Tectonic evolution of Paleo-Tethys in NE Iran

2021 ◽  
Author(s):  
Yang Chu ◽  
Bo Wan ◽  
Mark B. Allen ◽  
Ling Chen ◽  
Wei Lin ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Foreland Basin ◽  
Passive Margin ◽  
Causal Mechanism ◽  
The South ◽  
Clastic Rocks ◽  
Tethys Ocean ◽  
Depositional Age ◽  
Detrital Zircon Ages ◽  
Ne Iran

<p><span>The timings of the onset of oceanic spreading, subduction and collision are crucial in plate tectonic reconstructions, but not always straightforward to resolve. The evolution of the Paleo-Tethys Ocean dominated the Paleozoic-Early Mesozoic tectonics of West Asia, but the timeline of events is still poorly-constrained. In this study we present detrital zircon ages from NE Iran, in order to determine the timing of tectonic events in the region, and the wider implications for regional tectonics, paleogeography and climate change. Paleozoic clastic rocks record two major age peaks at ~800 Ma and ~600 Ma. The consistency in age patterns shows a dominant provenance from the Neoproterozoic basement of northern Gondwana. We interpret deposition on a long-lasting passive continental margin after the initial spreading of the Paleo-Tethys Ocean. Initial collision between the South Turan (Eurasia) and Central Iran (Gondwana) blocks caused coarse clastic deposition, the protolith of the Mashhad Phyllite, in a peripheral foreland basin on the Paleozoic passive margin. The Mashhad Phyllite yields major zircon age clusters at 450-250 Ma and 1900-1800 Ma, with a clear provenance from the active, Eurasian, margin. The Paleozoic ages reveal a long-lived subduction zone under the South Turan Block began in the latest Ordovician. Analysis of the age spectra allows us to constrain the timing of initial collision as no later than 228 Ma, which is also a constraint on the maximum depositional age of the Mashhad Phyllite. Based on our new results and previous data, we discuss the interaction between the Rheic and Paleo-Tethys oceans, and explain how a new subduction zone may have initiated after continental collision. The timing of collision is similar to the Carnian Pluvial Event (CPE). Paleo-Tethys collision has previously been suggested as the trigger for this climatic change, and our study provides timing evidence that reinforces Paleo-Tethys closure as a causal mechanism for the CPE.</span></p>

scholarly journals U-Pb ZIRCON DATING OF MIDDLE EOCENE CLASTIC ROCKS FROM THE GERCUS MOLASSE, NE IRAQ: NEW CONSTRAINTS ON THEIR PROVENANCE, AND TECTONIC EVOLUTION

2021 ◽  
Vol 54 (1C) ◽  
pp. 1-15
Author(s):  
Nabaz Aziz
Keyword(s):  
Tectonic Evolution ◽  
Middle Eocene ◽  
Early Stage ◽  
Foreland Basin ◽  
Detrital Zircons ◽  
Passive Margin ◽  
Accretionary Complex ◽  
Depositional Sequence ◽  
Clastic Rocks ◽  
The North

The provenance of Middle Eocene clastic rock from the Gercus Molasse, NE Iraq was determined by detrital zircon (DZ) U-Pb geochronology. The Gercus Molasse in the Iraqi segment of the north-eastern Zagros Thrust Zone provides an ideal example of foreland system evolution with respect to the transition from passive margin to the accretionary complex terrene-flexural foreland basins. The DZ U-Pb age spectra from the Gercus Molasse suggest that the foreland sediments either influx from multiple provenances or are the result of recycling from the accretionary complex terrane. During pre-accretion, however, the radiolarite basin (Qulqula Radiolarite, 221 Ma) located along Arabian passive margin likely acted as an intermediate sediment repository for most or all of the DZ. Representative DZ U-Pb measurements revealed that the Gercus clastic rocks fall into several separable age population ranges of 92-102 (Albian-Cenomanian), 221 (Upper Triassic), 395-511 (Cambrian), 570- 645 (Neoproterozoic), 1111 (Mesoproterozoic), and lesser numbers of Paleoproterozoic (1622-1991 Ma) ages. The source of Proterozoic detrital Zircons is enigmatic; the age peaks at 1.1, 1.5, 1.6, and 1.9 Ga (Proterozoic) does not correspond to any known outcrops of Precambrian rocks in Iraq, and it may be useful to continue to search for such basement. The detrital zircons with age populations at 0.63–0.86 Ga probably originated from the Arabian-Nubian Shield. The age peak at 0.55 Ga correlates with Cadomian Magmatism reported from north Gondwana. The age peaks at ~0.4 Ga is interpreted to represent Gondwana rifting and the opening of Paleotethys. The youngest ages populations at 93 Ma indicate that fraction of DZ were transported directly from the contemporaneously active magmatic arc (Zagros Ophiolite segments). The paleogeography and tectonic evolution of the Neogene Zagros foreland basin were reconstructed and divided into two tectonic stages. The early stage is defined by the Campanian accreted terranes (i.e. orogenic wedge) form loads sufficient to produce flexural basin with a deepest part is situated next to the tip of the loads. This flexural basin is filled by the flysch clastics of the Maastrichtian– Early Eocene (i.e. referred to by the Tanjero-Kolosh flysch sequence). The late stage is marked by a synchronized modification of the clastics fill of the basin and changes in dip directions to compensate for the reduction of the load by both erosion and extension and the basin, therefore, was sealed by a shallowing upwards depositional sequence ending with the terrestrial Gercus Formation.

Burial Diagenesis of the Eocene Sobrarbe Delta (Ainsa Basin, Spain) Inferred From Dolomitic Concretions

2015 ◽  
Vol 85 (9) ◽  
pp. 1037-1057 ◽  
Author(s):  
Guilhem Hoareau ◽  
Francis Odonne ◽  
Daniel Garcia ◽  
Elie-Jean Debroas ◽  
Christophe Monnin ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Isotope Composition ◽  
Active Tectonics ◽  
Foreland Basin ◽  
Late Eocene ◽  
Passive Margin ◽  
Burial Diagenesis ◽  
The South ◽  
Rock Interaction ◽  
Fracture Development

Abstract:  Little attention has been focused on the burial diagenesis of deltas deposited on active foreland-basin margins, where tectonics is likely to strongly impact fluid–rock interactions. A petrographic, geochemical, and microthermometric study of several fractured dolomite concretions and enclosing prodelta marls provides insights into the evolution of burial diagenesis in the Eocene Sobrarbe deltaic complex (Ainsa Basin, Spain), and more generally, on the paleohydrology of the South Pyrenean foreland basin. Shallow burial diagenesis was controlled by microbial activity in marine-derived porewaters. Microbial sulfate reduction was first responsible for the formation of pyrite and early calcite, followed by the growth of dolomite concretions during methanogenesis. Subsequent diagenesis was limited to temperatures and depth of less than approximately 75°C and 2 km, respectively. Diagenesis was recorded in porous bioturbation traces and septarian fractures found inside dolomite concretions, as well as in tectonic shear fractures. Neomorphic tabular barite, found only in the bioturbation traces, is interpreted to have formed early in marine-derived porewaters. Septarian fractures were then filled by Fe-rich calcite and centimeter-size celestine. Stable isotopes indicate that calcite probably formed in meteoric-derived waters coming from the overlying fluvial delta plain. The sulfur isotope composition of celestine is compatible with precipitation in waters of mixed parentage, but the exact origin of dissolved sulfate remains poorly constrained. In tectonic fractures, celestine precipitated coevally with calcite displaying evidence of strong fluid–rock interaction. Dissolved sulfate may have migrated to the fractures during active tectonics from the late Eocene to the Oligocene. The paragenesis and the proposed paleohydrologic model are similar to those previously described for other deltaic systems deposited in active foreland basins, including the South Pyrenean foreland basin. These features point to common diagenetic processes in syntectonic foreland-basin deltas, involving both meteoric and marine fluid sources. Similar to passive margin settings, early diagenesis appears to be controlled mainly by relative variations of sea level, whereas during further burial, the development of permeable tectonic fractures is likely to facilitate the influx of basinal or continental waters into fine slope deposits, impacting the diagenetic record. These results emphasize the importance of fracture development in the fluid-flow regime of syntectonic foreland-basin deltas. They demonstrate the necessity to take this parameter into account in fluid-flow modeling of foreland-basin margins.

scholarly journals Integration of bedrock, seismic tomographic and plate kinematic constraints to test models of the India-Asia collision

2020 ◽  
Author(s):  
Andrew Parsons ◽  
Kasra Hosseini ◽  
Richard Palin ◽  
Karin Sigloch
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Passive Margin ◽  
Kinematic Constraints ◽  
Neotethys Ocean ◽  
Erosion Processes ◽  
Geological Processes ◽  
Test Models ◽  
Tethys Ocean ◽  
And Migration

<p>The India-Asia collision is one of the most well-studied orogenic events on Earth; it recorded the terminal stages of the central Tethys ocean basins and offers invaluable insight into the geological processes associated with continental collision. In this study, we integrate bedrock datasets, observations of subducted slabs in the mantle, and plate kinematic constraints, to constrain models for the India-Asia collision and the central Tethys oceans.</p><p>Previously proposed models for the India-Asia collision differ in terms of subduction zone configurations and paleogeographic reconstructions of Greater India, which represents to northern passive margin of India prior to collision. Five distinct subduction zone configurations have been proposed previously, which differ in the number of active trenches (one or two trenches) in the central Neotethys Ocean and differ in the respective timing, duration, location and migration of those trenches. Three distinct paleogeographic reconstructions of Greater India have been proposed previously, which differ in size and structure. Here, we consider the validity of these subduction zone configurations and Greater India reconstructions with respect to the bedrock record, plate kinematics and the deep mantle structure of subducted slabs beneath the Indian hemisphere.</p><p>Following the assumption that slabs sink vertically through the mantle, the positions and geometries of subducted slabs determined from seismic tomography constrain the locations and kinematics of paleo-subduction zones. Integrating this with bedrock constraints allows us to constrain post-Triassic subduction zone configurations for the central Tethys oceans. Our analysis demonstrates that the Neotethys Ocean was consumed by at least two subduction zones since the Jurassic. At the onset of the India-Asia collision at 59±1 Ma, one subduction zone was active along the southern Asian continental margin at ~20°N. At that time, a second may have been active at subequatorial latitudes, but support for this from a bedrock perspective is lacking. This subduction zone configuration allows for three reconstructions for Greater India: The (1) minimum-area; (2) enlarged-area; and (3) Greater India Basin reconstructions. We integrate these reconstructions and subduction zone configurations in a plate kinematic framework to test their validity for the India-Asia collision.</p><p>Our findings show that no single model is entirely satisfactory and each invokes assumptions that challenge accepted concepts. These include our understanding of suture zones, subduction-erosion processes, and the limits of continental subduction. We explore these challenges and their implications for our understanding of the India-Asia collision and continental collisions in general.</p>

The Heterogeneous Tethyan Oceanic Lithosphere of the Alpine Ophiolites

Elements ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 23-28 ◽  
Author(s):  
Elisabetta Rampone ◽  
Alessio Sanfilippo
Keyword(s):  
Oceanic Lithosphere ◽  
Passive Margin ◽  
Crustal Material ◽  
Crustal Accretion ◽  
Mantle Dynamics ◽  
Western Tethys ◽  
Mantle Peridotites ◽  
Slow Spreading ◽  
Tethys Ocean ◽  
Basaltic Crust

The Alpine–Apennine ophiolites are lithospheric remnants of the Jurassic Alpine Tethys Ocean. They predominantly consist of exhumed mantle peridotites with lesser gabbroic and basaltic crust and are locally associated with continental crustal material, indicating formation in an environment transitional from an ultra-slow-spreading seafloor to a hyperextended passive margin. These ophiolites represent a unique window into mantle dynamics and crustal accretion in an ultra-slow-spreading extensional environment. Old, pre-Alpine, lithosphere is locally preserved within the mantle sequences: these have been largely modified by reaction with migrating asthenospheric melts. These reactions were active in both the mantle and the crust and have played a key role in creating the heterogeneous oceanic lithosphere in this branch of the Mesozoic Western Tethys.

Sign in / Sign up

Export Citation Format

Share Document