Header menu link for other important links
Petrogenesis of flood basalts of the Narsingpur-Harrai-Amarwara-Lakhnadon section of eastern deccan province, India
Published in Springer Netherlands
Pages: 191 - 238
The present area of investigation falls in the Eastern Deccan segment where available field and geochemical data are rather limited. In the present study, five distinctive structural zones namely Lower Vesicular zone, Lower Colonnade Zone, Entablature Zone, Upper Colonnade Zone and Upper Vesicular Zone have been identified in different lava flows which are helpful for the purpose of stratigraphic correlation. All the lavas under investigation can be classified into three distinct geochemical groups (viz. Group I, Group 2 and Group 3) on the basis of their Mg′ number and TiO2 wt%. The Group 1 lavas are marked by low Mg′ No (0.39-0.45) and high TiO2 (2.9-3.6 wt%) while Group 2 lavas are characterized by moderate Mg′ No (0.45-0.50) and moderate TiO2 (2.4-2.9 wt%). On the other hand, high Mg′ No (0.49-0.54) and low TiO2 (1.91-2.31 wt%) characterize the Group 3 basalts. Interestingly, the basaltic flows corresponding to three distinct groups are intermixed with each other; in other words, lava flows belonging to several groups are juxtaposed with one another with increasing height. Evolutionary trends of the entire basaltic lava flows of the study area are also attempted based on the major and trace element (including REE) chemistry. All the investigated basaltic lava flows in general show a restricted compositional range and they fall in the basalt field in the total alkali versus silica diagram. They have, in general, a tholeiitic imprint (with a tendency of becoming high iron tholeiite). Closer examination of several variation diagrams involving different major-elements versus Mg′ No plot indicates that the three basaltic groups have distinct and secluded geochemical trends suggestive of their derivation from discrete magma pulses. However, each investigated group of basalts shows evidence of intra-group differentiation. Variation diagrams involving plot of several compatible elements/incompatible elements versus Mg′ number also indicate discrete or independent derivation of the three investigated basalt groups. The trace element variation-diagrams also reveal subsequent low to moderate degree of-internal fractionation within each investigated group. This observation (regarding derivation of three groups corresponding to different magmatic pulses and subsequent internal differentiation) has also been corroborated from plots of several major and trace elements versus Zr plot. Chondrite normalized rare earth element plots for the three investigated group of basalts indicate that their fundamental patterns for the REE variation are essentially the same showing most primitive pattern for the Group 3 basalts and the most evolved pattern for the Group 1 basalts. Further it has been found that Σ(REE)N for Group 3 basalts is the least while the same value corresponding to Group 1 basalts is the highest. The Σ(REE)N for Group 2 basalts is intermediate between those of Group 1 and Group 3. Several trace element-ratios namely Zr/Nb, La/Nb, Ba/Nb, Ba/Th, Rb/Nb, K/Nb, Th/Nb, Th/La and Ba/La were successfully employed to constrain the source characteristics of the investigated basalt-groups. On the basis of these trace-element ratios, it has been found that in general, Group 1 basalts have affinity either to EMI/EMII or HIMU sources while Group 2 and Group 3 basalts show a close proximity towards HIMU parentage although affinity towards EMI and EMII was also hinted. Thus a distinct enriched mantle character has been documented from due consideration of several critical trace element ratios. Consideration of other trace element ratios like Lu/Hf, La/Sm and Sm/Yb brings out an enriched garnet peridotite plume source material which subsequently underwent different degrees of partial melting corresponding to different ambient conditions. It has been shown by theoretical calculations that a relatively low degree of melting of the initial plume source generated the enriched type of basalts (Group 1 basalts) while a significantly higher degree of melting have produced the primitive group of basalts (Group 3). The intermediate group of basalts has geochemical characteristics intermediate between Group I and Group 3 and therefore might owe their origin to moderate degree of mantle melting. In each of the cases, the generated melt underwent different degrees of crystal cumulation, mixing of the supernatant liquids and the settled crystals to give rise to heterogeneous porphyritic basalts. It is also possible that the generated melts (corresponding to different degrees of mantle melting) might have mixed up with one another as evidenced by the petrographic analyses of the different group of basalts. The possibility of effusion of the parent magma along the Narmada-Tapti rift and related lineament-reactivation/subsequent rifting due to interaction of hot mantle plume with the lithospheric weak planes has also been critically viewed. © 2011 Springer Science+Business Media B.V.
About the journal
JournalData powered by TypesetTopics in Igneous Petrology
PublisherData powered by TypesetSpringer Netherlands
Open AccessNo