The Social Function of Amharic Folk Poetry With Reference to Shänä a in Rayya Qobbo

123 Pages·2002·4.04 MB·English

COMPOSITIONAL VARIATION OF ERTA’ALE BASALTIC
ERUPTION WITH TIME

By
Edelawit Lemma

A thesis submitted to the School of Graduate Studies of Addis Ababa University in
partial fulfillment of the requirements for the degree of Master of Science in
(Geochemistry)

June 2017
Addis Ababa University
0

Addis Ababa, Ethiopia
ADDIS ABABA UNIVERSITY
SCHOOL OF GRADUATE STUDIES
SCHOOL OF EARTH SCIENCES

COMPOSITIONAL VARIATION OF ERTA’ALE BASALTIC
ERUPTION WITH TIME

By

Edelawit Lemma

Advisor: Dereje Ayalew (Prof.)

A thesis submitted to the School of Graduate Studies of Addis Ababa
University in partial fulfillment of the requirements for the degree of
Master of Science in (Geochemistry)

June 2017
Addis Ababa University
Addis Ababa, Ethiopia
ADDIS ABABA UNIVERSITY
SCHOOL OF GRADUATE STUDIES
SCHOOL OF EARTH SCIENCES

COMPOSITIONAL VARIATION OF ERTA’ALE BASALTIC
ERUPTION WITH TIME

By

Edelawit Lemma

Approved by the Examining Committee
Dr. Balemwal Atnafu ________________ _______________
Head, School of Earth Sciences Signature Date

Prof. Dereje Ayalew ______________ _______________
Advisor Signature Date

Prof. Gezahegn Yirgu ______________ _______________
Examiner Signature Date

Dr. Mulugeta Alene _______________ ________________
Examiner Signature Date

i
Declaration of Originality
I hereby declare that the thesis is my original master‘s degree work under the supervision
of Prof. Dereje Ayalew, School of Earth Sciences, Addis Ababa University during the
year 2017. This work has not been presented or submitted to any other university or
institution for the award of any degree. All sources and materials used for the thesis have
been duly acknowledged.

Edelawit Lemma _____________ _______________
Signature Date
Approved by
Prof. Dereje Ayalew (Advisor) _____________ _______________
Signature Date
ii
Abstract

Erta’Ale lava lake is located at the center of the Erta’Ale volcanic range in the northern
afar depression. Erta’Ale is known by its two active lava lake situated at northern and
central part of the caldera. The thesis generally considered the compositional variation of
the Erta’Ale lava through time. Field investigation, petrographic and whole rock
geochemical studies have been applied to meet the objectives. The lava of Erta’Ale
volcano has MgO content ranging from (4.56-6.36 wt%) and SiO content (47-52 wt%)
2
which decrease with increasing of MgO. The Al O and CaO contents slightly increase
2 3
with decreasing MgO down to ~6 wt%, and then decrease with decreasing of MgO a
general positive trend for Fe O and TiO . The variations diagram of the Erta’Ale lava
2 3 2
show fractionation of mineral phase. In most of the Erta’Ale lava (Ce/Pb > 20) crustal
contamination is not major process. However there are some samples which have low
value of Ce/Pb ratio (<20) because of their high value of Pb . The Erta’Ale lava is
characterized by low La/Nb (<1) and Ba/Nb (<5) which is the characteristics of mantle
plume derived melts. Trace element data of the Erta’Ale basalt show that the source of the
Erta‘Ale basalt is Afar Mantle plume. The La/Nb, La/Sm and Ce/Pb versus time diagram
indicate that the source, depth and degree of melting of the Erta’Ale basalt don’t have a
significant change with time. The geochemical results show that there is no significant
compositional variation in the Erta’Ale basaltic rock. However, there is a slight chemical
variation between the 2017, 2010 and the others older lava. This variation is a result of
the difference in degree of fractionation.

i
Acknowledgment

The thesis is done by the help, support and inspiration of different organization and
peoples. Firstly, I would like to give my gratitude to Addis Ababa University School of
Earth Sciences and Bule Hora University for providing an opportunity to study my
master‘s degree and funding the research project. I would also like to give my gratitude to
my advisor Prof. Dereje Ayalew for his guidance, constructive comment and
encouragement to accomplish this thesis. I am also indebted to Prof. Asfawesson Asrat
for his support and valuable suggestion. At last but not least I would like to thank the
government official and local people of the Afar region for helping me during the field
work. My greatest gratitude goes to all of my friends and family who support me during
my thesis work. Any omission in this brief acknowledgement does not mean lack of
gratitude.

ii
Table of content

Abstract .............................................................................................................................................. i
Acknowledgment .............................................................................................................................. ii
Table of content ............................................................................................................................... iii
List of Figures .................................................................................................................................. vi
List of Table ................................................................................................................................... viii
Chapter one ....................................................................................................................................... 1
1. Introduction ...............................................................................................................................1
1.1 Background .........................................................................................................................1
1.2. Location and Accessibility of the study area .....................................................................2
1.2.2 Climatic condition and Vegetation ..........................................................................3
1.2.3 Physiographic and Drainage ........................................................................................3
1.2.4 Population and settlement ............................................................................................4
1.3. Statement of the problem ...................................................................................................5
1.4. Objective of the study ........................................................................................................5
1.4.1. General objective ........................................................................................................5
1.4.2. Specific objective ........................................................................................................5
1.5 Methodology .......................................................................................................................5
1.5.1 Introduction ..................................................................................................................5
1.5.2 Field Work ...................................................................................................................6
1.5.3. Laboratory analysis .....................................................................................................6
1.5.3.1 Petrographic analysis ............................................................................................6
1.5.3.2 Geochemistry analysis ..........................................................................................6
1.6. Significance of the research ...............................................................................................7
1.7. Previous work ....................................................................................................................7
Chapter two ..................................................................................................................................... 10
2. Regional geologic setting ....................................................................................................... 10
2.1. The Afar depression ........................................................................................................ 10
iii
2.1.1. Neoproterozoic basement, Mesozoic sedimentary rocks ......................................... 11
2.1.2 Miocene igneous rocks ............................................................................................. 12
2.1.3. Pliocene volcanic rocks ............................................................................................ 12
2.1.4. Quaternary volcanic and sedimentary rocks ............................................................ 13
2.2 Afar volcanism ................................................................................................................. 13
2.3. The Erta’Ale Range ........................................................................................................ 13
2.4. Erta’Ale Lava Lake ......................................................................................................... 16
2.4.1 Synthesis of Erta’Ale activity ................................................................................... 17
Chapter Three ................................................................................................................................. 19
3. Lithology and Petrography .................................................................................................... 19
3.1. Introduction ..................................................................................................................... 19
3.1.1 The new erupted active volcano ................................................................................ 20
3.2. Lithology and Petrography Description .......................................................................... 22
3.2.1. The 2017 lava flow .................................................................................................. 22
3.2.2. The 2010 lava flow .................................................................................................. 24
3.2.3. Basalt 3..................................................................................................................... 26
3.2.4. Basalt 4..................................................................................................................... 27
3.2.5. Basalt 5..................................................................................................................... 28
3.2.6. Basalt 6..................................................................................................................... 29
Chapter Four ................................................................................................................................... 34
4. Geochemistry ......................................................................................................................... 34
4.1. Introduction ..................................................................................................................... 34
4.1.2 Methodology ............................................................................................................. 34
4.2 Major element Geochemistry ........................................................................................... 38
4.2.1 Classification diagram............................................................................................... 38
4.2.2 Major element Variation diagrams ........................................................................... 39
4.3. Trace elements geochemistry .......................................................................................... 40
4.3.1 Trace element variation diagram ............................................................................... 41
4.4 The Rare earth element (REE) and Multi element Variation Diagram ............................ 44
Chapter Five .................................................................................................................................... 46
5. Discussion .............................................................................................................................. 46
5.1 Petrogenetic Evolution of Erta’Ale Basalt ....................................................................... 46
5.2 Source of the mantle ........................................................................................................ 48
iv
5.2.1 Crustal contamination ............................................................................................... 48
5.2.2 Source region of Erta’Ale lava .................................................................................. 50
5.3 Compositional variation of Erta’Ale Basaltic eruption with time.................................... 52
Chapter Six ..................................................................................................................................... 56
6. Conclusion and Recommendation ......................................................................................... 56
6.1. Conclusion ...................................................................................................................... 56
References ....................................................................................................................................... 59
APPENDIX I Petrography Analysis .............................................................................................. 65
APPENDIX II Trace element Ratio ................................................................................................ 67
APPENDIX III Trace element ....................................................................................................... 68
v
List of Figures
Figure 1.1 Regional view of Afar depression ..................................................................... 2
Figure 1.2 Location map of the study area .......................................................................... 3
Figure 1.3 Physiographic map of the Erta’Ale volcano and its surrounding. .................... 4
Figure 2.1 Geological map of the Afar depression ........................................................... 12
Figure 2.2 Geological map of the northern Afar/Danakil Depression ............................. 15
Figure 2.3 Fluctuation of the central pit lava lake level in the 2009/2010 year ............... 18
Figure 2.4 Fluctuation of the lake level of the Erta’Ale lava lakes .................................. 18
Figure: 3.1 Filed photograph of the extent of the r 2010 eruption lavas ......................... 20
Figure 3.2 : Satellite image of Erta’Ale volcano. .............................................................. 20
Figure 3.3 Satellite images of Erta’Ale volcano and the other active volcano ................. 21
Figure 3.4 Photograph of the new erupted active volcano ................................................ 22
Figure 3.5 Photograph of the locations of Erta’Ale and the new erupted active volcano22
Figure 3.6 Field photo graph of the 2017 basaltic lava flow ........................................... 23
Figure 3.7 Micro photo picture of 2017 lava flow under .................................................. 24
Figure 3.8: Field photograph of the 2010 lava flow ........................................................ 25
Figure 3.9 Micro photo picture of the 2010 lava flow ....................................................... 25
Figure 3.10 Field photograph of basaltic lava flow of Basalt 3 ....................................... 26
Figure 3.11 Micro photo picture of Basalt 3 under. ......................................................... 27
Figure 3.12 Field photographs of the Basalt 4. ................................................................. 27
Figure 3.13 Micro photo picture of lava flow of Basalt 4 ................................................ 28
Figure 3.14 Field photo graph of Basalt 5. ...................................................................... 29
Figure 3.15 Micro photo picture of lava flow of Basaltic 5 .............................................. 29
Figure 3.16 Field photograph of Basalt 6 ......................................................................... 30
Figure 3.17 Micro photo picture of lava flow of Basalt 6. ................................................ 31
vi