- Dona Paula, Goa, India.
- +91-0832- 2450327
- iiosc2020[at]nio[dot]org
Abstract Submission No. | ABS-2022-13-0315 |
Title of Abstract | Genesis and alteration of the Central Indian Ridge and Ocean Basin basalts: Implications on the mobility of elements during basalt alteration |
Authors | R DILEEPKUMAR REDDY*, SRIDHAR D. IYER, S BALAKRISHNAN, RAJNEESH BHUTANI, M ASHOK |
Organisation | PONDICHERRY UNIVERSITY |
Address | Research Scholar, Dept. of Earth Sciences, Pondicherry University, Kalapet Pondicherry, Puducherry, India Pincode: 605014 Mobile: 9443791648 E-mail: dilu.abc9@gmail.com |
Country | India |
Presentation | Oral |
Abstract | The petrography and geochemistry of fresh oceanic basalts help in understanding the magmatic processes. But the alteration of the basalts due to several factors such as metamorphism, interaction with seawater, hydrothermal fluids and so forth will affect their primary geochemical signatures. It is noted that the rate of alteration and elemental fluxes vary from the ridge to the ocean basin and these are characterized by the fluid responsible for the alteration. Therefore, the alteration processes and their products could provide information about the characteristics of the fluid responsible for the alteration. Several studies have been carried out to decipher petro-genesis of ocean basalts but not many studies have attempted to understand their alteration and elements mobility under deep-sea conditions especially of basalts from the slow-spreading Central Indian Ridge (CIR) and Central Indian Ocean Basin (CIOB). Samples were collected from different water depths from the CIR (1,875 to 3,000 m) and CIOB (>5,000 m). Based on textural, compositional and geochemical parameters, the CIR basalts are categorized as fresh and altered rocks and compared with those from the basin. Rapidly cooled CIR pillow basalts show concentric zoning with the least altered inner zone. Petrographic studies depict labradorite spherulites and laths along with phenocrysts of augite and forsterite in fresh basalts. The altered samples have essentially clinochlore and quartz which indicate a high degree of alteration. Both fresh and altered samples (CIR-35 samples, CIOB-6 samples) were digested and geochemical study was carried out using ICP-MS and TIMS. Prominent Pb enrichment prevails in all the samples (CIR and CIOB) while Sr, Zr and Hf are depleted in two altered samples. The positive Ce anomaly indicates an oxidizing environment of seawater in the sampled locations. The altered basalts are LREE enriched relative to HREE as evidenced by increasing La/Yb ratios from fresh and glass samples (̴1.68) to altered samples (̴ 3.56). A few samples show negative Gd anomaly. Negative Nb anomaly is increasing with the extent of alteration (Fresh ~ 0.83, Altered ~ 0.64, CIOB ~ 0.52) and glass has Nb anomaly ~ 0.67 as Nb is mobile in the glass. Change in 87Sr/86Sri is significant evidence for basalt alteration by seawater as it is independent of element partition in secondary phases. 87Sr/86Sri of fresh basalts ranges between 0.703010 and 0.703471, as in typical MORB from the CIR. In contrast, the altered basalts of CIR have 87Sr/86Sri up to 0.708488 which is close to the present day seawater (0.709211). Furthermore, 87Sr/86Sri of 0.706201 of the outer altered zone is skewed towards seawater and correlates positively with the Ce anomaly. These initial results would help to quantify the mass-elemental exchange between the CIR and CIOB basalts and the seawater. |