Whether swarms of preferentially oriented dykes are controlled by regional stress fields, or passively exploit basement structural fabric, is a much debated question, with support for either scenario in individual cas...Whether swarms of preferentially oriented dykes are controlled by regional stress fields, or passively exploit basement structural fabric, is a much debated question, with support for either scenario in individual case studies. The Sarnu-Dandali alkaline complex, near the northwestern limit of the Deccan Traps continental flood basalt province, contains mafic to felsic alkaline volcano-plutonic rocks and carbonatites. The complex is situated near the northern end of the 600 km long, NNWe SSE-trending Barmer-Cambay rift. Mafic enclave swarms in the syenites suggest synplutonic mafic dykes injected into a largely liquid felsic magma chamber. Later coherent dykes in the complex, of all compositions and sizes,dominantly strike NNWe SSE, parallel to the Barmer-Cambay rift. The rift formed during two distinct episodes of extension, NWe SE in the early Cretaceous and NEe SW in the late Cretaceous. Control of the southern Indian Dharwar structural fabric on the rift trend, as speculated previously, is untenable,whereas the regional Precambrian basement trends（Aravalli and Malani） run NEe SW and NNEe SSW.We therefore suggest that the small-scale Sarnu-Dandali dykes and the much larger-scale BarmerCambay rift were not controlled by basement structure, but related to contemporaneous, late Cretaceous regional ENEe WSW extension, for which there is varied independent evidence.展开更多
基金supported by the Industrial Research and Consultancy Centre (IRCC), IIT Bombay (Grant No. 09YIA001 to Sheth)supported by a Ph.D. Scholarship from the University Grants Commission (UGC), Govt. of India
文摘Whether swarms of preferentially oriented dykes are controlled by regional stress fields, or passively exploit basement structural fabric, is a much debated question, with support for either scenario in individual case studies. The Sarnu-Dandali alkaline complex, near the northwestern limit of the Deccan Traps continental flood basalt province, contains mafic to felsic alkaline volcano-plutonic rocks and carbonatites. The complex is situated near the northern end of the 600 km long, NNWe SSE-trending Barmer-Cambay rift. Mafic enclave swarms in the syenites suggest synplutonic mafic dykes injected into a largely liquid felsic magma chamber. Later coherent dykes in the complex, of all compositions and sizes,dominantly strike NNWe SSE, parallel to the Barmer-Cambay rift. The rift formed during two distinct episodes of extension, NWe SE in the early Cretaceous and NEe SW in the late Cretaceous. Control of the southern Indian Dharwar structural fabric on the rift trend, as speculated previously, is untenable,whereas the regional Precambrian basement trends（Aravalli and Malani） run NEe SW and NNEe SSW.We therefore suggest that the small-scale Sarnu-Dandali dykes and the much larger-scale BarmerCambay rift were not controlled by basement structure, but related to contemporaneous, late Cretaceous regional ENEe WSW extension, for which there is varied independent evidence.
