Benom Complex: Evidence of magmatic origin

Author : B.T. Yong, Azman A. Ghani, T.T. Khoo & Shafari
Publication : Bulletin of the Geological Society of Malaysia
Page : 55-60
Volume Number : 48
Year : 2004

Bulletin of the Geological Society of Malaysia, Volume 48, June 2004, pp. 55-60


Benom Complex: Evidence of magmatic origin


Department of Geology, University of Malaya, 50603 Kuala Lumpur


Abstract: The study area is underlain predominantly by syenite, monzonite and gabbro. The area lies on the western flank of Benom batholith. Field mapping has proven the intrusive nature of the suite of rocks into the surrounding country rocks. The country rocks were contact metamorphosed into various hornfelses of hornblende hornfels facies. The occurrence of a crystal settling layer within the suite of rocks is particularly convincing of an igneous origin. Moreover, the occurrence of accidental xenoliths in these igneous rocks, which correspond to the aureole rocks, indicate that the xenoliths were incorporated during magma intrusion. The presence of different types of cognate xenoliths ranging from pyroxinite to gabbroic and syenitic in composition, is also widespread in the study area. The occurrence of planar flow structure in the syenite and monzonite defined by megacrystic K-feldspar, is evident of magmatic flow. Petrographic studies reveal that igneous foliation in the suite of rocks is made up of euhedral to subhedral plagioclase and K-feldspar crystals.

Abstrak: Kawasan kajian terdiri daripada batuan syenit, monzonit dan gabro. Kawasan ini terletak di sebelah barat Komplek Benom. Pemetaan lapangan menunjukkan batuan ini menerobos batuan sekelilingnya yang terdiri daripada metamorfisma hornfel daripada fasis hornblende hornfel. Kewujudan lapisan pemendapan hablur di dalam suit batuan ini mencadangkan asalan igneus. Tambahan lagi kewujudan xenolit yang mempunyai ciri-ciri persamaan dengan batuan sekeliling mencadangkan xenolit tersebut telah terjatuh ke dalam magma semasa penerobosan magma tersebut. Kewujudan pelbagai jenis xenolit kognat berjulat daripada piroksinit ke gabroik dan syenitik juga banyak dijumpai di kawasan kajian. Kajian petrografi menunjukkan bahawa foliasi igneus di dalam batuan ini dibentuk oleh plagioklas yang berbentuk euhedral to subhedral plagioclase dan alkali feldspar.

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