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首页> 外文期刊>Journal of African earth sciences >Paleomagnetism of a late Neoproterozoic mafic-ultramafic layered intrusion of Gebel Dahanib, South Eastern Desert (Egypt): Implications for magma evolution and timing of magnetization acquisition
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Paleomagnetism of a late Neoproterozoic mafic-ultramafic layered intrusion of Gebel Dahanib, South Eastern Desert (Egypt): Implications for magma evolution and timing of magnetization acquisition

机译：古代古典古典古典主义的古马布 - 超空白分层侵入Gebel Dahanib，东南沙漠（埃及）：对岩浆进化和磁化采集时机的影响

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摘要

We present detailed rock magnetic and paleomagnetic results for a late Neoprotemzoic mafic-ultramafic layered intrusion of Gebel Dahanib, South Eastern Desert, Egypt. Gebel Dahanib intrusion (GDI) is an elliptical body with saucer or funnel shape, and was intruded into deformed country rocks at similar to 710 Ma. It consists of two main undeformed and unmetamorphosed sequences: I) a lower ultramafic sequence composed mainly of peridotite (dunite and lherzolite cumulate) and pymxenite (olivine websterite and websterite cumulates). Dunite cumulate occupies the basal part, which grades upward to lherzolite and pymxenite cumulates at the top of the ultramafic sequence; and II) an upper mafic sequence that comprises olivine gabbronorite, gabbmnorite, norite, and a chilled margin of fine-grained gabbronorite. An intrusive contact was observed between ultramafic and mafic sequences, which suggests an asynchronous emplacement history. To understand the magmatic evolution of GDI and to make a new contribution to the small African Neoprotemzoic paleomagnetic database, 260 oriented samples were collected from four rock units (peridotite, pyroxenite, gabbro, and fine-grained gabbro). Rock magnetic experiments combined with Fe-Ti microscopic observations and demagnetization procedures indicate that both sequences have different magnetic mineral contents and paleomagnetic components. A stable component with northwesterly declination and shallow negative inclination carried by magnetite and pyrrhotite was isolated from the ultramafic sequence (Dec = 326.6 degrees, Inc = -28.2 degrees, alpha(95) = 5.5 degrees, and k = 58.72), and the corresponding paleomagnetic pole lies at lat = 39.0 degrees N, long = 261.5 degrees E, A(95) = 4.6 degrees, and K = 83.13. Paleomagnetic analyses on the mafic sequence yielded northeast-directed declinations, with intermediate positive inclinations (Dec = 11.3 degrees, Inc = 47.6 degrees, alpha(95) = 3.9 degrees, and k = 103.19), and a paleomagnetic pole lat = 78.7 degrees N, long = 96.2 degrees E, A(95) = 4.4 degrees, and K = 81.49. We postulate that the Dahanib intrusion was emplaced in two pulses: the first includes the ultramafic assemblages at the base of the intrusion; the second magma pulse makes up the upper mafic sequence. Assessment of Egyptian paleomagnetic poles from a similar time period (similar to 710-540 Ma) indicates that only one pole (out of 21) can be considered reliable, and also from the African dataset only five of 43 poles are of high quality. These indicate that new high-quality paleomagnetic poles are needed to refine the late Neoproterozoic paleomagnetic database for Egypt and the African continent.
机译：我们为Gebel Dahanib，东南沙漠，埃及的后期旁观型古典佐奇MAFIC-Ultramafic分层侵入详细的岩石磁性和古磁性结果。 Gebel Dahanib入侵（GDI）是一种带碟子或漏斗形状的椭圆体，并侵入变形的国家岩石，类似于710 mA。它由两种主要的未变形和不掩盖的序列组成：i）较低的超微序列，主要由恒星（Dunite和Lherzolite累积）和Pymxite（橄榄石韦斯特岩和卵晶岩累积）组成。 dunite累积占据基部的基础部分，向上渐变到纯血清序列顶部的Lherzoleit和Pymxite累积;并且II）包含橄榄石加筋，Gabbmnorite，Norite的上部MAFIC序列，以及细粒的细粒状的冷冻余量。在超空白和MAFIC序列之间观察到侵入式接触，这表明了异步施加历史。要了解GDI的岩石演进并为小非洲旁观古代古磁石数据库做出新的贡献，从四个岩石单元（Peridite，Pyroxenite，Gabbro和细粒度Gabbro）收集260个取向样品。岩石磁性实验与Fe-Ti显微镜观察和退磁程序相结合，表明两个序列具有不同的磁性矿物质含量和古磁性组分。从超微序列中分离出具有磁铁矿和Pyrrhotite携带的西北倾斜和浅阴性倾斜的稳定部件（Dec = 326.6度，Inc = -28.2度，α（95）= 5.5度，以及相应的古磁极在拉特= 39.0度N，LONG = 261.5°E，A（95）= 4.6度，K = 83.13。肉草序列的古磁性分析产生了东北定向的下降，中间呈倾斜度（DEC = 11.3度，INC = 47.6度，α（95）= 3.9度和k = 103.19），以及古磁杆LAT = 78.7度N. ，长= 96.2°E，A（95）= 4.4度，k = 81.49。我们假设Dahanib入侵被置于两种脉冲中：第一个包括在侵入的基础上包括超微的组装;第二岩浆脉冲构成上部MAFIC序列。从类似的时间段（类似于710-540 mA）的埃及古磁极评估表明只有一个极点（21个）可以被认为是可靠的，而且来自非洲数据集中只有43个极的五个具有高质量。这些表明，需要新的高品质古磁珠来改进埃及和非洲大陆的晚期新蛋白古古磁磁性数据库。

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