Οι οφιτασβεστίτες της ΒΔ Τήνου. Ορυκτολογία, πετρογραφία, συνθήκες γένεσης και περιβαλλοντικές επιπτώσεις από τν εξόρυξη και την χρήση τους.

Postgraduate Thesis uoadl:1319259 444 Read counter

Unit:
ΠΜΣ με ειδίκευση στην Εφαρμοσμένη Περιβαλλοντική Γεωλογία
Library of the School of Science
Deposit date:
2012-12-14
Year:
2012
Author:
Μαυρογόνατος Κωνσταντίνος
Supervisors info:
Μαγκανάς Ανδρέας Καθηγ. (επιβλέπων), Κατή Μαριάννα Επίκ. Καθηγ., Λόζιος Στυλιανός Επικ. Καθηγ.
Original Title:
Οι οφιτασβεστίτες της ΒΔ Τήνου. Ορυκτολογία, πετρογραφία, συνθήκες γένεσης και περιβαλλοντικές επιπτώσεις από τν εξόρυξη και την χρήση τους.
Languages:
Greek
Summary:
The main goal of this work is to study the mineralogy and the petrography of
the ophicalcite which are located in the NW part of Tinos island, Cyclades,
Greece. This very complex lithology, better known as ‘green marble of Tinos’,
has undergone intense exploitation since ancient times. The beautiful contrast
between the green clasts and the numerous white veins is what made the ‘verde
di Tinos’ so famous among the rest of the decorative stones. It has been used
in many cases in sculpturing or in building and as a decorative material,
especially during Byzantine times.
Despite its high commercial value, very little detailed research on the
mineralogy, petrography and genesis of this ophicalcite has been made.
This work intends to focus on all the previous topics, as well as to record any
kind of environmental problems which arise from the use of the stone and the
operation of the quarries which produce it.
The studied ophicalcite is located in the NW part of Tinos island, 4km north of
the Marlas village. The elleipsoidal ophicalcitic bodies are enclosed in the
upper unit greenschists and it is notable that a talc-rich zone is always found
between the two lithologies.
The main methods used during this work, after the detailed sampling from the
filed, were optical and scanning electron microscopy (SEM), x-ray diffraction
(XRD) and whole rock chemical analyses conducted by ICP-MS. Composition of data
from this work proves that the ‘green marble’ of Tinos is a polygenetic
serpentinitic breccia with calcitic cement. Its mineralogical composition
consists mainly of serpentine (antigorite) and calcite, whereas dolomite,
Cr-rich chlorite, epidote, tremolite, sericite, talc, spinel and magnetite are
present as accessory minerals.
Mineralogical, textural and geochemical data support the idea of a
hartzburgitic and dunitic origin of the serpentines, which formed in a supra
subduction zone geotectonic setting of late Cretaceous age. The main genetic
cause of this irregular formation is tectonism of ultrabasic rocks due to
activation of intraoceanic detachment faults. Sedimentary processes played an
incidental minor role to the formation of Tinos ophicalcites and are usually
recognized at the upper parts of the ophicalcites, which are attributed to
debris-flows deposits. A hydrothermal overprint can also be traced, based on
mineralogical alterations of the rock.
The most possible geotectonic setting where such a polygenetic rock formed,
could be along a large scale intraoceanic detachment, which brought the deepest
part of the ophiolitic sequence (ultrabasic rocks) at the seabed and thus,
caused their serpentinization and tectonic fracturing. Later, these fractures
were filled by calcite, which precipitated from hydrothermal fluids as well as
from the reaction of the ultrabasic rock with the sea water. Locally,
matrix-supported breccias were formed, due to debris flows which took place in
topographic lows, along the fault scarps.
This present work comes to the conclusion that Tinos ophicalcite indicates a
cataclastic tectonic breccia which was formed along an intraoceanic detachment,
in contradiction to the typical alpine ophicalcites (Totalp, Davos etc.), which
were formed by tectonosedimentary mechanisms along a mid-ocean ridge.
Lastly, a few environmental matters were noted, regarding the presence of
serpentine minerals in the ophicalcite as well as the environmental degradation
due to the operation of the quarries in the broader area. Despite the fact that
no important problems were detected, few proposals are made in order to
optimize the production of the ‘green marble’ and to protect the local
environment as well.
Keywords:
Tinos, Green marble, Ophicalcites, Tectonic breccia
Index:
No
Number of index pages:
0
Contains images:
Yes
Number of references:
98
Number of pages:
159
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