干旱区生态环境知识资源中心(Arid): Origin and geotectonic evolution of Mir Tertiary basaltic andesite dykes, Western Desert, Egypt: Constraints from mineral and bulk-rock chemistry

Arid

DOI	10.1002/gj.3296
	Origin and geotectonic evolution of Mir Tertiary basaltic andesite dykes, Western Desert, Egypt: Constraints from mineral and bulk-rock chemistry
	Farahat, Esam S.; Ali, Shehata
通讯作者	Ali, Shehata
来源期刊	GEOLOGICAL JOURNAL
ISSN	0072-1050
EISSN	1099-1034
出版年	2019
卷号	54 期号:4 页码:2274-2287
英文摘要	Compared with widespread Egyptian Tertiary basaltic rocks, Mir Tertiary basaltic dykes from the Western Desert of Egypt show distinct mineralogical and geochemical characteristics that provide insights into the nature of their mantle source and geotectonic evolution as well as melting and crystallization conditions. Their mineralogical features (i.e., presence of orthopyroxene and lack of olivine) distinguish them from the other Egyptian Tertiary basalts. They have basaltic andesite compositions (SiO2 = 53.55-55 wt.%, Na2O + K2O = 4.64-4.8 wt.%, MgO = 2.66-3.02 wt.%) with tholeiitic character. Temperature of crystallization ranges from 1,112 degrees C to 1,140 degrees C for plagioclase; from 1,085 degrees C to 1,123 degrees C for clinopyroxene; and from 1,034 degrees C to 1,090 degrees C for orthopyroxene. These results are in harmony with petrographic observations which suggest early crystallization of plagioclase, followed by simultaneous crystallization of plagioclase and clinopyroxene, and soon thereafter by orthopyroxene crystallization. Titanomagnetite-ilmenite intergrowths indicate oxygen fugacity (integral O-2) of -12.09 and -9.4 log units, suggesting crystallization at relatively oxidized conditions. Their temperature ranges from 959 degrees C to 1,125 degrees C, suggesting that the titanomagnetite joins the crystallized phases at early stages and continued until later stages. Mir basaltic andesite (MBA) has low Ni (15-27.9 ppm), Cr (19.8-48.5 ppm), and Sc (20-25 ppm) concentrations together with high FeOt/MgO ratios (3.18-3.58) relative to primitive basalts, arguing for their evolved nature. They have sub-chondritic Nb/Ta ratios (15.5-17) similar to ocean-island basalts and higher than those of continental crust, ruling out a significant effect of crustal contamination. The high La/Nb (>1.4) with the negative Nb, Ta, and Ti anomalies on the primitive mantle-normalized patterns most likely indicates that their primary magma was derived from partial melting of a mantle source previously metasomatized by influx of subduction-related slab fluids/melts. Moreover, the super-chondritic Zr/Hf ratios (39.55-55.21) and the negative K and Ti anomalies point to carbonate metasomatism of their mantle source. This inference is further supported by their high (K2O + Na2O)/TiO2 ratios (>1) which are comparable with experimentally produced carbonated peridotite melts. The high Zr/Y (average 9.75) and La/Yb ratios (8.6-10) of the MBA suggest that they were generated via low degrees of partial melting. Indeed, modelling calculations indicate generation by lower melting degrees (<10%) of a garnet-bearing lherzolite mantle source. The melting region was at the garnet stability field suggesting a deeper origin (exceeds similar to 85 km) for MBA. Field and geochemical characteristics of the Egyptian Tertiary volcanism proved that it is spatially and temporally related to extension that has occurred during Red Sea rifting. Extension most likely due to the NE-SW tensional stresses which reactivated the old fractures and triggered mafic magma generation through passive upwelling of the asthenospheric mantle.
英文关键词	asthenospheric mantle basaltic andesite Egypt Mir Western Desert
类型	Article
语种	英语
国家	Egypt
收录类别	SCI-E
WOS记录号	WOS:000477016000025
WOS关键词	CONTINENTAL FLOOD VOLCANISM ; NORTHERN RED-SEA ; LITHOSPHERIC MANTLE ; TRACE-ELEMENT ; ARABIAN PLATE ; 3 GPA ; GEOCHEMISTRY ; RIFT ; MAGMATISM ; PLUME
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/2XILL650/215960
作者单位	Menia Univ, Fac Sci, Geol Dept, Al Minya 61519, Egypt
推荐引用方式 GB/T 7714	Farahat, Esam S.,Ali, Shehata. Origin and geotectonic evolution of Mir Tertiary basaltic andesite dykes, Western Desert, Egypt: Constraints from mineral and bulk-rock chemistry[J],2019,54(4):2274-2287.
APA	Farahat, Esam S.,&Ali, Shehata.(2019).Origin and geotectonic evolution of Mir Tertiary basaltic andesite dykes, Western Desert, Egypt: Constraints from mineral and bulk-rock chemistry.GEOLOGICAL JOURNAL,54(4),2274-2287.
MLA	Farahat, Esam S.,et al."Origin and geotectonic evolution of Mir Tertiary basaltic andesite dykes, Western Desert, Egypt: Constraints from mineral and bulk-rock chemistry".GEOLOGICAL JOURNAL 54.4(2019):2274-2287.