact of this nappe is poorly exposed in the northern Ampelos Massif at the central north coast of the island. Whereas there is no unambiguous evidence as to whether this contact is a thrust-type or normal shear zone, it has been speculated that the latest penetrative ductile deformation might have normal-sense kinematics relating to the Eocene motion of the Selçuk Normal Shear Zone (Ring et al., 2007b). The Selçuk Normal Shear Zone separates the Ampelos Nappe from the overlying Selçuk Nappe. Using detailed 40 Ar/ 39 Ar and Rb Sr dating of mylonitic rocks, Ring et al. (2007a) showed that the Selçuk Normal Shear Zone represents the roof of a late Eocene extrusion wedge. Normal shearing caused extensive retrogression of the high-pressure parageneses in the Selçuk Nappe (see further discussion in the following section). Normal shearing is a geometric effect that facilitated the extrusion of the Ampelos Nappe (together with its western Turkish equivalent, the Dilek Nappe); it is not related to wholesale crustal extension of the region. The next major contact in the tectonic sequence is the Kallithea Detachment in western Samos, which was active between 10 and 8.5 Ma (Ring et al., 1999a). Zircon fission-track dating (Brichau, 2004; Kumerics et al., 2005) revealed that the Kallithea Detachment, or a splay of it, continued moving until, or was reactivated at, ca. 7 Ma. The Miocene basins on Samos have a complex architecture and tectonic history. It seems that formation of the basins was related to extensional reactivation of the Pythagoras Thrust in the middle Miocene in a transtensional setting. Based on the facies distribution and basin geometry, Ring et al. (1999a) argued that a transtensional scenario might best explain the abrupt lateral facies changes of the Hora and Pythagorion Formations. There is plenty of evidence for folding in the Hora and Pythagorion

19 14 Gessner et al. Formations, which was caused by a short-lived shortening event at >ca. 8.6 to 9 Ma. Structural History and Deformation-Metamorphism Relationships Structural and metamorphic analysis (Ring et al., 1999b, 2001a, 2007b; Ring and Layer, 2003) shows that deformation can generally be divided into four main stages: 1. Eocene and earliest Oligocene approximately ESE- WNW oriented nappe stacking (D 1 and D 2 ) was associated with blueschist- and transitional blueschist-greenschist-facies metamorphism (M 1 and M 2 ). Maximum high-pressure assemblages in the Cycladic Blueschist Unit developed during the first deformational event, D 1, and are therefore referred to as M 1. The associated S 1 foliation was porphyroblastically overgrown by glaucophane, chloritoid, and kyanite during a static growth event. Internal imbrication of the nappes of the Cycladic Blueschist Unit under M 1 peak high-pressure metamorphism occurred at ca Ma and followed, and also was followed by, high-pressure mineral growth (Ring et al., 1999b; Ring and Layer, 2003). D 2 deformation caused emplacement of the Cycladic Blueschist Unit onto the Kerketas Nappe, which started at ca Ma and eventually caused high-pressure metamorphism in the latter at Ma (Ring et al., 2001a). Maximum pressure in the Kerketas Nappe occurred during the D 2 deformation, and therefore the mildly blueschist-facies event in the Kerketas Nappe is regarded as M 2. D 2 thrusting was out of sequence and occurred during decompression, bringing kbar rocks of the Cycladic Blueschist Unit on top of 8 10 kbar rocks of the Kerketas Nappe. During D 2 deformation the M 1 high-pressure assemblages in the Cycladic Blueschist Unit were replaced by M 2 transitional blueschist-greenschist facies assemblages. The deformation-related greenschist facies overprint in the Selçuk Normal Shear Zone at the top of the Selçuk Nappe occurred at the same time as the basal nappes of the Cycladic Blueschist Unit were thrust onto the foreland (Ring et al., 2007b). As mentioned above, these data that constrain greenschist facies metamorphism in the uppermost Selçuk Nappe can generally be grouped into the M 2 event, having occurred before 32 Ma. 2. Subsequent Miocene horizontal crustal extension occurred during D 3 deformation. In the Ampelos Nappe there is evidence that D 3 took place before, during, and after a greenschist facies metamorphism (M 3 ). This greenschist-facies metamorphic overprint was characterized by the prograde formation of garnet and more rarely by biotite in metapelite of the Agios Nikolaos and Ampelos Nappes, constraining metamorphic conditions to ca. 6 7 kbar and C (Chen, 1995) for M 3, with slightly higher temperatures in the western than in the eastern part of the island. The data show that M 3 occurred during further decompression but with increasing temperature. This M 3 greenschist-facies event cannot be related to the above mentioned >ca. 32 Ma greenschist facies metamorphic event in the uppermost Selçuk Nappe and must be a second greenschist facies event that can also be seen as a post-high-pressure metamorphic event in the Kerketas Nappe (characterized by the reaction of diaspore to corundum during increasing temperature and decreasing pressure) and should therefore be younger than the high-pressure emplacement of the Cycladic Blueschist Unit onto the Kerketas Nappe at ca. 21 Ma (Ring et al., 2001a). Ductile flow during D 3 was characterized by a high degree of coaxial deformation, but in general caused displacement of upper units toward the ENE. Fission-track dating shows that ductile top-ene extensional reactivation at the base of the Selçuk Nappe occurred in the early Miocene, as indicated by zircon fission-track ages of Ma (Brichau, 2004). The zircon fission-track ages consistently young ENE in the direction of hanging-wall slip (Kumerics et al., 2005). One zircon fission-track age of 14.1 ± 0.8 Ma from a conglomerate at the southern slopes of Kerkis Mountain suggests that the Kerketas extensional system is slightly younger than the extensional fault at the base of the Selçuk Nappe. The pattern of fission-track ages suggests that both extensional fault systems are unrelated. Late-stage D 3 emplacement of the Kallithea Nappe had a top-nw to NNW sense of shear (Ring et al., 1999b). Inception of the Kallithea detachment is fairly well dated at ca. 10 Ma. 3. A short period of brittle E-W crustal shortening (D 4 ) occurred between >ca. 8.6 and 9 Ma. D 4 shortening caused numerous W-vergent folds and reverse faults and affected only the lower sequence of the Neogene sediments below the unconformity. 4. A phase of N-S directed normal faulting ensued (D 5, 8.6 Ma to Holocene). A granodiorite dike truncated by the Kallithea Detachment yielded a zircon fission-track age of 7.3 ± 0.6 Ma (Brichau, 2004), indicating that the Kallithea Detachment continued to operate or was reactivated during D 5 extension. The cause for the short-lived D 4 shortening event between 9 and 8.6 Ma remains enigmatic. It is also not fully clear whether E-W shortening during D 4 was coeval with N-S extension as suggested for the central Cyclades (Avigad et al., 2001); however, the general absence of NW-striking sinistral and NE-striking dextral strike-slip faults suggests that E-W shortening was not coeval with N-S extension. However, it might be that the extensional emplacement of the Kallithea Nappe continued during the short-lived shortening event. Day 1 Localities 1.1 to Locality 1.1. Ridge East of Mount Kerkis Summary. Traverse from Ampelos into Kerketas Nappe. Excellent exposure of variegated sequence of the Cycladic Blueschist Unit that rests above dolomite of the Kerketas Nappe (see Figs. 11 and 12). 1 A Google Earth file containing the Samos and other localities is available in the GSA Data Repository. GSA Data Repository Item is available at or on request from editing@geosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO , USA.

20 Field Guide to Samos and the Menderes Massif 15 Day 2 Locality 1.1 Day 1 Samos Locality 1.6 Dilek Peninsula Figure 11. Above: areas of Samos covered on Days 1 and 2 (Fig. 17). Below: location map for stops on Day 1. Modified from Google Maps ( 2011 Google Map data 2011 Basarsoft, Tele Atlas). Location maps such as these are intended for basic reference and to show the relations of the localities to one another. Locality 1.5 Locality 1.4 Locality 1.2 Locality 1.3 Location. About 2 km NW of Marathokambos ( N, E). Access. Take the road from Marathokambos to Kastania, and after ~100 m turn left and take a dirt road to the windmills; there are some modern windmills and ruins of old windmills. Carry on for ~5 6 km up the hill until you reach the top of a saddle from where the road drops down to the N. Park your car here ( N, E) and follow a goat track toward the southwest to the end of the section (~ N, E). Geology. You will walk through a generally moderately E-dipping variegated sequence of phyllite (in part carbon bearing and thus dark gray to black), marble, greenschist, chlorite-rich schist, and quartzite of the Ampelos Nappe (Fig. 12). Most rocks are strongly foliated and have a WNW-trending stretching lineation. After ~1 km you will reach the grayish-white dolomites of the Kerketas Nappe. Directly at the contact a dolomite slice is present in the phyllite. The contact zone is well exposed, but no distinct mylonitic shear zone has been mapped. Instead, it appears that the relatively strong deformation recorded in the Ampelos Nappe rocks on the ridge took up the deformation heterogeneously. The metadolomite of the Kerketas Nappe, in contrast, has only a weak to moderately developed foliation, and no increase in foliation intensity is observed as the contact is approached. Figure 12. Panoramic view of contact between Ampelos Nappe (right) and light-gray, dolomitic marble of Kerketas Nappe (left). Schists of Ampelos Nappe are usually covered by greenish-brown vegetation, whereas dolomite commonly has no vegetation. The sequence dips E (right).