Petrogenesis of Maobei rutile eclogites from the southern Sulu ultrahigh‐pressure metamorphic belt, eastern China
Petrogenesis of Maobei rutile eclogites from the southern Sulu ultrahigh‐pressure metamorphic belt, eastern China
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DOI：
10.1111/j.1525-1314.2006.00665.x
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发表时间：
2006-10
影响因子：
3.4
通讯作者：
Z. M. Zhang;J. Liou;X. Zhao;C. Shi
中科院分区：
文献类型：
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作者：
Z. M. Zhang;J. Liou;X. Zhao;C. Shi
茅北杂岩位于苏鲁超高压变质带南部，主要由层状榴辉岩、石榴橄榄岩和正片麻岩组成。根据模式矿物和全岩成分，将茅北杂岩中的榴辉岩分为石英榴辉岩、富石英榴辉岩、金红石榴辉岩、富金红石榴辉岩和榴辉岩。岩性和化学成分的空间变化表明该杂岩可划分为10个韵律层。金红石榴辉岩具有高的TiO 2（2.4-5.9重量%），通常与高的P2 O 5（高达4.1重量%）的内容耦合;大多数显示分馏稀土元素模式与轻微的正Eu异常。富金红石榴辉岩具有非常高的TiO 2（3.3-5.7重量%），FeOT（17.5-25.3重量%），V（126-1163 ppm）和Co（14-132 ppm），以及极低的SiO2（38.0-42.3重量%），Zr（24-85 ppm），Nb（0.3-6.9 ppm），钽（<0.1-0.6 ppm）和总REE（10.7- 334.0ppm）含量，轻稀土亏损程度不同，Eu正异常（Eu/Eu* = 1.1-2.9），并且Ti与其他高场强元素解耦。这些特征与典型层状侵入体的铁钛辉长岩一致，意味着在演化的玄武岩浆房中有斜长石、单斜辉石和丰富的副磁铁矿的堆积。在正常地层层序中，随着结晶分异程度和地层高度的增加，茅北杂岩表现出先富铁后富碱的趋势。结合SHRIMP锆石U-Pb年龄（773.7 ± 8.0 Ma），表明茅北杂岩的原岩为新元古代层状侵入体，由橄榄辉长岩基底、辉长岩主体和少量花岗闪长岩组成。三个金红石榴辉岩层中Ti、V、P含量异常高，是潜在的经济矿床。
The Maobei complex in the southern Sulu ultrahigh‐pressure (UHP) metamorphic belt, eastern China, mainly consists of layered eclogites, garnet peridotites and orthogneisses. Based on the modal mineral and whole‐rock compositions, eclogites from the Maobei complex are divided into quartz eclogite, quartz‐rich eclogite, rutile eclogite, rutile‐rich eclogite and eclogite. The distinct spatial changes in the lithology and related chemical compositions indicate that this complex includes 10 rhythmic layers. The rutile eclogites have high TiO2 (2.4–5.9 wt%), commonly coupled with high P2O5 (up to 4.1 wt%) contents; most show fractionated REE patterns with slight positive Eu anomalies. The rutile‐rich eclogites have very high TiO2 (3.3–5.7 wt%), FeOT (17.5–25.3 wt%), V (126–1163 ppm) and Co (14–132 ppm), and very low SiO2 (38.0–42.3 wt%), Zr (24–85 ppm), Nb (0.3–6.9 ppm), Ta (<0.1–0.6 ppm) and total REE (10.7–334.0 ppm) contents, variable degree of LREE depletion, and positive Eu anomalies (Eu/Eu* = 1.1–2.9), and the Ti is decoupled from other high‐field‐strength elements. These characteristics are consistent with Fe‐Ti gabbros of typical layered intrusions, implying a cumulate of plagioclase, clinopyroxene and abundant accessory magnetite in an evolved basaltic magmatic chamber. Based on a normal stratigraphic sequence, the Maobei complex shows an iron‐enrichment trend, followed by alkaline enrichment with increasing fractionated crystallization and stratigraphic height. These facts, together with SHRIMP U‐Pb zircon ages of 773.7 ± 8.0 Ma, indicate that the protolith of the Maobei complex is a Neoproterozoic layered intrusion consisting of a base of peridogabbro, a main body of gabbro and minor granodiorite. Unusually high Ti, V and P contents in three rutile eclogite layers suggest that they are potential economic ore deposits.