山西五台山区滹沱群变质玄武岩岩石学、地球化学特征及其成因意义

在野外地质调查的基础上,选取滹沱群豆村亚群底部四集庄组玄武岩、顶部青石村组玄武岩和东冶亚群中下部河边村组玄武岩,进行岩石学和地球化学研究。分析结果表明：玄武岩主量元素高TiO2、TFeO,低MgO,具有演化的基性岩浆的特征。稀土元素含量相对较高,具有弱—中等程度的轻稀土元素富集,中等程度的轻重稀土元素分异,轻微的Eu异常;玄武岩中Cr、Ni含量变化较大,但与Mg#具有很好的正相关性。微量元素配分图解中具有明显的Sr负异常,部分样品具有Nb、Ta和Ti负异常,无Zr、Hf负异常,与岛弧火山岩不同;同时Nb、Ta无分异,Zr/Hf值较高,具有板内玄武岩浆的特征。综合分析认为,滹沱群玄武岩可能形成于板内裂谷环境。在岩浆上升过程中发生橄榄石与尖晶石的分离结晶作用,同时不同程度地受到地壳的混染。     

陆相断陷盆地二级层序时限构造沉降与湖平面变化的响应关系

针对陆相断陷盆地构造沉降与湖平面变化的响应关系问题, 笔者通过二维回剥分析, 并引入沉降通量和沉降速率通量两个参数以评价盆地沉降的整体特征。黄骅坳陷中区东营组二级层序内三角洲体系发育, 可细分为4个三级层序, 构造沉降上呈减弱到增强的变化, 并具有断陷作用逐渐减弱、坳陷作用加强的特点。拟合构造沉降、沉积演化、层序结构的关系表明, 湖平面下降、三角洲的繁盛与快速构造沉降耦合一致, 湖平面下降是不均衡的强烈构造沉降导致湖水体积向控凹断层或坳陷中心重新分配、且四周水系的补充滞后于构造沉降产生的新增可容纳空间的结果。相反, 湖平面上升和深湖相发育与慢速构造沉降耦合一致。此外, 湖平面变化与构造沉降总量的大小无关。     

松辽盆地长岭断陷早白垩世火山岩地球化学研究

长岭断陷早白垩世火山岩富硅、富碱,岩石以非碱性系列为主,包括钙碱性和高钾钙碱性系列,碱性系列火山岩为钾玄岩系列。酸性岩与中、基性岩的微量元素特征差别明显,岩石总体微量元素特征与造山带火山岩相似,富集LREE、Rb、K和大离子亲石元素,TiO2含量低,贫Sr。火山岩的形成与造山带岩石圈拆沉作用引起地壳拉张减薄的大地构造背景有关。研究区基性火山岩为地幔岩部分熔融作用的产物,岩浆演化过程中存在单斜辉石和橄榄石等矿物的分离结晶作用,中性岩为原生玄武质岩浆分异演化的产物,营城组酸性火山岩的形成与构造活动存在直接关系,为构造剪切挤压应力致使上地壳重熔的结果。     

川西新元古界开建桥组底部沉凝灰岩锆石SHRIMP U-Pb年龄及其地质意义

从凉红-苏雄剖面开建桥组底部沉凝灰岩中获得了801.3 Ma±7.2 Ma锆石SHRIMP U-Pb年龄,与前人获得的苏雄组803 Ma±12 Ma年龄高度一致,不仅有效地约束了开建桥组的沉积时代,还从地质年代学上进一步证实了两者之间的同时异相关系,为华南新元古界地层格架的建立提供了新的年龄证据。结合前人研究成果,本文认为开建桥组的沉积时限为800 Ma~725 Ma,与康滇地区澄江组、扬子东南缘莲沱组和上墅组可以对比。同位素年代学、岩石地球化学及沉积学等研究表明,800 Ma左右是整个华南地区裂谷盆地沉积充填序列第二个旋回的开启时间。     

Petrological and geochronological constraints on the formation, subduction and exhumation of the continental crust in the southern Sulu orogen, eastern-central China

Detailed petrological, geochemical and geochronological studies were carried out for the core samples from the Chinese Continental Scientific Drilling Main Hole (CCSD-MH) with a final depth of 5158 m. This borehole has penetrated into an ultrahigh-pressure (UHP) metamorphic slice consisting mainly of eclogites, gneisses, garnet-pyroxenites and garnet-peridotites. Geochemical characteristics indicate that their protoliths are igneous rocks, and occur in a continental rifting tectonic setting. Quartz-, rutile- and ilmenite-rich eclogites from 0 to 710 m occur as alternating layers; the eclogites, together with interlayers of peridotites and gneisses form a layered ultramafic-mafic-acidic intrusion, which was formed by extensive fractional crystallization of basaltic magma in continental environments. The granitic gneisses from 1190 to 1505 m and 3460 to 5118 m show affinity to within-plate granite, whereas the granitic gneisses from 710 to 1190 m and 1505 to 3460 m exhibit characteristics of volcanic-arc granite. Zircon U-Pb dating demonstrates that the magmatic zircon cores, which have relatively high Th/U ratios (mostly > 0.4), from both eclogites and gneisses, yield the same age at c. 788.8 Ma, suggesting that the protoliths of UHP rocks were formed by bimodal magmatism in Neoproterozoic rifting tectonic zones along the northern margin of the Yangtze Plate, in response to the breakup of the supercontinent Rodinia. U-Pb dating of metamorphic zircons with coesite and other eclogite-facies mineral inclusions and with relatively low Th/U ratios (mostly < 0.14) gives similar Triassic ages, which define two main zircon-forming events at 221.1 Ma and 216.7 Ma. We suggest that the older weighted mean age represents the peak-UHP metamorphic event at a pressure of 5.0 GPa (corresponds to ∼ 165 km depth), whereas the younger mean age reflects the UHP/HP retrograde event at a pressure 2.8 GPa (∼ 92 km depth). Therefore, a maximum rate of vertical movement during early exhumation of the UHP rocks from the Sulu orogen would be 17 mm/year, which is quite similar to initial exhumation rates (16 to 35 mm/year) of many UHP terranes in the world.     

云南易门狮子山铜矿床黄铜矿-斑铜矿Re-Os定年与S同位素组成

易门狮子山铜矿床是康滇地区元古宙昆阳裂谷中的典型铜矿床之一,受狮子山背斜北西翼次级构造控制明显,矿石以脉状、浸染状、块状为主,少量呈层纹状.为厘定构造改造成矿时代,开展与石英、方解石脉共生的富黄铜矿、斑铜矿脉岩相学研究,挑选黄铜矿、斑铜矿单矿物,进行高精度的Re-Os同位素定年测试,获得了三组模式年龄,从早到晚依次为:...     

四川盆地裂陷槽研究新进展 ——关于裂陷槽成因机制与形成时间的探讨

最新钻井和地震资料研究表明,四川盆地裂陷槽内大部分地区缺失震旦系(埃辿卡拉系)灯影组灯四段、灯三段及灯二段上部地层,灯二段仅残留富藻层及以下地层,震旦系地层具有环状剥蚀特征;残留的灯二段岩性主要为泥粉晶白云岩、藻纹层白云岩、藻格架白云岩、雪花状构造白云岩及砂砾屑白云岩,局部层段葡萄花边构造发育,沉积相属于典型的局限台地...