Petrology and geochemistry dataset of lava from the Ijen Crater and Mount Blau, Banyuwangi, East Java, Indonesia

This article presents rock texture and mineralogy, as well as major and trace elements of lava from Ijen Crater and Mount Blau, Ijen Volcanic Complex (IVC), East Java, Indonesia related to article entitled “Rock Magnetic, Petrography, and Geochemistry Studies of Lava at the Ijen Volcanic Complex (IVC), Banyuwangi, East Java, Indonesia” [1]. Six lava samples were taken from three lava flows that are the product of the eruption of the Ijen Crater and three lava samples from a lava flow that is the product of the eruption of Mount Blau. The samples were crushed and used for measuring major and trace elements using XRF method. Meanwhile, the thin sections of all samples were used to analyze rock texture and mineralogy. These data are invaluable in identifying the lithology, tectonic setting, and magmatism process through the analysis of total silica alkaline and Harker diagram. Other researchers can analyze the other diagrams and graphs to know in more detailed information as intended. On the other hand, the data can be used as a comparison for other lava products from different eruption sources.


Specifications
Geochemistry and Petrology Specific subject area Whole rock geochemistry, mineralogy, and rock texture of lava Type of data Table  Image Graph Figure  How data  Value of the Data The data presented in this article can be used in the study of petrology and geochemistry of the lava from the Ijen Crater and Mount Blau, mainly in lithology, tectonic setting, and magmatism process.
Researchers that are currently working in the field of volcanology, mainly in geochemistry, mineralogy, and rock texture, can use this data according to their studies. The data presented in this article can be compared with other data to understand the similarities and differences with other lava flow from different eruption sources. With further statistical analyses, more detailed information about lithology, tectonic setting, and magmatism can be obtained. The data presented in this article complement the data obtained from the previous study [1].

Data
Fig . 1 shows the geological map from the study area. Sampling locations are shown on the map as the black dots. Samples were taken from four different lava flows. Three lava flows are the product of the eruption of the Ijen Crater (IL3B, IL3E, IL3F, IL3H, IL3J, and IL3K), meanwhile, one other lava flow is the product of Mount Blau's eruption (BLA, BLB, and BLC). The coordinates of the outcrops can be seen in Table 1.
The thin sections of the samples from the Ijen Crater and Mount Blau are shown in Fig. 2. All samples from the Ijen Crater have porphyritic texture with phenocryst 25e35%, as plagioclase (15e21%); pyroxene (3e9%); olivine (1%); and opaque minerals (2e7%) with the size of 0.1e5.25 mm with groundmass that is consisted of minerals such as plagioclase microlite (15e37%); pyroxene (7e15%); olivine (1%); opaque minerals (2e4%); and glass (12e39%). Meanwhile, the lava sample from Mount Blau has phenocryst approximately 35e40%, consisted of plagioclase (22e30%); pyroxene (3e5%); and opaque minerals (7e8%) with the size in the range of 0.1e4 mm with groundmass that is consisted of plagioclase microlite (2e3%); pyroxene (1%); opaque minerals (1%); and glass (40e56%). Table 2 shows the geochemistry data of the lava samples from the Ijen Crater and Mount Blau. All of the samples have Lol in the range of 0.13e1.94 %weight. This means that all of the samples are in fresh condition. Based on the total alkali silica (TAS) diagram ( Fig. 3), lava samples from the Ijen Crater could be classified into two lithologies: basaltic andesite and andesite, meanwhile, lava samples from Mount    Blau had andesite lithology. As a comparison, we also plotted the lava samples data from the Ijen Crater that were used in the previous study [1]. Major elements contents of the Ijen Crater lava samples from Ref. [1] are shown in the Table 3. Lava samples from the Ijen Crater obtained from Ref. [1] had basalt and basaltic andesite lithologies. The differences of geochemical characteristics of the samples used in Ref. [1] with the samples from this study could be influenced by the sampling locations. In the previous study [1], the samples which used only from one lava flow (Fig. 1), meanwhile, in this study we used samples from three lava flows. This data is also apt with the data in the other studies [1e3], which showed that lava samples from the Ijen Crater could be classified into three lithologies: basalt, basaltic andesite, and andesite. The data explained before also shows that the geochemical characteristics of the samples from the Ijen Crater are varied, whereas the samples from Mount Blau are relatively homogenous.
The magma characteristic from the Ijen Crater and Mount Blau are affiliated with moderate-K calcalkaline to high-K calc-alkaline magma series (Fig. 4). Moreover, lava samples from both sources contain TiO 2 less than 1.4 %weight, this indicates volcanic rocks that are derived from a subduction system [4]. The previous studies [1,3] obtained the same data. Fig. 5 shows plot between some major element oxides and SiO 2 content of all samples. As a comparison we also plotted the geochemical data of Ijen Crater and Mount Blau lava samples from previous study [1,3] showed in the Table 3. Fig. 5. Indicates that the major element oxides of the samples from Mount Blau are relatively similar. Meanwhile, negative correlations are observed between SiO 2 and each of FeO, CaO, and Al 2 O 3 . In contrast, positive correlations are present Fig. 3. Plots of Na 2 O and K 2 O in respect with SiO 2 in TAS diagram from (a) [5] and (b) [6]. Red squares indicate lava samples from the Ijen crater. Ijen crater samples from Ref. [1] are shown with black squares and Mount Blau samples are presented the red diamonds.   , the Ijen Crater from previous study [1] (black squares) and [3] (green squares), Mount Blau (red diamonds), and the Mount Blau from previous study [3] (green diamonds).
between SiO 2 and each of MgO and K 2 O (Fig. 5). These data relatively similar with the data from previous studies [1,3], except the correlation between MgO and Na 2 O with SiO 2 . In the [3], the correlation between MgO and SiO 2 is negative, whereas between Na 2 O and SiO 2 is positive. Meanwhile, in the present and previous data [1], the correlations between them are vice versa.
The data indicate that MgO and Na 2 O content which were obtained in this research have a problem due to the contamination both in sample preparation process and XRF measurement. We suggest the readers to be cautious when using the data. But, the all data (except MgO and Na 2 O) are still in the good condition. These data broadly overlap with those of [3], and the error on MgO and Na 2 O doesn't seem to affect the other elements. The percentage reduction of FeO along with the increasing percentage of SiO 2 is caused by the formations of olivine and pyroxene minerals that contain a lot of Fe at the start of magma cooling. This is what caused magma differentiation to happen. The residual magma contains a higher percentage of SiO 2, while Fe content decreasing . On the other hand, the decreasing of CaO and Al 2 O 3 can be the effect of the continuing formation of the plagioclase mineral from the start until the end of the magma cooling process [8,9]. The variation of the major element oxides diagrams in Fig. 5 shows that the magmatism process of the Ijen Crater is also controlled by magma mixing or contamination, based on the data obtained from Refs. [1e3].

Experimental design, materials, and methods
Sampling locations were chosen based on the geological map of the Ijen Volcanic complex [2] and followed the previous studies [1,10,11]. Samples were taken from three different lava flows that are part of lava flow 3 of the Ijen Crater (Il3) and one flow from the lava flow 3 of the Mount Blau (Bl3) [2]. Samples were taken from the unused outcrops from the previous studies [1,10,11]. These outcrops were chosen with the intention of complementing the data from the earlier studies.
A total of 20e50 g in each sample was crushed to the size of 50 mm using Jaw Crusher (Retsch, Germany) and Pulveriser (Fritsch, Germany). Geochemistry measurements were performed to get Lol data, major elements, and trace elements. The grain size should have a relatively similar size. The Lol measurements were done by heating the samples using muffle furnace with a temperature from 100 C to 1000 C. The samples were heated at 100 C overnight, at 200 C for 15 minutes, at 400 C for 15 minutes, at 600 C for 15 minutes, at 800 C for 15 minutes, at 1000 C for 20 minutes. Before the heating, samples' masses were measured using balance weighing with the accuracy ±0.0002 g and then stored in ceramic crucibles. After the heating at 1000 C, the samples were left to cool down and then the masses were measured again to find the weight loss to calculate the Lol. Meanwhile, major elements and trace elements were measured using XRF (X-Ray fluorescence) method with the Thermo Scientific ARL 990 (Thermo Electron Corporation, Switzerland) in the Geological Survey Center Laboratory, Bandung, Indonesia. The error on major and trace elements are showed in the Table 2. All samples were also prepared in the form of thin sections with a thickness of 0.003 mm. These thin sections were used for mineralogy and rock texture analysis using Ci-POL polarizing microscope (Nikon, Tokyo, Japan) at the Petrographic Laboratory, Faculty of Earth Sciences and Technology, Institut Teknologi Bandung.