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DOI10.2475/08.2017.02
THE LATE NEOPROTEROZOIC DAHANIB MAFIC-ULTRAMAFIC INTRUSION, SOUTH EASTERN DESERT, EGYPT: IS IT AN ALASKAN-TYPE OR A LAYERED INTRUSION?
Azer, Mokhles K.1; Gahlan, Hisham A.2,3; Asimow, Paul D.4; Al-Kahtany, Khaled M.2
通讯作者Asimow, Paul D.
来源期刊AMERICAN JOURNAL OF SCIENCE
ISSN0002-9599
EISSN1945-452X
出版年2017
卷号317期号:8页码:901-940
英文摘要

In Egypt, mafic-ultramafic complexes have been classified into three major types: incomplete ophiolite sequences; Alaskan-type intrusions, concentricallyzoned bodies formed in a subduction arc environment; and layered intrusions, vertically-zoned bodies intruded in post-collisional tectonic environments and rift-related bodies associated with the opening of the Red Sea. We present new field work, geochemical data, mineral chemistry and interpretations for the late Neoproterozoic Dahanib mafic-ultramafic intrusion in the South Eastern Desert of Egypt (northernmost Arabian-Nubian Shield, ANS). The Dahanib intrusion shows no evidence of metamorphism or deformation, with excellent preservation of intrusive contacts, well-preserved textures and primary mineralogy. Field relations indicate that it is younger than the surrounding metamorphic rocks and syn-tectonic granitoids. The intrusion is composed of a basal suite of ultramafic rocks (dunite, lherzolite, wehrlite and pyroxenite) and an overlying suite of mafic rocks (olivine gabbronorite, gabbronorite and anorthosite). It displays evident layering of modal abundance, visible directly in outcrop, as well as cryptic layering discernible through changes in mineral compositions. The western and eastern lobes of the Dahanib intrusion occur in the form of a lopolith with readily correlated layers, especially in the upper mafic unit. The present-day dip of the layering decreases from the ultramafic units into the mafic sequence. Structural and compositional relations show that the ultramafic units are cumulates from a high-Mg tholeiitic parent magma emplaced at deep crustal levels and evolved via fractional crystallization rather than any kind of residual mantle sequence. Fo content of olivine and Mg# of pyroxenes display a systematic decrease from ultramafic to mafic rocks, well-correlated with whole-rock Mg#. Spinels in ultramafic samples vary from Cr-rich to Al-rich and have Mg# and Fe3+# similar to spinels from typical stratiform complexes and clearly different from those found in ophiolitic and Alaskan-type complexes. Although the mafic and ultramafic units are clearly related and can be derived from common parent magma, they were not emplaced coevally; rather, they represent different pulses of magma. The Dahanib mafic-ultramafic intrusion does not display any features that convincingly identify it as a typical Alaskan-type body, particularly the lack of clinopyroxenite and hornblendite, rarity of primary hornblende, and the notable abundance of orthopyroxene and plagioclase in its rocks. Our results confirm that it is more akin to a layered mafic-ultramafic intrusion with a multistage evolution. It was emplaced into a stable post-orogenic cratonic setting, with a trace element signature indicating contamination of the mantle source by previous subduction events.


英文关键词Neoproterozoic Arabian-Nubian Shield Eastern Desert layered intrusion post-collision
类型Article
语种英语
国家Egypt ; Saudi Arabia ; USA
收录类别SCI-E
WOS记录号WOS:000413093500002
WOS关键词ARABIAN-NUBIAN SHIELD ; NW CHINA IMPLICATIONS ; RED-SEA ; ZABARGAD-ISLAND ; TRACE-ELEMENT ; SM-ND ; CLINOPYROXENE COMPOSITION ; CHEMICAL CHARACTERISTICS ; TECTONIC EVOLUTION ; CRUSTAL EVOLUTION
WOS类目Geosciences, Multidisciplinary
WOS研究方向Geology
来源机构King Saud University
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/197267
作者单位1.Natl Res Ctr, Geol Sci Dept, Cairo 12622, Egypt;
2.King Saud Univ, Dept Geol & Geophys, Riyadh 11451, Saudi Arabia;
3.Assiut Univ, Geol Dept, Assiut 71516, Egypt;
4.CALTECH, Div Geol & Planetary Sci, Pasadena, CA 91125 USA
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Azer, Mokhles K.,Gahlan, Hisham A.,Asimow, Paul D.,et al. THE LATE NEOPROTEROZOIC DAHANIB MAFIC-ULTRAMAFIC INTRUSION, SOUTH EASTERN DESERT, EGYPT: IS IT AN ALASKAN-TYPE OR A LAYERED INTRUSION?[J]. King Saud University,2017,317(8):901-940.
APA Azer, Mokhles K.,Gahlan, Hisham A.,Asimow, Paul D.,&Al-Kahtany, Khaled M..(2017).THE LATE NEOPROTEROZOIC DAHANIB MAFIC-ULTRAMAFIC INTRUSION, SOUTH EASTERN DESERT, EGYPT: IS IT AN ALASKAN-TYPE OR A LAYERED INTRUSION?.AMERICAN JOURNAL OF SCIENCE,317(8),901-940.
MLA Azer, Mokhles K.,et al."THE LATE NEOPROTEROZOIC DAHANIB MAFIC-ULTRAMAFIC INTRUSION, SOUTH EASTERN DESERT, EGYPT: IS IT AN ALASKAN-TYPE OR A LAYERED INTRUSION?".AMERICAN JOURNAL OF SCIENCE 317.8(2017):901-940.
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