scholarly journals Moho carbonation at an ocean-continent transition

Geology ◽  
2021 ◽  
Author(s):  
Rémi Coltat ◽  
Philippe Boulvais ◽  
Yannick Branquet ◽  
Antonin Richard ◽  
Alexandre Tarantola ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Continental Crust ◽  
Detachment Fault ◽  
Strontium Isotope ◽  
Hydrothermal Conditions ◽  
Continental Breakup ◽  
Ocean Ridges ◽  
Thermal Regimes ◽  
Mantle Exhumation ◽  
Fluid Sources

Carbonation of mantle rocks during mantle exhumation is reported in present-day oceanic settings, both at mid-ocean ridges and ocean-continent transitions (OCTs). However, the hydrothermal conditions of carbonation (i.e., fluid sources, thermal regimes) during mantle exhumation remain poorly constrained. We focus on an exceptionally well-preserved fossil OCT where mantle rocks have been exhumed and carbonated along a detachment fault from underneath the continent to the seafloor along a tectonic Moho. Stable isotope (oxygen and carbon) analyses on calcite indicate that carbonation resulted from the mixing between serpentinization-derived fluids at ~175 °C and seawater. Strontium isotope compositions suggest interactions between seawater and the continental crust prior to carbonation. This shows that carbonation along the tectonic Moho occurs below the continental crust and prior to mantle exhumation at the seafloor during continental breakup.

scholarly journals Fluid–rock interactions along detachment faults during continental rifting and mantle exhumation: the case of the Urdach lherzolite body (North Pyrenees)

2020 ◽  
pp. jgs2020-116
Author(s):  
Jehiel Nteme Mukonzo ◽  
Marie-Christine Boiron ◽  
Yves Lagabrielle ◽  
Michel Cathelineau ◽  
Benoit Quesnel
Keyword(s):  
Fluid Flow ◽  
Continental Crust ◽  
Continental Rifting ◽  
Detachment Faults ◽  
The North ◽  
And Migration ◽  
Mantle Exhumation ◽  
Crucial Part

The North Pyrenean Zone corresponds to the palaeopassive margin of the North Iberia plate, at the foot of which subcontinental mantle was exhumed during Albian times. Rare bodies of exhumed mantle rocks associated with strongly sheared lenses of continental crust are scattered among the North Pyrenean Zone metasediments. Significant fluid flow occurred along a major décollement at the basement–Trias interface in the Urdach massif (Chaînons Béarnais). Fluids with a broad range of salinity (10–38 wt.% NaCl equiv.), indicative of mixing between brines and more dilute waters, produced strong silicification of breccias. The brines circulated at c. 240–280°C under lithostatic pressures at c. 6 ± 1 km depth. The fluids became increasingly saline towards the final stages. The syndeposition of Cenomano-Turonian flysch layers then progressively isolated the lower aquifers close to the décollement where Triassic brines were predominant. The release and migration of significant volumes of brines during stretching and squeezing of the Triassic evaporites played a crucial part in the mineralogical and rheological transformations that occurred during the Pyrenean Cretaceous rifting event.

3D structures and sedimentary infill across the continent-ocean transition of the northern South China Sea: constraint by the drilling results from IODP Expeditions 367, 368 and 368X

2020 ◽  
Author(s):  
Chao Lei ◽  
Jianye Ren ◽  
Geoffroy Mohn ◽  
Michael Nirrengarten ◽  
Xiong Pang ◽  
...  
Keyword(s):  
South China Sea ◽  
Continental Crust ◽  
Oceanic Crust ◽  
South China ◽  
Lower Boundary ◽  
Seismic Survey ◽  
High Angle ◽  
Seismic Profiles ◽  
Continental Breakup ◽  
China Sea

<p>Apart from the Iberia-Newfoundland margins, the South China Sea (SCS) represents  another passive margin where continent-ocean transition basement was sampled by deep drilling. Drilling data from IODP Expedition 367-368 and 368X combined with seismic profiles revealed a narrow continent-ocean transition (COT) between the Distal High sampled at Site U1501 and the Ridge B sampled at Site U1500. Results suggested that major Eocene lithospheric thinning triggered Mid-Ocean Ridge type melt production which emplaced within hyperextended continental crust leading eventually to continental breakup.  </p><p>Because of available dense seismic survey consisting of deep-penetrated seismic data imaging as deep as 12 s TWT, as well as drilling results from IODP Expeditions 367-368 and 368X, the COT in the northern SCS enables us to investigate the 3D propagation of continental breakup and the interactions between tectonic extension and magmatism. The top of acoustic basement can be consistently interpreted through all of our seismic survey and reveal various types of reliefs and nature from hyperextended continental crust to oceanic crust. In the basement, deep-penetrated seismic profiles present series of densely sub-parallel high-amplitude reflections that occurred within the lower crust. The lower boundary of these reflections is often characterized by double continual and high reflections interpreted as the Moho. Across the COT, the basement structure is characterized by: 1) Series of tilted blocks bounded by high angle faults on the Distal High and filled by syn-tectonic sedimentary wedges, 2) Rounded mounds of the basement with chaotic seismic reflection and sedimentary onlaps on these structures, 3) Series of ridges delimited by high-angle normal faults with no sedimentary wedge on the first oceanic crust.</p><p>Based on the detail stratigraphic framework constraint by drilling results from IODP Expeditions, the nature and timing of formation of these basement highs can be investigated. Some of these highs are limited by extensional faults while the nature of mounded structures located on the thinnest continental crust remain mysterious.  Our detailed analyses emphasize the occurrence and local control of syn-rift magmatism in order to build such structures. At larger scale, the hyperextended continental crust is characterized by significant 3D morphological variations both observed on dip and strike profiles. In contrast, the initial oceanic crust is characterized by a more homogenous structure and consistently juxtaposed to continental crust over a sharp and narrow zone.</p><p> </p>

Partitioning between strike-slip and orthogonal extension in the western South China Sea

2020 ◽  
Author(s):  
Pan Luo ◽  
Jianye Ren ◽  
Xi He ◽  
Chao Lei ◽  
Junjie Xu ◽  
...  
Keyword(s):  
South China Sea ◽  
Continental Crust ◽  
South China ◽  
Large Scale ◽  
Strike Slip ◽  
Fault System ◽  
Relative Role ◽  
China Sea ◽  
Kinematic Evolution ◽  
Mantle Exhumation

<p>Our study focuses on the Zhongjianna (ZJN) (Phu Kham) Basin, located at the western termination of the South China Sea (SCS) and separated from the Indochina continent by the N-S striking East Vietnam Boundary Fault Zone, which is a large scale strike-slip fault system. The sedimentary infill history of the ZJN basin records the complete evolution and interaction of the Indochina-SCS system and allows the tectonic and kinematic evolution of the basin to be understood.. The discovery of hyper-extended continental crust and mantle exhumation in this basin leads to the question of what is the relative role of large-scale strike-slip and orthogonal faulting in controlling crustal thinning in the ZJN basin.  </p><p>  Our preliminary results confirm the existence of hyperextended continental crust flooring the ZJN basin. Two different types of structures can be identified in this area: extension related deformation in the eastern part and strike-slip related deformation in the western part. The analysis of fault geometries and kinematics linked to timing and subsidence rates suggest that the N-S-orientated strike-slip structures dominated the continental shelf and slope area on the west side of the basin. In the basin, however, most faults strike NE-SW and are parallel to the mid-ocean ridge. Thus, it appears that the ZJN basin resulted from the partitioning between strike-slip and orthogonal extension.</p><p>In our presentation we show the results of our seismic interpretation, strain and subsidence analysis and discuss the interaction between strike-slip and orthogonal extension in setting up the hyper-extended ZJN basin and its implications for the large scale tectonic and geodynamic framework.</p>

scholarly journals Mantle exhumation at magma-poor passive continental margins. Part I. 3D architecture and metasomatic evolution of a fossil exhumed mantle domain (Urdach lherzolite, north-western Pyrenees, France)

2019 ◽  
Vol 190 ◽  
pp. 8 ◽  
Author(s):  
Yves Lagabrielle ◽  
Riccardo Asti ◽  
Serge Fourcade ◽  
Benjamin Corre ◽  
Marc Poujol ◽  
...  
Keyword(s):  
Continental Crust ◽  
Cross Sections ◽  
Large Scale ◽  
Fault Zones ◽  
Rock Interaction ◽  
Crustal Rocks ◽  
Alkaline Lava ◽  
Two Samples ◽  
Mineralogical Study ◽  
Mantle Exhumation

In two companion papers, we report the detailed geological and mineralogical study of two emblematic serpentinized ultramafic bodies of the western North Pyrenean Zone (NPZ), the Urdach massif (this paper) and the Saraillé massif (paper 2). The peridotites have been exhumed to lower crustal levels during the Cretaceous rifting period in the future NPZ. They are associated with Mesozoic pre-rift metamorphic sediments and small units of thinned Paleozoic basement that were deformed during the mantle exhumation event. Based on detailed geological cross-sections and microprobe mineralogical analyses, we describe the lithology of the two major extensional fault zones that accommodated: (i) the progressive exhumation of the lherzolites along the Cretaceous basin axis; (ii) the lateral extraction of the continental crust beneath the rift shoulders and; (iii) the decoupling of the pre-rift cover along the Upper Triassic (Keuper) evaporites and clays, allowing its gliding and conservation in the basin center. These two fault zones are the (lower) crust-mantle detachment and the (upper) cover décollement located respectively at the crust-mantle boundary and at the base of the detached pre-rift cover. The Urdach peridotites were exposed to the seafloor during the Late Albian and underwent local pervasive carbonation and crystallization of calcite in a network of orthogonal veins (ophicalcites). The carbonated serpentinized peridotites were partly covered by debris-flows carrying fragments of both the ultramafics and Paleozoic crustal rocks now forming the polymictic Urdach breccia. The mantle rocks are involved in a Pyrenean overturned fold together with thin units of crustal mylonites. Continent-derived and mantle-derived fluids that circulated along the Urdach crust-mantle detachment led to the crystallization of abundant metasomatic rocks containing quartz, calcite, Cr-rich chlorites, Cr-rich white micas and pyrite. Two samples of metasomatized material from the crust-mantle detachment yielded in situ zircon U/Pb ages of 112.9 ± 1.6 Ma and 109.4 ± 1.2 Ma, thus confirming the Late Albian age of the metasomatic event. The cover décollement is a 30-m thick fault zone which also includes metasomatic rocks of greenschist facies, such as serpentine-calcite association and listvenites, indicating large-scale fluid-rock interactions implying both ultramafic and continental material. The lowermost pre-rift cover is generally missing along the cover décollement due to tectonic disruption during mantle exhumation and continental crust elision. Locally, metasomatized and strongly tectonized Triassic remnants are found as witnesses of the sole at the base of the detached pre-rift cover. We also report the discovery of a spherulitic alkaline lava flow emplaced over the exhumed mantle. These data collectively allow to propose a reconstruction of the architecture and fluid-rock interaction history of the distal domain of the upper Cretaceous northern Iberia margin now inverted in the NPZ.

scholarly journals Nature and Origin of Mineralizing Fluids in Hyperextensional Systems: The Case of Cretaceous Mg Metasomatism in the Pyrenees

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-18 ◽  
Author(s):  
Benoît Quesnel ◽  
Marie-Christine Boiron ◽  
Michel Cathelineau ◽  
Laurent Truche ◽  
Thomas Rigaudier ◽  
...  
Keyword(s):  
Continental Crust ◽  
Fluid Inclusions ◽  
High Salinity ◽  
Shear Zones ◽  
Passive Margin ◽  
Ore Deposit ◽  
Brine Migration ◽  
Mantle Exhumation ◽  
Seawater Concentration ◽  
Isotope Analyses

During the Albian, the hyperextension of the Pyrenean passive margin led to a hyperthinning of the continental crust and the subsequent subcontinental mantle exhumation. The giant Trimouns talc-chlorite deposit represents the most prominent occurrence of Albian metasomatism in the Pyrenees, with the occurrence of the largest talc deposit worldwide. Consequently, this deposit, which is located on a fault zone and a lithological contact, represents one of the major drains at the scale of the Pyrenees and one of the best geological targets in order to determine the origin(s) of the fluid(s) that circulated during this period. Talc-chlorite ore is characterized by the presence of brines trapped in dolomite, quartz, and calcite fluid inclusions in the vicinity of the talc-rich zone. Considered as being responsible for the formation of talc, these fluids may be interpreted in several ways: (i) primary brines expelled from Triassic evaporites, (ii) secondary brines produced through halite leaching by diagenetic/metamorphic fluids, and (iii) brines derived from seawater serpentinization of mantle rocks. Stable isotope analyses (δ13C, δ18O, δD, and δ37Cl) and Cl/Br ratio measurements in fluid inclusions and their host minerals were carried out in order to determine the origin of the fluid(s) involved in the formation of the ore deposit. The data are consistent with a primary brine origin for the mineralizing fluid, which could have been expelled from the Triassic levels. Other hypotheses have been tested, for example, the production of brines via the seawater concentration during serpentinization. The geochemical proxies used in this study provide equivocal results. The first hypothesis is by far the most realistic one considering the numerous occurrences of Trias formations nearby, their deformation during the extension, and the drainage of the expulsed brines as evidenced by the high-salinity fluid inclusions found all around the deposit. Alternatively, the exhumation of the mantle is considered as a major source of heat and stress that favored brine migration along the major shear zones. Our results fit well with brine circulation in a hyperextensional geodynamic context, which is related to the formation of the talc-chlorite ore, the thinning of the continental crust, and the exhumation of the subcontinental mantle, in accordance with recent works.

Mobilization of lithospheric mantle carbon during the Palaeocene-Eocene thermal maximum

2021 ◽  
Author(s):  
Thomas Gernon ◽  
Ryan Barr ◽  
John Fitton ◽  
Thea Hincks ◽  
Jack Longman ◽  
...  
Keyword(s):  
North Atlantic ◽  
Lithospheric Mantle ◽  
North Atlantic Ocean ◽  
Continental Breakup ◽  
Ocean Ridges ◽  
The North ◽  
Igneous Provinces ◽  
Thermal Maximum ◽  
Carbon Reservoir ◽  
Iceland Plume

Abstract The early Cenozoic exhibited profound environmental change influenced by plume magmatism, continental breakup, and opening of the North Atlantic Ocean. Global warming culminated in the transient (170 thousand year, kyr) hyperthermal event, the Palaeocene-Eocene thermal maximum (PETM) 56 million years ago (Ma). Although sedimentary methane release has been proposed as a trigger, recent studies have implicated carbon dioxide (CO2) emissions from the coeval North Atlantic igneous province (NAIP). However, we calculate that volcanic outgassing from mid-ocean ridges and large igneous provinces associated with the NAIP yields only one-fifth of the carbon required to trigger the PETM. Rather, we show that volcanic sequences spanning the rift-to-drift phase of the NAIP exhibit a sudden and ∼220-kyr-long intensification of volcanism coincident with the PETM, and driven by substantial melting of the sub-continental lithospheric mantle (SCLM). Critically, the SCLM is enriched in metasomatic carbonates and is a major carbon reservoir. We propose that the coincidence of the Iceland plume and emerging asthenospheric upwelling disrupted the SCLM and caused massive mobilization of this deep carbon. Our melting models and coupled tectonic–geochemical simulations indicate the release of >104 gigatons of carbon, which is sufficient to drive PETM warming. Our model is consistent with anomalous CO2 fluxes during continental breakup, while also reconciling the deficit of deep carbon required to explain the PETM.

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