Petrology of the Freetown Layered Complex, Sierra Leone: Part I. Stratigraphy and Mineral-Chemical Evidence for Multiple Magma Injection
Abstract
The Freetown layered complex, located on the western coast of Sierra Leone, is a rift-related tholeiitic intrusion associated with the Jurassic (∼193 Ma) opening of the Atlantic Ocean at midlatitude. The complex is ∼ 60 km long, 14 km wide, and 7 km thick along a major E-W traverse extending from Waterloo to York. Gravity data and dips of laminations in the layered rocks suggest that the intrusive complex is lopolithic in shape, with some parts presently being submarine. The exposed rocks consist of a rhythmically layered sequence of troctolite, olivine gabbro, gabbronorite, gabbro, and anorthosite. The complex has been divided into four zones delineated by (1) topographic expression, whereby the base of each zone forms a scarp, and the top forms dip slopes and strike valleys; and (2) cyclical repetition of rock types (Wells, 1962). A new detailed stratigraphic section along the Waterloo-York traverse is presented, in which Zone 3 is subdivided into an upper 2000-m-thick anorthosite-gabbro interval and a lower 1700-m-thick rhythmically layered subzone. Inverted pigeonite first became a cumulus phase at the bottom of Zone 2, before disappearing near the middle of Zone 3 at the anorthosite-gabbro interval, only to reappear at the top of Zone 4 with cumulus titanomagnetite. Mineral compositions in the complex range from An72 to An72 plagioclase, Fo56 to Fo75 olivine, En38.5 to En44.8 augite, and En54.9 to En74.6 orthopyroxene. The compositions of plagioclase and olivine in Zone…
Integrity signals
Registry
Cites
Statistics
Claims the paper makes
Claims other papers make about this one
Each is checked against this paper’s own text: does it say what the citing paper says it does?
The variable thickness loamy to clay soils and poorly consolidated, weathered rock of the mountainside result from humid tropical weathering of olivine and plagioclase-rich rocks of the Freetown Igneous Complex.
“The variable thickness loamy to clay soils (Usamah 2017) and poorly consolidated, weathered rock of the mountainside is a result of the humid tropical weathering of olivine and plagioclase-rich rocks (anorthosite, troctolite, olivine gabbro, and related mafic rock types; Chalokwu et al. 1995) of the Freetown Igneous Complex of layered igneous intrusives (Goodenough et al. 2018).”
From The cost of rapid and haphazard urbanization: lessons learned from the Freetown landslide disaster (2019) · cites this paper as Chalokwu et al. 1995
Bedrock geology across the Freetown Peninsula is dominated by the Freetown Layered Complex, a 65 km long, 14 km wide, 7 km thick tholeiitic intrusion that intruded the West African Craton during the Early Jurassic about 200 Ma.
“Bedrock geology across the Freetown Peninsula is dominated by the Freetown Layered Complex, a 65 km long, 14 km wide, 7 km thick tholeiitic intrusion which intruded the West African Craton during the Early Jurassic ~200 Ma (Callegaro et al 2017; Chalokwu et al. 1995; Chalokwu, 2001).”
From The 2017 Regent Landslide, Freetown Peninsula, Sierra Leone (2019) · cites this paper as Chalokwu et al. 1995
Cites
Dixey, F. (1922) · Quarterly Journal of the Geological Society of London · doi:10.1144/gsl.jgs.1922.078.01-04.12 · Cited by 17 · see citing works
Flagged first, then by citations
Cited by
Sorted by citations
The cost of rapid and haphazard urbanization: lessons learned from the Freetown landslide disaster
Cui, Y., Cheng, D., Choi, C. E., Jin, W., Lei, Y., & Kargel, J. S. (2019) · Landslides · doi:10.1007/s10346-019-01167-x · Cited by 175 · see citing works
The 2017 Regent Landslide, Freetown Peninsula, Sierra Leone
Redshaw, P., Boon, D., Campbell, G., Willis, M., Mattai, J., Free, M., Jordan, C., Kemp, S. J., Morley, A., & Thomas, M. (2019) · Quarterly Journal of Engineering Geology and Hydrogeology · doi:10.1144/qjegh2018-187 · Cited by 23 · see citing works
- Authors
- Chalokwu, C. I., Armitage, A. E., Seney, P. J., Wurie, C. A., & Bersch, M.
- Affiliations
- Auburn University (US)
- b Geological Surveys, , Ministry of Mines , Freetown, Sierra Leone
- University of Alabama (US)
- Venue
- International Geology Review
- Publisher
- Informa UK Limited
- Published
- 1995-03
- Volume
- 37
- Issue
- 3
- Pages
- 230-253
- ISSN
- 0020-6814 (ISSN-L)
- 1938-2839
- OpenAlex
- W2040792234
- Cited by
- 16
- References
- 1
- Citations by year
- 2026: 1 · 2024: 2 · 2021: 2 · 2020: 1 · 2019: 3 · 2018: 1 · 2017: 2
- FWCI
- 0.00
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- International Geology Review (publishedVersion)
- Funders
- National Science Foundation
- Geological Society of America
- Topics
- Physical Sciences › Earth and Planetary Sciences › Geophysics › Geological and Geochemical Analysis
- Physical Sciences › Earth and Planetary Sciences › Geology › Geological and Geophysical Studies
- Physical Sciences › Earth and Planetary Sciences › Geochemistry and Petrology › Geochemistry and Elemental Analysis
- Keywords
- layered intrusions, Atlantic Ocean opening, lopolith, stratigraphy, mineral chemistry, cryptic variation, olivine Fo content, troctolite
About these checks
Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
Statistics and arithmetic are recomputed, not judged.
Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.
What counts as a claim ›How we measure confidence ›How we check this ›
Are you an author, or do you see a problem with this page? Request a review
