Discussion
Despite being older, the Aravali rocks from the type area are lower grade than the juxtaposed Delhi metasediments :
Answer: B
The key explains it as the two units were temporally apart then accreted.
In normal burial the older, deeper rocks are of equal or higher grade than younger rocks above them. If the older Aravalli rocks are of lower grade than the Delhi rocks beside them, the two cannot have been metamorphosed together in a single sequence. They must have been metamorphosed at different times or places and then brought together later by tectonic juxtaposition.
Option A would not explain an older unit ending up lower in grade at one place, option C invokes lava flows for which there is no basis in a regional metamorphic belt, and option D contradicts the stem, which says the Aravallis are older.
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