Question

Which of the following statements on mantle partial melting are correct?

• A. Shallow melting produces tholeiitic basalts.
• B. Low-degree melting produces alkaline basalts.
• C. Presence of $CO_2$-rich volatiles favors the formation of tholeiitic basalts.
• D. Presence of $H_2O$-rich volatiles favors the formation of alkaline basalts.

Answer 1

The Correct Option is A, B

Understanding the Formation of Tholeiitic and Alkaline Basalts 

Step 1: Evaluating the Given Statements

• (A) Shallow melting produces tholeiitic basalts: Correct. Tholeiitic basalts typically result from partial melting of the mantle at shallow depths, leading to basaltic magma with low alkali content.
• (B) Low-degree melting produces alkaline basalts: Correct. Alkaline basalts generally form from low-degree partial melting of the mantle, leading to enrichment in alkalis such as sodium and potassium.
• (C) Presence of CO₂-rich volatiles favors the formation of tholeiitic basalts: Incorrect. CO₂-rich volatiles typically favor the formation of alkaline basalts rather than tholeiitic basalts, as they contribute to increased alkalinity in the melt.
• (D) Presence of H₂O-rich volatiles favors the formation of alkaline basalts: Incorrect. H₂O-rich volatiles tend to favor tholeiitic basalts, as they lower the melting temperature and influence the composition of the melt.

Step 2: Selecting the Correct Options

From the above analysis, the correct statements are:

\[ \mathbf{(A)\ and\ (B)} \]

Final Answer:

Thus, the correct options are: (A) and (B).