Troodos: A Giant Serpentinite Diapir

doi:10.4236/ijg.2011.22010

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International Journal of Geosciences, 2011, 2, 98-101

doi:10.4236/ijg.2011.22010 Published Online May 2011 (http://www.SciRP.org/journal/ijg)

Troodos: A Giant Serpentinite Diapir

Roelof Dirk Schuiling

Institute of Geosciences, Utrecht, The Netherlands

E-mail: [email protected]

Received September 18, 2010; revised February 19, 2011; accepted April 1, 2011

Abstract

Troodos is a classical ophiolite complex. It is proposed that the serpentinized harzburgites that now form the

top of the mountain and represent the originally lowest part of the ophiolite sequence rose as a diapir. This

diapiric rise is caused by the pervasive serpentinization of a suboceanic harzburgite, due to rock-sea water

interaction. The serpentinization caused a 44% expansion of the rocks. Contrary to salt diapirism, the driving

force for this diapiric rise is not so much the difference in density, but the volume increase asscociated with

the transformation of harzburgite into serpentinite. The overlying gabbros, sheeted dike complex and pillow

lavas were pierced by this serpentinite diapir but barely deformed. Their interaction with sea water was li-

mited to some pyroxenes in the gabbros being transformed to amphiboles, and epidotisation of some of the

dikes in the sheeted dike complex. The location of steep faults in the Troodos massif is determined by the

contrasting expansion behavior of different rock-types on both sides of the fault.

Keywords: Ophiolites, Seawater Interaction, Serpentinization, (Lack of) Deformation, Cyprus, Olympic Flame

1. Introduction

Troodos is a classical ophiolite complex, representing a

slow spreading zone. Pillow lavas, sheeted dike complex,

gabbros, layered dunites and mantle rocks (serpentinized

harzburgites) are all represented. In its upper part there

are radiolarites and even some umbers, formed by sub-

marine exhalations, which also deposited the famous

copper deposits of Cyprus. The top of Troodos Mountain

is composed of pervasively serpentinized harzburgites,

which represent the lowest part of the ophiolite sequence.

It is well known that serpentinites can be easily duc-

tilely deformed under stress, like rock salt. In analogy to

salt diapirism, the serpentinized harzburgites around the

top of Troodos mountain on Cyprus are interpreted as a

serpentinite diapir. Serpentinite diapirism has been de-

scribed many times, often from fore-arc environments

[1,2]. The volume expansion associated with serpentini-

zation is considered to be the main driving force behind

the serpentinite diapirism. In future research on ophiolite

complexes this tectonic role of serpentinization should be

taken into account.

2. Observations

The harzburgites are pervasively serpentinized. Serpenti-

nization proceeds by

Mg2SiO4 + MgSiO3 + 2 H2O → Mg3Si2O5(OH)4

The molar volume of the serpentine on the right hand

side is 108.5 cm3, whereas the sum of the volumes of

olivine + enstatite is 75.3 cm3 [3]. This means that a

harzburgite expands 44% during pervasive serpentiniza-

tion. Even if the ratio enstatite/olivine in the original

harzburgite was not exactly 1:1, once the conditions are

in the stability field of lizardite, slight amounts of either

magnesium or silica which are required for the formation

of monomineralic serpentine rock will be extracted from

the large volume of percolating seawater. This is com-

monly observed in the formation of monomineralic zones

during metasomatism. In case the iron becomes oxidized

to magnetite during serpentinization, one can write the

reactions as follows (there is a large variation range of

possible reactions, all leading to fairly similar results).

The olivine will have had a composition close to

Mg0.92Fe0.08SiO4, as is common in peridotites. During the

oxidation of FeO to magnetite, possibly with an interme-

diate stage of ferroan brucite [4], the silica associated

with the iron end-members of the olivine and enstatite

will be released. This silica will react with the abun-

dantly available magnesium in the percolating sea water

to form additional serpentine, according to

R. D. SCHUILING99

0.04 Fe2SiO4 + 0.04 FeSiO3 + 0.12 [Mg2+] + 0.01 CO2 +

0.22 H2O →0.04 Fe3O4 + 0.04 Mg3Si2O5(OH)4 + 0.01

CH4 + 0.24 H+

If we sum up the volume changes of the solid phases

in both reactions, we find that the volume change when a

harzburgite is serpentinized in a large volume of hot

seawater, and the iron is transformed into magnetite is

almost 50%. This is in agreement with the data presented

by Jamtveit and Austrheim [5] who state “Complete ser-

pentinization results in a solid volume increase of nearly

50% and causes a pronounced change in rheology”.

As there are many variations possible, we can con-

clude that the associated volume change is of the order of

40% to 50%. In the reaction the divalent iron is oxidized

by the simultaneous reduction of CO2 and water to me-

thane. Methane emanations are often associated with

actively ongoing serpentinization. A famous example is

the famous Yanartaşı (Turkish for “the rock that always

burns”) on the Turkish mainland, 250 km to the north-

west of the western tip of Cyprus, where methane flames

are permanently emerging from a dunite in the process of

serpentinization.

2.1. Intermezzo

The Yanartaşı has played an important role in classical

Greek history and mythology. Nearby was the ancient

Greek city of Olympos. On festive occasions the young

men of the town had to run to the mountain with a torch

in hand, to be lighted by the methane flames. The first

man to return to Olympos with a burning torch was the

winner. It is hard to believe that this is not the origin of

the Olympic flame.

It also plays a central role in the myth of Bellerophon

and his winged horse Pegasos. Bellerophon had to kill

the chimaera, a fire-breathing dragon that was ravaging

the country. After Bellerophon had spotted the dragon

from his flying horse, he dived into it and drove the dra-

gon into the ground. It is dead, but its flames are still

escaping.

2.2. Absence of Deformation

Most rocks of the Troodos complex are undeformed,

without foliation or preferred orientation. The gabbros

are even explicitly designated as “isotropic gabbros”,

showing that their lack of tectonic imprint is obvious.

Their chemical transformation is limited to local amphi-

bolitization of their pyroxenes. The sheeted dikes and the

pillow lavas are equally undeformed, having preserved

even delicate glass selvages between the pillows (Figure

1).

Figure 1. Pillow lavas with uncracked selvages of basaltic glass. Photo B.N.’tHart.

R. D. SCHUILING

100

The glass has remained unbroken throughout their geo-

logical history. Some of the dikes are tilted, but most are

(sub-) vertical. Dunites occasionally show igneous laye-

ring marked by chromite stringers, but are undeformed.

Some steep faults crosscut the complex, separating for

example the serpentinized harzburgites from gabbros.

We will assign no meaning to these faults, except that the

two rock masses must have moved with respect to each

other.

3. Where Does This Lead Us?

After the spreading activity had stopped, very little

movement has affected the Troodos massif since, except

some tilting and occasional faulting. A similar observa-

tion is made by Gass [6], who states “The least deformed

ophiolites appear to be vertically uplifted pieces of ocean

floor that have not yet undergone much horizontal de-

formation. Two such sequences are … and the Troodos

massif in Cyprus”. .

Plate tectonic models for the region require large

movements, but the rocks tell a different story. They

show no sign of large-scale movement, and lack the in-

ternal fabric associated with tectonic transport. Yet,

Troodos rises to 1952 meter asl, although the rocks that

are now at the top of the mountain represent the deepest

part of the ophiolitic pile. They were part of a spreading

ridge at a sea depth of 2 to 3 km.

In the absence of large-scale horizontal displacements,

applying Occam’s razor, “the simplest explanation is

usually the best”, it is proposed that these serpentinites

rose vertically from the depth of the oceans to their pre-

sent height.

Field evidence suggests that this vertical rise of the

center of the Troodos mountain was not only accompa-

nied by, but probably even caused by pervasive serpenti-

nization. To explain the total uplift of the Troodos Mt. by

serpentinization requires considerable seawater/rock in-

teraction. Serpentinites probably flow similar to salt,

particularly when heated to a certain extent by hydration

reactions [7], so in analogy to salt diapirs it is likely that

seawater/rock interaction first affected a broader area

than the diapir itself, but that the serpentinized were

squeezed upward through a narrower conduit. This is

analogous to what happens in salt diapirs, where the salt

in the diapir does not only derive from the salt that was

directly underneath, but also from salt that flowed side-

ways towards the diapir from a broader layer of salt. Salt

has a lower specific mass than the overlying sediments,

and likewise the serpentinized harzburgite is also con-

siderably lighter than the overlying ophiolitic rocks. The

serpentinized harzburgite has a specific mass of appr.

2.200 kg/m3, whereas the specific masses of the overly-

ing rock types (gabbros, dunites, diabase dikes and pil-

low lavas) range between 2.800 and 3.350 kg/m3. This

means that even without the enormous expansion there is

already a considerable force to set the diapiric movement

in motion. Yet, while in salt diapirism the density differ-

rence is the only driving force, in serpentinite diapirism

the expansion plays a more important role than the den-

sity difference.

When a rock expands, it must make room for itself. In

that sense it is more similar to the technology to raise

parts of the land by injecting sulfuric acid into subsurface

limestones. The resulting gypsum has twice the volume

of the original limestone, which causes the land to be

uplifted, making it safer for inundations [8]. In Germany,

considerable damage to houses is associated with uplift

caused by the transformation of anhydrite into gypsum.

Since September 2007, numerous buildings in Staufen’s

Old Town have begun to exhibit large cracks that have

formed due to the uplift of the substrata. The extent of

the damage is considerable and there is no end to the

uplift process in sight. A geochemical process called

anhydrite swelling has been confirmed as the cause of

these uplifts [9].

The pushing together of serpentinites that derive from

different corners and slightly different thermal regimes in

the suboceanic harzburgite reservoir as it undergoes ser-

pentinization may offer an elegant solution to the re-

markable δD and δ18O gradients observed by Nuriel et al.

[10].

Intense seawater/rock interaction is also evident from

many dikes that have been transformed into undeformed

epidotites, from which the submarine exhalative copper

deposits derive for which Cyprus is famous.

Each dike of the sheeted dike complex represents an

extension equal to the thickness of that dike, but the un-

derlying mantle must simultaneously have undergone a

similar extension, providing easy access to seawater that

will react rapidly with the anhydrous mantle rocks,

helped by the fact that the hydration reaction is strongly

exothermic [7]. The uneven thermal expansion that re-

sults may crack the rocks further, making them even

more accessible to seawater interaction.

A steep fault must separate gabbros from serpentinized

harzburgite, as one rock expands and rises 4 to 6 km,

whereas its neighbor does not move. Such steep faults

are typical of diapiric settings. The fact that the Amian-

thos Fault [10], separating the serpentinized harzburgites

from the adjoining gabbro dies out as soon as it leaves

the contact between these two rock-types with contrast-

ing expansion behavior is illustrative.

The diapiric rise of its central part has caused some

upward bending of the sediments around the Troodos

massif. Uplift continued at least to Miocene times, as

R. D. SCHUILING101

some Messinian gypsum layers are slightly tilted, sloping

away from the Troodos complex. Troodos may even still

be rising today, which could indicate that even now the

serpentinite has not yet reached its ultimate equilibrium

position.

During its formation Troodos was probably similar to

the Atlantis sea mount that rises 3 km above the ocean

floor [11] and is also composed of serpentinized mantle

rocks and gabbros, and associated with white smokers.

4. Conclusions

The Troodos mountain is a huge serpentinite diapir that

was formed by seawater/rock interaction.

5. References

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Seamounts in a Forearc Environment,” In: B. H. Keating,

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Islands, and Atolls, Geophysical Monograph Series 43,

American Geophysical Union, Washington DC, 1987, pp.

61-69.

[2] G. Boillot, et al., “Ocean-Continent Boundary off the

Iberian Margin: A Serpentinite Diapir West of Galicia

Bank,” Earth and Planetary Science Letters, Vol. 48, No.

1, 1980, pp. 23-34. doi:10.1016/0012-821X(80)90166-1

[3] R. A. Robie, et al., “Thermodynamic Properties of Min-

erals and Related Substances at 298.14 K and 1 Bar (105

Pascals) Pressure and at Higher Temperatures,” US Geo-

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[4] W. Bach, et al., “Unraveling the Sequence of Serpen-

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physical Research Letters, Vol. 33, No. 13, 2006, pp. 4-7.

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of Fluids,” Elements, Vol. 6, No. 3, 2010, pp. 153-158.

doi:10.2113/gselements.6.3.153

[6] I. G. Gass, “Origin and Emplacement of Ophiolites,”

Geological Society, Vol. 7, 1977, pp. 72-76.

doi:10.1144/GSL.SP.1977.007.01.07

[7] R. D. Schuiling, “Serpentinization as a Possible Cause of

High Heat-Flow Values in and near Oceanic Ridges,”

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[8] R. D. Schuiling, “Geochemical Engineering; Taking

Stock,” Journal of Geochemical Exploration, Vol. 62, No.

1-3, 1998, pp. 1-28. doi:10.1016/S0375-6742(97)00042-3

[9] News Archive Space, “TerraSAR-X Image of the Month:

Ground Uplift under Staufen’s Old Town,” 22 October

2009.

[10] P. Nuriel, et al., “Fault-Related Oceanic Serpentinization

in the Troodos Ophiolite, Cyprus: Implications for a Fos-

sil Oceanic Core Complex,” Earth and Planetary Science

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