Petrology and chemistry of basal lherzolites above the metamorphic sole from Wadi Sarami central Oman ophiolite
Petrology and chemistry of basal lherzolites above the metamorphic sole from Wadi Sarami central Oman ophiolite
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DOI：
10.2465/jmps.121026
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发表时间：
2013-02
影响因子：
0.7
通讯作者：
M. Khedr;S. Arai;M. Python
中科院分区：
文献类型：
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作者：
M. Khedr;S. Arai;M. Python
我们研究了基底lherzeles暴露沿着变质唯一的基础上，中央阿曼蛇绿岩（瓦迪Sarami）。我们认识到两种类型的lherzalgae（类型I和II）的基础上，现场发生，纹理和矿物成分。I型二辉橄榄岩是块状的，并过渡到方辉橄榄岩，而II型二辉橄榄岩是强烈的片理化与糜棱岩碎斑结构。II型二辉橄榄岩仅在与角闪质底直接接触的范围内出现，并在该底上方几米处，并被I型二辉橄榄岩覆盖和/或包围。第二型二辉沸石单斜辉石[Mg# = Mg/（Mg + Fe）= 0.89-0.94]中Al_2 O_3（4.5- 7.3wt%）、Na_2 O（0.5- 1.2wt%）、Cr_2 O_3（0.6- 1.4wt%）和TiO_2（0.2- 0.4wt%）的含量高于第一型二辉沸石。单斜辉石的Al_2O_3、Na_2O和TiO_2含量之间的正相关性表明，从I型二辉橄榄岩到亏损辉橄榄岩，存在明显的残余趋势，从而导致地幔底部的化学不均一性。二辉橄榄岩和方辉橄榄岩中的单斜辉石的成分趋势与正常海脊段的深海橄榄岩相似。橄榄石（Fo89.4-Fo91.5）显示Sarami橄榄岩的残留特征。原生尖晶石的Cr# [= Cr/（Cr + Al），0.04 ~ 0.53]和YFe [Fe/（Cr + Al + Fe），<0.046]范围较宽，与深海橄榄岩中的尖晶石相似。尖晶石Cr#的宽范围是由宽范围的部分熔融度造成的，二辉橄榄岩的部分熔融度高达10%，方辉橄榄岩的部分熔融度为~ 10-25%。第二类lherzitans，发生在附近的古断裂带位于瓦迪Sarami东部，代表残留的软流圈物质被困在底部的海洋岩石圈地幔（I型）在拆离和仰冲。I型二辉橄榄岩经历了高度的部分熔融，导致在耐火端形成方辉橄榄岩。Sarami辉石和尖晶石的模式和成分变化表明阿曼蛇绿岩在海洋扩张中心形成残留物的内在地幔异质性。
We studied basal lherzolites that are exposed along the metamorphic sole at the base of the central Oman ophiolite (Wadi Sarami). We recognized two types of lherzolites (Types I and II) based on field occurrences, textures, and mineral compositions. Type I lherzolites are massive and transition into harzburgites, whereas Type II lherzolites are strongly foliated with mylonitic to porphyroclastic textures. Type II lherzolites only crop out within a direct contact with the amphibolitic sole to few meters above this sole and are overlain and/or surrounded by Type I. The clinopyroxenes [Mg# = Mg/(Mg + Fe) = 0.89-0.94] of Type II lherzolites show higher contents of Al2O3 (4.5-7.3 wt%), Na2O (0.5-1.2 wt%), Cr2O3 (0.6-1.4 wt%), and TiO2 (0.2-0.4 wt%) than those of Type I lherzolites. Positive correlations among the Al2O3, Na2O, and TiO2 contents of clinopyroxenes show a pronounced residual trend from Type I lherzolites to depleted harzburgite, giving rise to chemical heterogeneities at the base of the mantle section. Clinopyroxenes in lherzolites and harzburgites show compositional trends that are similar to those in abyssal peridotites from normal ridge segments. Olivines (Fo89.4-Fo91.5) show a residual character of the Sarami peridotites. Primary spinels show a wide range of Cr# [= Cr/(Cr + Al) from 0.04 to 0.53] and low YFe [Fe/(Cr + Al + Fe), <0.046], similar to spinels in abyssal peridotites. The wide range of spinel Cr# is a result of a wide range of partial-melting degrees, which are up to 10% for lherzolites and ~ 10-25% for harzburgites. The Type II lherzolites, which occur near the paleo-fracture zone located to the east of Wadi Sarami, represent a remnant of asthenospheric materials trapped at the base of oceanic lithosphere mantle (Type I) during detachment and obduction. The Type I lherzolites experienced high-degree partial melting, resulting in the formation of harzburgites at the refractory end. The modal and compositional variations of Sarami pyroxenes and spinels indicate intrinsic mantle heterogeneity of Oman ophiolite formed as residues at an oceanic spreading center.