A Cretaceous paleo-accretionary wedge, the Ashin Complex, now exposed along the Zagros suture zone in southern Iran, exhibits mafic, metasedimentary and ultramafic lithologies. Field, geochemical and petrological observations point to an anomalous high-temperature event that gave rise to the formation of peritectic (trondhjemitic) melts associated with restitic garnet-bearing amphibolites. Lu-Hf isotopic dating of centimetre-sized garnet in amphibolite-facies metasediments yielded a crystallization age of 113.10 ± 0.36 Ma, possibly representing the age of prograde to near-peak metamorphic conditions. SHRIMP U-Th-Pb zircon dating from trondhjemitic leucosomes yields crystallization ages of 104 ± 1 Ma, interpreted as the age of the temperature peak, which occurred in the upper amphibolite-facies (c. 650-680 °C at 1.1-1.3 GPa), according to thermodynamic modelling and Ti-in-zircon thermometry. Rutile crystals from two leucosomes yield Zr-in-rutile temperatures in the range of 580-640 °C and a LA-ICP-MS U-Pb age range from 85 to 112 Ma, interpreted as a consequence of partial re-equilibration during incipient cooling. A late static recrystallization event is indicated by the presence of sodic-calcic clinopyroxene, sodic amphibole, Si-rich phengite, titanite overgrowths after rutile and lawsonite within former leucosomes and late fractures. This mineral assemblage is a typical blueschist-facies (high pressure-low temperature) paragenesis and is interpreted as reflecting long-term isobaric cooling that occurred until the end of the Cretaceous as a consequence of increasing slab thermal age. This first report of a melting event in the Zagros paleo-accretionary wedge reveals the presence of a transient, abnormally high thermal gradient of c. 18 °C/km that occurred at c. 105-113 Ma. We speculate that this could be explained by the subduction of a thermal anomaly such as a seamount chain, a transform fault system or, more likely, a spreading ridge under the southern Iranian margin. Indeed, paleogeographic reconstructions of the Tethyan realm suggest the entrance of the Northern Tethyan basin ridge into the subduction zone shortly after 120 Ma.
Cretaceous thermal evolution of the closing Neo-Tethyan realm revealed by multi-method petrochronology
Résumé
en
A Cretaceous paleo-accretionary wedge, the Ashin Complex, now exposed along the Zagros suture zone in southern Iran, exhibits mafic, metasedimentary and ultramafic lithologies. Field, geochemical and petrological observations point to an anomalous high-temperature event that gave rise to the formation of peritectic (trondhjemitic) melts associated with restitic garnet-bearing amphibolites. Lu-Hf isotopic dating of centimetre-sized garnet in amphibolite-facies metasediments yielded a crystallization age of 113.10 ± 0.36 Ma, possibly representing the age of prograde to near-peak metamorphic conditions. SHRIMP U-Th-Pb zircon dating from trondhjemitic leucosomes yields crystallization ages of 104 ± 1 Ma, interpreted as the age of the temperature peak, which occurred in the upper amphibolite-facies (c. 650-680 °C at 1.1-1.3 GPa), according to thermodynamic modelling and Ti-in-zircon thermometry. Rutile crystals from two leucosomes yield Zr-in-rutile temperatures in the range of 580-640 °C and a LA-ICP-MS U-Pb age range from 85 to 112 Ma, interpreted as a consequence of partial re-equilibration during incipient cooling. A late static recrystallization event is indicated by the presence of sodic-calcic clinopyroxene, sodic amphibole, Si-rich phengite, titanite overgrowths after rutile and lawsonite within former leucosomes and late fractures. This mineral assemblage is a typical blueschist-facies (high pressure-low temperature) paragenesis and is interpreted as reflecting long-term isobaric cooling that occurred until the end of the Cretaceous as a consequence of increasing slab thermal age. This first report of a melting event in the Zagros paleo-accretionary wedge reveals the presence of a transient, abnormally high thermal gradient of c. 18 °C/km that occurred at c. 105-113 Ma. We speculate that this could be explained by the subduction of a thermal anomaly such as a seamount chain, a transform fault system or, more likely, a spreading ridge under the southern Iranian margin. Indeed, paleogeographic reconstructions of the Tethyan realm suggest the entrance of the Northern Tethyan basin ridge into the subduction zone shortly after 120 Ma.
Auteur(s)
Regina Holtmann1
, Jesús Muñoz-Montecinos1, 2
, Samuel Angiboust1, 3
, Aitor Cambeses2
, Guillaume Bonnet4, 5
, Allison Brown6
, Besim Dragovic6
, Zeynab Gharamohammadi7, 8
, Mathieu Rodriguez9
, Johannes Glodny10
, Ali Kananian7, 8
, Philippe Agard4
1
IPGP (UMR_7154) -
Institut de Physique du Globe de Paris
( 1005035 )
- 1 rue Jussieu, 75238 Paris cedex 05 et Bât. Lamarck A case postale 7011, 75205 Paris CEDEX 13
- France
Institut national des sciences de l'Univers UMR_7154 ( 300045 )
;
Université de La Réunion UMR_7154 ( 300316 )
;
Institut de Physique du Globe de Paris UMR_7154 ( 300354 )
;
Centre National de la Recherche Scientifique UMR_7154 ( 441569 )
;
Université Paris Cité UMR_7154 ( 557826 )
2
Department of Mineralogy and Petrology
( 243323 )
- Espagne
Universidad de Granada = University of Granada ( 302726 )
3
LGL-TPE -
Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement
( 153787 )
- Université Claude Bernard, Lyon1 - Campus de la Doua, bâtiment Géode - 2, rue Raphaël Dubois - 69622 Villeurbanne Cedex
École Normale Supérieure de Lyon - 46, Allée d'Italie - 69364 Lyon cedex 07
Université Jean Monnet - Faculté des Sciences et Techniques - 23 rue du Dr Paul Michalon - 42023 Saint Étienne Cedex 02
UMR CNRS 5276
- France
École normale supérieure de Lyon ( 6818 )
;
Université Claude Bernard Lyon 1 ( 194495 )
;
Université de Lyon ( 301088 )
;
Institut national des sciences de l'Univers UMR5276 ( 300045 )
;
Université Jean Monnet - Saint-Étienne ( 300284 )
;
Centre National de la Recherche Scientifique UMR5276 ( 441569 )
4
iSTeP -
Institut des Sciences de la Terre de Paris
( 541927 )
- 4, place Jussieu BP CC129 75252 PARIS CEDEX 05
- France
Institut national des sciences de l'Univers UMR7193 ( 300045 )
;
Sorbonne Université ( 413221 )
;
Centre National de la Recherche Scientifique UMR7193 ( 441569 )
5
GEOL-UCSB -
Department of Earth Science [Santa Barbara]
( 179454 )
- College of Letters and Science, Santa Barbara, CA 93106-9630
- États-Unis
University of California [Santa Barbara] ( 300693 )
;
University of California ( 471291 )
6
SEOE -
School of the Earth, Ocean and Environment [Columbia]
( 1054243 )
- University of South Carolina, 701 Sumter Street, EWS 617, Columbia, SC 29208
- États-Unis
University of South Carolina [Columbia] ( 82529 )
7
School of Geology (Iran)
( 1068265 )
- University of Tehran, Enghelab Sq., Tehran, Iran
- Iran
8
University of Tehran
( 301046 )
- 16th Azar St., Enghelab Sq., Tehran
- Iran
9
LGENS -
Laboratoire de géologie de l'ENS
( 1308 )
- 24 Rue Lhomond 75231 PARIS CEDEX 05
- France
Institut national des sciences de l'Univers ( 300045 )
;
Centre National de la Recherche Scientifique UMR8538 ( 441569 )
;
Département des Géosciences - ENS Paris ( 506084 )
;
École normale supérieure - Paris ( 59704 )
;
Université Paris Sciences et Lettres ( 564132 )
10
GFZ -
German Research Centre for Geosciences - Helmholtz-Centre Potsdam
( 239972 )
- Telegrafenberg, 14473 Potsdam
- Allemagne
Nom de la revue
Lithos
(ISSN : 0024-4937)
Publié par Elsevier
Revue non référencée dans Sherpa-Romeo
Regina Holtmann, Jesús Muñoz-Montecinos, Samuel Angiboust, Aitor Cambeses, Guillaume Bonnet, et al.. Cretaceous thermal evolution of the closing Neo-Tethyan realm revealed by multi-method petrochronology. Lithos, 2022, 422, ⟨10.1016/j.lithos.2022.106731⟩. ⟨insu-03747293⟩