Anorogenic plateau formation: The importance of density changes in the lithosphere

International audienceAway from active plate boundaries the relationships between spatiotemporal variations in density and geothermal gradient are important for understanding the evolution of topography in continental interiors. In this context the classic concept of the continental lithosphere as comprising three static layers of different densities (upper crust, lower crust, and upper mantle) is not adequate to assess long-term changes in topography and relief in regions associated with pronounced thermal anomalies in the mantle. We have therefore developed a one-dimensional model, which is based on thermodynamic equilibrium assemblage computations and deliberately excludes the effects of melting processes like intrusion or extrusions. Our model calculates the "metamorphic density" of rocks as a function of pressure, temperature, and chemical composition. It not only provides a useful tool for quantifying the influence of petrologic characteristics on density, but also allows the modeled "metamorphic" density to be adjusted to variable geothermal gradients and applied to different geodynamic environments. We have used this model to simulate a scenario in which the lithosphere-asthenosphere boundary is subjected to continuous heating over a long period of time (130 Ma), and demonstrate how an anorogenic plateau with an elevation of 1400 m can be formed solely as a result of heat transfer within the continental lithosphere. Our results show that, beside dynamic topography (of asthenospheric origin), density changes within the lithosphere have an important impact on the evolution of anorogenic plateaus

Evolution structurale et métamorphique des nappes lyciennes et du massif du Menderes (Sud-Ouest de la Turquie) (implications géodynamiques et corrélations avec le domaine égéen)

L'Anatolie occidentale, prolongement vers l'est du domaine égéen, est constituée de plusieurs unités tectono-métamorphiques au sein desquelles affleurent des roches de haute-pression/basse température (HP-BT). Si certaines d'entre elles sont des vestiges des orogenèses Pan-Africaine et Cimmérienne, d'autres témoignent de l'orogenèse Alpine. Au Sud-Ouest de la Turquie, le massif du Menderes forme un large domaine chevauché au Nord par les unités de la zone de suture d'Izmir-Ankara, à l'Est par la Zone d'Afyon, et au Sud par les nappes lyciennes. Ce travail de thèse a permis de mettre en évidence l'existence de paragenèses à Fe-Mg-carpholite largement distribuées dans les sédiments des nappes lyciennes, ainsi que dans les séries de couverture de la partie la plus méridionale du massif du Menderes. Cette découverte révèle que ces deux complexes de nappes ont enregistré des conditions de HP-BT pendant l'orogenèse Alpine. Les conditions P-T du pic de métamorphisme sont de 10-12 kbar/400ʿC pour les nappes lyciennes, et de 12-14 kbar/470-500ʿC pour le massif du Menderes, ce qui correspond à un enfouissement d'au moins 30 km pendant le processus de subduction et d'empilement de nappes. L'analyse de la déformation ductile couplée à des calculs thermobarométriques basés sur la notion d'équilibres multiples indique que les métasédiments des nappes lyciennes ont enregistré des chemins d'exhumation distincts après le pic de métamorphisme. Les roches situées loin du contact entre les nappes lyciennes et le massif du Menderes, là où les paragenèses de HP sont préservées, ont enregistré des chemins froids (décompression en refroidissement) accompagnés de cisaillements vers le NNE liés à là zone de cisaillement d'Akçakaya. Cette zone de localisation de la déformation est un contact intra-nappe qui a fonctionné pendant les premiers stades d'exhumation des roches de HP, dans le champ de stabilité de la Fe-Mg-carpholite. En revanche, les roches situées au contact avec le massif du Menderes, là où les paragenèses de HP sont totalement rétromorphosées en chlorite et mica, ont enregistré des chemins d'exhumation plus chauds (décompression avec réchauffement) associés à un cisaillement intense vers l'est. Cette déformation s'est produite postérieurement à la mise en place des nappes lyciennes vers le sud, et est contemporaine de la réactivation du contact 'massif du Menderes/nappes lyciennes' en une zone de cisaillement majeure (la zone de cisaillement de Gerit) le long de laquelle se sont exhumées les paragenèses de HP sous des gradients plus chauds...Western Anatolia that represents the eastward lateral continuation of the Aegean domain is composed of several tectono-metamorphic units showing occurrences of high-pressure/low-temperature (HP-LT) rocks. While some of these metamorphic rocks are vestiges of the Pan-African or Cimmerian orogenies, others are the result of the more recent Alpine orogenesis. In southwest Turkey, the Menderes Massif occupies an extensive area tectonically overlain by nappe units of the Izmir-Ankara Suture Zone in the north, the Afyon Zone in the east, and the Lycian Nappes in the south. In the present study, investigations in the metasediments of the Lycian Nappes and underlying southern Menderes Massif revealed widespread occurrences of Fe-Mg-carpholite-bearing rocks. This discovery leads to the very first consideration that both nappe complexes recorded HP-LT metamorphic conditions during the Alpine orogenesis. P-T conditions for the HP metamorphic peak are about 10-12 kbar/400ʿC in the Lycian Nappes, and 12-14 kbar/470- 500ʿC in the southern Menderes Massif, documenting a burial of at least 30 km during subduction and nappe stacking. Ductile deformation analysis in concert with multi-equilibrium thermobarometric calculations reveals that metasediments from the Lycian Nappes recorded distinct exhumation patterns after a common HP metamorphic peak. The rocks located far from the contact separating the Lycian Nappes and the Menderes Massif, where HP parageneses are well preserved, retained a single HP cooling path associated with top-to-the-NNE shearing related to the Akçakaya shear zone. This zone of strain localization is an intra-nappe contact that was active in the early stages of exhumation of HP rocks, within the stability field of Fe-Mg-carpholite. The rocks located close to the contact with the Menderes Massif, where HP parageneses are completely retrogressed into chlorite and mica, recorded warmer exhumation paths associated with top-to-the-E intense shearing. This deformation occurred after the southward emplacement of Lycian Nappes, and is contemporaneous with the reactivation of the 'Lycian Nappes-Menderes Massif contact as a major shear zone (the Gerit shear zone) that allowed late exhumation of HP parageneses under warmer conditions...ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

The Aral sea (a palaeoclimate archive)

La Mer intracontinentale endoréique de l'Aral constitue une excellente archive sédimentaire des changements paléoclimatiques en Asie Centrale. Une analyse multi-paramétrique à haute résolution (palynologie, sédimentologie, géochimie) a été réalisée sur des carottages sédimentaires prélevés au NW de la Grande Mer d'Aral. S'il apparaît probable que l'homme ait influencé modérément l'hydrologie de cette région au cours des 2000 dernières années, les changements environnementaux successifs ont été primordialement modulés par le climat en réponse au forçage interne du système. Ainsi, le bilan hydrologique du bassin de l'Aral est contrôlé par les températures printanières dans le bassin versant où la fonte des neiges alimente les tributaires du lac, et par le système cyclonique de la Méditerranée orientale où des dépressions se forment et migrent en Asie Centrale. L'anticyclone Sibérien constitue le principal régulateur de la dynamique éolienne contrôlant l'amplitude des apports détritiques dans le bassinLYON1-BU.Sciences (692662101) / SudocLYON1 - UFR Sciences de la terre (692662208) / SudocSudocFranceF

Batı Anadolu’da Eosen Yüksek Basınç Metamorfizması: Kikladik Kompleks - Anatolidler Arasındaki Tektono-Metamorfik İlişki

Doğu-batı yönde yaklaşık 600 km yayılım sunan ve Toroslar’ın metamorfikeşleniği olan Anatolidler Tavşanlı Zonu (TZ), Afyon Zonu (AZ),&nbsp; Menderes Masifi (MM) ve Kırşehir Masifi’ndenyapılıdır. Bunların yanı sıra, Batı Anadolu’da Kikladik Kompleks’e (KK) aitmetamorfikler de yüzeylemektedir. Bu kompleksin Batı Anadolu’daki doğuya devamıMenderes Masifi’nin kuzeybatı kenarı ile sınırlanmaktadır. Güneybatı-kuzeydoğu yönelimliKikladik Mavişist Ünitesi (KMÜ) Dilek Yarımadası’ndan Simav’a kadar birbirindenkopuk tektonik dilimler şeklinde, yaklaşık 250 km’lik bir uzanım sunar.&nbsp; Ünite, alt dokanağını MM, üst dokanağını ise AZve/veya Bornova Filiş Zonu ile tektonik olarak yapmaktadır. KMÜ eklojit vemavişist fasiyesi metamorfizması kayaları ile tanımlanmaktadır. Bu ünite,olasılı Triyas-Geç Kretase yaşlı pasif kıta kenarı sedimentlerinden türemedüzenli seri ve onu tektonik dokanakla üzerleyen, Geç Kretase yaşlı SelçukMelanjı’ndan yapılıdır. 40Ar/39Ar beyaz mika yaşları(44-40 My), alt düzeylerinde mermer-şist ardalanması, üst düzeylerinde ise korunmuşrudist fosilli, kalın platform türü metakarbonatlardan yapılı düzenli serininorta Eosen’de epidot-mavişist fasiyesinde (1.15±0.15 GPa ve 490±25 °C)metamorfizmaya uğradığını göstermektedir. Selçuk Melanjı pelitik bir matriks veyüksek basınç (YB) kayası bloklarından yapılıdır. Matriksi etkileyenepidot-mavişist metamorfizması (1.3±0.15 GPa ve 520±15 °C)&nbsp; 40Ar/39Ar beyaz mikayaşlarına göre en geç Paleosen - erken Eosen (57-54 My) olarak saptanmıştır.Pelitik matriks içindeki eklojitlerin&nbsp;(1.8±0.2 GPa ve 570±30°C) YB metamorfizma yaşı U/Pb zirkon yönteminegöre, benzer şekilde 56±1.5 My olarak belirlenmiştir. Düzenli seri ve SelçukMelanjı’nı yeşilşist fasiyesi koşulunda üzerleyen retrograd metamorfizmanınyaşı ise 40Ar/39Ar beyaz mika verilerine göre 36-32 My (geçEosen – en erken Oligosen) olarak saptanmıştır. Gondvana’nın kuzey kenarındagerçekleşen geç Permiyen transgresyonu ile ilişkili karbonatların Anatolid veToridler’de ortak varlığı bu iki ünitenin metamorfizma öncesi ilkselkorelasyonunu mümkün kılmaktadır. Anatolidler’de kuzeyden güneye doğru gözlenenmetamorfizma yaşındaki gençleşme (TZ: 2.3-2.4 GPa / 430-460°C, ~80 My; AZ: 0.8-1.3 GPa / 400-445°C, ~70 My; MM: 0.6-0.8 GPa / 450-550°C, ~45 My) NeotetisOkyanusu’nun kapanmasıyla ilişkili olarak, platformun kuzey ucunun Sakarya Zonualtına Geç Kretase-Eosen yitimi ile ilişkilendirilmektedir. Fosilli üstPermiyen karbonatları Ege adalarından sadece Paros ve Andros da belirlenmiştir.Bunlar KK’i tektonik dokanakla üzerlemektedir ve 116 My yaşlı YB metamorfizmasıverisi içermeleri ile KK’den ayrılmaktadır. Ayrıca, KK’in Variskan Orojeneziile ilişkilendirilen kristalen temel içermesi bu üniteyi geç PaleozoyikteLavrasya’nın güney kenarına konumlandırmaktadır. KK’in Eosen YB metamorfizmasıPindos Okyanusu’nun kapanması ile ilişkilendirilmektedir. Günümüzde Anatolidlerile KK arasındaki tektonik dokanak sünümlü bir makaslama zonu niteliğindedir.Bu ünitelerdeki bölgesel ölçekli stratigrafik ve tektono-metamorfik farklıklargöz önüne alındığında Anatolidler ve KMÜ arasındaki orijinal dokanağın Triyasda oluşmuş litosferik ölçekte bir transform fay zonu olduğu öngörülebilir.&nbsp;</p

The evolution of the northern margin of the Tethys in eastern Switzerland

The former northern margin of Tethis is being studied in the Alpine chain by IGCP Project 198("Evolution of the Northern Margin of the Tethys"). This paper summarizes the present state of the knowlege from the opening phase of this Mesozoic to early Paleogene seaway in Eastern Switzerland. Basement rocks and sediments of the previous margin are now exposed here in the stack of the Alps and their European foreland

Progress towards the establishment of the IUGS Deep-time Digital Earth (DDE) programme

The Deep-time Digital Earth (DDE) programme of the International Union of Geological Sciences (IUGS) has been developed to address the formidable challenge of so called ‘long tail’ data in the geosciences - the unstructured and inherently heterogeneous geoscience data that resides in institutions, universities and on individual geoscientists’ computers. DDE’s vision is to transform Earth science by connecting and harmonising long tail deep-time data ‘islands’ to support broad-based scientific studies relevant to the entire Earth system. The results of these and other studies will help us understand Earth’s natural environment and help in the wise use of natural resources for the prosperity of nations and the quality of human life. This harmonisation is now possible through the digital revolution, but new protocols, platforms and programs are needed to secure compatible and interoperable databases, so that the vast amounts of existing (and new) deep-time geoscience data can be linked. Since the first DDE meeting in January 2019, great progress has been made in defining statutes and byelaws, governance structures and preliminary informatics and scientific aims