نتایج جستجو برای: metamorphism and igneous

تعداد نتایج: 16828157  

Journal: :Geosciences 2022

In metamorphic rocks, mineral species react over a range of pressure–temperature conditions that do not necessarily overlap. Mineral equilibration can occur at varied points along the (PT) path, and thus different times. The sole or dominant use zircon isotopic compositions to constrain evolution rocks might then inadvertently skew geological interpretations towards one aspect moment rock’s his...

Journal: :Proceedings of the National Academy of Sciences of the United States of America 2015
Monika A Kusiak Daniel J Dunkley Richard Wirth Martin J Whitehouse Simon A Wilde Katharina Marquardt

Zircon (ZrSiO4) is the most commonly used geochronometer, preserving age and geochemical information through a wide range of geological processes. However, zircon U-Pb geochronology can be affected by redistribution of radiogenic Pb, which is incompatible in the crystal structure. This phenomenon is particularly common in zircon that has experienced ultra-high temperature metamorphism, where io...

2015
T. K. Ambrose K. P. Larson C. Guilmette J. M. Cottle S. Rai

Integrated pseudosection modeling and monazite petrochronology of paragneiss from the Kanchenjunga region of northeastern Nepal reveal the presence of cryptic tectonometamorphic discontinuities within the Himalayan metamorphic core. These new data outline a series of thrust-sense structures that juxtapose rocks that generally record a protracted history of early Eocene to latest Oligocene–early...

مجرد, منیر, موذن, محسن, موید, محسن,

Contact metamorphism in the Shahindezh Metamorphic Core (SMC), which is occurred due to intrusion of Pichaghchi granodiorite during Laramian orogeny (Upper Cretaceous), is studied here. The well deve loped mineral parageneses at the aureo le is quatz + plagioclase + biotite + cordierite ± chlorite ± K-feldspar ± muscovite ± andalusite ± sillimanite ± garnet. Pressure and temperature of the...

Journal: :Geological Society of America Bulletin 1897

A. Jayasheelan, P. Venkataramanaiah, S. Manjunatha,

Background: The concentrations of radionuclides like 226Ra, 232Th and 40K and the dose rate are measured in igneous and metamorphic rock formations in and around Chickmagalur. A total of 236 samples from 13 different locations around study area were analyzed. Materials and Methods: The activity concentrations of the three radioactive elements were determined for mean period of 25000 s using HPG...

2005
Eugene P. Gurov

The 18-km-diameter El’gygytgyn crater is located on the Chukotka peninsula, northeastern Russia. It represents the only currently known impact structure formed in siliceous volcanics, including tuffs. The impact melt rocks and target rocks provide an excellent opportunity to study shock metamorphism of volcanic rocks. The shockinduced changes observed in porphyritic volcanic rocks from El’gygyt...

2010
Mila Dalla Preda Roberto Giacobazzi Saumya K. Debray Kevin Coogan Gregg M. Townsend

Metamorphic malware apply semantics-preserving transformations to their own code in order to foil detection systems based on signature matching. In this paper we consider the problem of automatically extract metamorphic signatures from these malware. We introduce a semantics for self-modifying code, later called phase semantics, and prove its correctness by showing that it is an abstract interp...

M. Ahangari M. Moazzen R. Michaeli U. Altenberger

Metapelitic rocks in the Gasht area include micaschist, kyanite schist, andalusite schist, garnet schist, staurolite schist, cordierite schist and sillimanite schist. Tourmaline occurs as accessory mineral in all of these rock types. These schists are metamorphosed regionally and are affected by contact metamorpism subsequently. Based on the textural relations and the fact that CaO and TiO2 con...

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