Petrography and geochemical characterization of a granite batholith in Idanre, southwestern Nigeria

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 indicates they 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) indicates that the batholith is Within Plate Granite (WPG)

Rare earth elements and fractionation of Zr-Hf and Y-Ho: implication to petrogenesis of idanre granite, Nigeria

Idanre area which is situated within the Nigerian shield is affected by orogenic activities accompanied by emplacement of Pan-African granitoids. This paper presents a new information on geochemical behaviour of Rare Earth Elements (REEs) and High Field Strength Elements (HFSEs) Zr-Hf and Y-Ho that can explain post magmatic processes relating to the origin and evolution of the Idanre granite. Zr-Hf, Hf-(Zr/Hf) and Y-Ho, (Y/Ho)-Ho variation diagrams depicted similar mobility and migration patterns for Zr, Hf, Y and Ho. Binary plots of Log Zr/Hf vs Log Hf, Log Y/Ho vs Log Ho; high LREE/HREE and negative Eu anomaly shows extensive plagioclase and calcic amphibole fractionation. High Ce/Yb values 113.49, 134.97, and 123.6 reflects low partial melting in the source rocks. Similar Zr/Hf ratios 39.16; 39.3 and 43.26 for members of the granite suite suggest a common source for the minimally differentiated magmatic fluid. Y/ Ho ratios of 27.15, 27.12 and 25.91 indicate that the rock units are comagmatic. Mean Zr/Hf (41.69) and Y/Ho (27.18) ratios indicate the host migmatite may be the source rock for the Idanre granite complex

Peranan subduksi terhadap batuan volkanik berusia neogen di Semenanjung Semporna: perspektif petrologi dan geokimia

Batuan volkanik Semenanjung Semporna yang berusia Neogen terkenal dengan ciri-ciri geokimia subduksi dan menyerupai-OIB. Proses subduksi yang berlaku semasa usia Miosen menyebabkan magmatisme kaitan-subduksi diganti dengan magmatisme menyerupai-OIB. Batuan volkanik berusia Neogen di Semenanjung Semporna boleh dibahagi kepada basalt, andesit basalt, andesit dan riolit. Corak yang ditunjukkan oleh unsur major dan unsur surih mencadangkan magma batuan volkanik di Semenanjung Semporna telah mengalami penghabluran berperingkat. Berdasarkan kepada tren daripada mantel primitif dan REE, 3 jenis tren dapat dikenal pasti: Kaitan-subduksi; susutan Nb, Ta, P dan Ti, pengayaan pada LILE dan LREE dan susutan terhadap HFSE, menyerupai-OIB; pengayaan Nb, Ta and Ti, dan MORB; mantel primitif dan REE hampir rata. Pola REE turut menunjukkan batuan volkanik mempunyai nilai anomali Eu negatif dan positif, yang menjelaskan pengfraksian plagioklas dan pengumpulan plagioklas berlaku di dalam magma. Berdasarkan kepada sekitaran tektonik untuk Semenanjung Semporna, batuan volkanik kaitan-subduksi mempunyai sekitaran lava arka kepulauan dan basalt pinggir kepingan. Segitiga FeOT-MgO-Al2O3 pula menunjukkan batuan volkanik kaitan-subduksi tersebar pada kawasan orogeni dan pemuaian pusat kepulauan. Sekitaran tektonik untuk batuan volkanik menyerupai-OIB (basalt, 18L5; andesit basalt, 18L9) dan MORB (andesit basalt, 11L5) ialah basalt dalam-kepingan dan lava dalam-kepingan yang terbentuk di sekitaran benua (Segitiga FeOT-MgO-Al2O3)

Petrology and geochemical features of Semporna volcanic rocks, South-East Sabah, Malaysia

The volcanic rocks in Semporna Peninsula, Sabah, Malaysia forms parts of the Miocene subjected slab during the Miocene-Pliocene orogeny. This study presents new petrographic and geochemical data of volcanic rocks in Semporna area. The volcanic rocks range in composition from basaltic andesite, andesite, dacite to rhyolite, with most of the volcanic shows calc-alkaline affinity with a minor tholeiitic feature. The trace elements shows enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE) suggesting that the volcanic rocks have similar geochemical patterns and might come from similar magma source. The petrochemical data suggests that volcanic rocks of Semporna shows characteristic of subduction zone (negative Nb, Ta, and Ti). Decreasing magnitude of Europium anomalies from intermediate to acid lavas suggests an important role of plagioclase in the fractional crystallization. Negative Ce anomaly in part of Semporna volcanic rocks suggest that those volcanic rocks may related with emergence of oxygenated deep-sea environment. Tectonic diagrams showed that the Semporna volcanic rocks were formed in an island arc setting