Chemical weathering and lateritisation
The depleted Si, Ca and Na and enhanced Al, Fe, Mn and P content of the sediments relative to that of PAAS in both size fractions (Tables 2 and 3) indicate that the river sediments are the products of chemical weathering. The SiO2/Al2O3 ratio helps to classify the sediments whether are laterite derived. This ratio is < 1.33 for laterites, 1.33–2.0 for lateritic soils and > 2.0 for non-lateritic, tropically weathered soils (Martin and Doyne 1927; Narayanaswamy 1992). The SiO2/Al2O3 ratio in lateritic soils, however, can range from 1.33 to 2.2 (Martin and Doyne 1997). The mean SiO2/Al2O3 ratio for the clay (1.95 ± 0.47) and silt (2.29 ± 0.61) fractions of sediments from the Archean-Proterozoic terrain (A-P terrain) (Tables 2 and 3) suggest they are characteristic of lateritic soils. Within the A-P terrain, the gradually increasing mean SiO2/Al2O3 ratio for the clay fraction of sediments from Kerala (1.45) to Karnataka (2.22) and then to Goa (2.24) suggests laterite soils are diluted by the weathered material from the hinterland rocks. The Fe2O3 content of the clays from Karnataka (max. 17.3%; mean: 12.4%) and Goa (max. 17.7%; mean: 13.2%; Table 2) is much higher than in UCC (5%). The decreasing Al2O3 coinciding with increasing Fe2O3 in the sediments of Karnataka and Goa suggests that the Fe-Mn ores located in the hinterland drained by their rivers contributed high iron content to the sediments. Iron and manganese ore deposits occur in the northern Karnataka and Goa (Gokul et al. 1985; Dhoundial et al. 1987; Naqvi 2005; Desai et al. 2009) and are being mined by open cast method. The rivers drain these deposits during the SW Monsoon and carry both dissolved and particulate Fe and Mn. Furthermore, ore material is transported from the mines to the port through these rivers (Shynu et al. 2011). Consequently, high concentrations of dissolved and particulate ore material were reported in the suspended and bed sediments of the rivers and estuaries (Shynu et al. 2011, 2014; Prajith et al. 2015; Kessarkar et al. 2015; Suja et al. 2017). On the other hand, the mean SiO2/Al2O3 ratio for the clay (2.82 ± 0.53) and silt (3.43 ± 0.66) fractions of sediments from the Deccan Trap terrain (Tables 2 and 3) suggest that the sediments are non-lateritic and chemically weathered soils. Relatively high Ti content in the sediments from DT terrain indicates the influence of source rocks.
The CIA values of sediments as well as A-CN-K diagram (Fig. 2) reveal that the clay fraction of sediments from Kerala, Karnataka, Goa and southern Maharashtra are strongly weathered, while those of northern Maharashtra and Gujarat are intermediately weathered (Fig. 2). The silt fraction of sediments from A-P terrain exhibits strong weathering. Within the DT terrain the silt sediments of Maharashtra exhibit intermediate to strong weathering while that of Gujarat exhibit weak to intermediate weathering (Fig. 2). The gradually decreasing values of the index of lateritisation (IOL; Table 2) from Kerala (47.4) to Gujarat (24.3) suggest that the river sediments of Kerala are weakly lateritised and, lateritisation decreased as one moves upwards from Kerala in the south to Gujarat in the north.
Correspondence between ƩREE and chemical weathering
In general, REE concentrations tend to increase with increasing intensity of chemical weathering (Du et al. 2021). Remarkably high ƩREE corresponding to high CIA in the sediments from Kerala agree with the above statement. However, low ƩREE corresponding to high CIA of the sediments from Karnataka, Goa and Maharashtra suggest that the weathering products of laterites may have been admixed with sediments weathered directly from source rocks at the site of deposition.
The strong correlation of ƩREEs with P2O5 and, moderate to strong correlation with Fe2O3, MnO and K2O in the clay fractions of sediments from A-P terrain (Fig. 4) suggest REEs are bound to secondary mineral phases such as Mn-Fe oxy- (hydr)oxides and phosphate. Negative or poor correlation of ƩREE with Al2O3 in the sediments suggests that REE may not reside with clay mineral lattice. On the other hand, strong correlation of ƩREEs with Al2O3 and Fe2O3 and moderate correlation with MnO, K2O, P2O5 and TiO2 in the clays from DT terrain indicates that most of the REE reside in the clay mineral lattice while a small part is adsorbed onto the surfaces of secondary weathering products such as Mn-Fe (hydr)oxides and phosphate minerals. It appears that that the secondary weathering products are the important reservoirs for REE in the A-P terrain and, clay minerals are major reservoirs for REE in the DT terrain. REE adsorbed into Fe-Mn oxides and phosphates have been reported (Pourret et al. 2013; Du et al. 2021).
The strong correlation of ƩREE with K2O, TiO2 and P2O5 in the silt fraction of sediments from Kerala and, strong correlation of ƩREE with Al2O3, Fe2O3, K2O, MnO and P2O5 in the silts of Karnataka and Goa (Fig. 4) suggest mica, titanium and apatite minerals, clay minerals and Fe-Mn-(hydr) oxides contributed REE to the silt sediments of A-P terrain. However, in the DT terrain strong correlation of ƩREE with P2O5 and moderate correlation with other oxides of major elements indicate secondary mineral phases such as clay minerals, Fe-Mn oxides and phosphate minerals formed during weathering contributed abundantly to the REE content.
The high heavy metals (U, Th, Zr and Hf) content in the sediments of A-P terrain compared to UCC and PAAS (Table 2) and their moderate to strong correlation with ƩREE of sediments (Fig. 5) (except the clay fraction of Kerala) suggest heavy metal enriched minerals contributed REE. Since heavy minerals are important host for heavy metals and REE (McLennan 1989), heavy minerals contributed significantly to the total REE of the sediments. The strong correlation of ƩREE with Th (Fig. 5) and P2O5 (Fig, 4) in the clay fractions of Kerala, however, suggest Th-rich clay minerals (Th adsorbs heavily on clay minerals), or monazite (Th and P-rich phase) are present in the sediments. Monazite-rich placers have been reported abundantly in this region (Mallik et al. 1987).
The peak high ƩREE corresponding to high heavy metal content in the silt fraction of sediments from southern Kerala (Fig. 3; Table 3) may be related to heavy minerals content in the sediments. It is because the hinterland rocks in the southern Kerala are felsic, comprising of khondalite-granulite-granites intruded by large pegmatites (Soman 2002). McLennon (1989) reported that the heavy metals and rare earths are more enriched in the felsic rocks than in mafic rocks. Heavy minerals have been reported in clayey silts of sediments (Marchandise et al. 2014). Placer minerals dominated by monazite, zircon, garnet, sillimanite, ilmenite and mica have been reported abundantly in the coastal sediments of south Kerala (Mallik et al. 1987). Therefore, REE concentrations in silt fractions of southern Kerala are controlled by weathering -resistant minerals like heavy minerals which hosts high REE and heavy metal content (Du et al. 2021). The clay fractions of sediment usually show high concentrations of total REE as these fractions contain clay minerals with high surface area and high adsorption capacity for REE. However, higher mean values of ƩREE in the silt fractions of sediments from Kerala, Karnataka and Gujarat (Table 3) than in clay fractions (Table 2) suggest heavy minerals in silt fractions contributed high REE.
Controls on the Sm/Nd and Y/Ho ratios of sediments
The varied Sm/Nd and Y/Ho ratios in river sediments indicate that the Sm - Nd and Y - Ho are fractionated significantly (Fig. 6A and Fig. 7A), However, the linear and strong correlations of Sm with Nd and, Y with Ho in both fractions of sediments (Figs. 6B and 7B) indicate that their geochemical behaviour during weathering is similar. The low Sm/Nd and Y/Hos ratios coinciding with high values of CIA and IOL (Fig. 6C-D and Fig. 7C-D) in the sediments of Kerala suggest that the increase in the intensity of chemical weathering and laterization decreased their ratios. The inverse correlation of Sm/Nd ratio with P2O5 (Fig. 6E) in both fractions of sediments also points out that the Nd released during chemical weathering may have adsorbed onto secondary phosphates resulting in low Sm/Nd ratio (Ohlander et al. 2014). In the case of Y/Ho ratio, Y was mobilised preferentially because of intense chemical weathering. This is also indicated in the plot between Y and Ho (Fig. 7B), wherein the Y and Ho values plot more towards Ho, suggesting higher mobilisation of Y relative to Ho. Nozaki et al. (1997) and Feng (2010) suggested remarkable fractionation between Y and Ho occur during chemical weathering and different complexations and phosphate salt solubilities. In other words, both Sm-Nd and Y-Ho are fractionated effectively during intense chemical weathering and laterization. Several investigators reported low Sm/Nd and Y/Ho ratios associated with high CIA and/or high IOL values of sediments (Babechuk et al. 2014, 2015. Feng et al. 2011, Feng et al. 2021) and suggested that the intensity of chemical weathering plays an important role in modifying these ratios.
As mentioned above, the river sediments of Karnataka and Goa represent lateritic soils admixed with particulates weathered from Fe-Mn ores. Prajith et al. (2015) reported that the Sm/Nd and Y/Ho ratios of Fe-Mn ores from Goa are 0.27 and 31.98, respectively. Relatively low Sm/Nd ratio in the sediments of southern Karnataka and slightly increased ratios in the northern Karnataka and Goa (Fig. 6A) may have resulted due to the presence of lateritic soils (low Sm/Nd ratios) in southern Karnataka and admixture of lateritic soils and ore particulates (high Sm/Nd ratio) in the northern Karnataka and Goa. Unlike Sm/Nd ratio, the Y/Ho ratio increased sharply in the sediments of Karnataka (Fig. 7A). First, the Y mobilised and lost during chemical weathering was to some extent compensated by addition of ore particles with high Y/Ho ratio, resulting in increased Y/Ho ratio. Second, since Y shows stronger tendency to adsorb onto solid particulates (Nozaki et al. 1997), redistribution of dissolved Y by adsorbing onto secondary mineral phases, like clay minerals, Fe-Mn oxides and phosphates may have favoured further increase in the Y/Ho ratios. The positive correlation of Y/Ho ratio with Fe2O3, MnO and P2O5 indicates that Y may have been redistributed in these sediments.
In contrast to the sediments of Kerala, high Sm/Nd and Y/Ho ratios correspond to high CIA in the sediments of Maharashtra and, low CIA in the sediments of Gujarat (Fig. 6C and Fig. 7C). The SiO2/Al2O3 ratios point out that these sediments are non-lateritic and chemically weathered soils. REEs are mobilised and fractionated during late stages of weathering and not during moderate stage of weathering (Ma et al. 2007). Therefore, the high Sm/Nd and Y/Ho ratios corresponding to strong and intermediately weathered samples of Maharashtra and, weak to intermediately weathered clays and silts of Gujarat (Fig. 2 and Fig. 6C and Fig. 7C) suggest that the intensity of weathering may not be a sole factor controlling these ratios. This inference also contrasts with that of Babechuk et al. (2015), who suggested that the magnitude of fractionation of Y/Ho is linked to the degree of chemical weathering of basalts and, Y/Ho ratio has potential as a silicate weathering proxy. Another interesting feature evident from the Sm vs. Nd plot (Fig. 6B) is that the Sm and Nd values for the sediments of Maharashtra and Gujarat plot slightly away from the linear line and more towards Sm, indicating increased Sm content resulted in high Sm/Nd ratio. High Sm/Nd and Y/Ho ratios of the sediments may be explained as follows: Since the rivers draining DT terrain in this region bring sediments from the great escarpment of the Western Ghats it is possible that the sediments are the weathered products of both physical and chemical weathering and transport of sediments into the rivers in great abundance because of heavy monsoonal rainfall. Moreover, the rivers of Gujarat also bring sediments from alluvium and older rocks (Fig. 1) weathered under semi-arid conditions. Therefore, it is likely that the rivers transported more Sm and Y to the sediments resulted in high Sm/Nd and Y/Ho ratios. Therefore, high ratios are due to the cumulative effect of physical and chemical weathering and high supply of REE during transport. Feng et al. (2021) proposed involvement of organic complexation processes at the outcrop could cause high Sm/Nd ratio. They argued that the chemical fractionation of real Sm-Nd occurs at an outcrop scale and during migration.
Normalised REE patterns: Influence of laterites, source rocks and Fe-Mn ores
The (MREE)n is the most dominant over (LREE)n and (HREE)n in the sediments of all rivers, except those of Kerala (Tables 2 and 3). Nesbitt and Markovics (1997) found MREE-enrichment in the river sediments subjected to intense chemical weathering. Bayon et al. (2018) reported MREE- and HREE-enriched patterns in clay fractions of sediments than the bulk sediments. Merchel et al. (2017) reported weathering of phosphate minerals causes MREE enrichment in river sediments. In this study, MREE-enrichment is associated with intensely weathered (high CIA) and intermediately weathered (low CIA) sediments. Strong correlation of (MREE)n with P2O5 and Fe2O3 implies MREEs enrichment may be related to strong adsorption onto secondary phosphate phases and Fe-oxyhydroxides (Munemoto et al. 2020).
The LREE- enriched REE patterns in both fractions of sediments from Kerala (Fig. 8) agree well with the intensity of chemical weathering and laterization and, composition of source rocks. During intense chemical weathering HREE gets released from primary REE bearing minerals in the parent rocks and carried away as soluble ions. Since LREE are less mobile than HREE, more LREE are retained with the residues. The LREE-enriched REE patterns with highest (ƩLREE/ƩHREE)n ratio in both fractions of sediments from Kerala thus suggest their source from laterites. The LREE-enriched and HREE-depleted REE patterns have been reported in the intensely weathered sediments and lateritic profiles from different regions (Braun et al. 1990, 1993; Irzon et al. 2016; Su et al. 2017). Hard rocks are exposed in the channels of a few rivers. Felsic rocks comprising of khondalite-granulite-granites intruded by large pegmatites occur in the southern and central Kerala and, Archean schists and charnockites with mafic granulites in northern Kerala (Soman 2002). Felsic rocks are usually enriched in LREE while mafic rocks are enriched with HREE. Consequently, LREE-enriched and HREE-depleted REEs are expected from the weathering products of hinterland rocks. LREE-enriched sediments have been reported during granite weathering (Aubert et al. 2021). Therefore, the LREE-enriched patterns in the sediments of Kerala arise due to their weathering from laterites and hinterland rocks.
The LREE-enriched REE patterns (mean (LREE/HREE)n = 1.1; mean (La/Yb)n= 0.94) in the sediments of Karnataka change to HREE-enriched patterns ((LREE/HREE)n = 0.98 and (La/Yb)n = 0.8) in the sediments of Goa suggesting marginal increase in HREE content. The source rocks (green schists and gneisses belonging to the Western Dharwar Craton) in this region are covered by laterites in both regions. As discussed above, the weathering of laterites yields to LREE-enrichment over HREE. However, the rivers of northern Karnataka and Goa drain through banded iron formations and Mn-Fe ores. The Mn-Fe ores exhibit MREE- and HREE-enriched REE pattern with positive Ce and Eu anomaly (Prajith et al. 2015). The increase in the mean Fe2O3/Al2O3 ratio from 0.64 in the sediments of Karnataka to 0.74 in the sediments of Goa also attests increased particulate material from Fe-Mn ores. Therefore, the LREE-enriched patterns in southern Karnataka changing to HREE-enriched pattern towards the rivers of northern Karnataka and Goa arise due to high proportions of lateritic soils in the former and increase in particulate matter from Fe-Mn ores in the latter. Ore-material dominated sediments and MREE- and HREE-enriched REE patterns have been reported in the rivers and estuaries of northern Karnataka and Goa (Shynu et al. 2017; Prajith et al. 2015; Kessarkar et al. 2015; Suja et al. 2017). Therefore, it is likely that the lateritic soils are diluted by higher proportions of weathering products from Fe-Mn ores resulting in MREE- and HREE-enriched REE patterns. This could be due to quick washing and transfer of ore material because of intense and heavy rainfall during the SW monsoon.
Except the five rivers of southern Maharashtra, the other river sediments of Maharashtra and Gujarat exhibit MREE- and HREE-enriched REE patterns with weak positive to weak negative Ce anomaly and positive Eu anomaly (Fig. 8). These REE patterns are in accord with the dominant weathering products from Deccan Trap basalts, characterized by HREE-enriched and LREE-depleted REE pattern with positive Eu anomaly and no Ce anomaly (Goldstein and Jacobsen 1988; Bayon et al. 2015; Sai Babu et al. 2021). The hinterland rocks of Gujarat are volumetrically Deccan Traps, but Proterozoic rocks and alluvial sediments are exposed in the drainage basins of the rivers (Fig. 1). Despite semi-arid climate prevailing over Gujarat, the weathering products are dominated by Deccan Trap material, may be because basic igneous rocks (basalts) are weathered far more easily and quickly than the granitic and gneissic rocks.
Ce anomaly
In the intensely weathered profiles and lateritic soil layers, Ce3+ oxidizes to Ce4+ and forms CeO2, a stable compound, yielding to a positive Ce anomaly (Duddy 1980; Braun et al. 1990; Su et al. 2017). The sediments of Kerala resemble lateritic soils but contain weak positive to weak negative Ce anomalies (Fig. 7A). Sai Babu et al. (2024) interpreted that Ce/Ce* was altered or weakened during transport of weathered debris from laterites into the rivers, causing weak positive to weak negative Ce anomaly. Su et al. (2017) reported positive Ce/Ce* in the lateritic profiles and poor or no Ce anomaly in the river sediments and suggested that the hydraulic, sorting induced mineral redistribution weakened REE fractionation in river sediments. Sanematsu et al. (2021) reported weak Ce anomaly in the laterite profiles and suggested that the profiles were kept in reducing conditions.
Positive Ce/Ce* is characteristic of sediments from Karnataka and Goa (Fig. 9A). The river sediments are in this region are a mixture of lateritic soils and weathered material from Fe-Mn ores, gneisses and schists from hinterland. Since positive Ce/Ce* is typical in metamorphosed rocks and Fe-Mn ores, it is reflected in the sediments.
The positive Ce anomaly in the 5 rivers from southern Maharashtra is anomalous because the Proterozoic rocks laterally change over to Deccan Traps at the border of Maharashtra and Goa (Fig. 1). Since basalts exhibit no Ce anomaly, the sediments could be the mixture of weathering products of Deccan Traps and crustal rocks of Goa at the transition zone. It is well known that the thickness of Deccan Traps decreases gradually away from the plateau, and, at the transition zone, the Deccan Traps may have contaminated with crustal sediments. Moreover, the Western Ghats exhibit steep gradient in coastal Maharashtra. Heavy monsoonal rainfall over steep gradient promotes intense physical weathering resulting in exposure of subsurface rocks. Therefore, the weathering products of the 5 southern rivers could be a mixture of different proportions of material from the Deccan Traps and crustal rocks. Strong correlation of Ce anomaly with Eu anomaly (Fig. 9B) suggest that the Ce anomaly is related to increasing mafic component of the sediment. The weak positive or weak negative Ce anomaly in the river sediments of northern Maharashtra and Gujarat (Fig. 9A) agrees with the dominant weathering products of Deccan Trap basalts.
Eu anomaly
In general, the positive / negative Eu anomaly in river sediments is related to the presence / absence of plagioclase or to the sediment mineral assembly (Aubert et al. 2001). The negative correlation of Eu anomaly with (La/Yb)n and its positive correlation with (Lu/La)n in both fractions of sediments (Fig. 10B and C) suggest that the Eu anomaly decreased with increasing felsic fraction and increased with increasing mafic component in the sediments. This inference is also supported by the negative correlation of Eu anomaly with Th/Sc ratio of the sediments (Fig. 10D). It is known that Th content is high in felsic rocks and Sc content is high in mafic rocks like basalts. Therefore, positive Eu anomaly is correlated to decreasing felsic or decreasing Th/Sc ratio. Relatively low Eu anomaly in the sediments of Karnataka and Goa and high Eu anomaly in the sediments of Maharashtra (Fig. 10A) agree with the dominant weathering products of hinterland rocks. The silts of south Kerala typically show negative Eu anomaly and high ∑REE, high heavy metal contents (Fig. 4A, Fig. 10A and Table 3), characteristic features of the felsic component-dominated rocks (Taylor and McLennan 1985). Felsic rocks dominated by khondalites occur in the hinterland (Soman 2002) and, heavy mineral placers abundantly occur in coastal south Kerala (Mallik et al. 1987). Since heavy minerals are good host for high content of heavy metals and rare earths, heavy minerals associated with silt fractions of sediments are responsible for negative Eu anomaly.
Tetrad effect
The normalized REE patterns also exhibit tetrad effect in river sediments weathered from the Archean-Proterozoic rocks and Deccan Trap volcanic rocks and there is no change in the type of tetrads (Fig. 8). Tetrad effect has been recorded in the lanthanide patterns of seawater, suspended and bottom sediments of the rivers and estuaries, authigenic precipitates and in geological materials such as sedimentary rocks, bauxites, ore deposits and certain minerals in granites and granitoids (Kawabe et al. 1991; Bau et al. 1996; Irber 1999; Takahashi et al. 2002; Monecke et al. 2002; Censi et al. 2007; Feng 2010; Shynu et al. 2011; Abidini et al. 2019; Lee et al. 2021; Wei et al. 2021). The existence of tetrad effect in granites and granitoids is due to the fluid-melt interaction in the late-stage fractional crystallization or, redistribution of lanthanides between the immiscible liquid phases via a fluoride and/or silicate melt. Tetrad effect in bauxites has been attributed to variations in geochemical parameters and /or conditions during deposition (Abidini et al. 2019). Tetrad effect intimately associated with positive Y anomaly and large negative Eu anomaly has been reported and related to thermochemical effect (Kawabe et al. 1991; Takahashi et al. 2002) or, due to magmatic-hydrothermal transition (Lee et al. 2021). Wei et al. (2021) reported negative correlations between the Sm/Nd and Y/Ho ratios and the sizes of the third tetrad and suggested that Sm–Nd and Y–Ho fractionations were most likely affected by the tetrad effect, developed due to chemical complexation during water-rock interactions (Bau 1996; Nozaki et al. 1997; Feng 2010; Feng et al. 2011). In this study, tetrad effect occurs along with high Y/Ho ratios, positive Y and Eu anomalies in the sediments from both terrains (Figs. 7 and 8). Unfortunately, there are no significant variations in the size of Eu and Y anomalies and tetrad type despite source rocks are different. Moreover, the Sm/Nd ratio varied significantly in the river sediments between Karnataka and Gujarat (Fig. 6A) but no notable change in tetrad type (Fig. 8). Therefore, tetrad effect in our sediments may not have inherited from hinterland rocks or ore deposits but formed due to chemical complexation processes during water -rock interactions. Bau (1996) suggested that the tetrad effect in waters and suspended sediments is caused by complexation of REEs due to adsorption, co-precipitation, dissolution, and/or ligand exchange reactions. Censi et al. (2007) reported tetrad effect in the dissolved phase and sediments of the estuary and related to REE complexation processes.
Comparison of normalized REE patterns
The mean PAAS-normalized REE patterns of river sediments from each state are depicted in Fig. 11A. The LREE enrichment with positive Eu anomaly is typical of sediments from Kerala. The REE patterns of sediments from other states exhibit MREE- and HREE-enrichment with positive Ce and Eu anomalies. Despite source rocks are different, the near similar REE patterns in the river sediments are caused by admixture of lateritic soils with particulates from Fe-Mn ores in the rivers of Karnataka and Goa and, largely from Deccan Traps in the rivers of Maharashtra and Gujarat. The Narmada and Tapi Rivers, the major rivers of the west coast of India, drain heterogenic rocks, including Proterozoic rocks in the upper reaches and Deccan Trap basalts in the lower reaches (Krishnan 1968). The REE patterns (MREE- and HREE-enriched with positive Eu anomaly and minor Ce anomaly; Fig. 11A) of these sediments, however, resemble that of Deccan Traps. Since the weathering products of basalts are finer that those derived from crystalline rocks, sorting of sediments during transport probably favoured the sediments characteristic of DT terrain at the lower reaches. The West Coast of India Rivers Average Clay (WCIRAC) is an average sediment composition from the sediments of 90 rivers along the west coast of India. Comparison of the PAAS-normalized REE pattern of WCIRAC with Peninsular India Rivers Average Clay (PIRAC; Saibabu et al. 2020) and World Rivers Average Clay (WRAC; Bayon et al. 2015) and Upper continental crust (UCC; Rudnic and Gao 2003) indicates that the river sediments from both the east and west coast of India (WCIRAC and PIRAC) exhibit MREE- and HREE-enriched patterns with positive Ce and Eu anomalies, while those of WRAC and UCC exhibit LREE-enriched patterns with positive Eu and weak positive Ce anomaly (Fig. 11B). The sediments in the rivers of peninsular India are more mafic despite granitic and granodiorite terrain is predominant in the hinterland. Apart from source rocks, the chemical weathering, supply of REE and transport processes indeed played major roles in the fractionation of REE.