the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Jul 2023
Magmatic underplating associated with Proterozoic basin formation: insights from gravity study over the southern margin of Bundelkhand craton, India
Ananya P. Mukherjee
Animesh Mandal
Abstract. Extension tectonics responsible for intracratonic rift basin formation are often the consequences of active or passive tectonic regimes. The present work puts forth a plume-related rifting mechanism for the creation and evolution of two Proterozoic sedimentary basins outlining the Bundelkhand craton, namely the Bijawar and Vindhyan basins. Using global gravity data, a regional scale study is performed over the region encompassing the southern boundary of the Bundelkhand craton consisting of Bijawar basin, Vindhyan basin and Deccan basalt outcrops. The gravity highs in the central part of the observed Bouguer gravity anomaly as well as the upward continued regional anomaly, derived from global gravity grid data, suggests that the Vindhyan sedimentary basin overlies a deeper high-density crustal source. The deepest interface as obtained from the radially averaged power spectrum analysis is observed to occur at a depth of ~30.3 km, indicating that the sources responsible for the observed gravity signatures occur at larger depths. 3D inversion of Bouguer gravity anomaly data based on Parker-Oldenburg’s algorithm revealed the Moho depth of ~32 km below the Vindhyan basin, i.e., south of the craton. 2D crustal models along two selected profiles showcase a thick underplated layer with maximum thickness of ~12 km beneath the southern part of the Bundelkhand craton. The inferred large E–W trending underplating and deciphered shallower Moho beneath the regions south of the exposed Bundelkhand craton points to crustal thinning compensated by magmatic emplacement due to a Paleoproterozoic plume activity below the craton margin.
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Ananya P. Mukherjee and Animesh Mandal
Status: open (extended)
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RC1: 'Comment on egusphere-2023-1389', Anonymous Referee #1, 24 Oct 2023
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GENERAL COMMENT
The manuscript attempts to relate the creation and evolution of the proterozoic Bijawar and Vindhyan sedimentary basins of India to the plume-related rifting mechanism and the associated mafic subcrustal underplate emplaced at a depth of greater than 30 km. The authors used the global gravity grid data to show the spatial and depth extent of the high density mafic underplate in the two forward models they prepared. The topic is important and interesting and the manuscript is well written. However, there are points that need addressing in order to improve the quality of the manuscript and to make it relevant and make it suitable for publication in the form of a research paper.
SPECIFIC COMMENTS
- The title: Basin formation and evolution is attributed to the combined effects of all the sublithospheric actions including underplating as well as the lithospheric plate actions and the supergene action of the lithosphere itself as expressed in all the processes that take place on the earth’s surface. The title, as it is and at a glance, seems to carry the idea that underplating alone can play a significant role in basin formation.
- The authors have not shown the locations of the two basins. What they show on the map is the lithostratigraphic units bearing the names of the two basins.
- What is the rationale for upward continuing the gravity data to a 30 km height? It is more reasonable to base the continuation height on the corresponding depth estimates obtained from the radially averaged power spectrum.
- Gravity modeling is loosely constrained with only limited information. Hence the modeling result should be interpreted with caution.
- To generalize that the high density anomaly has sources extending from deep to shallow is an over simplification. The authors have done upward continuation to a single height and they base their conclusion on it. Try to upward continue to a height of 60 (corresponding to sources at a depth of 30 km and below) to justify presence of underplate at depths in the order of 30 km in the models. In addition, the central part of the models (central region) do not show the extension of high anomaly sources to shallower depths as shown by the residual anomaly.
- On Line 332 the paper asserts that there is striking similarity between the inverted Moho topography and the gravity signature. Please tone down this assertion. There is similarity but pay attention to the following remarks: a. the gravity anomaly from the inverted Moho topography shows a slightly southward shift and centered at the southern margin of the regional anomaly. b. at the southwestern corner the effect is in fact opposite. There is high anomaly in the both the regional and residual gravity but low anomaly in the gravity obtained from the Moho.
- I have serious reservation on the contradictory results obtained from the two approaches of the gravity modeling. The authors obtained the undulation of the Moho interface using the downward continuation formula as given by the modification of Parker-Oldenburg algorithm (Fig. 5a). As is also noted by the authors the Moho depth undulations obtained by this method beneath the basins where underplate is observed do not correspond to the depths obtained by forward modeling (Fig. 6 & 7). The underplate top is considered as Moho in Fig. 5a whereas the underplate bottom is considered as Moho in both Fig. 6 & 7. In addition, there is also a clear discrepancy in areas where there is no underplate. Compare, for example, Fig. 5a with Fig. 7. In northeast where there is no underplate the Moho depth varies between 37 and 39 km in the forward model in Fig. 7 whereas in Fig. 5a the depth variation for the same area is between 33 and 44 km. These contradictions should not have occurred since there is a clear density contrast between the mantle and the underplate and the Parker-Oldenburg approach is capable of recognizing the difference between them.
TECHNICAL CORRECTIONS
- On Line 29 “…..attributed to the presence of underplated layers, like rift basins…” Please remove the word “like”.
- On Lines 194 and 197- 8 the phrase h(x) and zo are redundant. Please eliminate the repetition.
- On Line 346 it must be “crustal uplift” and not “crustal upliftment”.
- In Fig. 5 contour values can be indicated on every other line to avoid congestion.
Citation: https://doi.org/10.5194/egusphere-2023-1389-RC1
Ananya P. Mukherjee and Animesh Mandal
Ananya P. Mukherjee and Animesh Mandal
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