Back to the full dot-point answer
EnglandGeologyQuick questions
Module 2: Foundations in geology - Minerals and rocks
Quick questions on Igneous intrusions and volcanic forms: dykes, sills, batholiths, chilled and baked margins - OCR A-Level Geology
6short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What are intrusive forms?Show answer
Magma that solidifies underground forms intrusive (plutonic) bodies, classified by shape and by their relationship to the bedding of the surrounding country rock:
What is evidence of intrusion?Show answer
You recognise an intrusion (rather than, say, a buried lava flow) from the way it has affected itself and its surroundings:
What is using cross-cutting relationships for relative age?Show answer
Because an igneous body must intrude rock that already exists, any intrusion that cuts another rock or feature is younger than it (the principle of cross-cutting relationships). A dyke cutting a sill is younger than the sill; a dyke cutting a lava flow is younger than the flow. A lava flow, being extrusive, bakes the rocks below it (not above) and is then buried by younger beds, which is how you tell a buried flow from a sill.
What is q1?Show answer
State whether a sill is concordant or discordant, and explain why. [2 marks]
What is q2?Show answer
Explain what a chilled margin shows about an intrusion. [2 marks]
What is q3?Show answer
A dyke cuts a sandstone and bakes it at the contact. State which is younger and why. [2 marks]
Have a question we have not covered?
This dot-point answer is short enough that we have not extracted many short questions yet. Read the full dot-point answer or ask Mo, our study assistant, in the chat for follow ups.