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Emplacement of the Jurassic Mirdita ophiolites (southern Albania): evidence from associated clastic and carbonate sediments

Domenii publicaţii > Ştiinţele pământului şi planetare + Tipuri publicaţii > Articol în revistã ştiinţificã

Autori: A.H.F. Robertson, C. Ionescu, V. Hoeck, F. Koller, K. Onuzi, I.I. Bucur, D. Ghega

Editorial: Springer, International Journal of Earth Science (Geol Rundsch), DOI 10.1007/s00531-010-0603-5, 2011.


Sedimentology can shed light on the emplacement
of oceanic lithosphere (i.e. ophiolites) onto continental
crust and post-emplacement settings. An example chosen
here is the well-exposed Jurassic Mirdita ophiolite in
southern Albania. Successions studied in five different
ophiolitic massifs (Voskopoja, Luniku, Shpati, Rehove and
Morava) document variable depositional processes and
palaeoenvironments in the light of evidence from comparable
settings elsewhere (e.g.NAlbania;NGreece). Ophiolitic
extrusive rocks (pillow basalts and lava breccias) locally
retain an intact cover of oceanic radiolarian chert (in the
Shpati massif). Elsewhere, ophiolite-derived clastics typically
overlie basaltic extrusives or ultramafic rocks directly.
The oldest dated sediments are calpionellid- and ammonitebearing
pelagic carbonates of latest (?) Jurassic-Berrasian
age. Similar calpionellid limestones elsewhere (N Albania;
N Greece) post-date the regional ophiolite emplacement. At
one locality in S Albania (Voskopoja), calpionellid limestones
are gradationally underlain by thick ophiolite-derived
breccias (containing both ultramafic and mafic clasts) that
were derived by mass wasting of subaqueous fault scarps
during or soon after the latest stages of ophiolite emplacement.
An intercalation of serpentinite-rich debris flows at
this locality is indicative of mobilisation of hydrated oceanic
ultramafic rocks. Some of the ophiolite-derived conglomerates
(e.g. Shpati massif) include well-rounded serpentinite
and basalt clasts suggestive of a high-energy, shallow-water
origin. The Berriasian pelagic limestones (at Voskopoja)
experienced reworking and slumping probably related
to shallowing and a switch to neritic deposition. Mixed
ophiolite-derived clastic and neritic carbonate sediments
accumulated later, during the Early Cretaceous (mainly
Barremian-Aptian) in variable deltaic, lagoonal and shallowmarine
settings. These sediments were influenced by local
tectonics or eustatic sea-level change. Terrigenous sediment
gradually encroached from neighbouring landmasses as the
ophiolite was faulted or eroded. An Aptian transgression was
followed by regression, creating a local unconformity (e.g. at
Boboshtica). A Turonian marine transgression initiated
widespread Upper Cretaceous shelf carbonate deposition. In
the regional context, the southern Albania ophiolites appear
to have been rapidly emplaced onto a continental margin in a
subaqueous setting during the Late Jurassic (Late Oxfordian-
Late Tithonian). This was followed by gradual emergence,
probably in response to thinning of the ophiolite by erosion
and/or exhumation. The sedimentary cover of the south
Albanian ophiolites is consistent with rapid, relatively shortdistance
emplacement of a regional-scale ophiolite over a
local Pelagonian-Korabi microcontinent.

Cuvinte cheie: Ofiolite, Sedimente, Albania, Paleoenvironment, Tethys // Ophiolite, Sediments, Albania, Paleoenvironment, Tethys