Petrography and Geochemical Characterization of a Granite Batholith in Idanre, Southwestern Nigeria

Abstract

Idanre granite batholith in southwestern Nigeria contain three rock types, namely, Older granite undifferentiated (OGu), Older granite porphyritic (OGp) and Older granite fine-grained (OGf). The granitoids intruded into a basement rock of primarily migmatite gneiss. Petrography indicates that quartz, orthoclase, hornblende, and biotite are common to all members while microcline is more prominent in OGp and plagioclase is poorly represented in OGf. Despite minor differences in petrographic features, the granite units generally have similar geochemical relationships. The average SiO2 contents in OGp (70.49%), OGu (68.7%) and OGf (65.8%) are comparable to similar Pan-African suites located in eastern and northern Nigeria. Na2O+K2O-CaO versus SiO2 diagram shows all the granite members are calcic, K2O vs SiO2 plot classify the granites as high-K calcic alkali to shoshonitic. ANK vs ACNK plot indicatesthey are peraluminous. Plot of A/CNK vs SiO2 and K2O vs Na2O diagrams classified the rock as S-type granite. The granitoids are calc-alkaline with elevated Na2O (>2.6%) and Al/(Na2O+CaO) contents (OGu, 2.1-3.4; OGp, 2.4-3.1 and OGf, 2.2-2.9). The tectonic diagram (Rb vs (Y+Nb) indicatesthatthe batholith is Within Plate Granite (WPG.

Field and petrographic studies of Basement Complex rocks in Saigbe and Environs, North-Central, Nigeria

“…Saigbe lies on the outskirt of Minna area, within the North-South trending Pan African (Neoprotozoic -Cambrian age) orogenic belt (i.e., the Basement Complex of NorthwesternNigeria) which lies towards the East, West and North of Africa (Figure 2; Rahaman, 1988;Goodenough et al, 2014;Lawal et al, 2017b;Ejiga, 2022). The major rock types in the area, similar to the rest of northern Nigeria, are deformed, Pan-African schists and granites and Archeanmigmatitic gneisses (Amadi et al, 2017;Akinola et al, 2021). An extensive, NNE-SSW trending faults and fractures constitute the major structural component of the geology of the area (Figure 2).…”

“…An extensive, NNE-SSW trending faults and fractures constitute the major structural component of the geology of the area (Figure 2). The Pan African orogeny itself is a tectonothermal, collision-related event associated with the slipping of the Eastward dipping Benioff's zone under the Pan-African region (Bessoles and Trompette, 1980;Akinola et al, 2021). These Pan African rock types comprises both "syn-collisional and post-collisional" (those typified high content of lithophiles and rare earth elements) alkaline and potassic, plutonic rocks (such as the batholiths of Abuja, Minna, and Bauchi areas; Goodenough et al, 2014).…”

“…These Pan African rock types comprises both "syn-collisional and post-collisional" (those typified high content of lithophiles and rare earth elements) alkaline and potassic, plutonic rocks (such as the batholiths of Abuja, Minna, and Bauchi areas; Goodenough et al, 2014). The plutons are distributed in "Western and Eastern" Nigeria and are said to be evident of Precambrian tectonic and magmatic activities that resulted in crustal building whose origin has been linked widespread orogeny and plutonism associated with the breakup of the supercontinent, continental drift and seafloor spreading that affected the region occupied by the Pan-African countries (Dada et al, 1995;Ferre et al, 1998;Goodenough et al, 2014).These events happened from 790-760 Ma and 650-450 Ma ago with mixed mantle and crustal magmas (Goodenough et al, 2014) or simply over 600 Ma ago (Akinola et al, 2021).…”