Abstract

This project was carried out in Great Soppo, Razel street in Buea south west region of Cameroon for a couple of days with the help of other students. It involved basaltic rocks that erupted from mount Cameroon in fako division. Campaign street was the main locality under study where most of the features where observe.

Ropy basalt was observe in different locations in campaign street, these ropy basalts comprised of many small vesicles and at different locations the vesicles where larger and longer regarding the nature of cooling. Non ropy basalt where also observe, basalts with smaller joints where observed at moki garage and compact basalts were also observe.

CHAPTER ONE

INTRODUCTION

Background GLY 498 entitled “Independent Field Mapping Project” is a research program offered by the Department of Geology of the University of Buea to all final year students as part of the curriculum and as a basic requirement for students to complete their BSc program. This field work took place at great soppo, small soppo, and razel street, it enables final year students to carry out studies practically in the field as well as to correlate theoretical work with field realities to widen their knowledge of Geology and to prepare them for future work and experience in Geosciences.

The Independent field mapping involves a mapping exercise which helps to show rock types, structures and possibly the relationship that exits between the rock types and history of the study area.  Mount Cameroon is in the South West region precisely in Buea town. It was nicknamed chariots of fire by sea loving Phoenicians in the 18th century during an eruption. It extends to Limbe and has a height of 13,435ft(4,095m). on the mountain there are rear species of animals, birds, chimps’ as well as very beautiful but rear species of flowers which grows at the fertile volcanic. Mount Etinde is a volcano situated on the southwestern flank of the large mount Cameroon. Its eruptions are dated at 0.65Ma and took place during the mount Cameroon eruptive cycle. The lava types which are unrelated to Mount Cameroon alkali basalts.

1.1 Location and Accessibility of Study Area

Buea the Headquarters of the Southwest region of CAMEROON. Campaign street is acm from the mainstream that is linked from a few kilometers from the  mile 17 park in Buea, campaign branche from the main road at royal pharmacy where there are divided into 8 streets. From street 8 it link up to Buea town. The place is easily accessible by taxi, bike, private car or on foot.  The people who live in the area are welcoming and are kind to assist u in any way possible.

1.2 Geographical Aspects 

1.2.1 Climate and Vegetation 

Buea GMT time is +1 hour and is mostly cloudy. It has an equatorial climate with 2 major seasons. Rainy season which runs from March to October and Dry season, from November to May). Temperature ranges between 20ºC to 28ºC while, annual rainfall ranges between 3000mm to 5000mm.  The conditions here are generally the tropical rainforest climate with rainfall almost during the entire year. However, average monthly High/Low Temperature for these urban spaces ranges from 23 low to 32  high. This temperature increases as one moves downwards from Buea station to Muea. Several factors are behind this.

Firstly, the principle of “higher one goes the colder it becomes” applies as the town is on the slopes of the mountain. Secondly, some areas have higher population intensity, activity and urbanization than others. Molyko for example has more infrastructures which reduces circulation and exchange of air.

1.2.2 Topography and Drainage 

The area is composed of undulating high and low lands with many rocks and gravels due to volcanic eruptions. The area is well drained due to the generally hilly nature of the terrain and the fact that they are free-draining.

1.2.3 Soils  

The soil type consists of basalts and is because of the first volcanic activity in the Fako Mountain area, which occurred in the cretaceous system. These soils have been weathered and partly covered by more recent deposits, thus the soils are black. The soil is very rich in nutrients and allows the cultivation of various crops such as tomatoes, cabbage, okro, pepper, corn, cocoyam, yams, cassava, plantains, beans, vegetables and even some cash crops such as palm trees, cocoa and bananas. Citrus trees are less prosperous as one ascends, and climate gets cooler. The soil and climate are very supportive for vegetation and agriculture though in some areas digging is difficult due to the stony nature of the rocks.

  1.2.4 Human Geography

Buea has an estimated population of about 200.000 inhabitants constituting essentially of the Bakweri (the indigenes). The Bakweri language spoken by the natives is equally written and documented. English and French are two official languages used for general interaction while pidgin is the lingua franca. The average life expectancy of this area is 50 years (1999 statistics) literacy rate is on the rise with some 60-75% of the youths having access to education.

In a whole five large regional-cultural divisions could be found within the Municipality:  Western highlanders (Semi-Bantu or grass fielders population);

1) Coastal tropical forest peoples, including the south west and littoral regions

2) Southern tropical forest peoples, from the Centre, south and east region;

3) Islamic peoples of the northern semi-arid regions and central highlands, including the Fulani (French: Peul) and the “Kirdi”, non-Islamic or recently Islamic peoples of the northern desert and central highlands.

4) Foreign migrant population from other countries.

1.3 The Cameroon Volcanic Line (CVL)

1.3.1 Origin of the Line 

The origin of the Cameroon volcanic line remains a controversial issue. Burke

(2001) invoked reactivation of a long-standing plume (the “711 plume”), at latitude 7_N, long 11.5_E, responding to a change in plate tectonic regime about 20 million years ago to create a shallow, short-wavelength mantle convection pattern, and the stress conditions created at the right-angle bend in the continental margin. This author also defined three remarkable distinct phenomena that originated the Cameroon volcanic line:

(1)        a position over the 711 plume for the past ca. 140m.yr.;

(2)        a location adjacent to a right-angled bend of the continental margin for ca. 125Ma.

(3)        the establishment of a new plate wide pattern of shallow-mantle convection at ca. 30 Ma when the African plate came to rest.

Deep-imaging reflection crossing seamount between Bioko and Príncipe Islands. Note how sedimentary reflections continue through seamount indicating crustal uplift. In addition, the Cameroon Volcanic Line is defined as a hot line essentially resulting from passive rifting (Nkouation et al, 2008), and interpreted as a mantle upwelling inside zones of weakness in the lithosphere after intra-continental extension. These volcanic chains form parallel hotlines that are products of mantle upwelling between Reyleigh-Bernard-type cylindrical convective rolls formed in the upper mantle (Meyers et al, 1998).

  1.3.2 Components of the CVL 

Cameroon volcano is a result of Cameroon volcanic line (CVL). Cameroon volcanic line extends over 1600 kilometers consist of a string of volcanoes extending from Atlantic Ocean (from St. Helens, Pagalu, Bioko, Principe, and Sao Tome) to continental segment in Cameroon (Mount Cameroon, Mt. Manengouba, Mount Lefo, Oku Mountain, Ngaoundere Plateau, Mandar Mountains Biu Plateau and lots more). Since Cameroon volcano go through oceanic – continental boundaries the are subjects of intensive scientific research and interest.

Prominent on Cameroon volcanic line is Mount Cameroon (aka Mt. Fako, Buea

Mountain). Mount Cameroon eruptions occurred in 1909, 1924, 1954, 1959, 1982 and 1999.Aside of the Mediterranean, Mount Cameroon is the only volcano documented back to fourth century  by Hanno from Carthage in North Africa.

 1.3.3 Geologic Setting of the CVL

1.3.3.1. Age and Rock Type of the Cameroon volcanic Line 

The Cameroon Line is constituted by 10 volcano-capped-swells of 1000-kmlong. The swells are small, 100 km across; arranged in a straight line. Half of these swells lie onshore and half offshore. Irregularly shaped basins are intermingled among the swells. The landward sector of the Cameroon volcanic line, from west to east, has a Y-shape form and comprises the Jos, Biu and, Ngaoundere swells. The Biu Plateau, Nigeria, at the northern end of the CVL, is constituted by Cenozoic Volcanism (Rankenburg et al, 2004). Lavas from the Biu plateau range in composition from basalt to basanite, with ages from 5.3 to 0.84 Ma.

Hence, the timing of the Jos plateau is thought to be much related to that of the other CVL volcanic centers. The magacryst suites of the Biu and Jos Plateaux comprise chemically homogeneous crystals of clinopyroxene , garnet , plagioclase  and ilmenite  (Rankenburg et al, 2004). Data from these authors reveal magmatic textures, temperatures and lack of zoning or exsolution lamellae,  Megacrysts must have been derived from magmas related to the recent (_5 Ma to present) magmatism on Biu and Jos Plateau (Rankenburg et al, 2004), as suggested by these authors.

In addition, crystallization of the Cameroon Cpx preceded that of plagioclase in the basic rocks, while it was sub contemporaneous to alkali feldspar and scarce oligoclase crystallization in the silicic rocks (Salvioulo et al., 2000).

Since Late Cretaceous, the volcanic history of the CVL has been dominated by alkali magmatism (Fitton, J.G, 1987), corresponding to magmatic activity ranging from 66 to ~ 30Ma. Many authors argue that these plutonic complexes were found to be constituted of gabbro, syenite, and alkali granite, with composition ranging from alkali Basalt to trachyte and alkali rhyolite.

On the other hand, there are no isotopic age determinations for the older basalts

(Rankenburg et al, 2004) from the Jos Plateau; their age estimate was around Paleocene. In addition, younger volcanic of both the Biu and Jos Plateaux are characterized by abundant inclusions of mantle xenoliths and megacrysts, as stated by these authors. Furthermore, lavas along the CVL do not reflect simple fractionation or equilibrium crystallization products, but instead reflect mixing of primitive and evolved batches of magma shortly before eruption (Rankenburg et al, 2004).

Virtually, crustal contamination has affected the rocks to some extent. Hedberg (1969) studied the geology of the Sao Tomé and the southern Cameroon. He found that the oldest rocks in Sao Tomé are quartzo sandstones that outcrop on the Ubabudo Plantation in the east central part of the island. He also stated that the remainder of the island is volcanic with exception of recent bioclasticlimestones found near sea level at several points along the cost.

Moreover, isotopic analysis data reveals that the older plateau building rocks of the Biu Plateau range from basanites to trachybasalts. Whereas, the younger cinder cones have more variable chemistry ranging from basanite to phonolite (Rankenburg et al, 2004). Data from these authors also demonstrated that only the younger suites of the Biu and Jos Plateaux contain xenoliths (peridotites, pyroxenites and crustal rocks) and megacrysts.

However, the absence of cooling features, such as recrystallization, diffusional gradients or exsolution lamellae, commonly found in pyroxenite xenoliths rules out the interpretation that the megacrysts were precipitated by an earlier magmatic event and stored in cooler lithosphere for a significant amount of time (Rankenburg et al, 2004). Hence, these authors propose that the megacrysts derive from magmas related to the recent (_5Ma to present) magmatism on the Biu and Jos Plateau.