عنوان

A petrological, geochemical and geochronological study of high-pressure, low-temperature metamorphic rocks from Saih Hatat, NE Oman

TLpq303959244

انگلیسی

A petrological, geochemical and geochronological study of high-pressure, low-temperature metamorphic rocks from Saih Hatat, NE Oman

[Thesis]

A. E.-D. K. El-Shazly

Stanford University

1991

365

Ph.D.

Stanford University

1991

The Saih Hatat area, NE Oman, is a tectonic window that exposes basement and shelf deposits structurally underlying the Semail ophiolite. High-pressure, low-temperature (high P/T) metamorphism of these deposits in Saih Hatat is evidenced by the occurrence of blueschists, eclogites, lawsonite schists and carpholite-bearing metasediments in several lithostratigraphic levels. Three thrust-bounded tectonometamorphic regions are identified in Saih Hatat based on the prevailing type of deformation, lithostratigraphic units exposed and metamorphic mineral assemblages. The structurally highest Region I consists of several thrust sheets of unmetamorphosed allochthonous continental slope deposits thrust onto a tectonic melange deposited during the Turonian in a foreland basin. Lawsonite + quartz schists and carpholite-bearing metasediments within this melange indicate that it was metamorphosed at P > 3 kbar, T 250-300C. Region II consists of several thrust sheets of the basement and shelf units that were also metamorphosed under high P (>6 kbar) and low T (250-300C) as indicated by the assemblages; crossite + albite + chlorite, and carpholite + chloritoid + illite, in mafic and pelitic units, respectively. The structurally lowest Region III is coherent, consisting of calcareous, mafic, quartzofeldspathic and pelitic Permian units metamorphosed under blueschist and eclogite facies conditions. This Region shows an eastward increase in grade and was subdivided into three metamorphic zones. Zone A in western and central Region III, was metamorphosed at P < 7 kbar and T < 340C, whereas zones B and C were metamorphosed at P > 7-11 kbar, and T of 380-500C and 500-550C, respectively. Petrochemical studies indicate that these rocks are characterized by "clockwise" P-T paths temperatures. White micas from pelitic blueschists in zones B and C, Region III, yield Ar/Ar age spectra characteristic of partial Ar loss, with mean plateau ages of 106-111 Ma. K-Ar and Ar/Ar dating of white micas and whole rocks from Region I and zone A, Region III, yield ages between 72 and 80 Ma. These ages suggest that Region III was metamorphosed in the Early Cretaceous as a result of partial subduction of the continental margin of Oman along an east-dipping subduction zone. The Late Cretaceous emplacement of the ophiolite resulted in partial loss of Ar from zone B and C white micas, recrystallization of micas in zone A, and formation of the high P, very low T assemblages of Regions I and II.

Earth sciences

Geochemistry

Geology

Mineralogy

Mineralogy

petrology

A. E.-D. K. El-Shazly

p

[Thesis]

276903

a

Y