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Q141. The correct combination of textural feature of magmatic rocks with corresponding petrological process is
The correct answer is Exsolution lamellae – Sub-solidus cooling. When a completely solid, super-hot crystal (like feldspar) slowly cools down entirely below its freezing point (sub-solidus), it can no longer hold its mixed chemicals. The chemicals naturally separate and bleed out into thin, zebra-like stripes inside the rock, known as 'exsolution lamellae'. The other textures listed are incorrectly matched with completely unrelated thermal or volcanic events.
Q142. The correct pair of metal and the ore mineral is
The correct answer is Tin - Cassiterite. An 'ore' is a natural rock that contains valuable metals. Cassiterite is a dark, heavy mineral and is globally the primary, most famous ore mined to get the metal Tin. The other pairings are completely wrong: Sphalerite is actually mined for Zinc (not Nickel). Pyrolusite is an ore of Manganese (not Zinc). Bornite is a famous ore of Copper (not Lead).
Q143. The diagnostic amphibole in a blueschist facies metabasalt is
The correct answer is glaucophane. 'Blueschist facies' rocks form when ocean crust gets violently dragged deep down into cold, high-pressure subduction zones. Under these intense, crushing conditions, the rock grows a very specific sodium-rich amphibole mineral called 'glaucophane'. It is this specific mineral that literally gives the rock its striking, diagnostic blue color. Hornblende and actinolite form in much warmer, greener rocks.
Q144. The Mesozoic Era approximately ranges from
The correct answer is 250-65 Ma. In the Geologic Time Scale, the Mesozoic Era (famous as the Age of Dinosaurs) began roughly 252 million years ago after the Permian mass extinction, and it abruptly ended 66 million years ago with the Cretaceous-Tertiary extinction event. Therefore, the 250-65 Ma option is the closest geological approximation. The other timeframes represent the Proterozoic, Paleozoic, and Cenozoic periods respectively.
Q145. The metamorphic facies series that explains oceanic subduction zone metamorphism is
The correct answer is Prehnite-Pumpellyite->Blueschist->Eclogite. When cold oceanic crust is suddenly dragged deep underground in a subduction zone, it experiences a massive, crushing spike in pressure without much time to heat up (Franciscan series). This unique high-pressure/low-temperature path perfectly creates the specific mineral sequence of Prehnite-Pumpellyite, shifting down into blue Glaucophane (Blueschist), and finally crushing into ultra-dense Eclogite.
Q146. The mineral sequence arranged in order of increasing degree of sharing of (SiO4)4- tetrahedra is
The correct answer is Olivine->Enstatite->Tremolite->Quartz. Silicate minerals are built from tiny silicon-oxygen pyramids. 'Olivine' stands alone and shares 0 corners. 'Enstatite' (a single-chain pyroxene) links up and shares 2 corners. 'Tremolite' (a double-chain amphibole) shares between 2 and 3 corners. 'Quartz' locks together completely, sharing all 4 corners to form a solid 3D framework. Option B correctly traces this geometric progression from least (0) to most (4).
Q147. The most abundant element in the Earth’s continental crust is
The correct answer is oxygen. While rocks look solid and metallic, they are actually mostly made of oxygen gas chemically bonded into solid minerals. Oxygen accounts for an overwhelming 46.6% of the entire continental crust by weight. Silicon is the second most abundant at around 27.7%. Aluminium and iron are abundant metals, but fall far behind oxygen in total crustal mass.
Q148. The strike (in degree notation) of a bed dipping 30° towards N45W is
The correct answer is 045-225. A rock's 'strike' line is always perfectly perpendicular (90 degrees) to its 'dip' direction. The dip direction is N45W, which translates to a compass azimuth of 315 degrees. To find the strike, we simply add and subtract 90 degrees from 315. 315 minus 90 gives 225 degrees, and 315 plus 90 loops past 360 to give 45 degrees. Thus, the strike line runs 045-225.
Q149. Which of the following oil field is NOT located in the western part of India?
The correct answer is Moran. Bombay High, Ankleshwar, and Gandhar are all famous and highly productive petroleum fields located in the western part of India (Gujarat and the offshore Arabian Sea). Moran, however, is a historic and active oil field located in the far eastern state of Assam, making it the only incorrect geographical location on the list.
Q150. Which of the following pairs is NOT correctly matched?
The correct answer is Gryphea - Gastropoda. In paleontology, animals are grouped into major families. 'Productus' is a famous fossil Brachiopod, 'Redlichia' is an ancient Trilobite (Arthropod), and 'Belemnites' are bullet-shaped squids (Cephalopods). However, 'Gryphea' (widely known as the 'Devil's toenail') is an extinct type of oyster. Because it has two shells hinged together, it is strictly a Bivalve, completely ruling it out as a snail-like Gastropod.