永梅坳陷二叠纪煤系的热演化特征与热历史分析

中国东南部海相和近海相地层普遍遭受多次后期复杂岩浆作用的改造,因而,尽管不乏富有机质地层,但热     

华北克拉通北缘及邻区印支期岩浆活动与钼和金成矿作用

对华北克拉通北缘及邻区19处钼矿床和5处金矿床的产出环境、形成时代和成矿机理及其与印支期侵入岩的关系进行了讨论。尽管各个矿床所处的地理位置不同,但是它们大都在前寒武纪或早古生代地层中产出,并且与印支期侵入岩具有密切的时空分布关系。印支期钼矿床的形成作用可以从早三叠世一直持续到晚三叠世,大规模成矿作用高峰期为230~220 Ma。相比之下,金矿床的形成时间明显早于钼矿床,同位素年龄数据集中分布在245~239 Ma。研究结果表明,自早三叠世开始,华北克拉通北缘及邻区曾发生过多期大规模伸展构造作用,并且形成若干条近东西向展布的裂陷带。张裂构造作用所诱发的富碱性岩浆作用及相关流体活动为钼或金矿床的形成提供了动力和物质来源,因此,印支期侵入岩发育区是寻找隐伏钼或金矿床的有利地区。     

辽宁青城子铅锌金银矿矿集区围岩原岩恢复及其构造背景

辽宁青城子矿集区产出在辽东裂谷凹陷带,是中国北方重要的铅锌金银多金属矿集区.矿体与含矿岩系呈整合产出,受一定层位和岩性控制,其中大石桥组是铅锌的矿源层,具有高金丰度和富As的盖县组是金银的矿源层,变质作用或者韧性剪切作用使得金得到富集而成矿.铅锌矿床围岩主要为大石桥亚群杨树沟岩组大理岩、变粒岩和浅粒岩;金银矿床围岩主要为上部盖县组片岩,少量大石桥组变粒岩.围岩的岩石地球化学特征及原岩恢复表明,青城子铅锌矿围岩中的大理岩原岩为灰岩、白云岩,变粒岩、浅粒岩原岩主要为泥质砂岩,个别为火山岩;金银矿围岩中的片岩类原岩为泥岩、砂质泥岩及粉砂岩,变粒岩原岩为泥质砂岩.青城子铅锌金银围岩中的大理岩和片岩构造环境应属稳定大陆边缘,变粒岩、浅粒岩构造环境应属活动大陆边缘或岛弧.结合区域构造演化历史认为,裂谷活动所造成的地壳拉张、变形及其相关的构造-岩浆活动,为铅锌矿床的形成提供有利环境;不同级别的裂谷盆地内的沉积作用以及海底火山喷气作用、沿同生断裂发生热水沉积作用,为矿源层的形成提供成矿物质和成矿流体;吕粱期变质作用对区内铅锌矿的叠加、富集起重要的控制作用.     

班公湖—怒江成矿带中、西段岩浆弧新认识及其对找矿的启示

笔者将班公湖—怒江成矿带中、西段初步划分为唐古拉、南羌塘、班公湖—怒江结合带和昂龙岗日—班戈4个成矿亚带,包括8个主要成矿远景区。该成矿带在近年来地质矿产调查和研究的主要进展包括对岩浆弧成矿地质特征的认识和以此为基础的找矿突破。尽管南羌塘南缘的扎普—多不杂岩浆弧未出露广泛的、连续的岩浆岩带,但本带的多不杂—青草山和材玛—弗野2个成矿远景区在近年来的找矿工作中取得重大进展,在已查明多龙超大型铜矿之后,又连续发现青草山、龙荣、巴工、弗野等一系列矿床和矿点。在昂龙岗日—班戈岩浆弧的4个主要成矿远景区中,已查明尕尔穷和嘎拉勒2个大型金铜矿,并又发现亚卓、雄梅、舍索、苦嘎、长给、补嘎错等多个矿床和矿点。班公湖—怒江成矿带中、西段已展现巨大的找矿潜力,但仍必须深入研究相关的重大地质问题。     

南海东北部构造及块体运动指向的地震相响应(英文)

南海的构造与演化与资源环境等关系密切是本文研究重点。本文针对南海的东北部构造及其块体构造方向,利用所采集的区域地震剖面,通过解析地震相与构造及其演化的关系,提出以下观点:(1)构造分区特点明晰,可划分为五个不同构造单元,构造单元之间既有联系又相互独立;(2)南海沉积盆地无论表现为拉张-弱挤压-强挤压的何种构造格局,其区域构造应力场是统一的;(3)首次发现反射地震剖面上显示出两个浅俯冲点。每个块体构造层呈手风琴风箱式折曲并向东聚敛,体现沉积盆地从发育、成长、结束、消亡不同阶段在南海的表现,其块体俯冲方向以及块体包络区域性倾伏方向均与区域应力场方向一致。     

新疆哈密葫芦岩浆Cu-Ni矿勘查地球物理异常特征

新疆哈密葫芦岩浆Cu-Ni矿处在土墩-黄山-镜儿泉-图拉尔根镁铁-超镁铁杂岩带的东部,矿区出露石炭系上统梧桐窝子组变质火山岩地层,橄榄岩、辉橄岩多见,是这个带上典型的镁铁-超镁铁岩型硫化物矿床。研究总结矿区勘查地球物理异常特征有助于深化整个杂岩带Cu-Ni矿勘查。根据新近在矿区开展的1∶5 000高精度磁法和瞬变电磁测深成果以及前人的激电剖面成果,将各种方法探测的异常与葫芦岩体和矿体的位置进行对比,发现葫芦岩体对应的是中高磁性、高极化率和中低电阻率异常组合;ΔT一般在500 nT以上,η_a大于6%,ρ_a小于200 Ω·m,是这个带上寻找这类含矿岩体的重要标志。根据钻探结果,在立体空间分析了这3种异常的成因和与矿体的关系,指出更低的低阻异常并不一定是矿体的反应。     

内蒙古中部地区晚古生代地层接触变质作用研究初探

内蒙古中部晚古生代地层由于中生代岩浆的侵入,部分发生接触变质,变质程度多处于沸石相或葡萄石绿纤石相。通过对典型剖面的泥质岩石中的粘土矿物、伊利石结晶度以及镜质体反射率的分析,得出以下结论：（1）粘土矿物以伊利石和绿泥石为主,只在极少数样品中有伊蒙混层和蒙脱石,多数缺乏伊绿混层;（2）伊利石结晶度为022~040;（3）镜质体反射率Ro值为15~40。其结果表明：在岩浆侵入地区有小规模的接触变质,为极低级变质带,并未发生大规模的低绿片岩相的区域变质,而且这种变质只影响到晚二叠世以前沉积的地层和油气,分布范围有限。     

Tausonite and aluminum-fluorine titanite from the metamorphosed metalliferous sediments of the Triassic chert formation of the Sikhote Alin

Rare strontium mineral tausonite and a peculiar Al- and F-rich titanite variety were found in the metamorphosed metalliferous sediments of the Triassic chert formation of the Sikhote Alin, which are distinguished by the abundance of native elements, intermetallic compounds, and metal solid solutions, as well as the presence of diverse Au, Ag, and PGE minerals. Tausonite was documented in the manganese (metamorphosed siliceous-rhodochrosite) rocks of the Ol’ga mining district and in the “brown cherts” (siliceous rocks with manganese garnet and spessartine) of the Dal’nerechensk district, Primorye. It forms rather numerous grains 2–10 μm across usually occurring as inclusions in quartz or rhodonite. According to the electron microprobe analysis, in addition to Sr, Ti, and O, the mineral contains only Fe³⁺ (up to 0.20 a.f.u.). Aluminum-fluorine titanite was found in the “brown cherts” of the Dal’nerechensk district of Primorye (upper reaches of the Gornaya River). Its crystals are up to 200 × 200 μm in size. The recalculation of the microprobe analyses to crystal chemical formulas indicated that up to half of the Ti sites in the structure of this mineral may be occupied by Al. The decrease of the total positive charge owing to the Al³⁺ substitution for tetravalent Ti⁴⁺ is compensated for by a decrease in the total negative charge owing to F^? substitution for O^2? via the scheme Al³⁺F^? → Ti⁴⁺O^2?. The occurrence of considerable amounts of F substituting for oxygen in the titanite structure and, as a consequence (owing to the crystal chemical features of the mineral), the high Al content were related to the reduced character of the metamorphism of the metalliferous deposits.     

Pressure–temperature conditions of ongoing regional metamorphism beneath the Japanese Islands

We evaluate the pressure–temperature (P–T) conditions of ongoing regional metamorphism at the top of the oceanic crust of the subducted Pacific and Philippine Sea plates through a combination of phase diagrams and hypocenter distribution and based on the dehydration-induced earthquake hypothesis. The brute-force method was employed to find the best match thermal structure to link the hypocenter distribution and dehydration. The estimated thermal structure varies far from the values obtained from numerical simulation. Our estimates are consistent with the qualitative physical prediction for the variation of temperature in different subduction zones and provide quantitative constraints for the models.In northeastern Japan, the P–T path for the top of the oceanic crust turns to the high-T side at a depth of around 90 km. The depth corresponds to the location of the volcanic front and an active convection of the wedge mantle below this depth is suggested. Our computations also reveal the effect of an exceptional scenario beneath the Kanto region. The temperature in the Kanto region, where the cold lid of the Philippine Sea plate prevents heating by the return-flow of mantle wedge above, is much lower than that of northeastern Japan. The subduction of younger Philippine Sea plate leads to a higher-temperature in the oceanic crust. In the central Shikoku region, the thermal structure exhibits high-T/P nature. Heating by shear deformation can explain the high-T/P path in the depth range from 20 to 35 km. The Kyushu area shows moderate type T/P path reaching up to eclogite facies conditions. In the Kii and central Shikoku region, the thermal structure exhibits high-T/P nature. However, the absolute values for the areas seem to have problem in physical context. Our results has risen the significance of sediment subduction in the southwest Japan and requirement for further improvements in this technique including the aspect of variation of the bulk composition of the subducted material.     

Multi-stage zeolite facies mineralization in the Hvalfjördur area,Iceland

The Hvalfjördur area, 30 km north of Iceland’s capital Reykjavik, belongs to the sequence of Late Tertiary to early Quaternary flood basalts with minor intercalations of hyaloclastites and rhyolites. The basalts are affected by progressive low-temperature metamorphism, caused by the burial of the lava succession and higher heat flow from nearby central volcanoes. Low-grade zeolite facies metamorphism of basaltic lavas in the Hvalfjördur area results in two distinct mineral parageneses that can be correlated to events in the burial and hydrothermal history of the lava pile. Stage Ia represents syn-eruptive near-surface alteration in which celadonite and silica were precipitated along primary pores. During regional burial metamorphism (stage Ib), hydrolysis of olivine and glass led to the formation of mixed-layer chlorite/smectite clays. The chlorite content of stage Ib phyllosilicate vesicle rims increases with increasing burial depth and temperature. Stage II occurred after the burial and is marked by zeolite mineralization caused by higher heat flow from the Laxárvogur and Hvalfjördur central volcanoes. Altogether 11 different zeolites were found in the Hvalfjördur area: analcime, chabazite, epistilbite, heulandite, laumontite, levyne, mesolite, stilbite, stellerite, thomsonite and yugawaralite. In total, three separate depth and temperature-controlled “zeolite zones” occur in the Hvalfjördur area.