Petrology of Igneous Rocks in Northern Golpayegan, Iran

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｓｔｕｄｉｅｄａｒｅａｉｓｌｏｃａｔｅｄｉｎｔｈｅｎｏｒｔｈｏｆＧｏｌｐａｙｅｇａｎ,Ｉｒａｎ,ｂｏｕｎｄｅｄｂｙｌａｔｉｔｕｄｅｓ３３．３１°Ｎａｎｄ３３．３７°Ｎａｎｄｌｏｎｇｉ－ｔｕｄｅｓ５０．１１°Ｅａｎｄ５０．...     

广东从化石岭方钠石正长岩矿物学特征及成因

广东省从化市石岭方钠石正长岩是南岭地区唯一已知的早白垩世硅酸不饱和碱性岩。岩石由方钠石、霞石、钠－钙角闪石、霓石－普通辉石、铁黑云母和条纹长石组成，不含独立相斜长石，是一种超溶线碱性正长岩。侵入于佛冈黑云母花岗岩中（γ5^2(3))，侵位年龄为127.5Ma。据霞石、方钠石和钠－钙角闪石估算，结晶时温度分别为700-800℃，660℃和600－750℃。钠－钙角闪石反映其形成在中等氧逸度下（lgfO2=-20～-25)。液相线方钠石存在反映其形成时流体压力应不高于160MPa，岩体定位深度约5－6km。钕同位素具有接近于零的εt^Nd值（-0.43～-0.47)，低的钕模式年龄（t2DM=0.96Ga)，指示岩浆可能起源于岩石圈地幔。推测在早白垩时期，南岭地区应力作用已转入拉张为主，大规模拉张作用，造成岩石圈减薄，有利于碱性岩浆形成和侵入。     

Comparison of petrogenetic signatures between mantle-derived alkali silicate intrusives with and without associated carbonatite, Namibia

We compare the petrogenetic and chemical signatures of two alkali silicate suites from the Cretaceous Damaraland igneous province (Namibia), one with and one without associated carbonatite, in order to explore their differences in terms of magma source and evolution. The Etaneno complex occurs in close spatial proximity to the Kalkfeld bimodal carbonatite–alkali silicate complex, and is dominated by nepheline (ne)-monzosyenites and ne-bearing alkali feldspar syenites. The Etaneno samples have isotopic compositions of ⁸⁷Sr/⁸⁶Sr(i)=0.70462–0.70508 and Nd=−0.5 to −1.5, with the highest ⁸⁷Sr/⁸⁶Sr(i) and lowest Nd values observed in evolved samples. The magma differentiated via olivine, feldspar, clinopyroxene, and nepheline (ne) fractionation in a F-rich system, which fractionated Zr from Hf, and Y from Ho. Partly glassy, recrystallized inclusions in some samples are less evolved than their host rocks and contain a cumulate component (nepheline, plagioclase). The Kalkfeld ne-foidites (ijolites) and ne-syenites have ⁸⁷Sr/⁸⁶Sr(i)=0.70285–0.70592 and Nd=0.5 to 1.1. The isotope ratios show no consistent variation with rock composition, and they are in the same range as the associated carbonatites. The Kalkfeld silicate magma fractionated nepheline and alkali-feldspar in a CO₂-dominated, F- and Ca-poor system. As a result, the rocks display some major and trace element trends distinctly different from those of the Etaneno samples.

We suggest that the Etaneno and the Kalkfeld magmas represent different melt fractions of a heterogeneous mantle source, resulting in different compositions especially with respect to CO₂ contents of the primitive, parental magmas. In this scenario, the carbonated alkali silicate Kalkfeld parental melt contained a critical CO₂ concentration and underwent liquid separation of carbonate and silicate melt fractions at crustal depths. The resulting silicate melt fraction experienced a very different mode of differentiation than the carbonate-poor Etaneno parental magma. Thus, the Kalkfeld rocks are depleted in Ca and other divalent cations, as well as F, rare-earth elements (REE), Ba, and P relative to the Etaneno syenites. We interpret these differences to reflect the partitioning of these elements into the carbonate melt fraction during immiscible separation.     

洛南任家滩—荞麦山正长斑岩成因及其对古元古代晚期裂解的指示——岩石化学及锆石U- Pb年龄和Lu—Hf同位素特征

华北克拉通南缘的陕西洛南—河南豫西地区出露一系列形成于1. 8~1. 6 Ga的碱性岩,对这些碱性岩的研究有助于提高对华北克拉通南缘古元古代构造环境的认识。笔者等选取陕西省洛南县任家滩—荞麦山一带碱性侵入体进行系统的岩石学、LA- ICP- MS锆石U- Pb年代学、Lu—Hf同位素分析和岩石地球化学研究,讨论了其成因机制和构造背景。研究表明,任家滩—荞麦山岩体的主体岩性为正长斑岩,加权平均年龄为1689±20 Ma（MSWD=0. 12）,表明其侵位时代为古元古代。该岩体富碱（Na2O+K2O=7. 95% ~ 9. 5%）,高钾（K2O=4. 67% ~ 8. 51%）;稀土元素总量较高（496. 15×10-6 ~ 650. 16×10-6,平均543. 06×10-6）,轻、重稀土元素分馏比较明显,轻稀土元素相对富集（LREE=454×10-6 ~ 605×10-6）,重稀土元素亏损（HREE=39. 3×10-6 ~ 45. 6×10-6）,具有弱负铕异常;K、Rb、Ba、Th富集,Nb、Ta、P、Ti亏损,并且具有明显的Sr负异常。εHf（t）值<0,TDM1值为2038 ~ 2218 Ma,TDM2值为2250 ~ 2516 Ma,说明岩浆源区物质与富集地幔有关或受到过地壳物质的混染。因此,任家滩—荞麦山岩体是由地幔玄武质岩浆与地壳基底太华杂岩形成的中酸性花岗质岩浆混合后形成的熔体,经强烈的结晶分异作用形成的,其形成于陆内裂谷的构造环境,是华北克拉通南缘对哥伦比亚超大陆裂解事件的响应。     

滇中楚雄盆地老街子Pb- Ag矿床和白马苴Au(Cu)矿床赋矿岩体对比及成矿模式

滇中老街子Pb- Ag矿床和白马苴Au(Cu)矿床位于金沙江- 红河富碱斑岩成矿带中段,是楚雄盆地中与喜山期富碱斑岩体时空关系密切的两个矿化中心,二者相距仅2km,但是矿种和矿化类型均不同,金属矿物组合差异显著。两个矿化中心同空间、不同矿化类型的深部结构不清,成因联系不明,制约了姚安富碱斑岩区多金属矿床的理论认识与深部勘查。通过岩石组合、赋矿岩体组构及地球化学特征对比,总结矿化元素空间分布规律,研究认为：①老街子正长斑岩具斑状结构,斑晶为正长石,岩体内发育脉岩;白马苴正长斑岩具似斑状结构,斑晶为正长石和少量斜长石。岩石组合和组构特征差异反映后者形成深度较前者更深;②岩石地球化学特征总体一致,均明显富集大离子亲石元素（K、Rb、Ba和LREE等）,相对亏损高场强元素（Ta、Nb、P和Ti等）,系中酸性富碱、高钾的正长岩- 石英二长岩钾玄质准铝- 过铝质系列岩石组合,为同源同期岩浆演化的产物。主要差异为老街子正长斑岩稀土总量及Rb/Sr比值整体较白马苴正长斑岩高,反映其岩浆结晶分异演化程度较白马苴正长斑岩高;③对比老街子矿床深部三个中段矿化元素异常分布特征,显示Cu- Mo异常往深部逐渐增强,矿床具有浅部Pb- Ag和深部Cu- Mo- Au的元素组合分带。白马苴矿床由岩体至接触带呈现出Au- Cu矿化/异常→Pb- Ag异常的分带特征。综合上述研究,认为白马苴、老街子矿床及其深部多金属矿化是成因上、时空结构上密切相关的矿床组合,属于浅成低温热液- 斑岩型Pb- Ag- Au（Cu- Mo）多金属成矿系统,深部具斑岩型铜、钼、金成矿潜力。在此基础上,构建了Pb- Ag- Au多金属成矿模式。研究工作对矿区深部及外围找矿预测具实践意义,对区域上同类矿床成矿理论研究和矿产勘查具参考价值。     

The Thermal History of the Huangmeijian Granite Intrusion in Anhiii and Its Relation to Mineralization: Isotopic Evidence

Abstract Whole—rock Rb—Sr, zircon U—Pb and hornblende, biotite and K—feldspar K—Ar ages are used to reconstruct the cooling history of the Huangmeijian intrusion in the Anqing—Lujiang quartz—syenite belt in Anhui. Oxygen isotope geothermometry of mineral pairs demonstrates that diffusion is a dominant factor controlling the closure of isotopic systems. Assuming the cooling of the intrusion is synchronous with a dicrease in local geothermal gradients, an emplacement depth of about 8 km and the magma crystallization temperature of 800 ± 50°C are estimated. The Huangmeijian intrusion experienced a rapid cooling process and uplifted after its emplacement and crystallization at 133 Ma B.P. with a cooling rate of 34.5°C / Ma and an uplifting rate of 0.35 mm/ a. The intrusion was rising until it rested at a depth of 3 km at a temperature of 300 ± 50°C about 14 Ma later. Then the intrusion was in slow cooling and uplifting with a cooling rate of 4.4°C / Ma and an uplifting rate of 0.04 mm/ a. U—Pb dating of pitchblende is done for the hydrothermal uranium deposit formed in the contact zone of the Huangmeijian intrusion. The result shows that the mineralization age is close to the closing time of the K—Ar system in biotite. The fluid inclusion thermometry indicates that the mineralization temperature is in agreement with the closure temperature of the biotite K—Ar system. This suggests a close relationship between the slow cooling of the intrusion and the hydrothermal uranium mineralization process.     

广东石岭碱性杂岩的岩石学特征及地质意义

广东石岭碱性杂岩体岩石矿物和岩石化学研究表明,杂岩体以霞石角闪正长岩、角闪正长岩为主,黑云母正长岩等岩石组成,为Ａ－型花岗岩分异结晶作用所形成。产于板内引张构造环境,与深大断裂有关。岩体本身已构成霞石正长岩矿床,具有较高的工业利用和经济价值。     

安徽冶父山岩体地球化学特征及含矿性评价

冶父山岩体主体岩性为石英正长斑岩。岩体富碱,尤其富钠,贫钙,镁,镁。其铜,铅,锌,金等成矿元素的初始富集现象不明显。岩石的稀土总量很低、轻、重稀土分馏显著,并具中一强的铕负异常。岩体中发育石英网脉,其网脉石英包裹体气、液相成分具富ＣＯ、Ｎａ＾２＋等特点。根据对上述特征的综合分析,同时在与铜、金矿化有关岩体特征广泛对比的基础上,指出冶父山岩体缺乏铜,金成矿的有利条件,找矿工作的重点应多着眼于岩体周围     

岩石标准物质的研制

研制了霓霞正长岩，粗面岩，花岗闪长岩，辉长石，流纹岩及白云岩６种不同类型的岩石标准物质，对用Ｘ射线荧光光谱均匀性检验实际取样量进行了探讨，选择分析测试方法时，除采用了标准方法和长期应用的分析方法外，还采用了近年发展起来的新技术新方法，在定值中应用了多参数统计定值模式，给出了６９个元素的标准值和参考值，该批标准物质于１９９１年１月经国家技术监督局审核批准为国家一级标准物质，编号分别为ＧＢＷ０７１０９