Age, cooling history, and origin of post-collisional leucogranites in the Karakoram Batholith; a multi-system isotope study

Journal Article · Thu Mar 01 04:00:00 EST 1990 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629395· OSTI ID:6285761

Schaerer, U ^[1]; Copeland, P ^[2]; Harrison, T M ^[3]; Searle, M P ^[4]

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1. Universite du Quebec a Montreal (Canada)
2. State Univ. of New York, Albany (USA)
3. Univ. of California, Los Angeles (USA)
4. Univ. of Leicester (England)

U-Pb dating on zircon and monazite from different varieties of leucogranites in the Karakoram Batholith reveals two distinct pulses of plutonism at 25.5 + 0.3/{minus}0.8 and 21.4 +0.3/{minus}0.6 Ma. A crustal origin of the granites, and long crustal residence times of the source rocks are confirmed. In a Pb evolution diagram, initial isotopic compositions for both the granites and the rocks from the metamorphic complex plot far above the reference field for MORB documenting very close affinity to the Eurasian (Tibetan) continental crust. {sup 40}Ar/{sup 39}Ar step heating analyses from the leucogranites yield isochron ages of 6.4 {plus minus} 0.1 and 7.4 {plus minus} 0.2 Ma for biotite, 6.6 {plus minus} 0.1 and 6.4 {plus minus} 0.1 Ma for muscovite, and 4.6 {plus minus} 0.2 Ma for K-feldspar. The two rocks from the metamorphic complex define isochron ages of 10.6 {plus minus} 0.1 and 4.7 {plus minus} 0.1 Ma for biotite, 14.9 {plus minus} 0.3 Ma for muscovite, and 8.9 {plus minus} 0.4 and about 4 Ma for K-feldspar. All K-feldspars analyzed contain trapped non-atmospheric Ar components to various degrees. The radiometric ages show that the leucogranites cooled from 750-650C at 25-21 Ma to 250-350C at 6 Ma, i.e., their cooling through the Ar blocking temperature in mica and K-feldspar occurred 15 to 20 Ma after granite emplacement. This strongly suggests a major and rapid uplift in latest Miocene to Pliocene times. In contrast to the leucogranites, cooling of portions of the metamorphic complex reached mica-K-feldspar blocking temperatures about 5 to 10 Ma earlier, documenting earlier uplift in the Karakoram Metamorphic Complex than in the Karakoram Batholith.

• OSTI ID: 6285761
• Journal Information: Journal of Geology; (USA), Journal Name: Journal of Geology; (USA) Vol. 98:2; ISSN JGEOA; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTINIDE COMPOUNDS
ACTINIDE ISOTOPES
AGE ESTIMATION
ALKALINE EARTH ISOTOPES
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOTITE
CENOZOIC ERA
CONTINENTAL CRUST
COOLING
DIKES
EARTH CRUST
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FELDSPARS
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GRANITES
GROUND UPLIFT
HIMALAYAS
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LEAD ISOTOPES
LIGHT NUCLEI
MAGMA
MATERIALS
METAMORPHIC ROCKS
MICA
MINERALS
MIOCENE EPOCH
MONAZITES
MOUNTAINS
MUSCOVITE
NEODYMIUM ISOTOPES
NUCLEI
ORIGIN
OROGENESIS
OXYGEN COMPOUNDS
PHOSPHATES
PHOSPHORUS COMPOUNDS
PLIOCENE EPOCH
PLUTONIC ROCKS
PRECAMBRIAN ERA
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
RADIOISOTOPES
RARE EARTH COMPOUNDS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SOURCE ROCKS
STABLE ISOTOPES
STRONTIUM ISOTOPES
TERTIARY PERIOD
THORIUM COMPOUNDS
THORIUM MINERALS
THORIUM PHOSPHATES
TRANSITION ELEMENT COMPOUNDS
URANIUM ISOTOPES
YEARS LIVING RADIOISOTOPES
ZIRCON
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES