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会东菜园子地区位于扬子地块西缘，产出有玄武岩、辉绿岩脉、花岗岩体和产出于玄武岩与花岗岩接触带的铁矿床。这些地质体研究程度很低，年代学、矿物学、地球化学数据缺乏，严重限制我们对该区构造历史和地质演化的理解。本文在总结前人工作的基础上，对岩浆岩的岩相学、年代学、元素地球化学、同位素地球化学等多方面进行系统研究，结合地质关系探讨菜园子基性–酸性岩浆活动的形成时代、岩浆源区、岩浆演化、构造背景等。同时通过原位技术测定菜园子磁铁矿矿床中磁铁矿的微量元素成分，对铁矿成矿过程进行限制。（1）SIMS锆石U–Pb同位素分析显示，菜园子辉绿岩的锆石Pb–Pb年龄为1778 ± 14 Ma，与上交点年龄1799 ± 22 Ma 在误差范围内一致。SIMS磷灰石U–Pb同位素分析显示，菜园子玄武岩的磷灰石Pb–Pb年龄为1796 ± 55 Ma，与U–Pb年龄1760 ± 17 Ma在误差范围内一致。结合区域上~ 1.83 Ga变质事件，菜园子玄武岩形成时代应该在1.83–1.76 Ga之间。因此，菜园子基性岩浆活动形成于~ 1.8 Ga。（2）菜园子辉绿岩属于碱性玄武岩系列，在蛛网图上表现出大离子亲石元素（LILE）和高场强元素（HFSE）的强烈富集，且无Nb–Ta–Zr–Hf的亏损。主量元素和Ni–Cr–Sr–Eu元素特征支持其母岩浆经历橄榄石和辉石类矿物的分离结晶；高Nb/La、Nb/Th特征及异常高εNd(T)（9.0–9.6）表明其形成过程没有经历强烈的地壳混染过程。高εNd(T)特征暗示其母岩浆来自于极其亏损地幔源区。结合全球对~ 1.8 Ga极其亏损εNd(T) 样品的报道，菜园子辉绿岩源区为上地幔浅部的极其亏损地幔源区，可能是太古代地壳增长后残留的地幔源区。稀土元素分异特征指示其母岩浆产生于尖晶石二辉橄榄岩的上地幔低程度部分熔融（~ 10 %）。（3）菜园子玄武岩属于拉斑质玄武岩系列，具有明显的拉斑玄武结构，分为三组。主量和Ni–Cr–Sr–Eu元素特征表明第一组和第二组玄武岩主要经历橄榄石、辉石类矿物和少量斜长石的结晶分异。第三组玄武岩相比与前两组经历更高程度的演化，无铁钛氧化物的分离结晶，沿着富铁趋势演化，Fe2O3T含量最高可达~ 23.0 wt%。在微量元素蛛网图中，第一组玄武岩表现出与E–MORB类似的配分模式，且无明显的Nb–Ta–Zr–Hf亏损；第二组玄武岩微量元素含量与第一组相当，但表现出轻微的Nb–Ta–Zr–Hf亏损；第三组玄武岩微量元素含量很高，整体与菜园子辉绿岩相当，但表现出显著的Nb–Ta–Zr–Hf亏损和极端的Sr负异常。第二组和第三组玄武岩中εNd(T) （2.15–3.38）变化范围小，同时εNd(T)与MgO及Nb/La之间无正相关关系，同时(Nb/Th)N值较高（大部分大于1），表明其母岩浆演化–侵位过程中没有经历显著的地壳混染过程。第二组和第三组玄武岩样品中高Nb/Ta比值、Nb/Ta与La/Yb的负相关性、Hf/SmN与Ta/LaN的正相关性均指示其源区可能经历了碳酸盐熔体的交代作用。这种推论进一步得到了蛛网图中Th与REE元素分异的验证。受碳酸盐熔体交代影响较小的第一组玄武岩的稀土元素模拟显示其源区为尖晶石二辉橄榄岩主导的上地幔。菜园子玄武岩的母岩浆可能起源于碳酸盐熔体交代的岩石圈地幔。（4）菜园子基性岩浆岩具有拉斑质和碱性特征，有高的Zr、Ti、V和Zr/Y值，指示其形成于大陆裂谷背景。~1.8 Ga板内岩浆活动明显早于区域上1.7–1.5 Ga与Columbia超大陆裂解相关的非造山岩浆活动记录，表明1.8 Ga是扬子地块西缘从 Columbia 超大陆初始裂解时间。异常亏损地幔源区的破坏与将扬子地块置于Laurentia西北缘和Australia东部的Columbia重建模型吻合。（5）菜园子花岗岩SIMS锆石U–Pb年龄为1048.5 ± 4.9 Ma 和 1043.1 ± 5.1 Ma，与元谋花岗岩的LA–ICP–MS 锆石Pb–Pb加权平均年龄 1041 ± 12 Ma在误差范围内一致，表明二者侵位时代相同。（6）菜园子花岗岩具有高FeO*/MgO、Ga/Al比值和高HFSE含量，具有A型花岗岩特征。这些岩石具有正的全岩εNd(t) (+0.58 – +4.4)、锆石εHf(t) (+6.0 – +8.3)、高Nb/La 和 Nb/Th 比值，与区域上同时代基性岩浆岩一致。锆石O同位素值为6.2–7.2 ‰，略高于“地幔锆石”的值（5.3 ± 0.6 ‰）。结合异常高的锆石饱和温度（~ 1081 °C），菜园子花岗岩是幔源岩浆分异而来或新生高温下地壳重融产物。（7）元谋花岗岩在地球化学上也表现出A型花岗岩特征。其全岩εNd(t) 和锆石εHf(t) 分别为 -2.0 – +0.59和 -1.5 – +5.1。其锆石饱和温度较低，约为835 °C。结合锆石Hf模式年龄（~ 1.56–1.97 Ga），元谋花岗岩可能是晚古元古代基性下地壳重融产物。（8）扬子地块西缘~ 1.04 Ga的A型花岗岩与造山带内的A型花岗岩在化学特征上类似，如Lachlan Fold Belt中的铝质A型花岗岩。这些花岗岩具有高温–异常高温成因，与Grenville造山带内同时代的高温花岗岩相似。同时，华南板块与Grenville Province中在变质和岩浆记录上具有完美的契合性，这支持扬子地块西南缘~1.04 Ga的A型花岗岩是Grenville高温花岗岩带的一部分。（9）菜园子铁矿的磁铁矿具有高Si，低Ti、Cr、V特征，表明其具有热液成因。在大陆地壳标准化的多元素图解中，菜园子磁铁矿表现出Ga和V的峰值、Cr–Mg–Si的谷值，与岩浆热液矿床IOCG矿床中磁铁矿配分模式类似，指示成矿热液可能与岩浆热液有关。菜园子磁铁矿具有显著高含量的W–Mo元素，且W–Mo之间呈明显的正相关性，说明菜园子磁铁矿具有部分花岗岩成分的加入。结合菜园子铁矿床产出于菜园子花岗岩与玄武岩的外接触带上的特征，本文认为二者均为菜园子铁矿的形成提供了成矿物质。在此基础之上，本文提出两阶段的成矿模型。第一阶段是菜园子玄武岩母岩浆在深部岩浆房经历分离结晶并沿富铁趋势演化，随后喷出形成富含气孔的富铁熔岩。第二阶段时菜园子花岗岩侵位，分异的高温岩浆流体萃取深部富铁熔岩中铁质，在花岗岩体顶部的围岩中形成富矿体。

The Huidong Caiyuanzi area is located in the western Yangzte Block, where basalts, dolerite dykes, granite intrusions and an iron ore deposit crop out. These geological bodies have little data of geochronology, mineralogy, and geochemistry, which restricts our understanding of regional geological evolution and tectonic setting. In this study, we present new chronological and geochemical data for Paleoproterozoic to late Mesoproterozoic ignouse rocks to discuss their genesis and tectonic implications for Yangtze Block at that time. We aslo report trace elements of magnetite to constrain the ore–forming process for the Caiyuanzi iron deposit. (1) The Caiyuanzi dolerite dyke has a SIMS ziron Pb–Pb age of 1778 ± 14 Ma, identical to its upper intercept age of 1799 ± 22 Ma within error. Meanwhile, the Caiyuanzi basalts have a SIMS apatite Pb–Pb age of 1796 ± 55 Ma, overlapped with their U–Pb age of 1760 ± 17 Ma within error. Combined with observation that Caiyuanzi basalts have not exprienced regional ~1.83 Ga orogenic metamorphism, the Caiyuanzi basalts formed at 1.76–1.83 Ga. Dating results suggest that the Caiyuanzi mafic magmatism occurred ~ 1.8 Ga ago. (2) The Caiyuanzi dolerites belong to alkaline basaltic series. In spider diagram, they exhibit patterns with extreme enrichrichments in HFSEs and LILEs similar to OIB. Major elements and Ni–Cr–Sr–Eu features support significant fractional crystallization of olivine and pyroxenes. On the other hand, high Nb/La, Nb/Th and extremely elevated εNd(T) (9.0–9.6) indicate insignificant crustal assimilation. Nd isotopic compositions and REE fractionation suggest a shallow ultra–depleted mantle source for the Caiyuanzi dolerites. Combined with global reports of ultra–depeletd meta–basalts at ~1.8 Ga, we proposed that the Caiyuanzi dolerites have parental magmags derived from an ultra–depeletd source at upper mantle, which is possible debris of depleted mantle caused by Achean crustal growth.(3) The Caiyuanzi basalts are tholeiitic basaltic rocks with and were divided into three groups. They are typically characterized by tholeiitic texture of abundant euhedral plagioclase microcrystals accompanied with Fe–Ti oxide grains. As indicated by major elements and Ni–Cr–Sr–Eu features, Group 1 and 2 basalts have experienced moderate fractionation of olivine, pyroxenes and minor plagioclase, whereas Group 3 basalts are more evolved and have differentiated along iron–rich trend with Fe2O3T contents up to 23.0 wt%. In spider diagram, Group 1 basalts exhibit E–MORB–like patterns without significant Nb–Ta–Zr–Hf anomalies, Group 2 basalts have trace elements similar to Group 1 samples but with weak depletions in Nb–Ta–Zr–Hf, and Group 3 basalts are characterized with extremely high contents of trace elements, close to those of the Caiyuanzi dolerites and show remarkable depeletions in Nb–Ta–Zr–Hf and Sr. Group 2 and 3 basalts have a narrow range of εNd(T) (2.15–3.38), which show no positive correlation with MgO and Nb/La ratios. This suggest that their parental magmas have experienced insignificant crustal contamination en route, consistent with their high (Nb/Th)N values (mostly > 1). However, elevated Nb/Ta values and relationships in Nb/Ta vs. La/Yb and Hf/SmN and Ta/LaN diagrams indicate carbonate melts metasomatism in source regime. This interpretation is further supported by decoupled Th and REE in most samples. The least–contaminated by carbonate melts samples have REE fractionation that indicates a shallow mantle origin. Thus, it is proposed that parental melts for the Caiyuanzi basalts are originated from lithospheric mantle metasomatized by carbonate melts.(4) The Caiyuanzi mafic rocks show alkaline and tholeiitic features and have high Zr, Ti, V and Zr/Y ratios, indicating a continental rifting setting for them. The ~1.8 Ga mafic magmatism is precursor of intensive 1.7–1.65 Ga rifting event in the region, and possibly represent the western Yangtze Block’s early attempt of separation from the supercontinent Columbia. The destruction of ultra–depeleted mantle regime at ~ 1.8 Ga is consistent with construction of Columbia supercontinent palcing Yangtze Block between eastern Australia and northwestern Laurentia. (5) The Caiyuanzi granites have SIMS zircon U–Pb ages of 1048.5 ± 4.9 Ma and 1043.1 ± 5.1 Ma, whereas the Yuanmou granites were dated at 1041 ± 12 Ma by LA–ICP–MS. Their ages are indistinguishable within error, suggesting that they were emplaced contemporaneously.(6) The Caiyuanzi granites show geochemical features typical of A–type granites, including high FeO*/MgO, Ga/Al ratios and elevated contents of high–field–strength elements (HFSE). They exhibit positive whole–rock εNd(t) (+0.58 to +4.4) and zircon εHf(t) (+6.0 to +8.3) values close to those of regional coeval mafic rocks. They have a narrow range of zircon δ18O from 6.2 ‰ to 7.2 ‰, which is slightly higher than the ‘mantle zircon’ value of 5.3 ± 0.6 ‰. High Nb/La and Nb/Th ratios in these rocks overlap with those of regional coeval mantle–derived rocks. Along with extremely high zircon saturation temperatures of ~ 1081 °C, we suggest that the Caiyuanzi granites formed mainly by fractionation from tholetiic magmas, or alternatively by partial melting of hot juvenile mafic crust.(7) The Yuanmou granites have low whole–rock εNd(t) (-2.0 to +0.59) and zircon εHf(t) (-1.5 to +5.1) values and a Hf isotope crustal model age of ~ 1.56–1.97 Ga, suggesting that its parental magmas may be generated by partial melting of late Paleoproterozoic mafic lower crustal source during intrusion of mantle–derived magmas.(8) Ca. 1.04 Ga granites in the region show geochemical features similar to A–type granites in orogenic belts, e.g., the aluminous A–type granites in the Lachlan Fold Belt, Southeast Australia. They are also characterized by high–extremely high (>1000 °C) temperature in their genesis, similar to coeval hot Grenville granites globally. Temporal correlation of metamorphic and magmatic records between South China and the Grenville Province leads us to conclude that the ~ 1.04 Ga A–type granites in the western Yangtze Block form parts of the hot Grenville granites emplaced during post–orogenic crustal extension.(9) Magnetite in the Caiyuanzi iron deposit is characterized with high Si and low Ti, Cr and V, suggesting a hydrothermal origin. In continental crust–normalized multiple elements diagrams, Caiyuanzi magnetite show patterns with peaks in Ga and V and thoughs in Cr, Mg and Si, which is similar to those of magnetite from IOCG deposit, indicating possible magmagtic hydrothermal nature of ore–forming fluids for the Caiyuanzi deposit. Specially, Caiyuanzi magnetite grains have remarkable high W–Mo concentrations, which are positively correlated. This observation supports significant material contribution from the Caiyuanzi granites. However, more iron input from iron–rich country rocks is suggested. Combined with the preferential occurrence of iron orebodies in outer contact zone of basalts and granites, we propose a two–stage model for the genesis of the Caiyuanzi iron deposit. In the early stage, parental magmas of Caiyuanzi basalts differentiated along the iron–enriched trend in deep magma chamber and subsequently eruppted as iron–rich lavas with vesicular structure. In the late stage, the Caiyuanzi granites emplaced into the iron–rich lavas and high–temperatured magmatic fluids leached and transported iron from deeper iron–rich country rocks and finally deposit high–grade orebodies along the upper contact zone between granites and basalts.