ANISOTROPY OF MAGNETIC SUSCEPTIBILITY STUDIES IN LAVA FLOWS OF

THE EASTERN ANATOLIA REGION, TURKEY Hakan Ucar and Mualla Cengiz Cinku

Istanbul University, Faculty of Engineering, Dept. of Geophysical Engineering, 34320, Avcilar, Istanbul, Turkey

(hakan.ucar@ogr.iu.edu.tr)

1) SUMMARY

In this study, anisotropy of magnetic susceptibility measurements were carried out on 21 different sites from

the Eastern Anatolian Region to determine the determine the flow direction of lavas. In total, 133 volcanic

samples from Pliocene-Quaternary ages were measured on 18 different measurement position by using

Bartington MS2B susceptibility device and AMS-BAR software. As a result of the AMS measurements,

magnetic lineations associated with a magma flow in horizontal direction have been determined. The magma

flow directions are generally towards the volcano vent.

Detailed rock magnetic experiments, including thermomagnetic measurements, acquisition of isothermal

remanent magnetization (IRM), and thermal demagnetization of three-axes composite IRM, were conducted on

each pilot sample. Thermomagnetic experiments were performed on representative samples by heating in air,

using an Bartington MS2 susceptibility bridge fitted with an oven unit. IRMs were acquired using an ASC

pulse magnetizer (Model IM-10-30). Steps of 1, 0.4, and 0.12 T were imparted along the Z-, Y-, and X-axis,

respectively. Subsequently, samples were thermally demagnetized to identify the magnetic carriers based on

their coercivity and unblocking behaviour. As a result of this measurements, most of the samples are

characterized by titanomagnetite.

2) AIM OF THE STUDY

This study was carried out to determine the relationship between magma flow directions of the

samples(Pliocene-Quaternaty ages) from three volcanoes(Tendurek, Suphan and Girekol) and magnetic

lineation with the help of AMS measurements.

3) GEOLOGICAL SETTING OF THE REGION

Eastern Anatolia comprises one of the high plateaus of the Alpine-Himalaya mountain belt with an average

elevation of ~2 km above the sea level. Available geochronologic data indicate that the volcanism started in the

south of the region around the north of Lake Van and continued towards the norths in a age interval of 15.0 Ma

to 0.4 Ma. The products are exposed as stratovolcanoes like Ağrı, Tendürek, Süphan and Girekol with the

eruption of andesitic to rhyolitic lavas, ignimbrites and basaltic lava flows (Pearce vd., 1990; Keskin vd.,

1998).

4) SAMPLING AREA

Figure 1: Plate motions of Turkey and its

environment. According to GPS measurements,

Arabian Plate moves towards Northwest at a rate of

18±2 mm every year. As a result of this movement,

Anatolian block moves towards West at a rate of

24±2 mm across North Anatolian Fault(NAF) and

9±2 mm across East Anatolian Fault(EAF) every

year. Also, West Anatolian Region moves towards

Southwest at a rate of 30±1 mm every year(Okay

and Tüysüz, 1999).

Figure 2: Tectonic units, distribution of collision-

related volcanic products and volcanic centers across

Eastern Anatolia. E-K-P: the Erzurum-Kars Plateau;

NATF and EATF: North and East Anatolian

Transform Faults. I : The Pontide unit which is

represented basically by a magmatic arc, II :

Northwestern Iran Unit, III : The Eastern Anatolian

Accretionary Complex (EAAC), IV : The Bitlis-

Poturge Massif (BPM) and V : Arabian Plate. Green

areas : Ophiolitic melange, Pink and red areas :

Volcanic units which is related to the collision, White

areas : Young units (Keskin et al., 2003)

Figure 3: Geological setting of the region and locations of the samples(modified after MTA, 2002)

5)

Figure 4: Lavas belonging to

Tendurek volcano.

Figure 5: Lavas belonging to

Girekol volcano. Figure 6: Lavas belonging to

Suphan volcano

6)

7) THERMOMAGNETIC MEASUREMENTS, IRM AND THERMAL DEMAGNETIZATION OF

THREE-AXES COMPOSITE IRM Figure 7: The results of the

thermomagnetic analysis

reveal three different types of

behaviour (Fig. 7a, d, g).

Most samples with minor

alteration are characterized by

a single ferromagnetic phase

and Curie temperatures

between 550 and 580 °C,

indicating the presence of Ti-

poor titanomagnetites (Fig.

7a). In the second group, low

Curie temperatures between

260 and 280 °C are observed

that are typical of titanium-

rich titanomagnetite or low-

temperature oxidized titano-

maghemite (Fig. 7d).

The increase in magnetization seen in the cooling curve suggests oxidation of high-titanomagnetite/

titanomaghemite to low-Ti magnetite. The third group is defined by two different thermomagnetic phases during

heating and a single phase in the cooling curve. The cooling curves show a loss in magnetization, indicating

oxidation of Ti-poor titanomagnetite to Ti-rich titanomagnetite. The Curie temperatures for these types of samples

are 550 and 580 °C (Fig. 7g). In the heating curves, a decrease in susceptibility between 320 and 350 °C shows

the transformation of titanomaghematite to magnetite, and a Curie point between 550 and 580 °C. Typical

examples of IRM acquisition and thermal decay experiments are shown in Fig. 7. IRM curves show rapid

acquisition of magnetization to about 300 mT in general, suggesting the existence of low-coercivity ferromagnets

(Fig. 7b, e, h). Thermal demagnetization of the cross-component IRM shows that the low-coercivity component is

gradually unblocked beneath 400 °C (Fig. 7i) and 600 °C, showing the existence of Ti-poor magnetite (Fig. 7c).

Another group, is characterized by the thermomagnetic curves, a slower increase in IRM, and a higher unblocking

temperature (Fig. 7e, f). (Hisarlı et al., 2016)

8) AMS MEASUREMENTS

Figure 8: Lineations are in horizontal direction and have low inclination angles for D31, D27, D10, D12, D13, D14, D2, D5, D8,

D6, D20, D22 sites. Blue squares : Kmin(Foliation), Green triangles : Kint, Red circles : Kmax(Lineation).

Figure 9: Lineations are in horizontal direction and have low

inclination angles for D1, D18, D21, D3, D7, D42, D43 sites.

Blue squares : Kmin(Foliation), Green triangles : Kint, Red

circles : Kmax(Lineation).

Figure 10: Graph representation of Flinn diagram

(Lineations – Foliations)

9) MAGNETIC LINEATION AND

MAGMA FLOW DIRECTION

Figure 11: In the Tendürek volcano, the

magnetic lineations represent a magma flow in

the horizontal direction, and the lineations are

generally towards the volcano vent.

Figure 12: In the Süphan volcano, the

magnetic lineations represent a magma

flow in the horizontal direction, and

lineations(arrows with red point) are

generally towards the volcano vent.

Figure 13: In the Girekol volcano,

the magnetic lineations(arrows with

red point) represent a magma flow in

the horizontal direction.

11) CONCLUSIONS

According to the thermomagnetic measurements, isothermal remanent magnetization

(IRM) and thermal demagnetization of three-axes composite IRM, most of the samples

are characterized by titanomagnetite.

When percentages of susceptibility and SiO2 of specimens were evaluated, it was

determined that generally basic specimens have high susceptibility and susceptibility

decreases relatively for acidic specimens.

Three different volcanoes was investigated to determine the relationship between magma

flow direction and magnetic lineation. In the Tendurek, Girekol and Suphan volcanoes,

magnetic lineations are associated with a magma flow in the horizontal direction, and the

lineations are generally towards the volcano vent. It is understood that the magnetic

lineations correspond to magma flow direction.

10) SUSCEPTIBILITY AND

CHEMISTRY OF VOLCANISM

Figure 14: Graph representation of

volcanic rocks obtained due to

susceptibility and SiO2 component.

12) REFERANCES 1) Keskin, M., Pearce, J.A. and Mitchell, J.G. (1998). Volcano-stratigraphy and geochemistry of collision-related volcanism on the Erzurum-Kars

Plateau, North Eastern Turkey, Journal of Volcanology and Geothermal Research, V.85/1-4, pp. 355-404.

2) Keskin, M. (2003). Magma generation by slab steepening and breakoff beneath a subduction–accretion complex: an alternative model for

collision-related volcanism in Eastern Anatolia, Turkey. Geophysical Research Letters 30 (24).

3) MTA (2002) Geological map of Turkey (1:500000 scale). General Directorate of Mineral Research and Exploration, Ankara

4) Okay, A.I. and Tüysüz, O. (1999). Tethyan Sutures Of Northern Turkey. In: Durand, B., Jolivet, L., Horváth, F. & Séranne, M. (Eds), The

Mediterranean Basins: Tertiary Extension Within The Alpine Orogen. Geological Society, London, Special Publications,156, 475-515.

5) Pearce, J.A., Bender, J.F., De Long, S.E., Kidd, W.S.F., Low, P.J., Güner, Y., Saroglu, F., Yilmaz, Y., Moorbath, S. and Mitchell, J.G. (1990).

Genesis of collision volcanism in Eastern Anatolia, Turkey, J. Volcanol. Geotherm. Res., 44, 189-229.

6) Hisarlı, Z. M., Çinku, M. C., Ustaömer, T., Keskin, M., & Orbay, N. (2016). Neotectonic deformation in the Eurasia–Arabia collision zone, the

East Anatolian Plateau, E Turkey: evidence from palaeomagnetic study of Neogene–Quaternary volcanic rocks. International Journal of Earth

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