Properties of wave velocity for two types of granitoids at high pressure and temperature and their geological meaning

The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure and high temperature. The laws of velocity changes for them differ with the pressure boost and temperature rise, and the velocity change of S-type is more violent than that of I-type. The “softening point” of compressional wave velocity (V μ) is also revealed during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth of “softening”, V_p after “softening” and the percentage of V_p’s drop around the “sofrening point” for two types of granitoids are obviously different. The depth of “softening” is 15 km approximately and V_p after “softening” is 5.62 km/s for S-type granitoid. But for I-type granitoid the depth of “softening” is 26 km approximately and V_p after “softening” is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the “softening” of elastic-wave velocity is caused by the partial melting of granite. Combined with the results of geophysical prospecting, these results suggest that the low-velocity layers developing in the interior of Earth crust are related to thc partial melting of different types of granitoids. The formation of the low-velocity layer in the upper-middle Earth crust is closely related to the development of S-type granitoid, but that in the lower Earth crust is closely related to the development of I-type granitoid.     

黑龙江东南部穆棱地区“麻山群”的特征及花岗岩锆石SHRIMPU-Pb定年——对佳木斯地块最南缘地壳演化的制约

通过对佳木斯地块南缘穆棱地区常兴村-新兴村剖面的研究,认为这里是“麻山群”和“黑龙江群”的结合部位．具有古大陆边缘的性质。穆棱地区的“麻山群”为佳木斯地块南缘的陆壳基底,其南侧的“黑龙江群”为包括洋壳残片在内的增生-碰撞杂岩。对“麻山群”混合岩的SHRIMP锆石U-Pb定年结果表明：佳木斯地块存在中-新元古代的结晶基底,并遭受到约500Ma变质作用的影响。侵入“麻山群”杂岩的花岗岩的岩石学、地球化学研究表明,这些花岗岩具有S型花岗岩的特征;其SHRIMP锆石U—Pb分析表明,其形成年龄为486Ma＋3Ma,略晚于前人确定的“麻山群”杂岩约500Ma的麻粒岩相变质作用,为同碰撞或碰撞后花岗岩。这些资料进一步证明,该地区可能经历了晚泛非-早加里东期的碰撞造山作用。     

西秦岭北缘天水地区新元古代花岗质片麻岩地球化学特征及其形成环境

西秦岭北缘新元古代花岗质片麻岩位于天水地区分隔北秦岭造山带和北祁连构造带的新阳-元龙韧性剪切带中。花岗质片麻岩具高Si、高Al的特征,属高钾钙碱性系列,A/CNK在1.104～1.389之间,为硅、铝过饱和类型,属典型的强过铝质S型花岗质岩石。轻、重稀土元素分馏较强,具中等负Eu异常。岩石富集大离子亲石元素（Cs、Rb、Ba、Th、U、K、La等）,强烈亏损高场强元素（Nb、Ta、Ti、Hf等）,明显的Ba、P、Sr负异常,相对富集Zr。该花岗质岩石是一种典型的壳源成因类型,主要为上地壳中以成熟度较低、含泥质成分较高的杂砂岩、岩屑杂砂岩为原岩的古元古界秦岭岩群中含水矿物相脱水部分熔融形成的,可能存在少量的分离结晶作用。该花岗质片麻岩具有同碰撞型花岗岩的特征,可能是北秦岭微地块与相邻地块在新元古代早期发生汇聚的产物,是Rodinia超大陆在西秦岭地区汇聚的响应。     

Geochemistry and petrogenesis of Sikait leucogranite, Egypt: an example of S-type granite in a metapelitic sequence

 The Sikait leucogranite (SLG) is a body of porphyritic garnet granite intruded a metapelitic sequence and interlayered orthogneisses. Multiple deformation and low- to medium-grade metamorphism of the sequence was closely associated with pluton emplacement. Textural features of the SLG indicate that subsolidus plastic deformation was induced during the extensive thrusting. The granite is strongly peraluminous, alkali-rich and HFS (high field-strength) elements-depleted with low contents of REE, all facts that substantiate the geochemical characteristics of S-type granites. The geologic and geochemical features are consistent with a dehydration melting model of the hosted metapelites to generate the peraluminous SLG. However, geochemical modelling of trace elements and REEs suggest that the anatectic partial melt was subsequently affected by fractional crystallization of feldspars. This could explain much of the chemical attributes of SLG. Received: 20 September 1994 / Accepted: 2 August 1996     

甘肃天水夏家坪金矿地质特征

夏家坪金矿位于西秦岭反＂S＂弧形构造东段Au-Ag-Cu-Fe-Pb-Zn成矿带中,矿体产出受下古生界李子园群沉积-火山岩系控制。矿体多呈带状、透镜状产出,具收缩膨大、尖灭再现及分支复合特征。容矿岩石主要为变砂（泥）岩、破碎石英脉、硅化角砾岩等。矿石类型以构造蚀变岩型为主,局部为石英脉型。围岩蚀变具分带性,矿化可分为早期的金和晚期的银铅锌两个主要成矿阶段。     

安徽大别山团岭花岗岩体岩石学特征及成因

团岭花岗岩体侵位于大别山南部超高压变质带变质表壳岩中, 由细粒少斑二长花岗岩和中粒少斑二长花岗岩组成。通过岩石学、岩石化学、地球化学的研究, 确定其为Ｓ 型花岗岩, 源岩可能来自大别山变质杂岩。结合同位素资料, 认为其属燕山期花岗岩, 侵位机制为底辟式强力就位。     

华北克拉通北缘隆化地区S型花岗岩的独居石年龄图谱

位于华北克拉通北缘中段的隆化S型花岗岩由石榴石黑云母花岗岩、石榴石花岗岩以及片麻理化的黑云母花岗岩组成.其主体岩性石榴石黑云母花岗岩SiO2和Al2O3含量分别为64.09%～69.6%以及14.6%～16.13%,K2O/Na2O>1.0,A/CNK>1.0,Mg#在20.76～34.89之间变化,具有明显的Nb、Ta、P、Ti和Sr亏损以及Rb、K和Th富集.石榴石黑云母花岗岩(样品JB6031-1)采用独居石电子探针U-Th-Pb化学法进行测年,获得了2553±120Ma、2180±42Ma和1854±24Ma三个年龄峰值.一颗独居石内部成分分带上6个分析点定年结果构成2553±120Ma的峰值年龄,这一年龄与我们最新获得的2506±7Ma和2541±8Ma(继承锆石年龄)LA-ICP-MS锆石U-Pb同位素年龄相似,我们将这一独居石年龄解释为继承独居石的年龄,表明在赤城.隆化断裂以北存在太古宙陆块,并且在后期构造-热事件中发生部分熔融形成s型花岗岩.该独居石颗粒幔部成分分带上10个分析点的测年结果揭示的峰值年龄为2181±42Ma,该年龄也是出现频率最高的年龄值,我们建议2181±42Ma为s型花岗岩的结晶年龄,反映了S型花岗岩的侵位时代.独居石颗粒外部成分分带上8个分析点的测年结果构成1854±24Ma的峰值年龄,该年龄与华北克拉通中部带的变质年龄接近,我们将其解释为S型花岗岩的变质年龄,表明华北克拉通北缘的构造演化与中部带的构造演化密切相关.     

Geochemistry of S-type granitic rocks from the reversely zoned Castelo Branco pluton (central Portugal)

The zoned pluton from Castelo Branco consists of Variscan peraluminous S-type granitic rocks. A muscovite>biotite granite in the pluton's core is surrounded successively by biotite>muscovite granodiorite, porphyritic biotite>muscovite granodiorite grading to biotite=muscovite granite, and finally by muscovite>biotite granite. ID-TIMS U–Pb ages for zircon and monazite indicate that all phases of the pluton formed at 310 ± 1 Ma. Whole-rock analyses show slight variation in ⁸⁷Sr/⁸⁶Sr_310 Ma between 0.708 and 0.712, Nd_310 Ma values between − 1 and − 4 and δ¹⁸O values between 12.2 and 13.6. These geological, mineralogical, geochemical and isotopic data indicate a crustal origin of the suite, probably from partial melting of heterogeneous Early Paleozoic pelitic country rock. In detail there is evidence for derivation from different sources, but also fractional crystallization linking some of internal plutonic phases. Least-squares analysis of major elements and modelling of trace elements indicate that the porphyritic granodiorite and biotite=muscovite granite were derived from the granodiorite magma by fractional crystallization of plagioclase, quartz, biotite and ilmenite. By contrast variation diagrams of major and trace elements in biotite and muscovite, the behaviours of Ba in microcline and whole-rock δ¹⁸O, the REE patterns of rocks and isotopic data indicate that both muscovite-dominant granites were probably originated by two distinct pulses of granite magma.     

辽宁省海城市小孤山铅锌多金属矿集区成矿地质特征及成因分析

勘查结果表明,小孤山矿集区的成矿作用受印支期花岗岩体、脉岩、断裂和地层的多重控制。康家岭铅锌矿区含矿围岩与正常大理岩碳同位δ13C存在明显差异,分别为+0.186和-6.055。说明矿集区的成矿作用在成岩作用之后,这种差异是成矿过程中热液蚀变造成的。铅同位素模式年龄均为负值,具明显异常铅特征,表明本区铅锌矿体的成矿物质具多源性。根据矿集区内唐望山印支期花岗岩体的化学成分及特征值判断,岩体为S型花岗岩。其Pb、Zn、Au、Ag的丰度均低于辽河群地层。岩体在早期侵入过程中,同化围岩并在岩体边部发生分异作用,使围岩中成矿元素在岩体边部及脉岩内富集,随着岩体及脉岩的进一步分异形成含矿热液,与脉岩在共同的断裂系统内运移,并在有利的岩性组合和断裂内充填成矿;岩体在侵入的晚期,随着温度和压力的下降,同化围岩及富集成矿元素的能力都相应减弱,并在与围岩接触部形成大规模的碎裂岩带,从而形成大规模的硅化带和地球化学异常。     

苏门答腊岛(印尼)成矿带的岩浆作用和源区及其对比

本文介绍了苏门答腊岛上两个成矿带(即铜-金矿成矿带和锡矿成矿带)的矿产分布,岩浆岩的岩石类型和地球化学特征。根据本研究课题在巴东地区岩石化学资料,本文总结了铜-金矿成矿带含矿母岩的地球化学特征,探讨其岩浆岩成因和源区。同时,将其锡矿成矿带岩浆岩的岩石类型和地球化学-大地构造环境与其相邻地体进行对比。研究结果表明:西苏门答腊地体的铜-金矿成矿带的含矿母岩为SI-型埃达克质花岗岩,形成于活动大陆边缘(ACM)火山弧构造环境,其岩浆物质主要来源于俯冲洋壳板片局部熔融叠加上弱的地幔楔熔融-混染作用(MASH)。而东苏门答腊地体‘锡岛’和"暹缅马苏"地体的锡矿带含矿母岩为过铝质(S-型)花岗岩类,其形成构造环境为碰撞带的弧后盆地和陆内裂谷,物质源区来自地壳重熔和岩浆分异。地球化学资料表明,该两地体具有共同的深部岩浆源区。