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El-Shazly, February, 16
FIELD TRIP TO SAIH HATAT
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HOMEWORK PROBLEM # 5
HIGH PRESSURE METAMORPHISM IN SAIH HATAT
This field trip is aimed at examining some of the high pressure, low temperature
metamorphic rocks which occur in the Saih Hatat area (structurally underlying the Semail
ophiolite), and at illustrating some of the deformational and metamorphic events that
predated or were contemporaneous with the Semail ophiolite emplacement.
High pressure, low temperature (high P/T) metasediments from this area were first
reported by Michard et al. (1982). Blueschists were then described by Lippard (1983).
More detailed petrologic studies by Le Métour et al. (1986), Goffé et al. (1988), ElShazly et al. (1990) and El-Shazly and Liou (1991), Searle et al. (1994) have led to the
proposition of several tectonic models for the area (e.g. Lippard et al., 1986; Le Métour et
al., 1990; El-Shazly and Coleman, 1990; El-Shazly and Lanphere (1992), El-Shazly
(1994)). Keep in mind that all these models are controversial, and that the relationship
between deformation and metamorphism remains poorly understood.
Following this field trip, you are supposed to write a short essay (3-5 pages long) on high
pressure metamorphism in Saih Hatat. The questions on this handout are designed to help
you write this essay, so be sure to have them all answered before you leave each stop! In
this essay, you should point out the different mineral assemblages occurring in rocks of
different bulk compositions that you have seen, the tectonostratigraphic positions of these
units or rock types and the directions of increase in metamorphic grade throughout Saih
Hatat (detected by mineralogical changes in rocks of the same composition). Afterwards,
you should:
1- plot the different mineral assemblages on Figs. 1 and 2
2- identify the "index minerals" characteristic of certain rock types in each area, and label
what you think may be metamorphic zones accordingly. How do your metamorphic zones
compare with those of Le Métour et al. (1990), shown on Fig. 3?
3- Prepare a paragenetic sequence diagram for metapelites in all of your metamorphic
zones (similar to the one shown on the last page of this handout, copied from Le Métour
et al. (1990) for metabasites).
4- Based on field relations, you should then critique one or two of the tectonic models
mentioned above, keeping in mind that you do not have to agree with any of these
models! Use the papers cited above to your advantage!
Introduction:
The Saih Hatat area is an uplifted dome or tectonic window that exposes the pre-Permian
basement and Permian to Cretaceous shelf units structurally underlying the ophiolite.
Figure 1 is geologic map of the Saih Hatat area, simplified after Le Métour et al. (1986).
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El-Shazly, February, 16
According to this map, the pre-Permian units, which consist of metagreywackes,
metavolcanics, metadolomites and quartzites, are exposed in the core of the dome in
central and western Saih Hatat, and are flanked from all sides by shelf units that almost
always dip away from the core of the dome (Fig. 1). El-Shazly and Coleman (1990)
subdivided the Saih Hatat area into three thrust-bonded regions. The structurally highest
Region I is limited to the Ruwi-Hamiriya area in northern Saih Hatat, and consists of
Hawasina cherts, basalts and serpentinites thrust onto sediments of the Muti Formation
metamorphosed under high pressures (Le Metour et al., 1986; Goffé et al., 1988; ElShazly and Coleman, 1990). Region II consists of several thrust sheets of folded and
recrystallized sediments and volcanics that range in age from the Precambrian to the
Cretaceous. In the northern part of this region, the shelf units are folded into a series of
south-verging tight folds. Region III, the structurally lowest region, is coherent and
contains the highest grade metamorphic rocks. Le Métour et al. (1986) mapped the
metamorphosed carbonates, volcanics quartzites and shales of this region as parts of the
Permian Saiq Formation based on fossil finds in northern Wadi Hulw. Earlier workers
(e.g. Glennie et al., 1974 and Bailey, 1981) had mapped the same rocks as pre-Permian
schists.
Stop 1: The Ruwi Hill
There are at least five different rock types in this outcrop. List these rock types and
describe them carefully. What are the structural and/or stratigraphic relationships between
these different rock types? What is the relationship between these rocks and (a) the
carbonates on top of the hill? (b) the carbonates across the street, south of the Ruwi hill?
What is the importance of these rocks and structures to reconstructing the tectonic history
of the area? Sketch the major structures in this area.
Stop 2: Wadi Aday
At the major bend in the Wadi, you can see outcrops of a mafic volcanic body
interlayered with the Permian Saiq carbonates. Chemically, this mafic body has an
alkaline affinity (Le Métour et al., 1986; El-Shazly et al., 1994), consistent with rifting
during the Permian. The rocks are characterized by the preservation of relict volcanic
textures, as well as the development of sodic amphiboles in the matrix, indicating that
they have undergone high P/T metamorphism. Examine these rocks very carefully. Name
at least two of these relict textures. (You don't need a microscope to identify these
textures!). What name would you give these rocks, knowing that they have been
metamorphosed?
Notice the thrust to the south of this outcrop. Compare and contrast the different
directions of vergence and tightness of folds on both sides of this thrust.
Stop 3: Wadi Hulw
Close to the mouth of Wadi Hulw, near Yitti. Notice the folding in the shelf carbonates in
this area. Which way are these folds verging? How does this vary as we head southwards
along the road?
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El-Shazly, February, 16
Stop 4: Wadi Hulw
Wadi Hulw, south of Hulw village. We have now crossed into Region III of El-Shazly
and Coleman (1990). Examine the mafic rocks of this outcrop and compare them
(texturally and mineralogically) to the metavolcanic body that we have seen in Wadi
Aday (stop 2). What minerals can you identify in these rocks? What is the vergence
direction of the folds in this area?
Stop 5: As-Sifah
Top of the mountain, 3 km west of As-Sifah. This outcrop contains interlayered
metapelites, quartz mica schists and metabasites. Examine samples from each layer
carefully. Compare the mineralogy of these rocks with those seen in stops 5 and 6. What
"new" mineral formed in the metabasites? What minerals occur in the metapelites? What
is the direction of fold vergence in this area?
Stop 6: As-Sifah
Coastal outcrop, 2.5 km north of As-Sifah. The same compositional varieties of rocks
exposed in the last stop can be seen here, but several interesting and new assemblages can
be identified. What are the textural and mineralogical differences between metabasites
exposed in this outcrop and those cropping out in stop 6? What do these textural and
mineralogical changes indicate?
References
El-Shazly, A. K. and Coleman, R. G., 1990. Metamorphism in the Oman Mountains in relation to
the ophiolite emplacement, in Robertson, A. H. F., Searle, M. P. and Ries, A. (eds), The
Geology and Tectonics of the Oman Region: Geol Soc London Special Pub, v. 49, p. 475495.
El-Shazly, A. K.; Coleman, R. G. and Liou, J. G., 1990, Eclogites and blueschists from NE
Oman: Petrology and P-T evolution: J Petrology, v. 31, p. 629-666.
El-Shazly, A. K. and Liou, J. G., 1991, Glaucophane chloritoid bearing assemblages from NE
Oman: Petrologic significance and a petrogenetic grid for high P/T metapelites: Contrib
Mineral Petrol, v. 107, p.180-201.
El-Shazly, A. K., and Lanphere, M. A., 1992: Two high pressure metamorphic events in NE
Oman: Evidence from 40Ar/39Ar dating and petrological data. Journal of Geology, v.
100: 731-751.
El-Shazly, A. K., 1994. Petrology of lawsonite, pumpellyite and sodic amphibole - bearing rocks
from Saih Hatat, NE Oman. Journal of Metamorphic Geology, 12: 23 - 48.
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El-Shazly, A. K., Worthing, M. A., Jayawardane, J. and Varne, R., 1994. Geochemistry of
metamorphosed mafic rocks from Saih Hatat: Insights into the pre-obduction history of
NE Oman. Journal of the Geological Society, London, 151: 999 - 1016.
El-Shazly, A. K. 1995. Petrology of Fe-Mg carpholite-bearing metasediments from NE Oman.
Journal of Metamorphic Geology, 13: 379 - 396.
Glennie, K. W.; Boeuf, M. G. A.; Hughes Clark, M. H. W.; Moody-Stuart, M.; Pilaar, W. F. and
Reinhardt, B. M., 1974, Geology of the Oman mountains: Verh. K. Ned. geol.
mijnbouwkd. Genoot., v. 31, p. 1-423.
Goffé, B.; Michard, A.; Kienast, J.R. and Le Mer, O., 1988, A case of obduction related high P
low T metamorphism in upper crustal nappes, Arabian continental margin, Oman: P-T
paths and kinematic interpretation: Tectonophysics, v. 151, p. 363-386.
Le Métour, J.; de Gramont, X.; Villey, M., 1986, Geological map of Masqat and Quryat, sheets
NF40-4A, NF40-4D. Scale 1:100,000. Ministry of Petroleum and Minerals, Directorate
General of Minerals, Sultanate of Oman.
Le Métour, J.; Rabu, D.; Tegyey, M.; Bechennec, F.; Beurrier, M. and Villey, M., 1990,
Subduction and obduction: two stages in the Eo-Alpine tectonometamorphic evolution of
the Oman Mountains, in Robertson, A. H. F., Searle, M. P. and Ries, A. C. (eds), The
Geology and Tectonics of the Oman Region. Geol Soc London Special Pub, v. 49, p. 327339.
Lippard, S. J.; Shelton, A. W; and Gass, I. G., 1986, The ophiolite of northern Oman. Oxford:
Blackwell Scientific Publications, 178 p.
Lippard, S. J., 1983. Cretaceous high pressure metamorphism in NE Oman and its relationship to
subduction and ophiolite nappe emplacement: Jour Geol Soc London v.140, p. 97-104.
Michard, A.; Goffé, B. and Ouazzani, M., 1982, Obduction-related high presure-low temperature
metamorphism in upper crustal materials, Muscat, Oman: Terra Cognita, v. 3, p. 187.
Searle, M. P., Waters, D. J., Martin, H. N. & Rex, D. C., 1994. Structure and metamorphism of
blueschist - eclogite facies rocks from the northeastern Oman Mountains. Journal of the
Geological Society, London, 151, 555 - 576.