Geochemical variability of MORBs along slow to intermediate spreading Carlsberg-Central Indian Ridge, Indian Ocean

We present new major and ICP-MS trace element data of the Carlsberg Ridge MORBs from two different locations (i.e., 3°35 / N/64°05 / E and 3°41 / N/64°09 / E) and reassess the intra-ridge geochemical variations of Carlsberg Ridge- Central Indian Ridge MORBs in the present work. Geochemically, the trace element contents of the Carlsberg Ridge MORBs are similar to the Rodriguez Triple Junction MORBs [e.g., LIL and REE spidergrams and (La/Sm)N ratio etc.] and both are closely resembling to the average N-MORB in composition. The MORBs from the northern- and southern Central Indian Ridge, however, significantly vary in composition between average N- and E-MORBs. The Carlsberg Ridge- Central Indian Ridge MORBs, in general, show much less fractionation in FeOt in MgO-CaO-FeOt diagram compared to those of the Mid Atlanticand East Pacific Rise MORBs. Further, the depleted LREE and nearly flat HREE patterns of the Carlsberg Ridge- Central Indian Ridge MORBs, along with their least variability of compatible trace element (Ni, Cr, Sr) contents against increasing incompatible trace element (Y, Zr) contents in the log-log plots and their increasing incompatible trace element ratios in the process identification plots favor partial melting dominated process for their petrogenetic evolution. Our review on isotope data (Sr, Nd, Pb) shows that the Carlsberg Ridge-Central Indian Ridge MORBs were derived from a depleted mantle source that was variously contaminated by continental crust perhaps during the third stage of Gondwana break up between 155-135 Ma or later due to the strike slip movement along a mega fracture, a member of the Davie Transform Faults in the Somali Basin, that broke the Gondwanaland into the East and West Gondwanas and during subsequent movement of these two blocks away from each other. The 208 Pb/ 204 Pb versus 206 Pb/ 204 Pb plot of above mentioned MORBs suggests that the depleted mantle source of the Rodriguez Triple Junction MORBs was contaminated by ~21% lower continental crust, whereas the mantle source of the Central Indian Ridge MORBs was contaminated by upper continental crust, which are ~19% for the Carlsberg Ridge and Northern Central Indian Ridge MORBs and ~32% for the Southern Central Indian Ridge MORBs. The contaminated mantle sources were compositionally similar to the Al-depleted Komatiite basalt in composition and significantly enriched in Rb, Ba, La and Ce over the depleted mantle.