جيوكيمياء القواطع المافية في أجزاء من معقدة سينغابوم الجرانيتية: الأصل الصخري والوضع التكتونى

Abstract

Singhbhum granitoid complex has been intruded by numerous mafic dykes trending in different directions. The studied dykes were originated from subalkaline magma, ranging in composition from basalt through basaltic-andesite to andesite. In the present work, the studied dykes are divided into two groups on the bases of abundance of SiO 2 , MgO, Al 2 O 3 , Ni, and Cr. The first one has higher Mg# than that of group II. These dykes have enriched incompatible trace element patterns. These are particularly enriched in the light rare earth elements and large ion lithophile elements with depleted high field strength elements (Nb, P, Ti). High Ba/Nb and Sr/P ratios of present mafic dykes are the indications of subduction signature. The geochemical characters of the back arc extension basalt tectonic setting is suggested for the studied dykes. Higher PM-normalized Th/Nb, Rb/Nb, and Ba/Nb ratios of studied samples support their non-plume source.

Boninitic geochemical characteristics of high-Mg mafic dykes from the Singhbhum Granitoid Complex, Eastern India

“…Large ion lithophile elements (LILEs) are generally considered as mobile during secondary processes like metamorphism, metasomatism and hydrothermal alteration (Pearce and Cann 1973;Condie and Sinha 1996). However, low values of Rb/Sr (0.11-0.41) and Rb/Ba (0.10-0.27) ratios in the studied dykes do not indicate any major effect of post-magmatic processes on the primary concentrations of LILEs (Lafleche et al 1992;Mir et al 2011). To examine trace element behavior in studied samples, a few immobile elements (particularly Zr, Nb, Th, Yb, V, and Ce) are plotted against Mg number (Mg#) (Fig.…”

“…The Jagannathpur lavas in the south have faulted boundaries with the Kolhan rocks (Banerjee 1982). NDDs, the youngest magmatic activity, intrude SGC in four distinct orientations: N-S, NNE-SSW, NNW-SSE, and E-W, among which the NNE-SSW trend is the most dominant (Mir et al 2011). Consistent age data on these dykes is not available.…”

40Ar–39Ar age and geochemistry of subduction-related mafic dikes in northern Tibet, China: petrogenesis and tectonic implications

“…In addition, crustal contamination increases LILEs, K 2 O, and Na 2 O, but decreases P 2 O 5 , TiO 2 , and Nb/La (e.g. Zhao and Zhou 2007;Mir et al 2011). The Xiaomiao mafic dikes exhibit an obvious negative correlation between P 2 O 5 versus Mg # and no correlation between Nb/La versus Mg # (Figures 7A and 7I), which suggests insignificant crustal contamination.…”

“…Assimilation and fractional crystallization (AFC) has been recognized as an important process during magmatic evolution, which can modify the elemental and isotopic compositions of the initial magma (DePaolo 1981; Halama et al 2004;Mir et al 2011). AFC does not readily take place in the shallow crust, as the cool shallow crust cannot provide enough energy for the process and is difficult to consume (Scarrow et al 1998).…”

Mafic and ultramafic rocks in parts of the Bhavani complex, Tamil Nadu, Southern India: Geochemistry constraints

“…Such lower values are not expected to be produced by processes of contamination by an average crustal component. Thus, it can be inferred that these trace element characteristics may have been obtained by studied rocks due to LREEs-LILEs enriched source characteristics with depletion of high field strength elements (such as Nb) at plate margin settings (Weaver and Tarney, 1983;Ahmad and Tarney, 1994;Mir et al, 2011Mir et al, , 2013. Enrichment of LILEs and depletion of HFSEs may also occur in within plate tectonic setting rocks due to crustal contamination, but, studied rocks show least crustal contamination.The geochemistry of mafic and ultramafic rocks is most commonly used to discriminate tectonic setting.…”