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Geology of the Suswa Region, Kenya

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Geology of the Suswa Region, Kenya GEOLOGIC HISTORY Legend PLEISTOCENE: Sediments Pl-tat Tandamara Trachyte SQv Reworked Ash %% %% %% %% % Kedong Flood (100 ka): sand and fine gravel that covers the Ol Tepesi plain to the south. Evidence for a % %% %% %% %% %% %% % flood is given by Baker & Mitchell (1976), and the source was likely the sudden emptying of a lake that % % Pl-mp % % % Maiella Pumice Scoria cones % % % % % Holocene-Upper Pleistocene % % % % % % % % % % % Geology of the% Suswa Region, Kenya filled the Kedong Basin in the map area. % % % % %% % % % % % % % % % % % % % % % %% % % % % Qvs % % % % %% % % Pl-ma % % Mau Ashes % Volcanic soils % %% %% % % Pleistocene (Calabrian) %% %% %% %% %% % Suswa (0.1 - 240 ka): trachyte & trachyphonolite shield volcano with some recent eruptive material still % %% %% %% %% %% %% %% % 36.0 °E For area to North see: Geology of the Naivasha Area, KGS Report 55 & report by Clarke et al. (1990) 36.5 °E % %% %% %% %% %% %% %% % unvegetated. The post-caldera lava cone Ol Doinyo Onyoke/Nyukie marks the overall summit at 2356m. Qvo % Pl-gt % % Pl-mb % % Mosiro Basalt %% % Volcanic Outwash, % %% % % Gesumeti Trachyte % -1.0 ° % %% % 2 % %% %% % 2 % % -1.0 ° % % 0 0 Pl-mp % Lt-ap %% % 0 % %% % 0 % %% %% % 4 % Lt-ap % % % % % SQv: Reworked pyroclastic material 2 % % % 0 0 % Lt-a % % % Pl-pt 0 % % 2 0 % Alluvial fan % %% % 2 2 % Pl-ab Magadi Trachyte % % Longonot %% %% % Oloombokoshi % % 2 % %% % S9: Recent phonolite lava % % ! % %% %% %% %% %% %% %% %% %% %% %% %% % S8: Late, post caldera phonolite lavas % % Pl-kl % % % % Lt-t Pl-tv % % Kedong Lake % % Longonot Tepesi Benmoreite % % % Lt-ap % % % % S7: Post caldera pyroclastics and phonolites % % % % % Lt-ap % 0 % % % 0 % % % S6: Early post caldera phonolite lava flows (0.1 +/- 0.01 Ma) 2 2 % % % % % Pl-tb 0 2 2 % Lt-a 2 % Lacustrine Sediments % 0 % 0 0 Ashes & Pumice Tepesi Basalt % Pl-ab % % % 0 S5: Enkorika fissure trachyte flows and domes Pl-m% p % % Lt-ap % % % % % % % 0 % % Nairagiengare 0 % % S4: Western Pumice Group; trachyte pumice lapilli fall tuffs 2 % %% 22 2 % ! % 00 ! % % Pl-lv % Kedong Flood % % % Limuru Pantellerite % % % % % Suswa S3: Ring Feeder Group; trachyte agglutinate flows and phonolite 0 % % Lt-ap % 0 % % 2 % Lt-ap % % 1 0 % 2 % 6 % 0 % % % 0 S2: Syncaldera pyroclastics; trachyte, carbonatites, trachybasalts % 2 % 0 % % % Pl-kt 2 % % % % % % North Kordjya % % % % S1 % S1: Precaldera lava shield trachytes % Volcanics % % % 00 % % 6 % % 1 % % %% %% %% %% %% % % %% %% %% % % % %% %% %% %% %% % % % %% %% % % %% % % % ¤¤¤¤ % % % % % % % % % % % %% % % % % % %%%% ¤¤¤¤ % %% % % % S2 Pleistocene (Gelasian) Longonot (0.2 - 400 ka): trachyte stratovolcano and associated deposits. Materials exposed in this map % Pleistocene (Upper) %% % % % S5 % % Qvo % ¤¤¤¤ % % % % % % % section are comprised of the Longonot Ash Member (3.3 ka) and Lower Trachyte (5.6-3.3 ka). The % % % % % % % % % % % % % Pl-cv % Pl-mt % % % % % % % trachyte lavas were related to cone building, and the airfall tuffs were produced by summit crater formation % S2 % S3 Mosiro Trachyte % % Cinder cones % % % % %% % % % %%%%% (Clarke et al. 1990). % % % % % % % % %% % 0 S1 % Ntulelei % 0 % % Pl-et % 0 % 2 % % % ! % % % % % S4 Ewaso Ngiro Trachyte %% %% %% %% %% % Pleistocene (Ionian) % %% % S3 S2 % %% %% %% %% %% % Akira Pumice (5-18 ka): trachytic pumice and ash beds created by plinian eruptions at Longonot. % %% % % % % % S2 % % % % % % E E E E % Pl-lut % % ! % % % Pl-ap % % Composed of 5 Members, both fall and surge deposits are recognized (Clarke et al. 1990). % S3 S5 Limuru Trachyte Akira Pumice %%% % % E E E E % % % % % % % % % 0 % % % % % % 0 S3 %% % % 0 %% % % E E E E % % % 2 % %% % % % P-Ma % Kedong Valley Tuff (20-40 ka): trachytic ignimbrites and associated fall deposits created by caldera % Pl-ab % S6 % % % % % % Pliocene % % Akira Basalt % % % % % % % % % 0 % % formation at Longonot. There are at least 5 ignimbrite units, each with a red-brown weathered top. In % % % % S6 0 % % % % % % % 8 %% % % % 1 % % % % some regions the pyroclastic glass and pumice has been replaced by calcite (Clarke et al. 1990). % Pl-lb % S7 0 % % % 18 % % % 00 Mau Tuffs 0 % % % Lolonito Basalt% % % A' % 0 % % % % % 2 % % % % % % % % % %% % %% %% % % % % Akira Basalt: benmoreite and mugearite lava flows with pyroclastic, scoria, and spatter cones (Clarke et al. %% Pl-kvt % S8 % A %% S2 % % % % % %%% ! Kedong Valley% Tuff % %% % Miocene % %%%% S8 % %% % % % %% % 1990). Youngest cone is unvegetated and may only be a few hundred years old (Macdonald et al. 2008). %%% %% % % % %% % % F % 0 % %% %% % % 0 S6 o % % 0 %% % % 2 % r % S9 % % Pl-bt % Mlt % % % SQv a Barajai Trach%yte % % % Lengitoto Trachyte % % % r % % % % % % Tandamara Trachyte: welded pyroclastics and some lavas (or rheomorphic ignmibrites) associated with Pl-ma S4 e % % 2 %% % % 0 a % % % % % % 0 S9 % % % % % % % 0 ! t % % % % % o % % the local elevation highs of Tandamara (Olomoroj) and Lolkidongoe (Clarke et al. 1990). Geographically % % % % % % % % % E % % % 20 % % % 00 % a % % S7 % % associated with the Lolonito and Akira Basalts (Macdonald et al. 2008). % 2 S3 % % % s % % % 2 % % % 0 t % % % % % % 0 s % % % % % % % e % S3 % % % ! % e %%%%%%%%%%%%%%%%%%% % % % : faults-larg% e City rivers Road-major % Lolonito Basalt (<0.45 Ma): vesicular basalt and trachybasalt, this is a possible earlier phase of the Akira % % %% G % %% 1 % % 8 % % % S3 e Noolpopong %% 0 1 % 0 % % 6 o Basalt (Macdonald et al. 2008). ! % % 0 % ! % l % 0 % %% o %% % %% % % % g %%% faults-sma% ll Town 200m-contour Road-minor % % % 0 % S3 y % 1800 S3 % % 0 % ! % % o % % 0 % f % % % 2 % % Barajai Trachyte: (0.37-0.41 Ma) five aphyric trachyte flows distinguished from the Plateau Trachytes by % % ! % t % %% % % % % h % %%%%%%%%%%%%%%% % %% % e Village Road-track % ! % % % Baker et. al (1988) based on element ratios; otherwise they are indistinguishable in hand sample. May be % % % ! N % %% % % % % a % % % % i % % % earliest eruptive products from Suswa. The mapped areas have been tentatively located around the r % % S1 % o % % %% % % % % % b % % % S6 STRUCTURE % % % % i % % % S3 % Barajai Gorge based on the written description of extent in Baker et. al (1988). S6 % % % A % % %% % % % % % The southern part of the area is cut by numerous "grid faults" that run roughly parallel to each other in a north/south fashion through r % % % % % % e % % % %% % % a % % % the center of the%% rift. These post-date the eruption of the Plateau Trachytes, but generally do not cut the Suswa volcanic pile. , % %% % % K %%% % %% Maiella Pumice: trachyte and possible panterllerite pumice and ash fall deposits. Probably plinian eruption % %%% G % %%% % %% 0 % % %%% % S %% 8 % %% % % ECONOMIC DEPOSITS 1 products from centers of the Olkaria Complex to the north (Clarke et al. 1990). t % % R % % r % 8 % % % % S9 % o e % % 0 % % Gu%ano deposits are found in lava-tunnels on Suswa, and the Munyu wa Gicheru deposits (1.65 - 1.96 Ma) on the eastern edge of p p % % 0 % % S1 %% e % o % Ongata Naado % Pl-kl % % % ! r % R % %%the Kedong basin (Trauth et al. 2007) have been quarried for diatomite (east of the map area). % t %% Mau Ashes (est. 0.6 Ma): comendite pyroclastics that blanket a large portion of the western rift flank. % %% % S1 9 %% S % %% % % 8 % % %% % % G % % % , % % % These ashes are particularly well exposed where the Ewaso Ngiro river cuts through the rift escarpments % ! % % K % D % % %% % % S2 % WATER RESOURCES , % % % i % % % g % % Pl-mt % a S1 % % % % % i (Crossley and Knight 1981). % e % t % % % Rivers from the Mau Highlands are generally perennial, as is the Ewaso (Uaso) Ngiro river. The Kedong river is likely seasonal, and r % a % % % % % % % l % A % % % % % % % % % S6 0 v % % 0 % % % the southeast section of this area has poor water supplies. Omenda (2007) reports that the water table in the rift floor is quite deep, % % % k % % e % % 0 0 % % S1 %% % % % o % % 8 % 6 % r % r % % %% % s % 1 % S1 % possibly over 300 m. 1 1 % % % Mosiro Basalt (0.6 Ma): a 8 % % transitional basalt with rare plagioclase phenocrysts up to 1.5cm length. Fissural % i % % 0 % % % o % 0 % % % % % % % % % N % % % % % S2 % n % % % % % Pl-pt S1 % % % % % % % % % e % % 0 % % % b % eruption from/near the Mosiro fault (Crossley and Knight 1981). % % % % % % % % h % 0 % % % % % y t % % % % % % % %% GEOTHERMAL PHENOMENA %% % % % 6 % % %% % 1 % f % % A %% % % % % 0 % 1 %% % % % 6 Pl-bt o % 0 % % % % % % % . 8 % % %% % 0 % % 1 Pl-pt Steam jets are associated with Suswa, and this area may have potential for geothermal energy production, as Omenda (2007) % % % % % % % G y % % % 0 % % % % % % % % % g % % % % % u % Plateau/MagadiTrachyte: (0.8-1.4 Ma) peralkaline flood trachyte that is very prominent between Suswa % % %% % % % % % o % suggests temperatures are in excess of 250°C at depth. Biggs et al. (2009) recognized periodic inflation/deflation of several rift % % % t l % % % %% h % MSe-l % % %%% o % % % % % % % % % % e % and Lake Natron in Tanzania. One of several expansive "flood trachytes" that cover the rift floor. % % % volcanoes including Suswa, which is interpreted as the result of an active magmatic system. Elevated carbon dioxide soil gas and an % % % % % % % % 1 % G % % % % 6 % % % : 1 % % active fumarole are associated with Mt. Margaret, a small trachytic cone just to the east of this map (Clarke et al. 1990). % 0 % % % % 1 % % e 4 % % % % % 1 0 % 1 % % % % 6 % % % e 0 % % % 4 4 % % % %% % % 0 % % % s % 0 % % % % % % 0 0 % % % % %% % 0 % % Ol Tepesi Basalts (1.4-1.65 Ma) and Benmoreites (1.42Ma): these two formations
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