Fold interference patterns in Meso-Proterozoic Champaner fold belt (CFB) Gujarat, western India

Abstract

This paper documents three phases of folding within the Meso-Proterozoic Champaner Fold Belt (CFB) located at the eastern part of Gujarat, western India. The first phase ($\hbox {F}_{1})$ displays WNW plunging $\hbox {F}_{1}$ fold of moderately inclined nature in the schists of the Khandia Formation. The second phase ($\hbox {F}_{2})$ refolded $\hbox {F}_{1}$ along a similar trend to produce folds of tight isoclinal nature in the Khandia and Narukot quartzites. Additionally, these $\hbox {F}_{1}$ folds depict second-order tight, and $\hbox {F}_{2}$ folds as first-order open type in the younger sequences of the CFB with varying amplitude vs. wavelength ratio. The ratio for $\hbox {F}_{1}$ folds ranges from 2:1 to 3:1, obtained along 3–4 m length across 3–6 $\hbox {m}^{2}$ area, whereas for $\hbox {F}_{2}$ folds the ratio ranges from 1:4 to 1:5 and is obtained along 1–2.5 km length across 0.5–1.5 km$^{2}$ area. The fold interference pattern developed on account of $\hbox {F}_{1}$ and $\hbox {F}_{2 }$ folds has resulted into Type-III or hook-shaped geometry regionally. The last phase of folding is characterised by N–S trending $\hbox {F}_{3}$ folds of open type over kilometre long limbs of $\hbox {F}_{1}$ and $\hbox {F}_{2}$ folds. The superposition of $\hbox {F}_{1-3 }$ folds developed map scale Type-I or Dome and Basin geometry over Type-III superposed folds. The overall compressional direction for $\hbox {F}_{1}$ and $\hbox {F}_{2}$ folds ranges from N–S to NNE–SSW and for $\hbox {F}_{3}$ ranges from E–W to ESE–WNW.

1 Introduction

In any area, the existence of interference fold patterns indicates refolding of earlier folds. A derivative of these interference geometries ranges from micro- to mega-scale (see, e.g., Platt 1983; Ghosh 1993; Fossen and Holst 1995; Mamtani et al. 2001; Caritg et al. 2004; Tian et al. 2013; Fossen 2016). The interference geometries are important as they provide significant clues on shortening direction and decode the multiple deformational events (Forbes and Betts 2004; Forbes et al. 2004). A combination of such refolded folds on map scale has been documented in the present work with the aid of detailed fieldwork.

Fig. 1

(a) Location sketch of the Champaner Group; (b) lithostratigraphic map of SAMB, NW, India. Modified after Mamtani and Greiling (2005). Red square indicates the study area. Magnetic foliation data presented within Godhra granite is after Mamtani (2014).

The area under investigation is the part of Southern Aravalli Mountain Belt (SAMB) exposed along the eastern fringe of Gujarat, India (figure 1a). Rocks of this region belong to the Champaner Group of Meso-Proterozoic age, forming the youngest part of the Aravalli Supergroup (Gupta et al. 1992, 1995, 1997). Initially, the structural history of the Champaner Group was thought to be very simple with respect to the main Aravalli domain. The idea proposed by Roy (1985, 1988) and Merh (1995) suggests that the Champaner Group represents one single phase of deformation and possesses no superposed folds. Later on the detailed work carried out by Karanth and Das (2000) and Das (2003) in order to decode the deformational history of the Pre-Champaner Gneissic Complex in Chhota Udepur region gave a comparative study about the deformational style between Pre-Champaners and Champaner rocks. They illustrated two phases of folding within the Champaner Group having orthogonal axial planes. However, they did not comment on the existence of superposed folds within the Champaner Group of rocks, unlike that in the Pre-Champaner Gneissic Complex of Chhota Udepur region. In the light of hitherto work, more research is needed in order to address the structural complexity in the form of interference fold pattern within the rocks of the Champaner Group.

2 Geological setting

The Champaner Fold Belt, consists of the Champaner Group, is a part of upper Aravalli exposed along the southern most fringe of SAMB in Gujarat (Gupta et al. 1992, 1995) (figure 1b). The Champaner Group is characterised by Meso-Proterozoic low-grade metasedimentary rocks and are intruded by Neo-Proterozoic ($955{\pm }20$ Ma) Godhra granite (Rb/Sr method; Gopalan et al. 1979). Lithologically, it comprises metasubgraywacke, phyllite, carbonaceous schist, quartzite, gneisses and petromict metaconglomerate with bands of dolomitic limestone and mangeniferous phyllite (Gupta et al. 1980, 1997) (figure 2a). Based on the homogeneity in terms of rock type, strike persistency and occurrence of intraformational conglomerate, the Champaner Group has been divided into six formations (Gupta et al. 1997) (table 1; Gupta et al. 1980, 1992). Greenschist facies condition demarcates the regional grade of metamorphism, whereas the contact metamorphic grade has reached up to the hornblende hornfels facies (Jambusaria and Merh 1967; Jambusaria 1970; Gupta et al. 1997; Das 2003; Das et al. 2009).

Fig. 2

(a) Geological map of the Champaner region, modified after Jambusaria (1970), Gupta et al. (1997) and Joshi et al. (2018; b) detailed structural map of the Narukot dome; (c) sub-area I: lower hemisphere stereographic projection of the $\hbox {L}_{2}$ ($\hbox {S}_{2}$–$\hbox {S}_{0})$ intersection lineation data collected from $\hbox {F}_{1}$ dominated area. The $\pi _{1}$ axis of $\hbox {F}_{1}$ fold (red triangle) orientation fits well with the pucker axes lineations measured in the field (filled square); (d) contoured Pie diagram of sub-area I showing $\hbox {F}_{1}$ fold axis ($\pi _{1})$: $n=15$, $\hbox {S}_{0}$; contours = 7%, 14%, 28% per unit area; (e) sub-area II: stereographic projection of the $\hbox {L}_{2}$ intersection lineation (secondary cleavage planes and $\hbox {S}_{0})$ data collected from $\hbox {F}_{2}$ dominated area. The $\pi _{2}$ axis of $\hbox {F}_{2}$ fold (red triangle) orientation fits well with intersection lineations measured in the field (filled square); (f) contoured Pie diagram of sub-area II showing $\hbox {F}_{2}$ fold axis ($\pi _{2})$: $n=29$, $\hbox {S}_{0}$; contours = 4%, 8%, 16%, 32% per unit area; (g) sub-area $\hbox {III}_{\text {a and b}}$: lower hemisphere stereographic projection of steeply plunging $\hbox {F}_{3}$ fold axis collected from the field. The $\pi _{3}$ fold axis (red triangle) matches with the field lineations of $\hbox {F}_{3}$ fold axis (filled square); and (h) contoured Pie diagram of sub-area $\hbox {III}_{\text {a and b}}$ showing $\hbox {F}_{3}$ fold axis ($\pi _{3})$: $n=14$, $\hbox {S}_{0}$; contours = 8%, 16%, 32% per unit area.

Table 1 Proterozoic stratigraphic succession of Gujarat and south Rajasthan; after Gupta et al. (1980, 1992).

3 Structural setup

The existing structural set up of the Champaner Group suggests that the rocks are polydeformed forming a regional ‘S’ shaped pattern consisting two major anticlines and synclines (Jambusaria 1970). Two phases of deformation have been recorded so far, viz., $\hbox {D}_{1}$: E–W trending $\hbox {F}_{1}$ folds of tight/isoclinal upright nature; and $\hbox {D}_{2}$: N–S trending $\hbox {F}_{2}$ folds with N plunging open warps with kink bands (Jambusaria and Merh 1967; Gopinath et al. 1977; Shah et al. 1984; Srikarni and Das 1996; Karanth and Das 2000; Das 2003; Limaye and Bhatt 2013; Limaye 2016a, b; Patel et al. 2016). $\hbox {F}_{1}$ and $\hbox {F}_{2}$ folds are also affected by numerous axial planar slippages depicting radial pattern (Jambusaria and Merh 1967; Yellur 1969; Jambusaria 1970; Joshi et al. 2018). The axial planar slippages scattered in a radial pattern show signatures of sinistral/dextral faults (figure 2a). Moreover, there also exists signature of top-to-east cross-sectional reverse shears within the rocks of the Narukot Formation (figure 2a) (Joshi et al. 2018). A combination of $\hbox {F}_{1}$ and $\hbox {F}_{2}$ folds along the E margin of the Champaner Group has generated interesting dome structures at Narukot and Poyli areas (Jambusaria 1970). One such dome situated at Narukot within the Khandia and Narukot Formation has been worked out in detail, which provides significant insight in terms of overall deformation undergone by the Champaner Group of rocks.

Fig. 3

(a) $\hbox {L}_{2}$ ($\hbox {S}_{2}$–$\hbox {S}_{0})$ intersection lineation in schist of Khandia Formation (camera faces southern direction); (b) sub-parallel relationship between $\hbox {S}_{0}$ and $\hbox {S}_{1}$ in quartzite demarcated over the outcrop with black pen markings. Discrete secondary cleavages can be appreciated over $\hbox {S}_{\mathrm{0}}$ (camera faces southeastern direction); (c) steep F3 fold axes preserved in quartzite (camera faces southern direction); (d) second-order tight $\hbox {F}_{1}$ folds in phyllite of Shivrajpur Formation (camera faces western direction); (e) second-order tight $\hbox {F}_{1}$ folds within the right limb of first-order open $\hbox {F}_{2}$ fold in quartzite of Shivrajpur Formation (camera faces western direction); (f) second-order tight $\hbox {F}_{1}$ fold in quartzite of Lambhia Formation (camera faces western direction); (g) first-order $\hbox {F}_{2}$ fold in quartzite of Rajghar Formation (camera faces eastern direction); (h) N–S trending Kink band in phyllite of Narukot Formation (camera faces northern direction); (i) field photograph after Joshi and Limaye (2014), showing discordant relationship between intruding coarse-grained granite into fine-grained granite (camera faces eastern direction); (j) xenolith of schistose rock within granite (camera faces western direction); (k) xenolith of fine-grained granite in coarse-grained granite (camera faces northern direction); (l) sharp intrusive contact between granite and the Champaner metasediments (camera faces eastern direction); (m–p) top-to-east ductile shear along the cross-section. S schistosity fabric dipping steeper than the C-plane. Photograph (n–p) after Joshi et al. (2018).

Regional-scale fold mapping carried out at the ‘Narukot dome’ differs from the existing structural set up presented by the earlier workers. Dome appearance at Narukot is composed of the combination of $\hbox {F}_{1}$ to $\hbox {F}_{3}$ folds regionally (figure 2b). In order to carry out the structural analysis the area has been divided into sub-areas, i.e., I, II, $\hbox {III}_{\mathrm{a}}$ and $\hbox {III}_{\mathrm{b}}$, representing $\hbox {F}_{1}$, $\hbox {F}_{2}$ and $\hbox {F}_{3}$ dominated regions, respectively. Sub-area I represents $\hbox {F}_{1}$ fold with an axial trace dipping due WNW in Khandia schist located at the eastern part of the dome. $\hbox {F}_{1}$ fold has resulted due to folding of $\hbox {S}_{0}$ bedding plane by generating $\hbox {S}_{1}$ schistosity plane. Due to the manifestation of $\hbox {F}_{2}$ over $\hbox {F}_{1}$, $\hbox {S}_{0}$ shows sub-parallel relationship with $\hbox {S}_{1}$ and axial planar $\hbox {S}_{2}$ schistosity plane has been developed generating $\hbox {L}_{2}$ lineations on $\hbox {S}_{0}$ (figure 3a). These lineations are intersection lineations formed by $\hbox {S}_{2}$–$\hbox {S}_{0}$ intersection, which plunges 46$^{\circ }$ in the direction of 279$^{\circ }$N and form pucker axis over the hinge line. By plotting several such lineations over lower hemisphere stereographic projection, the orientation of $\pi _{1}$ axis fits well with the pucker axes lineations obtained from the field (figure 2c). The fold is moderately inclined having pitch of the $\hbox {F}_{1}$ fold axis 47$^{\circ }$ in the direction of 280$^{\circ }$N (WNW) measured on $\hbox {S}_{0}$ plane (figure 2d). Tight to isoclinal $\hbox {F}_{2}$ folds affected quartzite band as $\hbox {F}_{1}$ folds refolded along a similar trend. In quartzites the $\hbox {S}_{0}$–$\hbox {S}_{1}$ relationship is sub-parallel to each other and $\hbox {S}_{0}$ dips slightly steeper as compared to $\hbox {S}_{1}$ (figure 3b). $\hbox {S}_{2}$ orientation is feeble and mostly appears as discrete cleavages to form $\hbox {L}_{2}$ intersection lineations between secondary cleavage planes and $\hbox {S}_{0}$ over $\hbox {S}_{1}$. $\pi _{2}$ axis of $\hbox {F}_{2}$ fold matches with the data set of intersection lineations recorded from $\hbox {F}_{2}$ dominated area (figure 2e). The core of the $\hbox {F}_{2}$ fold is traceable for 1 km at the western margin of the Narukot dome and can be seen in sub-area II of figure 2b. The N and the S limb of $\hbox {F}_{2}$ strike $\sim$E–W having due N and due S dip directions, respectively. The fold axis plunges towards W with an amount of 20$^{\circ }$ and possess a sub-vertical axial plane (figure 2f). Sub-area $\hbox {III}_{\text {a,b}}$ depicts $\hbox {F}_{3}$ open fold trending N–S axial trace over kilometre long limbs of $\hbox {F}_{1}$ and $\hbox {F}_{2}$ folds. The axial plane can be traced from the N to the S fringe of the dome dividing it into two approximately equal portions. Steeply dipping mesoscopic $\hbox {F}_{3}$ fold axes have been observed along outer rim of quartzite near SW of Wadek (figure 3c). These lineations fit well with the fold axis $\pi _{3}$ (figure 2g). The folds possess vertical axial plane and have a northerly plunge of its axis (figure 2h). Representation of $\hbox {F}_{1-3}$ folds along with the orientation of the axial plane and fold axis in the Narukot dome, depicted by SRTM worldwide elevation data (3-arc-second resolution) downloaded from Global mapper (v17) (figure 4).

An attempt has been made to study the derivates of these three fold events across the Champaner Group. The results signify that further to the W of the Narukot dome, where the younger Formation of the Champaner Group is encountered, $\hbox {F}_{1}$ folds exhibit second-order tight and $\hbox {F}_{2}$ folds as first-order open with varying amplitude vs. wavelength ratio (figure 3d–g). The ratio for $\hbox {F}_{1}$ folds has been calculated in the field as the folds are meso-scopic in nature. The ratio ranges from 2:1 to 3:1, obtained along 3–4 m length across 3–6 $\hbox {m}^{2}$ area. However, for $\hbox {F}_{2}$ folds the ratio ranges from 1:4 to 1:5, obtained along 1–2.5 km length across 0.5–1.5 $\hbox {m}^{2}$ area. These $\hbox {F}_{2}$ fold ratios have been acquired through satellite image and validated during mapping. $\hbox {F}_{3}$ folds gradually die out in the form of mega-scale open wraps to meso-scale kink bands from eastern to the western stretch of the Champaner Group, respectively (figure 3h).

Fig. 4

SRTM-derived shaded relief map of the Narukot Hammer head anticlinal structure. Respective orientations of the axial planes and fold axis have been demarcated.

4 Discussions

Analyses of individual folds from $\hbox {F}_{1}$ to $\hbox {F}_{3}$ at Narukot were helpful in interpreting the regional-scale deformation interference pattern. The combination of $\hbox {F}_{1}$ and $\hbox {F}_{2}$ fold has generated map scale hook or Type-III interference pattern of Ramsay (1962) and Ramsay and Huber (1987), demonstrating a comprehensive hammer head anticlinal structure. Their fold axes are sub-parallel ($\hbox {F}_{1} \sim$ WNW; $\hbox {F}_{2}{\sim }$ W) with $\sim$ orthogonal axial planes. Overprinting of $\hbox {F}_{3}$ fold on $\hbox {F}_{1}$ and $\hbox {F}_{2}$ developed regional-scale dome and basin geometry or Type-I interference pattern (Ramsay 1962; Ramsay and Huber 1987). Moreover, N–S trending $\hbox {F}_{3}$ fold developed by E–W shortening has its maximum effect along the eastern margin of the Champaner Group by closing up of domes at Narukot and Poyli areas (locations in figure 2a).

In order to postulate the possible causes of the fold trends recorded from the Champaner Group, the proto-continent accretion concept (primarily given by Naqvi et al. 1974; Radhakrishna and Naqvi 1986; Rogers 1986; Naqvi and Rogers 1987) for the Aravalli, the Dharwar and the Singhbhum proto-continents proved to be useful. The ‘Y’-shaped lineaments, viz., the Narmada, Son and Godavari, along which the Aravalli–Dharwar, the Aravalli–Singhbhum and the Dharwar–Singhbhum proto-continents accreted, respectively, during the Meso-Proterozoic times. Based on a ‘Working Model’ or ‘Working Hypothesis’ given by Mamtani et al. (2000) in terms of deformation pertaining to the SAMB it clearly suggests that, there is an impact of accretionary event on southern part of the Aravalli proto-continent the manifestation of which is in the form of changes in the structural trends and growth of metamorphic minerals. Further the model illustrates that the E to NW trending structures in SAMB formed suturing between the Aravalli and the Dharwar Protocontinents (ca. 1400–935 Ma). In case of the present study, the N–S to NNE–SSW shortening direction generated on account of the suturing has led to the development of ESE–WNW to E–W trending structures across the Champaner Group. Furthermore, the area located at the core of the Champaner Group has experienced intense compression due to regional deformation, engendering refolding of earlier folds at the Narukot dome and imparting westerly plunge to $\hbox {F}_{1}$ and $\hbox {F}_{2}$ folds (figure 5a). Similar concept of protoplate tectonics has been anticipated to explain the deformational patterns observed in the southern parts of the Delhi Fold Belt (by Sychanthavong and Desai 1977; Sychanthavong and Merh 1981, 1985; Sychanthavong 1990).

Fig. 5

(a) Cartoon showing suturing of proto-continents and refolding of earlier folds along with the plunge on account of regional deformation as well as emplacement of syntectonic granite; (b) closing up of earlier refolded folds orthogonally and development of sinistral/dextral faults along the pre-existing axial planes due to post-intrusive pulse. Granite of post-tectonic nature holds xenoliths of Champaner metasediments and earlier syn-tectonic granite. These cartoons have been modified after Winter (2012).

Fig. 6

SRTM-derived shaded relief map of the Champaner region. Red region demarcates the granite country and shades of grey depict the folded Champaner metasediments. Curved thin red line shows the axial trace of the rim synclines developed along the periphery of the granite pluton.

Granites located in and around the Champaner Group of rocks display signatures of syn to post-plutonic emplacement (Joshi and Limaye 2018). Distinguishing characteristic of syn/post-tectonic granite can be very well appreciated along the east of the Jhand area (location presented in figure 2a), where coarse-grained post-tectonic granite is having intrusive relationship with the fine-grained syn-tectonic granite (figure 3i) (Joshi and Limaye 2014). The coeval pulse of granite emplaced during progressive deformation has magnetic foliation trending WNW–WSW (figure 1b). Feldspar laths within syn-tectonic granites too trend WNW to W striking trends (Mamtani 1998; Mamtani et al. 2002; Mamtani and Greiling 2005; Sen and Mamtani 2006). Existing geochemical records of syn-tectonic granite suggest that the granite is of ‘S-type’ evolved on account of partial melting of the continental crust during continent–continent collision (figure 5a) (Merh 1995; Goyal et al. 1997).

Table 2 Summarisation of various interference fold patterns along with the fold and fault events observed within the Champaner Group (data of out-of-sequence deformation is after Joshi and Limaye 2018).

The granite of post-tectonic nature is characterised by forceful emplacement deforming the country rocks along N–S trend and developed strike slip faults of sinistral/dextral nature along pre-existing axial planar weak zones throughout the group (figures 2a and 5b). The model given by He et al. (2009) for Fangshan pluton, SW Beijing, forms the rim syncline along the margin of the pluton. Similar style of N–S trending rim synclines is found to be developed along the eastern margin of the Champaner Group bordering the pluton. SRTM-derived shaded relief map of the Champaner region demarcates folded metasediments and its relationship with the adjacent pluton (figure 6). The post-tectonic granite having the geochemical affinity of ‘A-type’ representing transitional or post-orogenic uplift (suggested by Maithani et al. 1998 and Goyal et al. 2001), has been intruded by accommodating the space within the Champaner metasediments and pre-existing syn-tectonic pulse (figure 5b). Such inference has been derived by collecting xenolith evidence of (i) Champaner metasediment and (ii) fine-grained granite from coarse-grained granite variety (figure 3j–k). One such location is at the northeastern fringe of the Champaner region near Sukhi dam, where intrusive contact between Godhra granite and Champaner metasediments is exposed (figure 3l).

Geophysical studies carried out by Joshi et al. (2018) using Microtremor method suggests pluton hump exactly below the Narukot dome. The surface manifestation of pluton hump can be corroborated by the development of the cross-sectional reverse shear having top-to-east shear sense, in the vicinity of the Narukot dome (figure 3m–p). Recent work carried out by Joshi and Limaye (2018) at Jothwad region on isolated calc-silicate bands from khandia Formation records signatures of out-of-sequence deformation due to post-tectonic granite. The Jothwad region, part of the Champaner Group, represents superimposition of Type-II interference pattern over cylindrical upright fold. Moreover, these interference fold patterns are rootless and depict no continuity in the subsurface as well as are unmatched with the existing structural set up of the Champaner Group.

5 Conclusions

• The Meso-Proterozoic Champaner Group represents interference fold patterns ranging from Type-1 to Type-III (table 2).

• Type-III interference fold pattern is due to regional deformation and generated by combinations of $\hbox {F}_{1-2}$ folds ($\hbox {F}_{1} {\sim }$ ESE–WNW; $\hbox {F}_{2} {\sim }$ E–W).

• Regional deformation has imparted westerly plunge to $\hbox {F}_{1-2}$ folds and also characterised by syn-tectonic emplacement of granite having similar trend.

• Type-I interference pattern superimposed over Type-III by closing up of domes, represents $\hbox {F}_{3}$ folds ($\hbox {F}_{3} {\sim }$ N–S) due to post-intrusive granite. The same has been responsible for the development of sinistral/dextral faults throughout the group and cross-sectional reverse shears in vicinity of the Narukot dome.

• Type-II superimposed over rootless cylindrical upright folds represents out-of-sequence deformation of $\hbox {F}_{1-2}$ folds ($\hbox {F}_{1} {\sim }$ NW–SE to N–S; $\hbox {F}_{2} {\sim }$ NE–SW) suggests syn-post plutonic emplacement.