扬子陆块北缘上两地区二长花岗岩成因：锆石U-Pb年代学、Hf同位素及地球化学制约

本文通过对扬子陆块北缘上两地区二长花岗岩年代学、Hf同位素及地球化学研究,限定其形成时代、物质来源以及所处的大地构造环境。LA-ICP-MS锆石U-Pb测年结果表明上两地区二长花岗岩形成于新元古代早期,年龄为909±5Ma。锆石Hf同位素显示二长花岗岩的ε_(Hf)(t)既有正值也有负值,在-6~+3.4之间,变化较大。tDM2变化于1570~2156Ma,平均值为1802Ma,当ε_(Hf)(t)为最小负值-6.0时,tDM2为2156Ma。表明其物源主要是约1800Ma新生地壳的部分熔融,混染了部分古老地壳。地球化学显示,二长花岗岩的SiO_2含量较高,平均值达75.46%,均属亚碱性系列,且均为铝质过饱和(A/CNK=0.93~1.29);轻稀土富集,微量元素原始地幔蛛网图中显示富集大离子亲石元素(LILE)、具有明显的Nb、Ta负异常,并具有与上部陆壳非常相似的蛛网图曲线,在花岗岩的构造环境判别图解中落入弧花岗岩区,其应是扬子陆块北缘大陆边缘弧岩浆的产物。     

内蒙古西部阿拉善地区哈里努登花岗岩LA-ICP-MS锆石U-Pb年龄和地球化学特征

哈里努登岩体位于阿拉善地块北缘,主要由花岗闪长岩、黑云母二长花岗岩组成。锆石LA-ICP-MS U-Pb测年显示其形成时代为284.0Ma±1.8Ma,并非以往认为的志留纪。岩石SiO2含量为67%~72%,CaO为2.2%~4.4%,Na2O为3.7%~4.3%,K2O为2.1%~2.9%,具有较高的全碱含量,属钙碱性—高钾钙碱性系列,Al2O3含量为14.5%~17.2%,为准铝—弱过铝质（A/CNK=0.90~1.07）,总体显示出I型花岗岩的特征。稀土元素总量较低（35.2×10-6~130.6×10-6）,轻稀土元素相对富集,Eu呈正异常（δEu=1.04~1.90）。在原始地幔标准化图解中,大离子亲石元素（K、Rb、Ba、Sr）富集,亏损高场强元素（Ta、Nb、P、Yb、Y等）,显示出弧花岗岩的特征。结合区域背景分析,阿拉善北缘在早二叠世时可能还存在与弧物质有关的岩浆活动。     

Geochemical Characteristics of the Plagiogranites in the Vicinity of Bingdaban,Central Tianshan

The tectonic and geochemical characteristics suggest that the plagiogranites exposed in the vicinity of Bingdaban on the northen margin of the central Tianshan uplift zone show a distinct mantle-source character, and their enrichment in LREE and selected enrichment in LILE(large ion lithophile elements)reflect a setting related to an arc tectonic regime.These rocks represent the products formed at shallow levels from mantle-derived magmas modified with subduction components(or super crustal rocks).     

Oligocene subduction-related plutonism in the Nodoushan area,Urumieh-Dokhtar magmatic belt: Petrogenetic constraints from U–Pb zircon geochronology and isotope geochemistry

Geochemical data and Sr–Nd isotopes of the host rocks and magmatic microgranular enclaves (MMEs) collected from the Oligocene Nodoushan Plutonic Complex (NPC) in the central part of the Urumieh–Dokhtar Magmatic Belt (UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U–Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene (middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene (latest Chattian) for granodioritic and diorite porphyry units, respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite (SiO₂ = 47.73–57.36 wt.%; Mg# = 42.15–53.04); the host intrusions are mainly granite, granodiorite and diorite porphyry (SiO₂ = 56.51–72.35 wt.%; Mg# = 26.29–50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements (LILEs, e.g. Rb, Ba, Sr) and light rare earth elements (LREEs) relative to high field strength elements (HFSEs) and heavy rare earth elements (HREEs). These features, combined with a relative depletion in Nb, Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display I_Sr = 0.705045–0.707959, ε_Nd(t) = −3.23 to +3.80, and the Nd model ages (T_DM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with I_Sr ranging from 0.705513 to 0.707275 and ε_Nd(t) from −1.46 to 4.62. The MMEs have T_DM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust- and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle (SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr–Nd isotope data indicate that ∼50% to 90% of the lower crust-derived melt and ∼10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast, ∼45%–65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma (∼35%–55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite.     

云南宝丰寺岩体锆石微量元素特征及地质意义

云南宝丰寺岩体地处扬子陆块西缘金沙江-红河断裂与程海-宾川断裂夹持部位,属于金沙江-红河富碱斑岩带组成部分,由细晶黑云母花岗斑岩(FCBGP)和粗晶花岗斑岩(CGGP)组成。通过对宝丰寺岩体开展的锆石Ti温度、锆石Ce~(4+)/Ce~(3+)值和δEu和δCe值研究结果表明:两类岩石锆石Ti温度相差不大(FCBGP为618.55℃—792.75℃,均值为692.42℃;CGGP为560.35℃～820.41℃,均值为714.13℃),与S型花岗岩浆形成温度相似,反映宝丰寺岩体属S型花岗岩;锆石Ce~(4+)/Ce~(3+)值、δEu和δCe值总体较高(FCBGP的Ce~(4+)/Ce~(3+)值、δEu和δCe分别为24.51～1190.06、0.32～0.49和10.17～1231.19,均值分别为390.36、0.42和264.29;CGGP的Ce~(4+)/Ce~(3+)值、δEu和δCe分别为50.13～494.56、0.44～0.58和24.87～262.76,均值分别为232.98、0.49和141.82),与金沙江-红河富碱斑岩带含矿岩体特征值类似,表明宝丰寺岩体形成于高氧逸度环境,有利于岩浆体系中的成矿金属元素保留至岩浆分异演化的晚阶段,有利于形成斑岩型矿床。     

华北块体南缘上元古界氧碳同位素特征及其沉积环境意义

完善中国晚前寒武纪地层的标准剖面,使其成为国际地层对比的参考标准,是中国地质学家的追求。华北蓟县剖面和扬子块体三峡剖面一直被视为中国的标准剖面,多学科的研究、特别是生物地层和雪球事件地层学的研究取得了突破性进展。笔者试图通过化学地层学研究手段,对华北块体南缘豫西地区中-新元古代地层中碳酸盐岩进行氧碳同位素地球化学研究,试图建立新的扬子块体与华北块体震旦纪地层对比桥梁。同时,对华北南缘新元古代碳酸盐岩地层的形成环境进行了分析,解释了华北新元古代冰碛岩的时空关系。     

米仓山西段地质研究新进展

通过米仓山西段１∶５万区域地质调查研究，从元古界火地垭群中解体出后河岩群，属太古－早元古代。认为前震旦纪变质基底以穹盆构造、叠加褶皱、多期面理置换、韧性剪切带为特色，确立了光雾山推覆构造，提出盖层变形以层滑褶皱为主。对岩浆杂岩成功地进行了解体，认为侵入岩具多种成因类型并具多旋回演化特点，指出地台边缘的层序地层有别于陆棚边缘经典模式。     

宁阳—汶上煤田鲁西井田岩浆岩特征及其对煤层煤质的影响

宁阳—汶上煤田鲁西井田内的岩浆顺煤层或煤层顶底板侵入,对煤层和煤质都有严重影响。该文分折研究了岩浆岩的侵入层位、层数、厚度、岩性及其矿物成分,初步探讨了岩浆岩的来源、地质时代及其对煤层、煤质的影响。     

秦岭造山带若干岩石高温高压脱水熔融的特征及其意义

对秦岭造山带和邻区块状岩石样品进行了高温（1 100~1 300 ℃）和高压（1.2~1.8 GPa）脱水熔融实验。通过对实验产物综合分析发现许多样品中出现了熔融玻璃和雏晶。玻璃代表的熔体成分为基性和中性,部分接近于超基性范围,熔体与原来岩石全岩成分比较,更偏基性。熔体出现的空间和成分都显示了局部熔融体系的特征,即含水矿物（角闪石或黑云母）和浅色矿物（石英或斜长石）控制了熔融的发生并且决定了熔体的成分。脱水熔融产生了比原岩更偏基性的熔体,这意味着熔融后残留部分将愈偏酸性。如果这种机制存在于大陆中-下地壳,将对探讨大陆地壳的结构和物质组成,解释某些地区的长英质中下地壳的成因等具有重要的意义。     

大连金石滩国家地质公园地层特征

大连金石滩海岸带地层剖面由凉水湾始,经大林子海岸至葛屯金石滩港止,沿途可见新元古代震旦纪营城子组、十三里台组、马家屯组、崔家屯组、兴民村组和早古生代寒武纪葛屯组、大林子组、碱厂组及馒头组.其中,葛屯组和大林子组为二组层型剖面的命名地.除碱厂组和馒头组以外,其他各组命名地均来自大连地层小区,为大连地区独有.在考察珍贵地层剖面的同时,还可欣赏玫瑰园景群、恐龙园景群、南秀园景群和鳌滩园景群等丰富的地质地貌遗迹.