Mineral Composition and Provenance of Al-Chabbab Stream Sediments, Wasit, Southeastern Iraq

Abstract


Introduction
Minerals compositions are generally used to determine the source rocks, the provenance of the clastics, and the nature of the sedimentary processes of the depositional basin.Heavy minerals studies are applied to determine the weathering processes, provenance, and diagenesis of clastic rocks (Mange and Maurer, 1992;Dill, 1998;and Arribas et al., 2000).Heavy mineral components in river sediments closely refer to the nature of the source area, and their composition are sensitive to the processes occurring during the sedimentary cycle, such as weathering, transportation, deposition ,and diagenetic processes (Morton and Johnsson, 1993).Al-Chabbab stream is considered one of the seasonal tributaries of the Tigris River, it rises from the Zagros Mountains in to the east and northeast then drains to the south-west and inflows into the Tigris River in Wasit Governorate.Many researchers studied the mineral composition and texture of the Holocene sediments of the Tigris River such as Philip (1968); Jawad (1977); and Al-Juboury et al.
(2001a and b).These studies showed that the sandy sediments of the Tigris River are finer than those of other seasonal tributaries and composed from defferent source rocks.Twelve samples of the clastic sediments were collected from Al-Chabbab stream, Tigris River, and Al-Chabbab inflow; investigated by polarized microscope and X-Ray Diffraction (XRD) technique to detect the mineral compositions and source rocks of the studied area.

Geology
The study area includes the mouth of Al-Chabbab stream, which discharges into the Tigris River (Fig. 1).The coordinate of the area locates between 46˚ 13̍ 01̎ E and 32˚ 37̍ 05̎ N which is situated in the south-eastern part of the central area of Iraq.The basin of Al-Chabbab stream rises from the Iranian (tectonically unstable shelf Western Zagros Fold-Thrust belt) Zagros Mountain then flows in the direction of Iraqi lands and inflow into the Tigris River (Jassim and Goff, 2006;Malik et al., 2014).Geologically, many formations in the study area dating from Oligocene to recent were included.The formations cropping out in the study area are the Euphrates; Fatha; Injana; and Mukdadiya (Buday and Jassim, 1980).

Materials and Methods
Twelve recent clastic sediment samples were collected about 15cm depth, along the banks of Al-Chabbab stream, Tigris River and Al-Chabbab inflow.Laboratory techniques to separate the heavy from the light minerals using bromoform have a specific gravity 2.89 depending on Carver (1971).A polarizing microscope and XRD technique (Shimadzu X-Ray 6000) was accomplished in Iraq German Lab, spectra Germany 2010, are used to identify the mineral compositions.

Light Minerals
Quartz, rock fragments and feldspar are the predominant light components in all samples except Al-Chabbab inflow, in which gypsum are more than in other samples from Tigris and Al-Chabbab streams.The light mineral types and their percentages are listed in Table 1.

Quartz
The quartz content in the Tigris River samples was more than Al-Chabbab inflow and Al-Chabbab stream samples, with an average of 43%, 41% ,and 29%, respectively (Table 1).Quartz is a resistant mineral to weathering processes during long-distance transportation, the abundance of quartz minerals suggests felsic sources (Tucker, 1991).A petrographic study shows monocrystalline quartz (Fig. 1-a) and polycrystalline quartz (Fig. 1-b).monocrystallinequartz was more than polycrystalline quartz.Monocrystalline quartz refered to plutonic and volcanic felsic igneous origin.The average percentage of monocrystalline is 26.9%, whereas polycrystalline is 2.05%.The highest concentration of polycrystalline quartz was in the Tigris River, which was 3.15% (Table 1).Polycrystalline quartz probably sourced from metamorphic rocks (schist and gneiss) and plutonic, Blatt (1967) andFolk (1974).The high quantity of monocrystalline quartz in Tigris River refered to share felsic sours rocks.
The shape of monocrystalline quartz was sub-rounded to rounded (Fig. 2-a), and some quartz grains were unfractured.Quartz tested by X-ray diffraction technique (Figs. 4,5 and 6).

3.1.2.Rock fragments
Rock fragments have heterogeneous distribution in all samples.Carbonate rock fragments (Fig. 2c) are dominants in Al-Chabbab stream compared with chert (Fig. 2-d), igneous (Fig. 2-e), metamorphic (Fig. 2-f) and mudstone rock fragments (Fig. 2-a).The Tigris River samples have low percentage of rock fragments with an average 7.3%, whereas in Al-Chabbab stream and Al-Chabbab inflow samples are approximately equal 9% this may reflect more supplied of carbonate rock fragments in Al-Chabbab stream and Al-Chabbab inflow compared with Tigris River samples.Carbonate rocks tested by X-ray diffraction technique (Figs. 4,5 and 6).Rock fragments are considered valuable components that refer to the sedimentary source.The percentage of rock fragments in sediments is affected by the location of the source rocks.This percentage increases when the sedimentary basin is near the source rock area or has high topography (Stephen, 2000).Evaporates (Fig. 3-b) concentrated in Al-Chabbab inflow samples (7.2%), whereas in Al-Chabbab stream and Tigris River samples were found in trace amounts of 1.3%, 1.15% (Table 1).

.Feldspar minerals
Microcline, orthoclase and plagioclase were found in a moderate percentage compared with other light components in all samples of Al-Chabbab stream, Tigris River and Al-Chabbab inflow with an average (4.1%, 3.0%, 4%) respectively.Orthoclase (Fig. 3-d), appeared as angular grain approximately.Orthoclase and microcline are found in a wide variety of igneous and metamorphic rocks, which have crystallized at intermediate to low temperature (Hibbard, 2002).

Mineralogical Maturity and Distance of Transport
Mineralogical maturity is known as a compositional state of a clastics sedimentary body, which is a predominance of quartz and an absence or scarcity of less resistant minerals such as feldspars; detrital carbonates or lithic fragments as mentioned by Blatt et al. (1972) and Pettijohn et al.(1972).The mineralogical maturity index (MMI; Q+Ch /F +RF) (Ch= chert rock fragments) given by Pettijohn (1957) is determined for the Al-Chabbab stream (MMI=2.5),Tigris River (MMI=4.7) and Al-Chabbab inflow samples (MMI=3.4)(Table1).The average value of MMI Al-Chabbab, Tigris and Al-Chabbab inflow samples indicates the clasts generally are sub-mature; Tigris River clasts have high MMI referring to the long transportation.The maturity of these clasts relates to the high presence of quartz compared with the feldspar and rock fragments.This clasts type refers to long-distance of transportation.

Heavy Minerals
Heavy minerals defined as accessory minerals from the high-density clastic sediments (Mange and Maurer, 1992).Heavy mineral in the river has a specific gravity greater than quartz (2.65), and they settle at the bottom of an alluvial layer.These minerals have economic importance and could be an indicator of provenance that often used in the field of sedimentology (Hamizah and Hassan, 2010).Petrographic study of Al-Chabbab stream, Tigris ,and Al-Chabbab inflow samples determined many types and amount of heavy minerals listed in Table 2 and Fig. 7A, B and C. Heavy minerals in all samples composed about less than 2%.

3.3.1.Opaque minerals
The opaque minerals composed a majority of heavy minerals in all samples.Al-Chabbab stream samples have the highest percent of an average of 41.2%, Tigris 39.53%, and Al-Chabbab inflow samples have the lowest average of 34.28%.Opaque minerals were derived from felsic, mafic igneous and metamorphic rocks and the high specificity of these minerals related to the iron content (Folk, 1974).The highest percentage could be due to sediment inputs from the unstable shelf of Zagros Mountais.This area undergoes a lot of igneous activity, and produced various basic and felsic rocks (Jawad, 1977).These rock types commonly contain high amounts of opaque iron ore minerals.The shapes of the recognized opaque minerals are mostly rounded (Fig. 8-a).

3.3.2.Unstable minerals
Pyroxene mineral assemblage in average nearly 5% in all studied samples.Pyroxene is the most significant group of ferromagnesian rock-forming minerals.This group is found in all types of igneous and metamorphic rocks, especially basic and ultrabasic igneous rocks, and can be crystallized under a variety of different conditions, as cleared by Deer et al. (1992); Mange andMorton (2007, 1963); Pettijohn (1975) and Tucker (1991).Pyroxene is found as colorless to light green angular grains (Fig. 8b).
Hornblende and glaucophane belong to Amphiboles, which are a complex group of minerals that form in many igneous and metamorphic rocks (Pettijohn et al., 1973).Amphibole indicates a predominantly igneous source rock (Ehrmann and Polozek, 1999).The hornblende is characterized by light green (Fig. 8-c).Hornblende average in Al-Chabbab stream, Tigris river and Al-Chabbab inflow are 5.83%, 5.3% and 5.08% respectively.Glaucophane minerals (Fig. 8-d) absent in Tigris river samples were found as trace amounts in Al-Chabbab stream and Al-Chabbab inflow sediments on average, not in excess of 3%.

Flaky minerals (Biotite, muscovite and chlorite)
Biotite average does not exceed 6%, and the muscovite average is 7% in all samples, where chlorite decreases in average from Al-Chabbab stream, Tigris and Al-Chabbab inflow samples (8%, 6.45% and 5.55%).Biotite appears as brown to yellow flakes .Muscovite occurs as a small flaky grain with colorless (Fig 8 -j).Chlorite is a green color and rounded to subrounded (Fig. 8-k).Chlorite is a secondary mineral inherited from altered ferromagnesian silicate minerals and derived from metamorphosed rocks (Hibbard, 2002).Most flaky minerals within the Tigris River basin were mainly derived from the Unstable Shelf's metamorphic rocks and the fragmentation of older clastics formations within the Tigris valley (Al-Juboury and Ghazal, 2008).
Celestite minerals absent in the Tigris River samples were found as trace amounts in Al-Chabbab stream and Al-Chabbab inflow sediments on average, not more than 3%.It is found under the petrographic microscope as crystals of columnar shape (plate 4-g).This mineral mainly originated from sedimentary rocks such as bedded deposits of gypsum and halite, also in cavities of bedded limestone and dolomite (Anthony et al., 2003).

ZTR Maturity Index
ZTR referes to ultrastable minerals zircon, tourmaline and rutile.ZTR Maturity Index is a combined percentage of zircon, tourmaline and rutile among the transparent heavy minerals, excluding micas and authigenic species.Table (2) shows that the average value of the ZTR index of Al-Chabbab (0.4), Tigris River sediments (0.67) and Al-Chabbab inflow samples (0.74) which means that the sediments of the studied samples are sub-mature (Fig. 9) and could be referred to redeposition from older sediments; Aubrecht, (2001) illustrated that the higher index is more matured sedimentary material.

Heavy Minerals and Tectonic Regime
''The linkage between tectonic setting and sediment composition has been long recognized'' (Nechaev and Isphording, 1993) and could be used as indicators of tectonic environments.Nechaev and Isphording (1993) proposed a plate tectonic explanation of heavy mineral data by comparing the accumulation arrangement, with the possible sources of clastic sediments resulting from various stages of the plate tectonic cycle.Accordingly, a right-angle triangular diagram (MF, MT, and GM) was constructed to associate the plate tectonic setting and the heavy mineral assemblage.Heavy mineral data of clastic sediments of Al-Chabbab stream and Tigris River clastic samples listed in Table 2, was used and plotted on MF, MT, and GM diagrams.The Al-Chabbab and Tigris River samples tended toward sub-mature active continental margin more than the passive continental margin (Fig. 10).The field of immature active continental margins is characterized by a generally high percentage of minerals derived from basic igneous and metamorphic rocks due to unstable shelf within the Foothill zone.

4.Conclusions
• Al-Chabbab stream, Al-Chabbab inflow and Tigris River clastic sediments are composed of light minerals and heavy minerals; light minerals consisting of quartz, rock fragments and feldspar Which are the predominant minerals in all samples.• The quantity of quartz (monocrystalline quartz) in the Tigris River is more than Al-Chabbab stream, which shares felsic sours rocks to supply sediments to the Tigris River more than the sediments of Al-Chabbab stream.• The Carbonate rock fragments are more abundant in Al-Chabbab sediments because the source rocks are high topographically and close to Al-Chabbab stream rather than the Tigris River.
• The average value of MMI and ZTR index of Al-Chabbab stream, Tigris and Al-Chabbab inflow samples indicates that the clasts generally are sub-mature.Tigris River clasts have high MMI refer to the long transportation of sediments.• Heavy mineral assemblages of the recent sediments from the Al-Chabbab, Al-Chabbab inflow and the Tigris River are composed of opaque and transmitted minerals, including epidotes; pyroxenes; amphiboles (hornblende and glaucophane); garnet; zircon; tourmaline; rutile; kyanite; staurolite, flaky minerals (muscovite, biotite and chlorite) and celestite minerals.Glaucophane and celestite are absent in the sediment samples of the Tigris River.• Based on the mineralogical signatures, light and heavy minerals reflect metamorphic, mafic and felsic igneous rocks of the active margin of the unstable shelf in addition to the sedimentary carbonate, evaporate and mud rocks that could be sourced from the flood plain, Euphrates, Fatha and Injana formations.