Constraining paleo-latitudes of rocks from Christmas Island

The drifting of Australian landmass from Greater India around 136 Ma resulted in large volumes of volcanic eruptions in the Indian Ocean and surrounding continental margins. This was followed by later episodes of submarine eruptions. Evidence of this volcanism can be seen in the form of two exposed islands, Christmas Island and Cocos (Keeling) Island, and numerous submerged seamounts. Christmas Island is dominated by limestones and phosphates with some basalts and basanites. The island experienced three stages of volcanic activity the oldest one in Late Cretaceous followed by later phases in the Eocene and in the Miocene. Four sites were selected for paleomagnetic sampling, three on east and one on west coast. Samples were demagnetised using alternating field progressive demagnetisation with increments up to 70 mT. Characteristic Remanent Magnetisation was determined using PCA to remove low stability component. Fisherian statistical analysis gave two different mean inclinations (Im ) of 71 for Waterfall Spring & Dolly Beach and 55 for Winifred & Ethel Beach. The higher Im of the former sites could be due to lightening strikes that disturbed the original magnetic character. These Im were used to constrain the paleo-latitudes of the island using equation tan Im =2 tan . Steeper inclination gave a paleolatitude of 54 S where as shallower inclination gave 36 S which lies in conformation with the position of island observed in plate reconstruction models at approximately 50-65 Ma.