Rubric

The report and plots should use the major and trace element and isotopic data in

order to:

1.         Classify the rocks into one or more ‘groups’,

2.         Compare and contrast their compositions with more modern rocks and,

3.         Make some inferences as to the tectonic setting(s) in which the rocks

formed.

Answers:

1. There were three plots were made to classify the rocks into approximately 3 identified groups. These three plots are the Total Alkali vs Silica diagram, AFM diagram and MORB diagram where the diagrams are shown below labelled Figure 1.1, Figure 1.2 , and Figure 1.3 with appropriate explanations.

The results obtained from the three figures plotted are:

• Total Alkali vs Silica Diagram: Basalt to Basaltic Andesite.

Figure 1.1 shows a range of the rock type which forms in this graph, these are Basalt to Basaltic Andesite.

• AFM Diagram : Tholleitic

Figure 1.2 shows that the values plotted majorly occupy the Tholleitic region thus making the rock type is of Tholleitic.

• MORB diagram: Figure 1.3 (a) shows the plotting of La/Sm vs Mg concentration which displays that the majority of the rocks are placed in the Enriched MORB. To gain a deeper understanding another graph of Chondrite normalization REE graph is made and displayed in Figure 1.3 (b) which exhibits two trends consisting of E MORB and N

MORB which suggest that there were mixing of E-MORB and N-MORB due to existence of T-MORB as could be seen in Figure 1.2 (a). To strengthen this argument another two graphs (Figure 1.4 (a) and Figure 1.4 (b)) are made which are K2O and TiO2 vs Mg content which shows that the basalts were heterogenetic.

1. The samples are believed to be in two forms E-MORB and N-MORB. This is due to the richness of Magnesium weightage concentration. Therefore, the comparison between these basalts and the modern basalt suspected to be dependent on the depth of the formation itself. Figure 2 shows that E MORB might be similar to modern basalt as its lower in

depth and less chances for it not to undergo a cooling pattern. However, the

Magnesium richness and the depth of N MORB modern basalt suggests that it will undergo a differentiation, and by referring to the diagram.  It could be seen that N-MORB will differentiate to Tholleitic Basalt in mid-ocean ridge.

Based on Figure 2, the formation of the rocks could be at the mid-ocean ridge at the plate divergence. The movement of plates caused the E MORB plume to flow upwards leaving a depletion state of N MORB. Meanwhile, T-MORB occurred at a various depth during the ascending of magma to the surface, where the evidence of T-MORB could be seen at the magnified picture in Figure 2.0.

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