Neil’s Valley- A peep from the Jurassic Jos into the Precambrian Past
(Posted on Thursday, 22nd March 2011)

Neil’s valley is located on the NE outskirt of Jos, Plateau State, North-central Nigeria.

 

 

 

 

 

The entire plateau is inderlain by a suite of granites that intruded the basement in the Jurassic times (about 160 Ma). These granites intruded ring fractures caused by cauldron subsidence.

The plutons are called Younger Granites to distinguish them from the older Pan-African granites of the Precambrian Basement Complex, which were described as Older Granites.

 

They form one of the most impressive ring dyke provinces in the world. The province forms a southern extension of a series of granitic plutons and ring dyke complexes occurring to the north in Zinder, Air, Ahaggar, Tibesti and Adar des lforas regions of the Central Sahara.

The Younger Granites commonly overlap one another in part and many form chain-like alignments, igneous activity having ended in each centre before the initiation of a new centre. Ring-dykes occur both as regular arcs and in polygonal forms.

Everywhere in the province, you find the intrusions (ring-dyke complexes).

But at Neils Valley (Latitude. 9.9833333°, Longitude. 8.95° ), we find something interesting:

We approach the valley through a road from Jos city.

The terrain is underlain by the younger granites just as other parts of the province.

 

As one approaches the valley bottom, the whole area is stremn with pebbles and boulders of Welded Tuff and Breccies.

 

Suddenly, at the floor of Neil’s Valley, we find exposures of precambrian Migmatite Gneisses in a stream channel.

 

The migmatites trend 122º and dip to the north.

 

The Migmatites are the country rock which was intruded by the Younger Granites in the Jurassic Period.

This is unusual! What’s happening here????

It is simple!

The picture gets clearer when viewed from space.

 

 

 

Neil’s valley is actually one of the few surviving fractures that wasn’t exploited during the Jurassic magmatic intrusions that formed the Younger Granites.

Isn’t that awesome?

Virtually all the pre-existing fractures in the area were intruded and obliterated by the magma, and here we find one that survived that ‘plutonic swarm’.

Maybe we should just give Neil’s Valley a new name: ‘The Mega-Museum of the Precambrian in a Jurassic City’.

 

A Roadtrip through Oke-Mesi fold belt (Part 1)
(Posted on Thursday, 10th Feb. 2011)

Straddling the boundary between Ekiti and Osun States of Nigeria, West Africa, is an enormous and narrow area of elevated land known as Effon Ridge. By definition, a ridge is a long, narrow area of elevated land, usually with steep sides. Effon ridge stretches along a NS strike through a distance of a about 45km and spans a maximum width of approximately 18km. The geology of the ridge is a subtly interesting one as the ridge also consists of a long narrow ‘valley’ at its core that stretches the entire lenght of the ridge. The two arms of the ridge (the opposite elevated lands ) and the ‘valley’ floor in-between are also underlain by two slightly different lithologies. Therefore, the question pops up: How was this interesting ridge formed?

Lets take a east-west road trip across the ridge. We gain access into the ridge from the east through Ita-Ido pass.

At Ita-Ido pass, a roadcut reveals the constituent rock of the eastern ridge-arm as shown in the picture below. It is composed of massive quartzite . Note the steep dips to the east (direction and degree of inclination) of the rocks.

East-dipping quartzites at Ita Ido pass As one leaves the eastern ridge-arm and slowly descends into the gently undulating central valley, the lithology (rock type) changes into quartze-schist (foliated quartzite) as seen below.

At Effon Alaaye and Oke-Mesi towns- located on the western ridge-arm, we again encounter the massive quartzites.
What exactly is happening here?

Effon Ridge is composed of the Effon Psaamitic formation which is essentially the major fold structure within the Oke-MEsi fold belt. The psaamite formation have been folded antiformally along a NNE-SSW strike, with the rocks on the eastern side of the fold dipping to the east, and on the western side the rocks dip to the west and to the east in different areas. The later suggests the presence of minor folds on the main Okemesi fold structure. Oke-Mesi fold was formed during the deformational phase of the Pan-African orogeny (550±100 m.a.).

SW Nigeria and Her Seismicity
(Posted on Friday, 21st Jan. 2011)

The increase in reports of tremors affecting the SW Nigeria subregion within the past two decades is infact disturbing. And as a passionate geologist, my inquisitive mind, having gone through alot of research papers on the Ifewara-Zungeru mega-structure has been confronted with a number of questions among which were this:
1. Considering the spatial coverage of the effects of the tremors, is it possible that these seismicity had been produced by movements along a series of lithospheric faults cross-cutting the subregion, and not just the ifewara fault?
2. Would there not have been an increased lubrication along the source fracture-planes due to the repeated movements over time? If number two is probable, it means the subregion in study is gradually nearing a moment of earthquake disaster in the future if these tremors keep recurring. If you have any thoughts on this, kindly drop a note in the comment box below this page. Thanks.
Tags: Earthquakes, Seismicity, Nigeria, Faults, Tremors, Ifewara Fault, Zungeru Fault

Past Works

A. TALUS CAVES: GEOTOURIST ATTRACTIONS FORMED BY SPHEROIDAL AND EXFOLIATION WEATHERING ON AKURE-ADO INSELBERGS, SOUTHWESTERN NIGERIA. F. Kolawole and A.Y.B. Anifowose. (Paper presented at NMGS Conference, 10th March 2011).
Tags: Talus cave, Granite cave, Inselberg, Ikere-Ado Batholith, Geo-tourism.

B.       Kolawole F. & A. Y. B. Anifowose: Remote Sensing Analysis of a Dextral Discontinuity along the Zungeru Part of the Ifewara-Zungeru Megastructure, Nigeria.
(Research paper presented at the Nigerian Union of Planetary And Radio Sciences (NUPRS) Conference 2010 on Oct. 13-15, 2010).
Research paper now published in the Indian Journal of Science and Technology (vol.4, issue 1, 2011) Download Here
Tags: Remote Sensing, Ifewara-Zungeru, Metasediments, Bida Basin, Structural Mapping.

C.        A. Y. B. Anifowose & Kolawole F.: Geotourism Potentials of the Idanre Hills, Nigeria.
(Research paper presented at the Faculty of Science Annual Scientific Conference, OAU, Ife on Sept. 14-16, 2010).
Tags: Idanre Hills, Batholith, Geo-tourism.

D.       A. Y. B. Anifowose & Kolawole F.: Emplacement Tectonics of the Idanre Batholith, Southwestern Nigeria.
(Research paper received for review and publication by Journal of African Earth Sciences).
Tags:  Idanre, Batholith, Tectonism, Faults, Granite.

 

Presently on-going Research:

- Mapping of lithospheric faults in SW-Nigeria.

- The structural geology of Ebomi Lake Area, SW Nigeria.