Gabbro and related rock emplacement beneath rifting continental crust: UPb geochronological and geochemical constraints for the Galicia passive margin (Spain)

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.

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Late Neoproterozoic passive margin of East Gondwana: Geochemical constraints from the Anakie Inlier, central Queensland, Australia

Precambrian Research ◽

10.1016/j.precamres.2008.10.007 ◽

2009 ◽

Vol 168 (3-4) ◽

pp. 301-312 ◽

Cited By ~ 25

Author(s):

C FERGUSSON ◽

R OFFLER ◽

T GREEN

Keyword(s):

Passive Margin ◽

Late Neoproterozoic ◽

Geochemical Constraints

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Deep crustal structure across a young passive margin from wide-angle and reflection seismic data (The SARDINIA Experiment) – I. Gulf of Lion’s margin

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.186.4-5.309 ◽

2015 ◽

Vol 186 (4-5) ◽

pp. 309-330 ◽

Cited By ~ 20

Author(s):

Maryline Moulin ◽

Frauke Klingelhoefer ◽

Alexandra Afilhado ◽

Daniel Aslanian ◽

Philippe Schnurle ◽

...

Keyword(s):

Continental Crust ◽

Deep Structure ◽

Lower Layer ◽

Passive Margin ◽

P Wave ◽

Wide Angle ◽

Seismic Velocities ◽

Gulf Of Lion ◽

Conjugate Margins ◽

Domain I

Abstract The conjugate margins system of the Gulf of Lion and West Sardinia (GLWS) represents a unique natural laboratory for addressing fundamental questions about rifting due to its landlocked situation, its youth, its thick sedimentary layers, including prominent palaeo-marker such as the MSC event, and the amount of available data and multidisciplinary studies. The main goals of the SARDINIA experiment, were to (i) investigate the deep structure of the entire system within the two conjugate margins: the Gulf of Lion and West Sardinia, (ii) characterize the nature of the crust, and (iii) define the geometry of the basin and provide important constrains on its genesis. This paper presents the results of P-wave velocity modelling on three coincident near-vertical reflection multi-channel seismic (MCS) and wide-angle seismic profiles acquired in the Gulf of Lion, to a depth of 35 km. A companion paper [part II – Afilhado et al., 2015] addresses the results of two other SARDINIA profiles located on the oriental conjugate West Sardinian margin. Forward wide-angle modelling of both data sets confirms that the margin is characterised by three distinct domains following the onshore unthinned, 33 km-thick continental crust domain: Domain I is bounded by two necking zones, where the crust thins respectively from ~30 to 20 and from 20 to 7 km over a width of about 170 km; the outermost necking is imprinted by the well-known T-reflector at its crustal base; Domain II is characterised by a 7 km-thick crust with « anomalous » velocities ranging from 6 to 7.5 km/s; it represents the transition between the thinned continental crust (Domain I) and a very thin (only 4–5 km) “atypical” oceanic crust (Domain III). In Domain II, the hypothesis of the presence of exhumed mantle is falsified by our results: this domain may likely consist of a thin exhumed lower continental crust overlying a heterogeneous, intruded lower layer. Moreover, despite the difference in their magnetic signatures, Domains II and III present the very similar seismic velocities profiles, and we discuss the possibility of a connection between these two different domains.

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High-temperature metamorphism during extreme thinning of the continental crust: a reappraisal of the north Pyrenean paleo-passive margin

Solid Earth Discussions ◽

10.5194/sed-7-797-2015 ◽

2015 ◽

Vol 7 (1) ◽

pp. 797-857 ◽

Cited By ~ 9

Author(s):

C. Clerc ◽

A. Lahfid ◽

P. Monié ◽

Y. Lagabrielle ◽

C. Chopin ◽

...

Keyword(s):

High Temperature ◽

Continental Crust ◽

Thermal Gradient ◽

Carbonaceous Material ◽

Thermal Anomaly ◽

Passive Margin ◽

Ductile Deformation ◽

The North ◽

Crustal Thinning ◽

Mountain Belts

Abstract. An increasing number of field examples in mountain belts show that the formation of passive margins during extreme continent thinning may occur under conditions of high to very high thermal gradient beneath a thin cover of syn-rift sediments. Orogenic belts resulting from the tectonic inversion of distal margins and regions of exhumed continental mantle may exhibit high-temperature, low-pressure (HT-LP) metamorphism and coeval syn-extensional, ductile deformation. Recent studies have shown that the northern flank of the Pyrenean belt, especially the North Pyrenean Zone, is one of the best examples of such inverted hot, passive margin. In this study, we provide a map of HT-LP metamorphism based on a dataset of more than one hundred peak-temperature estimates obtained using Raman spectroscopy of the carbonaceous material (RSCM). This dataset is completed by previous PT estimates based on mineral assemblages, and new Ar–Ar (amphibole, micas) and U–Pb (titanite) ages from metamorphic and magmatic rocks of the North Pyrenean Zone. The implications on the geological evolution of the Cretaceous Pyrenean paleomargins are discussed. Ages range mainly from 110 to 90 Ma and no westward or eastward propagation of the metamorphism and magmatism can be clearly identified. In contrast, the new data reveal a progressive propagation of the thermal anomaly from the base to the surface of the continental crust. Focusing on the key-localities of the Mauléon Basin, Arguenos-Moncaup, Lherz, Boucheville and the Bas-Agly, we analyse the thermal conditions prevailing during the Cretaceous crustal thinning. The results are synthetized into a series of three regional thematic maps, and into two detailed maps of the Arguenos-Moncaup and Lherz areas. The results indicate a first-order control of the thermal gradient by the intensity of crustal thinning. The highest grades of metamorphism are intimately associated with the areas where subcontinental mantle rocks have been unroofed or exhumed.

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http://www.kscnet.ru/journal/kraesc/article/view/639

Bulletin of Kamchatka Regional Association «Educational-Scientific Center» Earth Sciences ◽

10.31431/1816-5524-2020-4-48-36-48 ◽

2020 ◽

Vol 4(48) ◽

pp. 36-48

Author(s):

A.A. Shaikhullina ◽

◽

E.P. Dubinin ◽

A.A. Bulychev ◽

M.S. Baranovsky ◽

...

Keyword(s):

Continental Crust ◽

Continental Margin ◽

Hot Spot ◽

Linear Structure ◽

Passive Margin ◽

Western India ◽

Continental Lithosphere ◽

Field Modeling ◽

Thinned Continental Crust ◽

Main Factor

The Chagos-Laccadiv Range is a linear-elongated structure adjacent to the passive margin of western India. The ridge consists of three segments: northern — Lakkadiv ridge, central — Maldives ridge and southern — bank (archipelago) Chagos. The ridges are separated by depressions and have different manifestations in morphology and anomalous gravitational field. Modeling of the density structure of the Chagos-Lakkadive Ridge tectonosphere showed that the Lakkadive and Maldive segments, most likely, represent submerged blocks of thinned continental crust, partially separated from the continental margin of India by a riftogenic basin. Along with the assumption that the Chagos Bank may contain fragments of the continental crust, the main factor in its formation is apparently the active magmatic activity of the Reunion hot spot, leading to an increase in the thickness of the crust due to underplating. Physical modeling showed that the formation of such a linear structure is possible in the presence of thermal (hot spot) and structural (faults and cracks) inhomogeneities in the model continental lithosphere, which within the continental margin led to a jump (jumping) of the spreading axis towards the young margin and partial separation from it narrow linearly elongated microblocks (ridges).

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