Is There any Change from Magma Mixing in Kelud Characteristics?

International Journal of Scientific and Technical Research in Engineering (IJSTRE)
www.ijstre.com Volume 2 Issue 11 ǁ November 2017.
Manuscript id. 726690163 www.ijstre.com Page 16
Is There any Change from Magma Mixing in Kelud
Characteristics?
Achmad Djumarma Wirakusumah1
and Hanik Humaida2
1
(Institue of Energy and Mineral Akamigas, Mininstry of Energy and Mineral Resources of Indonesia)
2
(Geological Agency, Mininstry of Energy and Mineral Resources of Indonesia)
ade.wirakusumah@gmail.com
ABSTRACT : Kelud volcano is located in East Java Province, Indonesia. According to Geochemical study of
Kelud Volcano, it could be divided into 3 periods which are Kelud I (older than 100 ky BP), Kelud II (40 – 100
ky BP), and Kelud III (younger than 40 ky BP). A specific petrogenesis of Kelud are dominatad by magma
mixing and fractional crystalization. New petrological data from Kelud volcano was taken through products of
the eruption in 1990 (Vulkanian type), 2007 (Lava plug forming) and 2014 (Plinian type). Petrographic study
on these rocks showed that reverse and oscilatory zoning on plagioclases, Shieve-like and corroded textures on
plagioclases and pyroxenes are common. However, normal zoning textures were also found on plagioclases and
pyroxenes. Whole rock study on these rocks showed all rocks were classified into Basalt to Andesite in
composition with calc-alkaline group. The study indicated that their magma origin derrived from slab with
fractional crystallization during in the magma reservoir, and magma mixing processes are dominant expecially
in magma pockets. Concequently, the magma origin and petrogenesis of Kelud magma after the 1966 eruption
are still the same as those of old magma of Kelud.
KEYWORDS : Fractional crystalization, magma mixing, petrogenesis.
I. INTRODUCTION
Mt Kelud is an active andesitic volcano in East Java, part of the Sunda arc, lying within a volcanic belt
that is about 150 km above the north deeping Benioff Zone, where the Indian Ocean Plate is beeing subducted
beneath Java (Fig 1and 2) [1].
Geological map of Kelud volcano have been made based on a convensional field survey during 1985-
1986 on the whole body of the volcano such as [2], also [3] based on a field survei on the summit area. On the
other hand, some petrographic study on some Kelud volcanic rocks at summit area has been made such as [4].
In 1987 the author remapped geologically Mt. Kelut much more detail than those done by the previous
authors. The map was done based on the volcano-stratigraphy method which was compiled by an interpretation
of aerial photographs of Kelud volcano. Rock units were divided on the basis of their source (vein origin) and
their eruption mechanism and cyclus. According to Geochemical study of Kelud Volcano, it could be divided
into 3 periods which are Kelud I (older than 100 ky BP), Kelud II (40 – 100 ky BP), and Kelud III (younger than
40 ky BP) [5]. The Kelud volcanic rock can be classified into 3 kinds of rocks such as basalt, basaltic andesite
and andesite [5]. The data was limited up to Kelud volcanic rocks derrived from eruptions products before the
1966 Kelud eruption.
According to last three Kelud eruptions which were in 1990 as a Vulkanian eruption type, in 2007 as a
Lava plug production, and in 2014 as a Plinian type eruption, is there any change in petrogenetic characteristics
expecially from magma mixing at Kelud? This question is interested to answer as it is closely related to Kelud
morphology which is irreguler and many found old craters at the summit area. These eruptions also occurred
through the recent crater (Kelud crater).

Is There any Change from Magma Mixing in Kelud Characteristics ?
Figure 1. Tectonics in Indonesian Archipelago [5]. Figure 2. Map of Kelud volcano and its
surroundings [5].
II. METHOD.
To understand wether there is a change or not in petrogenesis of Kelud magma after the 1966 eruption,
a survey and rocks sampling for those of Kelud volcanic rocks which were produced through the 1990, 2007,
and 2014 eruptions. Four samples of those of 2007, three samples of 2014, and some from 1990 samples were
taken in this study. These activities were condacted in 2016 (fig. 3).
Thin section of the above rock samples of Kelud were made in the Laboratory of Geological Agency at
Bandung. Petrographic analysis was done using Polarized Microscopes in the Geological Laboratory of Institute
of Energy and Mineral at Cepu, and in the Geological Laboratory of the Geological Agency at Yogyakarta.
Zoning analysis to know the magmatism evolution processes below Kelud volcano by using a partly-
quantitative method “Scanning Electron Microprobe” (SEM) was done in the Geochemical Laboratory at the
Geological Agency in Yogyakarta.
Preparation and Whole Rock Chemical analysis on those rock samples by using the XRF were done in
the Geochemical Laboratory at the Geological Agency at Yogyakarta (fig. 4).
Products of petrographic analysis and their whole rock chemiscal analysis for Kelud rocks older than
rocks product erupted before the 1966 Kelud eruption had been done [1], [5] and [6]. Finnally the last products
(Kelud volcanic rocks of 1990, 2007, and 2014) can be understood.
Figure 3. Situation of Kelud summit area. Figrure 4. XRF equipment used for whole rock chemical
analysis in this study.
III. DATA AND DISCUSSIONS
3.1. Geologi of Kelud Volcano and its surroundings.
Ten craters have been identified on the summit area and the west flank of Mt. Kelut with their volcanic
products. Their age relationships imply that the eruption center has moved clockwise (fig. 5) starting from

Lirang crater as the oldest (238 Ky BP) and Kelut crater as the youngest (perhaps 4 Ky BP) which are controlled
by the geologic structure at Kelud complex. Pre-Kelut rocks consist of volcanic rocks belonging to
Figure 5. Mecanism of crater forming at Kelud complex [1].
Figure 6. Volcano-stratigraphy of Kelud volcanic rocks [5].
South-mountain (TP), Mt. Anjasmoro (Av) and Mt. Butak and Mt. Kawi. (KBv). Mt. Kelut rock consists of
many kinds of lava flows, lava domes, pyroclastic flows and pyroclastic airfall deposits. The geologic map of
Kelud volcano was made by using volcano stratigraphy method and has estabished in [5]. The Kelut volcanic
rocks were erupted from ten craters on Kelut complex together with some volcanic products from two parasitic.
Stratigraphy of Mt. Kelud was shown in fig. 6 [5]. The Kelud volcanic rock can be classified into 3 kinds of
rocks such us basalt, basaltic andesite and andesite. The only basalt is formed from the lava flow of Gupit
(Klfg), while andesite from lava dome of Kombang (Kldk) and Keramasan (Kldr). The rest of the kelut volcanic
rocks are all basaltic andesites

In the last three centuris, Kelud volcano erupted in 1811, 1825, 1835, 1848, 1851, 1864, 1901, 1919,
1951, 1966, 1990, 2007, and 2014. Kelud volcano is an explosive volcano with the quiencing or time interval
between eruptions varies from16 to 24 years [7]. The rock samples of Kelud eruption products of 1990, 2007,
and 2014 were ejected from Kelud crater as the youngest crater (fig. 5).
3.2. Petrographical study.
Two major time breaks have occurred during eruption story of Mt.Kelut. The first one occurred
between the Gajahmungkur and Tumpak craters life. Kramasan dome (about 100 ky BP) was produced as
parasitic cone at the late stage of the Gajahmungkur crater. The second break occurred between The Sumbing II
and Gupit crater life (fig.6) . Tumpak Lava Dome (about 40 ky BP) is the late stage activity from the Gupit
crater . Base upon recognition of the 2 eruption breaks during Mt.Kelud activity, the petrology Mt.Kelud will be
divided into 3 periods. These are Kelud I (older than 100 Ka), Kelud II (40-100 Ka), and Kelud III (younger
than 40 Ka) [5].
According to the petrographic study on all lavas of Mt Kelud before 1966 indicate the solid phase were
in equilibrium with the liquid before the quenching stage reflecting that the magma had experienced of
fractional crystalization. However, many basaltic andesite of Kelud I, Kelud II, and Kelud III showed reversal
zoning pattern in texture on plagioclase and pyroxene. This features reflect indicate a disequilibrium magma
condition. However normal zoning in plagioclases and pyroxenes as indicate normal differentitation sequence.
Rock samples from Kelud eruption products of 1990 [6] as Vulkanian type, those of 2007 producing a
lava plug, and those of 2014 as a Plinian type petrographically showed resorbed crystal of plagioclase or
pyroxene and sieve-like texture on plagioclase, rounded crystals of plagioclase and pyroxene, and revers and
oscilatory zoning textures. These reflect that have solid phases were in equilibrium with the liquid before the
quenching stage (fig. 7). However, textures of porphyritic, sometimes glomeroporphyritic, rich in phenocrysts
Normal zoning pada
Plagioklas (KD-1B)
Oscilatory zoning dari Ca
pada Plagioklas (KD-1A)
Figure 7. Normal Zoning on plagioclase from lava of
2007 eruption product.
Figure 8. Oscilatory zoning on plagioclase from pumice
of pyroclastic flow as the2014 eruption product.
(fine-medium, sometime coarse grained) with a microcrystalline or glassy groundmass were also found. Most of
the lavas consist of more than 50% phenocrysts and the most abundan phenocrysts phase is plagioclase followed
by pyroxene, opaques and sometimes amphibole, normal zoning on plagioclase (fig. 8). This phenocryst
assemblage, reflects that have solid phases were in equilibrium with the liquid before the quenching stage.
3.3. Whole Rock Chemical Study.
Whole rock chemistry from Kelut volcano are classified as medium-K basalt, basaltic andesite and
andesite with calc-alkalic suite [5].
Whole rock chemical study on Kelud volcanic of 1990, 2007, and 2014 eruption products mostly
classified into basalic andesite with a few of them are basalt and andesite. Composition of SiO2, K2O, Rb, and
Sr are still in the range of those belong to the groups of Kelud I, of Kelud II, and of Kelud III.
According to the plot of Kelud rocks into the Harker Diagram, positive corelation between K2O and
Na2O to SiO2 and negative coreletion between CaO and Al2O3 to SiO2 are compatible with performance of

huge of plagioclase as phenocrysts in the rock samples of the eruption products of 1990, 2007, and 2014 which
are also the same composition as those of rock samples of Kelud I, Kelud II, and Kelud III.
Increasing in Rb, Ba and Sr versus SiO2 in all Kelud rocks (including the last three eruption products)
are compatible with process of fractional crystalization as a part of magma differentiation process.
According to the spider diagram plot for trace elemnts of Kelud rocks samples (including the last three
eruption products) which are nomalized to MORB, an enrichment to Ba and Sr and depleting to Zr, Y, and Nb.
These indicate that the Kelud volcanic rocks were derrived from impurity primitive magma. The enrichment in
Sr and Ba indicates that magma of Kelud volcano were derrived from metasomatism process which were
released from subduction slab fluids. This condition is compatible that the subduction zone beneath Kelud
volcano which is about 150 km depth.
3.4.Discussion
Petrographic data from Kelud rock of the 1990, 2007, and 2014 eruption products show strong
evidence of magma mixing. Resorption texture on pyroxene and plagioclase, sieve-like texture, reverse and
oscilatory zoning are common in these rocks. The resorbed and rounded pyroxene was formed because of
Figure 9. A magma mixing model. The magma reservoir beneath
Kelud volcano.
Figure 10. A model of magma origin beneath
Kelud volcano.
1 = metasomatim process
2 = fcartional crystalization.
3 = magma mixing.
melted on inner and outer part of mineral crysta1 when a basaltic magma coming into the previous magma. In
addition the inconsistency of the relation between major and trace elements and time reveals a magma mixing as
well. This features were also found in the old Kelud vocanic rocks. Thus, up to the last Kelud eruption, magma
mixing features process are probably still available for magmatism beneath Kelud volcano.
On the other hand, many features of normal zoning, glomero-porfiritic in the last three Kelut eruption
products indicating this liquid had experience of fractional crystalization. These features were also found in
many old Kelud rocks.
Consequently, the petrogenesis of Kelud magma which having experience of magma mixing and
fractional crystalization as one of the characteristicsof Kelud magmatism processes is still remain up to the last
Kelud eruption product (2014). Thus the model of recent magmatism petrogenesis beneath Kelud volcano is still
available as shown in fig. 9 [5]. According to the petrographic and whole rock chemical study, a model to show
magma origin for magmatism beneath Kelud volcano is shown in fig. 10.
IV. CONCLUSION
Kelud volcano has eruption points consisting of 10 craters and 2 parasitic lava plug. The eruption center has
moved clockwise starting from Lirang (the oldest at about 238 ka) to Kelud crater (the youngest at about 4 ka)
producing eruption rocks with composition of basalt to andesite but they are dominated by basaltic andesite with

calc-alkaline suite. According to the geologic structure and chemical composition, Kelut volcanic rocks are
divided into 3 periods. Kelut I for rocks older than 100 ka which were erupted from Lirang, Gadjahmungkur
crater and Kramasan dome ; Kelud II Tumpak erupted from Sumbing 1 and Sumbing 2 craters at 100 ka to 40 ka
; Kelud III rocks erupted from Dargo, Gupit, Badak 1, Badak 2 and Kelut craters since 40 ka. The last three
Kelud eruption products of 1990, 2007, and 2014 are included into Kelud III. Many of the last three
rock samples are petrographically and chemically show a lot of evidences indicating that the magma
have experience of magma mixing, and the rest show evidences indicating that the rocks have
experience of fractional crystalization. These features indicate that magma origin and magma genesis
during Kelud volcanic complex forming have remain characteristic. Magma mixing characteristic at
Kelud is compatible with the condition of craters position which were change from place to other
places producing irreguler mountain form at the summit area.
REFERENCES
[1] Wirakusumah, A.D., Some Studies of Petrology, Volcanology and structures of Mt. Kelut, East Java,
Indonesia. unpublished. Doctoral Diss, Victoria University of Wellington, New Zealand, 1991, 461 pp.
[2] Zaenudin, A., Dana, I., Wahyudin, D., and Hadisantono, R. D, 2000 , Peta Geologi G Kelut, JawaTimur
, Direktorat Vulkanologi, Direktorat Jenderal Geologi dan Sumber Daya Mineral, Kementerian Energi
dan Sumber Daya Mineral.
[3] Pardiyanto, L., , G. Kelut, Geologi, Aktivitas dan Pengawasannya, Unpublised script , Institute of
Technology of Bandung, Indonesia, 1968.
[4] Kemmerling, G. L. L., , De Uitborstirtg van den G. Keloet in den racht van den 19 den op den 20 sten
mei 1919, Vulk. Meded., II, Landsdrukkerij-Welterreden, 1921.
[5] Wirakusumah, A.D., Magma Mixing Processes at Mt Kelut, East Java , Proc. of the 22nd
annual
convention of the Indonesian Association of Geologist in 1993, 1993
[6] Humaida, H., Brotopuspito, K.S., Pranowo, H.D., dan Narsito, Pemodelan Perubahan Densitas dan
Viskositas Magma serta Pengaruhnya terhadap Sifat Erupsi Gunung Kelud , Jurnal Geologi Indonesia,
6(4) , 2011, p. 227-237.
[7] Geological Agency , Data Dasar Gunung api Indonesia , Second Edition, Geological Agency , Ministry
of Energi and Mineral Resources of Indonesia , p. 372-399.

Is There any Change from Magma Mixing in Kelud Characteristics?

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