Journal of Geology & Earth Sciences Volume 1| Issue 6 Review Article Open Access
Petrology and Geochemistry of Mafic, Ultramafic and Granitoid Rocks of Swarga area within The Mercara Shear Zone, Southern India
K.V. Sarath1, Aadith Narayan2, E. Shaji1* 1Department of Geology, University of Kerala, Kariavattom campus, Thiruvananthapuram, India-695581 2Department of Civil Engineering, Manipal Institute of Technology, Manipal Academy of Higher Education, Manipal, Karnataka, India. *Corresponding author: E. Shaji, Department of Geology, University of Kerala, Kariavattom campus, Thiruvananthapuram, India. Email: [email protected] Citation: E. Shaji (2021) Petrology and Geochemistry of Mafic, Ultramafic and Granitoid Rocks of Swarga Area Within The Mercara Shear Zone, Southern India: Nessa Journal Geology & Earth Sciences. Received: 23rd November2020; Accepted: 2nd March 2021; Published: 5th March 2021 Copyright: © 2021 E. Shaji et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
ABSTRACT
Mangalore-(Kasaragod)-Jalsoor-Mercara Shear Zone forms the north-western part of the south Indian granulite Terrain, India. Unlike other shear zones in Southern Granulite Terrain(SGT), the mafic-ultramafic suits occurred along Mercara Shear Zone (MRSZ) are least investigated. The present study documents the Swarga Mafic– Ultramafic Complex (SMUC), which occurs in the North-western part of the MRSZ. The mafic-ultramafic suits includescumulative pyroxenite, amphibolites, basalt and dolerite. The associated rocks includeBanded Hematite Quartzite (BHQ) and chert, and alkali granitoids, The geochemical signature of the hornblendite and dolerite indicates tholeiitic affinityand parent magma shows a mixed character of Mid Oceanic Ridge Basalt and oceanic island tholeiite. Tectonic settings of both amphibolite and granitoids fall in island arc tholeiite.The pyroxenites of SMUC have an overall cumulate texture and comprise clinopyroxene as dominant phase. Extremely high MgO
(21.08-21.45 wt %), low Fe2O3 (14.04-14.41wt %) and CaO (10.48-10.89wt %) content of the Swarga pyroxenite suggest its highly depleted nature.Geochemistrysuggests they are continental arc-related cumulates.
Keywords: Mangalore-(Kasaragod)-Jalsoor-Mercara Shear Zone, Swarga Mafic–Ultramafic Complex (SMUC), Mid Oceanic Ridge Basalt, Southern Granulite Terrain, and island arc
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Introduction
In the Southern Granulite Terrain (SGT) several mafic–ultramafic complexes are well studied for example (i) Puttetti complex, Trivandrum block (Rajesh et al. 2003) (ii) Bhavani-Mettupaliyam Ultramafic Complex (Yellapaet al. 2019; Rajesh 2004) (iii) The Sittampundi Anorthosite Complex (Ghosh and Kumar 2011 and Subramaniam1956) (iv) The Chalk hills of Salem Mafic–Ultramafic Complex with large magnesite deposits (Yellappaet al.2019;Kuttyet al. 1986 and Murthy 1979). TheMercara Shear Zone (MRSZ) exposes the interface between the high-grade granulite facies rocks to the south and the low-grade granite-greenstone sequences of the Western Dharwar Craton (WDC) to the north.The Mercara Shear Zone extends from the western coast of southern India and converges with Moyar Shear Zone in the east.A strike length of more than 100 km extends the shear zone and a breadth of 20–30 km displays dextral kinematics, and its covered through northern area of the Coorg Block (Chetty et al. 2012; Santosh et al. 2015).MRSZ is located between southwest of the Dharwar Craton and north of the Coorg Block (Amaldev et al. 2016). Krishnarajet al. (1994) studied the garnet-kyanite metapelitesand maficgranulitesalong the Mercara shear region. The rocks were formed under 7 to 8.6 kilobarspressure, 725-800℃temperature conditions.Texture like sillimanite overgrowth of kyanite in pelitesand orthopyroxene-calcic plagioclase symplectites along with the garnet in mafic rocksexplained that decompression/uplift of the region subsequent to crustal thickening (Krishnarajet al. 1994). Mesoarchaeanhigh pressure granulitesalso reportedfrom the Mercara shear zone and rocks in this region are of the oldest in India (Santosh et al. 2015;Amaldevet al.2016) Gopalakrishna (1984) had mapped the areas around Byalkuppe and Kushalnagara to the east of the Mercara Shear Zone.Santosh and Nair (1986) indicated the alkaline complex along Angadimogar in district of Kasaragod and categorized as syenite taking into account the alkali-felspar assertive mineralogy. Devaraju and Janardhan (2004) considered the MRSZ as Mangalore-Kasaragod-Mercara lineament that hosted younger intrusive bodies like that of Angadimogar syenite, Thalur granite and Sullya syenite.
Zircon U-Pb-Hf-O isotope data from the Coorg Block in southern India record evolving crust during three phases of magmatism. The earliest felsic melt recorded at ca. 3.5 Ga formed from a protolith extracted from the mantle at ca. >3.8 to 3.5 Ga. Phase 2 (ca. 3.37 to 3.27 Ga) and Phase 3 (ca. 3.19 to 3.14 Ga) record mixed magma sources, with juvenile input during each phase. All phases formed in a subduction-related setting, and that crustal thickening was assisted by increasing strength of the lithosphere (Roberts & Santosh, 2018).
2. Regional Geology
The Dharwar craton is divided into an eastern and western component by a 500 km long body of Closepet granite. The Western Dharwar craton consists of both early Archean and meso- to late Archean greenstone belts (Mukherjee et al. 2012; Jayanandaet al.2019). The southern part of the Archean Dharwar craton consists of Southern Granulite Terrane (SGT) it’s a montage of several Archean crustal blocks which show metamorphism from amphibolite to granulite faciessuch as the exotic Coorg, Nilgiri, Salem and Madras blocks withsuperseding collisional sutures or shears zones which developed through various orogenic cycles during Mesoarchean to late Neoproterozoic-Cambrian (Santosh et al.2017, 2015, 2013; Amaldevet al. 2016; Samuel et al. 2016, 2014; Yang et al. 2015; Shajiet al. 2014; Glorieet al. 2014; Lancaster et al. 2014 and Clark et al. 2009). Towards the south is the large crustal segment of Madurai Block, with an amalgamated assembly of northern Neoarchean, central Paleoproterozoic,and southern
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Neoproterozoic domains (Santosh et al. 2017 and Plavsaet al. 2012). The SGT is one of the best studied Precambrian crystalline terrain in the world. According to (Santosh, 2020) SGT can help to understand the deep crustal processes, crust mantle structural design, excessive crustal metamorphism, growth and recycling of continental crust, polyphase structural evolution and the assembly-evolution-disruption of supercontinents through time. The focus of studies to show the petrology and geochemistry of mafic, ultramafic, and associated rocks of Swarga and adjacent areas within the Mercara Shear Zone.
3. Geology of the Study Area
The Coorg block is described as an exotic Meso-Archean microcontinent welded to peninsular India at 1.2 Ga (Santhosh et al. 2015 and Ishwar-Kumar et al. 2013)composed of Tonalite-Trondhjemite-Granodiorite (TTG), charnockites, granulites, gneisses,diorites and felsic volcanic tuff. The Coorg Block is welded to the Dharwar Craton along the north Mercara suture which hosts younger intrusive bodies like that of Angadimogar syenite (638 Ma), Thalur granite (710 Ma) and Sullya syenite bodies (Boraiahaet al. 2020; Santosh et al. 1986) and to the south with Nilgiri Block along the Moyar suture(Figure 1A).
The study area Swarga and adjoining area is located 35 km north of the Kasaragod town with an area of 107sq km (Figure 1B). Kasaragod has unique topography with thick lateritic plateau, undulating hills, and valleys (Shaji et al. 2020). Detailed geological mapping has been carried out in and around Permuda, Badoor, Kudalmarkala, Angadimogar, Paivalike, Swarga, Kasaragod District, Kerala state, and falls in the survey of India topographic sheet No. 48L/13, 48L/14, 48P/2 of scale 1:50000.The study area is located between 12° 36' 3.348" and 12° 46' 26.04" latitudes and 74° 56' 8.98453" E and 75° 9' 52.1352"E longitudes. Major rock types of area include charnockite, pyroxene granulite, Hornblende biotite gneiss, BHQ (Banded Hematite Quartzite), columnar/mafic dykes, pyroxenite and alkali granitoids. The igneous rocks occur as intrusive bodies within the gneissic rocks. Mafic dykes and zeolite mineralclusters are also seen in the outcrops (Figure 2F). Mafic, ultramafic, and intermediate intrusive rocks exposed are located within the Mercara Shear Zone (Figure 1E).Ultramafics are coarse grained and the pyroxenite shows cumulative texture (Figure 2D).Granitic and biotite gneisses predominate among the various gneisses, with occasional garnetiferous hornblende/biotite. Migmatites and minor quartz veins are also common (Figure 1 C-D). Exact boundaries between different litho units are difficult to demarcate due to thick soil cover. Gneisses are the dominating rock types of the study area. The general strike of the rocks is EW to ENE-WSW and dipping towards north. Texture and mineralogy of various gneisses varies from outcrop to outcrop. Three varieties of gneisses occur viz., quartzo-felspathic gneiss, charnockitic gneiss and garnetiferous hornblende/biotite gneiss. Numerous granitoids occur in Permude and Angadimogar area (Figure 2A). It shows intrusive contact with the surrounding gneisses and lacks foliation or banding.
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4. Sampling and analytical methods
Detailed field work was carried out in and around Swarga and adjacent areas. For the petrographic studies 20 samples were collected from the study area namely, pyroxenite (6), dolerite (2),granitods(4), basalt (2),pyroxene granulite (4), garnet biotite gneiss (2), charnockite (1) and migmatite (1). Polished thin sections were prepared at the petrography lab, Department of Geology, University of Kerala, Trivandrum. For the geochemical studies six samples were collected such as pyroxenite (2) dolerite (2) and granitoids (2).Major element chemistry was determinedusing the XRF facility of National Centre for Earth Science Studies(NCESS). The XRF (Bruker) machine is a pioneer sequential wavelength-dispersive X-ray spectrometer withsample preparation units. XRF is equipped with agoniometer (which hold seven analysing crystals: OVO-55, PET, LiF 200, LiF 220, Ge, ADP and InSb4kW Rh X- ray tube, 0.23 and 0.46 collimators and latest SPECTRA plus software for qualitative and quantitative determination of elements. The chemical data is presented in Table 1.
Ultramafic Mafic Intermediate Sample No. LK8G LK8A LK4A LK1A LK8E LK2H LK2I Major oxides (wt.%)
SiO2 42.98 43.42 46.6 49.2 53.8 53.02 61.89
TiO2 0.46 0.4 2.96 2.08 0.71 1.78 0.86
Al2O3 8.14 7.82 13.39 15.12 11.26 15.55 17.36
MnO 0.24 0.24 0.26 0.19 0.2 0.21 0.06
Fe2O3 14.41 14.04 19.14 13.33 11.1 10.6 5.39
CaO 10.48 10.89 8.21 11.42 13.75 5.19 2.75 MgO 21.45 21.08 4.14 5.67 6.73 4.94 1.49
Na2O 1.22 1.09 2.58 2.01 1.52 4.38 5.51
K2O 0.08 0.07 0.83 0.26 0.16 3.06 3.83
P2O5 - - 1.27 0.26 0.09 0.46 0.53
Total 99.46 99.05 99.38 99.54 99.32 99.19 99.67
Table 1. Representative mafic ultramafic and intermediate rocks along Mercara Shear Zone.
5. Results
5.1 Petrography
Pyroxenite occurs as dark greenish coloured,coarse grained with cumulative texture (Figure2D-G). Microscopically the rock shows primary magmatic cumulus texture composed mostly of euhedral crystals of augite and diopside. Mineralogy of the rockmainly consistsof clinopyroxene and orthopyroxenes (enstatite and hypersthenes) (Figure3B). The clinopyroxene (cpx) grains are highly fractured and showwavy extinction. Exsolution Nessa Publishers| www.nessapublishers.com Page 4
Journal of Geology & Earth Sciences Volume 1| Issue 6 textures are also observed. Amphiboles (hornblende) occurs as secondary mineralalong the grain boundaries of both clinoand orthopyroxene and thesehornblendesare derived from the clinopyroxenes as evident from their relict texture. Most of the pyroxenes are also altered to chlorite.
Dolerite dyke occurs at Kudalmarkala area. The fine to medium grained dark coloured rock consists ofmainly plagioclase, pyroxenes, hornblende, and accessories. The rock shows subophitic texture with euhedral plagioclase surrounded by anhedral clinopyroxene. The large plagioclase laths showing oscillatory zoning indicating an igneous origin. The large laths are oriented in different directions with a feathery augite within it (Figure3D).
Amphibolite is seen associated with pyroxenite (Figure2E) and it shows a sharp contact with deformed basaltic rock.Microscopically, the rock composed ofhornblende, plagioclase, quartz and garnet with accessories like calcite, biotite, rutile and opaque minerals. Amphibole is greenish and subidioblastic. Garnet is also fine to coarse grained subidioblastic (Figure 3E). In some samples, garnet is locally surrounded by plagioclase andfine-grained amphibole, suggesting a progradereaction.
5.2 Geochemistry
Geochemistry of 2 pyroxenite samples (LK8G, LK8A) are presented in table (1). The Swarga pyroxenites have higher contents of MgO (21.08-21.45 wt %) high MgO are indicative of their origin from a primary magma (after
Velasco-Tapia et al. 2001 and Green 1971) and high CaO (10.48-10.89 wt %) but low Na2O (1.09-1.22 wt %), K2O
(0.03-0.21 wt %), and TiO2 (0.07-0.08 wt %). The binary plots with reference to MgO show positive correlation with
SiO2, Al2O3, Fe2O3, CaO, TiO2, and negative correlation with P2O5 (not detected). The concentration of SiO2 varies from 45.97 to 50.11 wt % and hence the samples can be termed as ultrabasic, the SiO2 content decreases with the increase in MgO (Figure 4). Negligible K2O and Na2O imply their non-potassic or non-sodic character.
The geochemistry of dolerite (LK4A, LK1A) shows relatively lower SiO2 (46.6-49.2 wt %), Al2O3 (13.39-15.12 wt
%), Fe2O3 (13.3-19.14 wt %), CaO (8.21-11.42 wt %),MgO(4.14-5.67wt %) and also relatively low TiO2 (2.08-2.96 wt %). In the total alkali vs. silica diagram, the samples plot in the basaltic field, the rocks follow a tholeiitic fractionation trend in the AFM diagram (Figure, 5B). K2O vs SiO2plot (Figure 5C) one dolerite sample plotted in calc alkaline series and other sample fall in tholeiitic series (after Peccerillo and Taylor, 1976).
The amphibolitesamples (LK8E) show narrow range in SiO2 (53.08 wt %), Al2O3 (11.26 wt %), Fe2O3 (11.1 wt %), and CaO (13.75 wt %). These rocks are also relatively low in TiO2(0.71 wt). In the total alkali vs. silica diagram, the samples plot in the basaltic field. Amphibolite sample fall in tholeiitic field in the AFM diagram (Figure, 5B). K2O vs SiO2 plot (Figure 5C) the sample falls in tholeitic series (after Peccerillo and Taylor, 1976).
The values ofPermuda granitoid samples (LK2H, LK2I) shows SiO2(53-61.88 wt%), Al2O3(15.5-17.35wt%) and
Na2O(4.938-5.51 wt%) and very low K2O(3.06-3.83 wt%). The plot in trachyte,trachydacite and basaltic trachy andesitic fieldin the total-alkali silica (TAS) diagram(Figure 5A),the samples belong to the calc alkaline series in
AFM diagram (Figure 5B).In K2O vs SiO2 plot (Figure 5C) one sample fall in shoshonite series andother samples fall
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Journal of Geology & Earth Sciences Volume 1| Issue 6 in-between high calc alkaline series and shoshonite series. (Figure 6B) represents trondhjemite and trondhjemite-calc alkaline trend, respectively.
5.3 Tectonic discrimination plots
The geochemical data from the pyroxenite, dolerite,amphibolites and granitoids of the Kasaragod-Mercara shear zone plotted on various major tectonic discrimination diagrams, which are typically used for distinguishing Mid
Oceanic Ridge Basalt (MORB) and Island Arc Tholeiite (IAT). In the TiO2-MnO-P2O5 ternary tectonic diagram (Figure 6D, after Mullen, 1983) one doleritie sample plot in the boundary of MORB and oceanic island tholeiite (OIT) and other sample fall in island arc tholeiite (IAT) field, both amphibolite and granitoid sample fall in island arc tholeiite (IAT) and in MgO-FeOt-Al2O3 ternary diagram each samples shows variation in tectonic setting amphibolites sample shows ocean island signatures, dolerite fall in continental field and granitoids shows orogenic and spreading centre signatures (Figure. 5B, afterPearce et al.1977). Further, in TiO2 vs. Al2O3 tectonic discrimination plot (Figure. 6C, after Mullen, 1983) three samples including two dolerite and one granitoid rock show within plate basalt signatures but one granitoid rock and pyroxenite, amphibolite shows arc related tectonic settings.
6. Discussion
Mafic–ultramafics and granitoid rocks have been described in variety of tectonic settings around the world, and their petrogenesis provides important information on regional tectonic evolution of Earth (Polatet al.2011). Our field observations and structural studies from Swarga pyroxenite and associated rocks from the surrounding region in Mercara Shear zone reveal that the rocks complex witnessed intense deformation. The Swarga mafic ultramaficcomplex (SMUC) is characterized by a complete sequence of pyroxenites, highly deformed, faulted basalts and columnar mafic dykes, Banded Hematite Quartzite (BHQ), chert, amphibolites, garnet amphibolites, migmatite, garnet hornblende biotite gneisses, pyroxene granulites, charnockites, granitoids and pegmatites. Petrological field studies of several lithologies from SMUC show that the rocks subjected to various degrees of alteration as indicated by the presence of chlorite in pyroxenite, epidoteveins in granitoids. The metamorphism isindicated by the highgrade metamorphic rocks; hornblende biotite gneiss, charnockites, pyroxene granulite and leptynites. The rock show both prograde metamorphism (with assemblages of orthopyroxene, K-feldspar and garnet) and retrograde metamorphism (by the presence of retrograde reactions and conversion of garnet to amphibole). The igneous layering (Figure 2H) structure and presence of cumulate texture in ultramafic rock (Figure 2D) indicate an origin by magmatic crystallization in a large magma chamber(s) from magma(s) of evolving composition (Jaques and Green 1980). In the pyroxenites, the spinels occur along the grain boundaries of pyroxenes. The observed mineralogy and textural characteristics of amphibolites indicate that their protoliths could be basaltic rocks. The presence and absenceof garnet in amphibolitic rocks reflects the differences in original bulk rock composition as well as different pressure–temperature conditions. The rocks suffered retrograde metamorphism as indicated by the conversion of garnet to amphiboles in these rocks.
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The limitations of this study includes less number of samples, only major elements analyzed, lack of data on trace elements and improper tectonic discrimination diagrams, the first author could only collect few representative ultramafic rock samples.
The data generated for a Masters project are used for this paper. Further we suggest that detailed study be undertaken on mapping the to collect a greater number of representative rock samples and generation of more data on geochemistry and mineral chemistry.
7. Conclusions
The following conclusions can be deduced from the present study
1. Field relations, lithological assemblages, and structural characteristics of Swarga ultramafic body is preserved in Mercara Shear Zone.
2. Extremely high MgO (21.08-21.45 wt %), low Fe2O3 (14.04-14.41wt %) and CaO (10.48-10.89wt %) content of the Swarga pyroxenite suggest its highly depleted nature.
3. It is the first study of pyroxenite from Swarga area ultramafic dykes are clinopyroxenites having a cumulate texture. Major oxides geochemistry suggests they are continental arc-related cumulates.
4. The petrological and geochemical characteristics of amphibolites reveal crystallization from tholeiitic basalts.
5. From the field, petrological and geochemical studies suggest major lithological units in the mercara shear zone are granitoids, garnet amphibolites, hornblende-garnet-biotite gneiss, pyroxene granulite, migmatite, columnarmaficdyke, ultramafics and BHQ (banded hematite quartzite).
6. First report of Sphene (titanite) granitoids from Permuda area.
7. From the tectonic discrimination plot studied granitoids shows diversity on its origin. Which shows within plate basalt signatures and arc related tectonic settings.
8. From the field observation and geochemical studies this is the first report of sheeted mafic dyke and associated zeolite group of mineralization in Angadimogar.
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Figure 1(A).
Figure 1(A). Regional geological map of Southern Granulite Terrane (SGT; modified after Yellappa et al. 2018; Santhosh et al. 2015 and source from Geological Survey of India maps) showing the study area, MCZ (Mercara Shear Zone); Mo: Moyar; Bh: Bhavani; PCSZ: Palghat–Cauvery Shear Zone; MSZ: Moyar Shear Zone; CSZ: Cauvery Suture Zone; AKSZ: Achankovil Shear Zone; WDC: Western Dharwar Craton; EDC: Eastern Dharwar Craton; Tz: Transition Zone; SMUC: Salem Mafic–Ultramafic Complex; MOC: Manamedu Ophiolite Complex; DOC: Devanur Ophiolite Complex; SAC: Sittampundi Anorthosite Complex; AMUC: Aniyapuram Mafic– Ultramafic Complex. Box represents study area.
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Figure 1.B-E
Figure 1(B). Location map showing the study area along Mercara Shear Zone; (C) Geological map showing granitoids, granulites, and mafic dyke intruding migmatitic gneiss country rock at Paivalike; (D) Geological map showing granitoids and columnar/mafic dykes intruding migmatitic gneiss country rock at Angadimogar; (E) Geological map showing mafic-ultramafic rocks intruding garnet kyanite gneiss country rock at Swarga.
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Figure 2.A - H
Figure 2. Field photos of different lithologies from the Kasaragod-Mercara Shear Zone: (A) Exposure of alkali granitoids from Permude area; (B) Columnar mafic dyke very close to Angadimogar syenite; (C) Outcrop of pyroxene granulite near to Paivalikea area; (D) Dark green coloured cumulate pyroxenite from Swarga; (E) Amphibolite from Swarga area associated with pyroxenite; (F) Zeolite (natrolite, scolecite, phillipsite and chabazite etc.) mineralization in fractured columnar dyke; (G) Layered Swarga pyroxenite well exposed in Mercara Shear Zone. (H) Banded Hematite Quartzite (BHQ) from Swarga.
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Figure 3.A - F
Figure 3. Thin section photomicrographs (in cross‐polarized light) of the different lithologies of Kasaragod-Mercara Shear Zone; (A) Euhedral coarse grained texture in pyroxene granulite with coarse cpx and opx (B) Euhedral Cpx and Opx showing cumulate texture in pyroxenite, clinopyroxene (Cpx) is the major mineral, with accessory orthopyroxene (Opx) and spinels (Spl); (C) Alkali granitoids with deformed K-feldspar (K-fel) and rich in sphene(Sph)/titanite; (D) Dolerite sample shows ophitic to subophitic texture; (E) Garnet amphibolites shows well developed twinned plagioclase feldspar laths with hbl (hornblende), Cpx, Opx and Grt (garnet); (F) zircon (Zr) grain in the margin of large k-feldspar is noticed in pyroxene granulite.
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Figure 4.
Figure 4. Binary plots of whole‐rock geochemical data for mafic, ultramafics, amphibolites and granitoids MgO (wt
%) vs. SiO2 (wt %); MgO (wt %) vs. TiO2 (wt %); MgO (wt %) vs. Al2O3 (wt %); MgO (wt %) vs. CaO; MgO (wt
%) vs. Na2O (wt %); MgO (wt %) vs. K2O MgO (wt %) vs. P2O5; MgO (wt %) vs. Fe2O3 (wt %).
(Diamond represents granitoids, square represents dolerite, triangle represents pyroxenite and circle represents amphibolite)
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Figure 5 (A)
Figure 5 (B)
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Figure 5 (C)
Figure 5. Geochemical variation diagrams of mafic, ultramafics, amphibolites and granitoids; (A) SiO2 (wt %) vs. total alkali content [Na2O (wt %) + K2O (wt %)] classification plot (after Le Maitre et al. 1989 and Bas et al. 1986);
(B) Fe2O3(wt %) – Na2O(wt %) + K2O(wt %) – MgO(wt %) plot (after Irvine & Baragar, 1971); (C) classification diagram of K2O (wt %) vs. SiO2 (wt %) (after Peccerillo and Taylor, 1976). (Diamond represent granitoids, square represents dolerite, triangle represents pyroxenite and circle represents amphibolite)
Figure 6 (A)
MgO-Fe2O3-Al2O3 ternary diagram (pearce et al., 1977)
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Figure 6 (B)
K2O+Na2O+CaO ternary plot (after Barker and Arth, 1976)
Figure 6 (C)
TiO2 vs. Al2O3 tectonic discrimination plot (after Mullen, 1983)
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Figure 6 (D)
TiO2-MnO-P2O5 ternary tectonic diagram (after Mullen, 1983)
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