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| Titel |
Rodingitization and carbonization processes in Triassic ultramafic cumulates and lavas, Othris Mt, Central Greece |
| VerfasserIn |
Petros Koutsovitis, Andreas Magganas, Georgios Economou |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250136764
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| Publikation (Nr.) |
 EGU/EGU2016-17874.pdf |
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| Zusammenfassung |
| A Triassic magmatic sequence from the south Othris region is comprised of early stage
basaltic pillow lavas, as well as late stage ultramafic rocks, lava flows, high-Mg doleritic
dykes and pyroclastic tuffs. The ultramafic rocks include slightly serpentinized wehrlites and
lavas consisting of cumulate olivine, variably textured clinopyroxene (cumulate, quench,
hollow, skeletal or blade shaped), magnesiohornblende, tremolite, phlogopite, spinel, chlorite,
garnet, serpentine, calcite and devitrified glass[1]. Part of their secondary mineralogy
developed due to percolation of metasomatic fluids during rodingitization and carbonization
processes.
In ultramafic rocks from Agia Marina and Mili, rodingitization was rather penetratively
and expressed with crystallization of hydrogarnets, accompanied by secondary diopside and
chlorite. Hydrogarnets are characterized by their low Ti-contents (<0.56 wt.%). These
include hydroandradites (Avg. Adr85.0Grs14.5Prp11.9Sps0.5Uv1.0), hydrogrossulars (Avg.
Adr14.4Grs75.7Prp14.3Sps0.9Uv0.6) and mixed series phases between hydroandradite and
hydrogrossular end-members (Avg. Adr46.4Grs47.0Prp9.3Sps0.6Uv0.4). Formation of
hydroandradite probably occurred at the expense of hydrogrossular under lower temperatures.
Small sized calcite amygdales and veinlets were occasionally formed in a subsequent phase.
Ultramafic lavas from the region of Neraida have experienced carbonation. They were
intensely penetrated by secondary calcitic veins forming remarkable infiltrating structures.
Apart from the predominant calcite, the Neraida ultramafics also include small sized
hydroandradites (Avg. Adr93.7Grs1.3Prp4.8Sps0.0Uv2.3).
Whole-rock chemistry data show that rodingitization resulted in restricted enrichment of
Ca, as well as depleting silica and alkalies. The hydrogarnet-bearing ultramafics display
subparallel REE patterns, with slightly enriched LREE (4.1–8.9×CN) and flat HREE patterns
(2.3-5.5×CN) [(La/Yb)CN =1.2–1.8]. Compared to non-garnet bearing ultramafics, they have
experienced a decrease in their ΣREE (∼33%). Calcite-rich lavas from Neraida have
also undergone a ΣREE reduction (∼47%), mostly affecting the HREE, due to
replacement of clinopyroxene. It is worth noting that a serpentinized ultramafic sample
has experienced greater ΣREE losses (∼62%) compared to the metasomatically
affected ultramafics. The PM-normalized patterns show that Sr and U are enriched
in the calcite-rich ultramafics, whereas the hydrogarnet-bearing ultramafics have
been moderately enriched in Pb and Nb and depleted in Ti, K, P, Cs, Rb, Sr, Zr and
Y.
Rodingitization, which is also observed in the associated Jurassic ophiolite of Othris[2],
may have taken place in an infant intraoceanic subduction system followed by carbonization
during continuous temperature decrease. Rodingitization fluids possibly infiltrated from the
subducted slab and/or produced during serpentinization and ocean water interaction.
Carbonization probably occurred when ultramafics reached close to the seafloor by
recycling thermal carbonated seawater, leached from the rifted Triassic platform
carbonates.
References. [1] Koutsovitis, Magganas, Ntaflos 2012: Lithos 144-145, 177-193; [2]
Koutsovitis, Magganas, Pomonis, Ntaflos 2013: Lithos 172–173, 139–157. |
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