Appendix I. Field descriptions and notes about the central Saurashtra dyke swarm, Deccan Traps

CENTRAL SAURASHTRA dykes
Rajkot and Amreli districts, Gujarat state
Survey of India Toposheets:41J/12, 41J/16, 41K/9, 41K/13, 41N/4, 41N/8, 41N/12, 41O/1, 41O/5, 41O/9 (1:50,000). Sampled December 2011, Hetu Sheth.
Sr. No. / Sample
No. / Dyke/
Flow / Trend / Width
(m) / Remarks
1 / CSD1 / Dyke / N80 locally, N87 overall / A few m / The Sardhar dyke, sampled near Ribda, N of Gondal. Sample is from 2.5 km W of Ribda on the road to Lodhika. Fine-grained, aphyric, basalt-dolerite.
2 / CSD2 / Dyke / N80 / A few m / Dyke on the road from Atkot to Sardhar, forming ridge on W of road, a few hundred meters after the turning for Boldhoi. Bouldery dyke, spheroids everywhere, sampled. Very fresh inside, fine-grained. Altered outside.
3 / CSD3 / Dyke / Kinked, N80 locally, N100 overall / A few m / Dyke just outside and E of Kundani. Unusually nicely jointed dyke with close-spaced, sheet-like vertical joints perpendicular to strike, in plan view. Fine-grained, aphyric basalt. Joint blocks sampled, are weathered outside and fresh inside. May represent the Sardhar dyke towards the E, and the dyke will be nearly 60 km long if so.
4 / CSD4 / Dyke / N83 / A few m / Polarpar dyke, sampled ~0.5 km E of that village. Very fresh, medium-grained, spotty. Seems to have much olivine, so olivine dolerite. Photos of ridge with small boulders. Several medium and small samples.
5 / CSD5 / Dyke / N90 (E-W) locally, N87 overall / A few m / Sardhar dyke, Saurashtra’s longest, sampled on road going W of Sardhar town, 0.5 km from it. Many cuts (quarry pits) are available. Rock is very weathered so took a few spheroid cores. Dyke shows multiple columnar rows. Fine-grained, aphyric basalt/dolerite, like its extension CSD1 sampled near Ribda, 30 km W of CSD5. Towards E, sample CSD3 may represent the same dyke, and dyke will be ~60 km long if so.
6 / CSD6 / Dyke / N80 / A few m / Dyke 2 km SE of Jangvad on the Atkot-Babra road, before Kotdapitha. Spheroid taken from low ridge. Hard, fine-grained, aphyric, typical dolerite.
7 / CSD7 / Dyke / Curved, N77 overall / A few m / The Isapur-Vasavad dyke, sampled ~1 km W of the highway between Untvad and Babra, on the road connecting Visapur to the highway. The road is parallel to and beside the dyke. Medium-grained olivine dolerite with a greenish tinge and waxy lustre. Very long (tens of km). Boulders on low ridge.
8 / CSD8 / Dyke / N90 (E-W locally), N77 overall / A few m / The same dyke sampled further SW, ~1 km W of Isapur, going towards Nadala, in road cut. The same olivine-rich, greasy look, very fresh.
9 / CSD9 / Dyke / N68 / A few m / The Thorkhan dyke sampled ~1.5 km SW of Thorkhan. Dyke passes through that village but cannot be seen or sampled. Very fresh, hard, medium-grained, greasy lustre so seems olivine-rich.
10 / CSD10 / Dyke / N70 / A few m / The dyke passing through Sanathli village. Quarry pits in dyke. Coarse dolerite, slightly weathered to fresh. Sampled ~200 m E of the village.
11 / CSD11 / Dyke / Bent, N80 locally, N113 overall / A few m / Dyke 2 km S of Dadva Mota on the way to Kanapar. Ridge crossing the road, quarried. No or rare outcrops, one spheroid taken. Weathered, fresh inside, medium-grained aphyric dolerite.
12 / CSD12 / Dyke / N75 / A few m / On the way from Kanapar to Pratappur, dyke E of and on road towards the 181 m hill with mata temple, across Bhadar river. Boulders sampled, medium-grained olivine dolerite, aphyric, fresh inside.
13 / CSD13 / Dyke / Curved, N320 (N40W) locally, N23W overall / A few m / Dyke cutting the Chavand-Dhasa road, 2 km E of Derdi Janbai. Forms a very low ridge. Sampled 0.5 km south of the road. Quarry pits all along, only small samples possible. Weathered on the outside to white colour, but very fresh, very fine-grained basalt inside. Shiny, possibly chilled margin of dyke. This may be the same curved dyke as CSD15 and ~30 km long if so.
14 / CSD14 / Dyke / N90 / A few m / Rhyolite dyke 1 km N of Junvadar, towards Sitapar. Dyke has no topographic expression and is essentially a quarry pit at the road junction. Red rhyolite, altered outside but OK otherwise, silicified. It is several km long by toposheets 41O/5 and 41O/9 (starts near here and ends near Dhasa).
15 / CSD15 / Dyke / N320 / A few m / Basalt dyke just NW of Barwala, sampled ~800 m out of village on the way to Kidi. Road is roughly parallel to the dyke, which forms a low ridge with rare outcrops, though the ones sampled are very good. Extremely fresh, compact, very fine-grained basalt. Joint columns observed which seem to dip steeply due east. Fresh samples taken. Trend N40W locally. This may be the same curved dyke as CSD13 and ~30 km long if so.
16 / CSD16 / Dyke / N80 locally, N70 overall / A few m / Olivine dolerite dyke going from near Dared to near Babra, sampled just W of Dared (first mound). Very fresh spheroids taken. Medium-grained, shiny. Trend N80 locally. Photo of ridge with top boulders.
17 / CSD17 / Dyke / Arcuate, N20 locally, N48 overall / A few m / Sizeable dyke arcuate in plan, sampled ~1.5 NE of Babra going towards Kariana. Medium-grained, fresh olivine dolerite with greasy lustre. Aphyric. Forms a ridge several km long with boulders on top. Sampled in cut at the entrance to the dam.
18 / CSD18 / Dyke / Arcuate, N70W overall, much different if CSD8 and CSD7 included / A few m / Major, very long curved dyke that comes from the W and meets CSD17. Because of soil cover it is impossible to say which cuts which, but the T-junction is well defined. CSD18 was sampled ~800 m from the junction on the middle heights of a segmented ridge. Is very fresh olivine dolerite, aphyric, nice view and photos of adjacent dyke ridge segment. This may be the same dyke as CSD8 and CSD7, though very curved, and will be ~30 km long if so.
19 / CSD19 / Dyke / N326 (N34W) / A few m / Very long (~20 km) dyke 1 km W of Taivadar on the road from Babra, sampled ~200 m inwards of the road. This cuts CSD17, and forms a low ridge. Joint block samples from quarry pit. Very fresh, black, fine-grained basalt, quite aphyric.

Submitted to Bulletin of Volcanology

40Ar/39Ar geochronology and geochemistry of the Central Saurashtra mafic dyke swarm: implications for magmatic evolution, magma transport, and dyke-flow relationships in the northwestern Deccan Traps

Ciro Cucciniello1*, Elena Demonterova2, Hetu Sheth3, Kanchan Pande3, Anjali Vijayan3

* Corresponding author (email: ; tel: +39-0812538176/+39-3280230319)

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