2010

News Registration Abstracts Accommodation Excursions Deadlines Organizing committee
First circular Participants Abstract submission Travel Program Seminar History Contact us

The geochemical characteristics of the boninites

of Eastern (SSZ) Albanian ophiolites

 

ABSTRACT

By

*Dr.Kristina Gjeçi*, **Msc.Sander Kovaci**

*Institute of Geosciences, Polytechnic University of Tirana (UPT), ALBANIA. Email:mirdita82@yahoo.com

**Faculty of Mathematical and Physical Engineering, Dept. of Mathematical Engineering, Polytechnic University of Tirana (UPT), ALBANIA.

 

In the Albanian ophiolites, boninites are found within Eastern (SSZ) type ophiolites as part of their volcanic sequence, and sheeted dike complex; in the plutonic gabbroplagiogranitic sequence and very rare in ultramafic intrusions and in uppermost part of ultramafic sequence. They are porphyric, microporphyric, vitroporphyric with CPx endiopsid(aught) chromitic with( Wo 38.5-43.58; en 50.98 53.37; fs 5.12 8.69);Cr2O3 > 0.15% and  OPx - enstatite-bronzite (Wo -18.12; en-80.61;fs-3.27), olivine phenocrysts and accessory cromspinelide.Absent plagioclase  phenochrits. Microphenocrysts are Opx rare Cpx and chromshpinelid .The groundmass is small grain, microlitic (Opx, Cpx, Pl), sometimes chlorite and obsidian (volcanic glass) with basic and average contain. They rare meet fresh, are partially or totally alterated.    

Chemical composition of boninites shows very low (< 0.45%) TiO2 content, low (average 0.5) CaO/Al2O3 ratio, high (> 7.5%)  MgO content and low ETR content. Boninites of the Eastern (SSZ) type ophiolite are mainly low Ca boninites, rarely high-Ca boninites according to Crawford et al. (1989) classification.

Based in chemical dates and petrographic charachterstics boninites of Albanian Eastern (SSZ) - type ophiolites correlation with another boninites suite by world, Cape Vogel, Chichi Jima, Mariana Trench, Baja California and Cyprus. Boninites of Albanian Eastern (SSZ) - type ophiolites are mainly low  - Ca boninites and rarely high Ca boninites according to Crawford et al.(1989) classification bat these boninites are differently on contain mineral and  petrographic charachterstics ,for example: the boninites of Albanian Eastern(SSZ) - type ophiolites (low  - Ca boninites) are more poor in SiO2 , Na2O,K2O and moor rich on Al2O3 as  Cape Vogel,Chichi Jima , Mariana Trench, Baja California(tab.1). The boninites of Albanian Eastern (SSZ) - type ophiolites (high Ca boninites) are richer on SiO2, Na2O.K2O and moor poor in CaO as boninites Cyprus (tab.1).

 The boninites of Albanian Eastern (SSZ) - type ophiolites correlation with boninite suites Cape Vogel, Chichi Jima, Mariana Trench, Baja California and Cyprus in contain LREE and ETR ( tab.2) Boninites are associated with high-MgO and  low-TiO2  basalts, and with andesitedacites and rhyodacites with boninitic affinity, forming a

Boninitic association, which together with predominating IAT basalt-andesite-rhyodacite constitute an association similar to the Western Pacific arc lavas generated at fore arc settings.

Formation of the boninites of Eastern-type ophiolite is caused by partial melting processes of the refractary mantle peridotite and mantle-melt interaction.

 

ETR.  Content for boninite from central Mirdita (Albania) and from suites Chichi Jima, Mariana Trench,    Cape Vogel, as Gjeçi K. (2008) based on the Hickey and Frey (1982) and Dilek Y., Furness H., Shallo M. (2007).                                                                                                                                              

                                                                                                    

Tab.2

 

Chichi Jima

2981        

Mariana Trench

 2980

Cape Vogel

2984       

Bon. Central Mirdita

90 Al-00

 

La

1.27

1.27

1.47

1.10

Ce

2.57

2.93

3.51

1.3

Nd

1.65

1.85

2.09

0.93

Sm

0.426

0.508

0.602

0.27

Eu

0.146

0.171

0.210

0.01

Tb

0.099

0.115

0.144

0.07

Yb

0.591

0.602

0.809

0.55

Lu

0.103

0.104

0.133

0.1

 

The average content of  indicators elements(major) for the boninite of Eastern (SSZ) Albanian ophiolites and for the boninite of World ophiolites,as Gjeçi.K(2008) based on the (Gjeçi K.,Shallo M.(2006);Shallo M. (1994,1995); Gjata,Beccaluva(1994 Milushi I.etc.(2002); Manika K. (1994); Manika K., Shallo M.,Gega D. (1999).

 

Tab.1

 

Bon.

Volc.

Sequ

ence

 

 

  Bon.

Shee

ted

dike complex

 

Bon.

plutonic gabbroplagiog. sequence

 

Bon.

Ultra

mafic

 intru

sions 

 

Bon.

New

 Cale

donia

suites

Bon

Mariana Trench

 suites

Bon.

 Seto

uchi

 suites

Bon

 Baja-

 Kalifo

- rnia

suites

 

Bon.

Chichi

-Jima 

suites

Bon.

Cape

Vogel 

suites

Bon. 

Cyprus

Bon.  Tonga Trench suites

SiO2

52.26

52.63

54.15

52.10

57.08

58.24

57.74

56.50

56.20

54.06

50.75

54.41

TiO2

0.31

0.23

0.13

0.21

0.26

0.17

0.51

0.69

0.13

0.21

0.23

0.33

MgO

9.26

11.58

17.83

11.72

12.58

13.25

8.61

8.0

11.19

14.57

11.0

14.84

CaO/

Al2O3

0.64

0.70

0.63

0.65

0.63

0.43

0.45

0.42

0.70

0.66

0.85

0.87

Mg#

0.51

0.55

0.86

0.50

0.38

0.63

0.57

0.58

0.57

0.61

0.57

0.62

Na2O

2.06

1.28

0.12

0.94

2.29

2.07

2.74

4.1

1.54

0.92

0.9

1.19

K2O

0.28

0.26

0.00

0.18

0.49

0.81

1.81

1.03

0.40

0.30

0.22

0.29

Alcaline

total

2.34

1.54

0.12

1.12

2.78

2.88

4.55

5.13

1.94

1.22

1.12

1.48

Boninites

of

 

 

Eastern

(SSZ)

Abanian

ophilites

 

Bon.

of

World

ophilites

 

 

 

 

 

 

Reference:

Crawford A. J., Fallon T. J. and Green D.H. (1989) Classificaton, petrogenesis and tectonic settings of boninites.

Dilek Y., Furness H., Shallo M. (2007) Suprasubduction zone ophiolite formation along the periphery   of Mesozoic Gondwana. Gondwana research 2007.

Hickey R., Frey F.A. (1982) - Geochemical characteristisc of boninite series volcanic Implications for their source. Geochim. Cosmochim. Acts 46, p. 2009 2115.

GJeçi K., Shallo M., (2006)  -Vendosja gjeologjike e boniniteve ne ofiolitet e tipit lindor te Shqiperise   dhe   veçorite   petrografike e gjeokimike te tyre. Buletini i shkencave gjeologjike, 1/ 2006, 3-16.

Gjeçi K.(.2008) -  Petrologjia e boniniteve te ofioliteve lindore te Shqiperise (PhD material).