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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Gurmeet Singh posted an Question
January 26, 2021 • 22:07 pm
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30 points
30 points
- IIT JAM
- Geology (GG)
What is the difference between a tholeitic basalt and an alkali basalt ? a tholeiitic basalt contains more conspicuous plagioclase and pyroxene crystals. a thol
What is the difference between a tholeitic basalt and an alkali basalt ? A tholeiitic basalt contains more conspicuous plagioclase and pyroxene crystals. A tholeiitic basalt contains no olivine. An alkali basalt contains potassium feldspar. An alkali basalt contains more conspicuous plagioclase and pyroxene crystals
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Saurabh 1 Best Answer
This seems to be MSQ. So as per options given, Correct option would be - A, B and C . Tholeiitic basalt (or calc alkaline basalt also) are subalkaline in nature which means they have less sodium as compared to alkali basalt. Tholeiitic basalt are mainly attributed to the MOR's and oceanic island. While alkali basalt is attributed to Island arcs or collisional zones. If we talk about the groundmass composition, olivine is absent in tholeiitic basalt but it is found commonly in alkaline basalt. Also K feldspar is found in case of alkali basalt but not in case of tholeiitic basalt. Also plagioclase and pyroxene is conspicuous (or clearly visible ) in case of tholeiitic basalt while they are less common or not majorly found in case of alkali basalt(orthopyroxene is absent in alkali basalt). Also this question has been made from the JD winter directly. You can see it in the chapter 'Mantle melting ' .