Geochemistry and K/Ar results of the Mesozoic-Cenozoic plutonic and volcanic rocks from the Meratus Range, South Kalimantan


Author : U. Hartono, M.H.J. Dirk, P. Sanyoto & S. PermanadewiPublication : Bulletin of the Geological Society of MalaysiaVolume : 43Page : 49-61Year : 1999


Description

Bulletin of the Geological Society of Malaysia, Volume 43, Dec. 1999, pp. 49 - 61

 

Geochemistry and K/Ar results of the Mesozoic-Cenozoic plutonic and volcanic rocks from the Meratus Range, South Kalimantan

U. HARTONO, M.H.J. DIRK, P. SANYOTO AND S. PERMANADEWI

Geological Research and Development Centre, JI. Diponegoro 57 Bandung 40122, Indonesia

 

Abstract: New geochemical and K/Ar data of the plutonic and volcanic rocks from the Meratus Range are presented. The data show that three main periods of magmatic activities occurred in this area, i.e.  Lower Cretaceous (131-103 Ma) represented by granitoid rocks, Upper Cretaceous (82-66 Ma) characterised by volcanic/subvolcanic and granitoid rocks, and Upper Paleocene-Lower Miocene (62-19 Ma) represented by volcanic and subvolcanic rocks. Although some samples show plagiogranites, which may have been derived from an oceanic basaltic magma, the Lower Cretaceous granitoid rocks are mostly calc-alkaline, I-type, subducted related volcanic arc granite (VAG). Preliminary geochemical studies on the Upper Cretaceous and Tertiary volcanics and subvolcanics confirm that they were produced in an island arc environment. The Upper Cretaceous volcanics vary from medium-K basalt to medium- and high-K andesite and dacite and the Tertiary volcanics, except one sample of low-K basalt, are medium basalt, andesite and dacite. Except the low-K Tertiary basalt, those two volcanics are enriched in LILE (Ba, Rb, Th and K), LREE (La, Ce and Nd) and depleted Nb relative to K and La. However, unlike many other subducted related rocks, part of the Upper Cretaceous andesite and most of the Tertiary volcanic have high MgO concentrations. While the high MgO Upper Cretaceous volcanics may have been produced in an immature island arc, the origin of the Tertiary high MgO volcanics is still open for discussion. Considering the tectonic evolution of the Meratus Range, the Tertiary high MgO volcanic might have resulted from a reaction between ascending melts and hot mantle peridotite.

 

Abstrak: Data baru geokimia dan K/Ar dari Pegunungan Meratus, Kalimantan Selatan disajikan. Data ini menunjukkan adanya tiga perioda utama kegiatan magma: Kapur Awal (131-103 jtl) diwakili oleh batuan granitan, Kapur Akhir (82-66 jtl) dicirikan oleh batuan vulkanik/dan granitan, dan Paleocene Akhir-Miosen Awal (62-19 jtl) diwakili oleh batuan vulkanik dan subvulkanik. Walaupun sebagian batuan granitan tergolong di dalam plagiogranit, sebagai turunan batuan basalt oseanik, batuan granitan Kapur Awal merupakan batuan busur kepulauan, bersifat kalk-alkali, tipe-I (VAG). Demikian pula ciri geokimia batuan vulkanik/subvulkanik Kapur Akhir dan Tersiernya menunjukkan bahwa mereka terbentuk di lingkungan busur kepulauan. Batuan vulkanik Kapur Almir bervariasi dari basalt-K sedang, andesit K-sedang dan tinggi sampai dasit, sedangkan Batuan vulkanik Tersier, kecuali satu contoh basalt-K rendah, berupa basalt- dan andesit-K sedang serta dasit. Kecuali satu contoh basalt-K rendah, kedua kelompok batuan itu kaya akan kandungan LILE (Ba, Rb, Th dan K), LREE (La, Ce dan Nd) dan dicirikan oleh deplesi Nb relative terhadap K dan La. Namun demikian tidak seperti layaknya batuan gunungapi busur kepulauan yang lain, sebagian batuan vulkanik/subvulkanik Kapur Akhir dan umumnya batuan yang Tersier mengandung magnesium tinggi. Sementara batuan vulkanik bermagnesium tinggi yang berumur Kapur Akhir barangkali terbentuk di busur kepulauan yang masih "immature", genesa batuan bermagnesium tinggi yang berumur Tersier masih perlu didiskusikan. Dengan mempertimbangkan evolusi tektonik daerah Kalimantan Selatan, Batuan Gunungapi Tersier bermagnesium tinggi ini diduga sebagai hasil reaksi antara magma dan mantel peridotit panas. 

https://doi.org/10.7186/bgsm43199906