东秦岭-大别山及其两侧的岩浆和变质事件年代学及其形成的大地构造背景

本研究成果以东秦岭-大别山地区野外地质资料、岩石学、地球化学和同位素年代学数据的采集为工作切入点,在现有和新增各种数据分析、解释、研究基础上,描述东秦岭-大别山地区变质岩石构造单元的岩石学组成、确定原岩的形成时间、主期变质作用特征、形成时间,以及该区发育的各时代花岗岩类、主要的岩浆岩事件和大地构造背景,进而建立新元古代以来东秦岭-大别山造山带及两侧的岩浆和变质事件年代学格架;编制了东秦岭-大别造山带及两侧岩浆和变质事件年代学地质图。     

岩浆矽卡岩铜锌矿床地质特征与成矿机制探讨——以西藏当雄县拉屋铜锌矿床Ⅴ号矿体为例

西藏当雄县拉屋铜锌矿床位于冈底斯—念青唐古拉成矿带江让—伯舒拉岭多金属成矿亚带.从矿体地质特征、稳定同位素、稀土元素、微量元素地球化学特征等方面对其Ⅴ号矿体进行分析,研究后认为其成因应为岩浆矽卡岩型,其机制是深部熔浆在上侵过程中经分异作用,以钾、钠硅酸盐为主的熔浆浮于上部,以钙、镁、铁为主的熔浆(矽卡岩岩浆)沉于下部,从而形成含矿矽卡岩岩浆,进而形成岩浆矽卡岩矿床.     

Platinum-group Elements Geochemistry of the Yangliuping Magmatic Ni-Cu-PGE Sulfide Deposit： Implications of Its Genetic Link with the Extrusive Basalts

Primitive mantle-normalized Platinum-group elements (PGE) concentration patterns for the Zhengziyanwo intrusion and Dashibao Formation basalts are of positive slope, similar to most of the world-class magmatic Ni-Cu-PGE sulfide deposits. Characters of this intrusion and its related ores and Dashibao Formation basalts are their negative Pt-anomaly and high concentration of Rh relative to Pt and Pd, facts being interpreted to be the results of crystallization and fractionation of Pt-alloys and spinel phase-free crystallization history for the magma, respectively. PGE parameters of the Dashibao Formation basalts are consistent with the general trend of those found for the Zhengziyanwo intrusion, and this might infer a genetic link between them.     

中国东部中生代“岩浆核杂岩”隆起-拆离带热液蚀变成矿问题——以胶东金矿区为例

胶东金矿是全球最大的与花岗岩有关的大型金矿床。前人研究多数与板块构造碰撞或俯冲联系起来,提出“造山带型金矿”或“变质核杂岩”等观点。本文指出,胶东金矿形成于中国东部板块拼合后的大陆,属于陈国达曾厘定的中生代地洼区（陈国达,1956,1985;邓军等,1998;翟明国等,2004）,受控于一种“岩浆核杂岩”的构造（吕古贤等,2016）。胶东“岩浆核杂岩隆起—拆离带蚀变岩金矿床”,在全球已知金矿床类型中是独特的（吕古贤等,1999,2013）。胶东“岩浆核杂岩”构造在中国中新生代复合大陆可能较普遍发育。     

大兴安岭南段红岭铅锌矿床岩浆演化序列与成矿动力学背景探讨

红岭是内蒙古东部地区的一处大型铅锌多金属矿床。矿体产于燕山晚期花岗岩与二叠系大石寨组的外接触带上,受NE向断裂控制。本文对红岭矿区及其外围主要岩浆岩开展了年代学研究,系统的LA-ICP-MS锆石定年结果表明:红岭矿区与矿化关系密切的乌兰坝岩体中浅褐黄色花岗斑岩、中粗粒花岗岩、灰褐色斑状花岗岩及深部钻孔揭露的细粒花岗岩测试结果分别为136.70±0.85Ma、144.1±1.5Ma、139.7±1.1Ma和144.82±0.81Ma,显示出由多阶段岩浆侵入形成的复式岩体的特征;乌兰楚鲁特岩体中浅褐灰色斑状花岗岩、含斑细粒花岗岩测年结果为141.9±1.2Ma、139.83±0.82Ma。根据锆石UPb测年的结果,得出两个岩体为同一次构造岩浆事件的产物的结论。岩石地球化学分析表明区内花岗岩类富SiO_2(75.50%~76.14%)、K_2O(4.38%~5.19%),贫Al_2O_3(12.25%~13.08%)、Ba(26.6×10~(-6)~164×10~(-6))、Sr(4.74×10~(-6)~46.0×10~(-6)),稀土元素配分曲线呈右倾轻稀土富集型,具明显铕负异常,δEu值为0.44~0.80,富集高场强元素Zr、Hf和大离子亲石元素Rb、U、Th,显示A型花岗岩地球化学属性,表明其形成于伸展构造体系的造山后环境。本文根据对矿区及外围侵入岩年代学研究,结合矿区地质和前人研究成果,将大兴安岭南段多金属成矿带构造演化史概括为:古亚洲洋双向俯冲可能延续到晚石炭世;约从二叠纪开始,该区进入了碰撞造山阶段;中三叠世-二叠纪的构造岩浆事件与碰撞造山后陆壳加厚和拆沉作用有关,同时标志着中亚造山带演化的终止;170~230Ma为该区构造活动的平静期;进入侏罗纪-早白垩世(120~170Ma),该区受到蒙古-鄂霍次克构造体系活动的远程影响;120Ma~今,鲜有关于岩体年龄的报道,据此我们认为该区域并未受到太平洋构造体系的强烈影响;并得出红岭铅锌矿的成矿动力学背景为蒙古-鄂霍茨克造山带碰撞造山后陆壳伸展环境的认识。     

东秦岭160～140Ma Cu(Mo)和Mo(W)成矿作用的差异性:来自成矿岩体的地球化学及其岩浆源区的证据

东秦岭地区在商丹断裂带南北两侧分别形成了矽卡岩-斑岩型Cu(Mo)矿床和斑岩-矽卡岩型Mo(W)矿床,两者均形成于160~140Ma。通过对不同矿床的地质特征和成矿岩体对比研究发现,Mo(W)矿床主要分布在商丹断裂带北侧的北秦岭和华北板块南缘,主要分布有新太古代至奥陶纪地层,由一系列变质程度不同的火山岩和沉积岩组成。Cu(Mo)矿床主要位于商丹断裂带南侧的南秦岭晚古生代弧前盆地,主要分布古生代地层,由粉砂岩、绢云板岩、灰岩、杂砂岩及白云岩等组成。Mo(W)矿床的成矿岩体以花岗斑岩为主,具有高硅、富钾,贫镁铁,较高的岩浆分异程度;Cu(Mo)矿床的成矿岩体以花岗闪长斑岩为主,具有低硅、低钾,富镁铁,低分异的特征。Mo(W)成矿岩体亏损Ba,富集U、Nb等元素,Cu(Mo)成矿岩体相对富集Ba,亏损U、Nb等元素;Cu(Mo)成矿岩体∑REE略高于Mo(W)成矿岩体,未表现出明显的Eu异常,而Mo(W)成矿岩体具有负Eu异常。Cu(Mo)和Mo(W)成矿岩体具有相似的结晶温度,Mo(W)成矿岩体具有相对较高的形成压力和氧化态。Mo(W)成矿岩体的岩浆源区以辉石为残留相,Cu(Mo)成矿岩体的岩浆源区则是以极少量角闪石为残留相。相对于Mo(W)矿床,Cu(Mo)矿床的成矿岩体具有较高的εNd(t)值(-28.8~-12.1和-4.75~-2.73)和εHf(t)值(-38~-7.9和-3.79~+1.79),这说明Cu(Mo)成矿岩体的岩浆源区中含有相对较多的地幔物质,而Mo(W)成矿岩体的岩浆源区中含有相对较多地壳物质。由于两种矿化位于不同的构造单元以及成矿岩体在岩石地球化学、温压条件、氧化还原状态和岩浆源区特征等方面的差异造成了160~140Ma岩浆活动在商丹断裂带南北两侧形成不同矿化类型。     

滇西腾冲曲石地区中更新世火山岩年龄及成因:SHRIMP锆石U-Pb定年和Hf同位素约束

本文报道了腾冲曲石地区英安岩测年结果和该区火山岩样品的地球化学特征。英安岩(TC7)的SHRIMP锆石UPb年龄为0.41±0.01Ma(MSWD=1.18),属于中更新世,是迄今在国内测得的最年轻的高精度锆石U-Pb年龄。该区的火山岩具有高钾钙碱性的特点,为一套粗面玄武岩-玄武粗安岩-粗安岩-粗面岩以及玄武岩-安山岩-英安岩岩石组合。岩石富集LILE、LREE,相对亏损Nb、Ta、Ti等高场强元素,具有高的原始地幔标准化(Th/Nb)N比值(大于6)、低的Nb/La(小于1)和Nb/U比值(3~13),相对富集Zr,Zr/Y比值较高。这些地球化学特征明显区别于典型岛弧钙碱性火山岩。锆石Hf同位素分析结果显示εHf(t)值为-11.0~-1.5,变化较大;tDM1、tDM2分别为747~1115Ma、951~1437Ma,模式年龄远大于SHRIMP测定的锆石U-Pb年龄。腾冲火山岩喷发时该区属于大陆板内环境,该区火山岩与地壳混染的大陆玄武岩地球化学特征相类似,是幔源物质遭受壳源富集组分强烈混染的产物。     

Magmatic and post-magmatic evolution of post-collisional rare-metal bearing granite: The Neoproterozoic Homrit Akarem Granitic Intrusion,south Eastern Desert of Egypt,Arabian-Nubian Shield

The Homrit Akarem granitic intrusion (HAGI) outcrops near the western edge of the south Eastern Desert basement exposure in Egypt. It is a composite of two cogenetic intrusive bodies: an early albite granite phase shallowly emplaced at the apex of a magmatic cupola, and a later subjacent pink granite phase with a marginal zone of muscovite granite and better preservation of magmatic features. Mineral chemistry of primary biotite and garnet, together with whole-rock chemistry, identify the HAGI as a highly fractionated A-type peraluminous intrusion. The chemistry of F-dominant, Li-bearing, Fe³⁺-rich primary magmatic mica in the pink granite resembles that typically found in highly evolved Nb-Y-F pegmatites. The HAGI is the evolved product of a primary magma generated by partial melting of juvenile crust of the Arabian-Nubian Shield (ANS), emplaced along a regional strike-slip fault system that promoted its ascent. The main emplacement mechanism and evolutionary sequence of the HAGI was magmatic, although secondary minerals and textures resulting from hydrothermal fluid interactions are observed, especially at its margins. Primary columbite-(Mn) crystallized from melt and was partly replaced by secondary fluorcalciomicrolite. The high fluorine content of magmatic fluids exsolved from the intrusion is indicated by quartz-fluorite veins, greisenization, albitization, and F-bearing secondary oxide minerals. The magmatic derivation of this fluid is demonstrated by the F-dominant primary mica, a siderophyllite-polylithionite solid solution commonly known as zinnwaldite. The chemistry of zinnwaldite constrains the F/OH activity ratio and oxygen fugacity of its parental melt and thereby resolves the ambiguity between pressure and the effects of F in controlling the normative quartz content of rare-metal granites. The HAGI is less mineralized than the post-collisional rare-metal granites found further east in the south Eastern Desert, replicating a trend observed previously in the central Eastern Desert and suggesting that east-west zoning in rare metal enrichment is a persistent feature across latitudes at the western edge of the ANS.     

安徽青阳—九华山复式岩体的成因及成矿潜力——来自锆石Hf同位素和微量元素的证据

青阳—九华山复式岩体是安徽南部地区出露面积最大、最具代表性的复式岩体,该复式岩体的岩浆源区、岩石成因和成矿联系等问题仍需要进一步查明。在前期对青阳—九华山复式岩体的地质、地球化学特征研究基础上,本文进一步开展了锆石微量元素与Hf同位素分析与研究。结果显示,青阳—九华山复式岩体4个阶段从早到晚（花岗闪长岩二长花岗岩正长花岗岩细粒花岗斑岩）,晚期(第三、第四阶段)比早期(第一、第二阶段)岩浆岩的锆石εHf（t）值呈显著增高趋势,岩浆形成温度升高（705.3℃ 715.9℃ 827.1℃ 805.5℃）,氧逸度降低（93.8 149.170.1 69.9）。进一步分析认为,青阳—九华山复式岩体源于同一具有壳幔混源的岩浆源区,随着时间的演化,岩浆房中幔源组分比例逐渐增高,幔源物质的加入,不仅提高了晚期岩浆形成温度,一定程度改变了源区组成。青阳—九华山复式岩体4个阶段花岗岩均经历了榍石、角闪石、金红石、斜长石等矿物的分离结晶,晚期（第三、第四阶段）花岗岩相比早期（第一、第二阶段）花岗岩具有更高的分异程度。青阳—九华山复式岩体中第一、第二阶段花岗岩具有较好的W—多金属矿床成矿潜力。     

Sticking together: Mechanisms of quartz synneusis in high-silica magma

The formation of crystal clusters by synneusis (magmatic sintering) affects a wide range of magmatic systems from olivine clusters in komatiite to quartz clusters in high-silica granite. A common feature of synneusis in any mineral phase is the alignment of neighbouring crystals in certain lower-energy orientation relationships. However, the underlying mechanisms involved with both the alignment of crystals in lower-energy orientations and the binding of crystal clusters are not well understood. In the absence of mechanisms that bind crystals together upon contact, the same hydrodynamic forces that may bring crystals together can in theory also serve to disaggregate clusters. Here I use cathodoluminescence imaging and crystal orientation data from quartz clusters in high-silica granite to show that i) rapid crystalline neck growth along attachment surfaces and ii) grain rotation are two mechanisms that reduce the grain boundary energy of crystal clusters while increasing clusters’ shear strength. The continued crystallization of sintered phases as the magmatic body cools further cements crystal pairs and resists cluster disaggregation. Together these mechanisms underpin both the formation and preservation of large crystal clusters in dynamic magmatic environments.