Arid
DOI10.1016/j.jseaes.2016.03.010
Fluid-related modifications of Cr-spinel and olivine from ophiolitic peridotites by contact metamorphism of granitic intrusions in the Ablah area, Saudi Arabia
Ahmed, Ahmed Hassan1,2; Surour, Adel Abdullah3
通讯作者Ahmed, Ahmed Hassan
来源期刊JOURNAL OF ASIAN EARTH SCIENCES
ISSN1367-9120
EISSN1878-5786
出版年2016
卷号122页码:58-79
英文摘要

The Ablah serpentinized peridotites and overlying layered metagabbros represent an allochthonous piece of a dismembered ophiolite in the southern Hijaz terrane that belongs to the Neoproterozoic Arabian Shield in Saudi Arabia. On both sides, the ophiolite is bounded by wider domains of granitic intrusions and volcano-sedimentary successions, all together follow a N-S trend. The protolith of the Ablah serpentinized peridotites is mainly harzburgite which is partly or totally serpentinized. Carbonate veins of variable sizes invade and hydrate the serpentinized peridotites. Away from the contact with the granitic intrusions, fresh primary (igneous) olivine and Cr-spinel are preserved in the partly serpentinized peridotites. These relict primary minerals are used to infer their tectonic setting of formation as a nascent spreading center rock association of mid-ocean ridge or back-arc basin setting. Based on the re-distribution of elements related to different thermal effects, three patterns of Cr-spinel modification can be defined. The first pattern can be followed in the partly serpentinized peridotites where Cr-spinel displays simple zoning that is characterized by sharp contact between primary Al-rich cores and secondary Fe3+-rich rims. These cores and rims are homogeneous and show progressive decrease in Mg, Al and Cr, but with remarkable increase in Fe3+ and Fe2+ toward the rims. Mineral assemblage in equilibrium with this type of Cr-spinel is primary olivine + antigorite +/- chlorite +/- talc chrysotile. The second pattern of Cr-spinel modification is represented by homogeneous weakly zoned Cr-rich spinel with no distinct sharp contacts between Cr-rich cores and magnetite rims. Cr-spinel cores of this type are rich in Cr and Fe2+, and poor in Mg, Al and Fe3+. The mineral assemblage in equilibrium with this Cr-spinel type is Fe-rich olivine + antigorite + enstatite + chlorite + tremolite + anthophyllite +/- talc. The third pattern is defined by pervasive heterogeneous modification in which the alteration starts from the cores outwards forming a very characteristic "atoll" textured SiO2- and Cr-rich porous spinel. This type is characterized by core-to-rim increase in Cr, Fe3+, Si, Mn, Ni and Ti, and decrease in Mg, Al and Fe". The mineral assemblage in equilibrium with this pattern is chlorite + carbonates + lizardite/ chrysotile antigorite. The first modification pattern is suggested to form under nearly solid-state conditions in the distal part from the granitic intrusion. The second pattern could be formed under reducing conditions with high temperature and fluid/rock ratio near the contact zone. The peak metamorphic temperature of this stage ranges from 500 to 650 degrees C that indicate upper amphibolite facies conditions. During retrograde metamorphism, the hydrothermal fluids are cooler and oxidizing which lead to the precipitation of thick marble-like carbonate veins within the serpentinized peridotites. In such a case, the aqueous fluids attack the Al- and Mg-rich cores, which are less resistant and replicable than the Fe-rich rims, and form the third chemical modification pattern of porous SiO2-rich spinel. The high SiO2 content in Cr-spinel is most probably attributed to the formation of Mg- and Al-rich silicates within the sub-microscopic pores of altered Cr-spinel. (C) 2016 Elsevier Ltd. All rights reserved.


英文关键词Serpentinized peridotites Contact metamorphism Cr-spinel Ferritchromite Atoll texture Ablah Saudi Arabia
类型Article
语种英语
国家Saudi Arabia ; Egypt
收录类别SCI-E
WOS记录号WOS:000378458800004
WOS关键词MAFIC-ULTRAMAFIC COMPLEX ; EASTERN DESERT ; MANTLE PERIDOTITES ; CHROMIAN SPINELS ; OMAN OPHIOLITE ; NEOPROTEROZOIC OPHIOLITE ; PETROGENETIC INDICATOR ; PODIFORM CHROMITITES ; LITHOSPHERIC MANTLE ; TECTONIC SETTINGS
WOS类目Geosciences, Multidisciplinary
WOS研究方向Geology
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/194229
作者单位1.King Abdulaziz Univ, Fac Earth Sci, Jeddah 21441, Saudi Arabia;
2.Helwan Univ, Fac Sci, Dept Geol, Cairo, Egypt;
3.Cairo Univ, Fac Sci, Dept Geol, Giza 12613, Egypt
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Ahmed, Ahmed Hassan,Surour, Adel Abdullah. Fluid-related modifications of Cr-spinel and olivine from ophiolitic peridotites by contact metamorphism of granitic intrusions in the Ablah area, Saudi Arabia[J],2016,122:58-79.
APA Ahmed, Ahmed Hassan,&Surour, Adel Abdullah.(2016).Fluid-related modifications of Cr-spinel and olivine from ophiolitic peridotites by contact metamorphism of granitic intrusions in the Ablah area, Saudi Arabia.JOURNAL OF ASIAN EARTH SCIENCES,122,58-79.
MLA Ahmed, Ahmed Hassan,et al."Fluid-related modifications of Cr-spinel and olivine from ophiolitic peridotites by contact metamorphism of granitic intrusions in the Ablah area, Saudi Arabia".JOURNAL OF ASIAN EARTH SCIENCES 122(2016):58-79.
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