黑龙江东部桦南地区早白垩世花岗闪长斑岩的成因及其地质意义

为确定黑龙江省东部桦南地区早白垩世花岗闪长斑岩的岩石成因及其构造背景,对花岗闪长斑岩样品进行了锆石U-Pb年代学与地球化学测试分析。LA-ICP-MS锆石U-Pb同位素分析结果显示,桦南地区花岗闪长斑岩形成于(123±1)Ma的早白垩世。岩石具有较高的SiO_2(66.06%~68.75%)和全碱(6.40%~7.23%)含量,较低的MgO(1.19%~1.50%)含量,并且富集大离子亲石元素(Rb、Ba、Th、U、K)和轻稀土元素,亏损Nb、Ta、Ti及P元素,显示其具有I型花岗岩属性。花岗闪长斑岩的正ε_(Hf)(t)值(+6.30~+11.51)及其二阶段模式年龄(778~445Ma)指示其原始岩浆来源于新生地壳物质的部分熔融。结合年代学、地球化学特征与区域地质调查结果,认为桦南地区早白垩世花岗闪长斑岩的形成与太平洋板块的俯冲作用有直接联系。     

朝鲜半岛西北部古元古代高温变质-深熔作用:宏观和微观岩石学以及锆石U-Pb年代学制约

朝鲜半岛左接中国大陆右连日本岛链,其地质位置重要不言而喻,对其区域地质演化历史和构造属性的准确厘定,直接关系到对整个东北亚地质的全面理解和认识。本文对朝鲜半岛狼林地块西部的南浦群和甄山群的相关岩石进行了研究。野外露头、手标本和岩相学观察表明,南浦群和甄山群岩石保存了深熔作用的宏观和微观证据,矿物组合以及矿物间的反应结构表明南浦群和甄山群混合岩经历了角闪岩相到麻粒岩相的变质作用,并且在晚期熔体结晶过程中发生了逆反应或退变质过程。7件样品的锆石U-Pb定年结果显示,朝鲜半岛西北部地区在古元古代经历了多阶段(期)的变质和深熔作用过程。南浦群岩石在1917Ma可能经历了第一阶段(期)变质作用,在1877~1855Ma经历了第二阶段(期)变质深熔和石榴石持续生长,熔体冷却结晶时代为1842Ma。甄山群样品给出的变质深熔和石榴石生长的时代为1841~1830Ma,1785Ma可能代表深熔作用中抽取的熔体冷却的时代。但是,为何南浦群和甄山群样品记录的变质和深熔作用时代显示较大的差异,尚需更进一步的研究。综述前人研究成果可知,狼林地块与华北克拉通东部辽吉活动带,在变质和深熔作用类型方面存在不同之处,然而它们所记录的古元古代高温变质-深熔时代的一致性,表明二者可能至少在古元古代之前就形成了统一的大陆。     

祁连南缘柴达木山复式花岗岩体中部二长花岗岩锆石U-Pb定年及其地质意义

文章对祁连地块南缘柴达木山复式岩体中部的似斑状二长花岗岩以及二长花岗岩进行了详细的岩石学、地球化学及锆石U-Pb年代学研究,结果表明似斑状二长花岗岩为富钾弱过铝质S型花岗岩,是杂砂岩在温度约820℃,压力0.8~0.9 Gpa的条件下,经黑云母脱水引发部分熔融形成,形成于同碰撞环境,时代为(456.2±3)Ma;二长花岗岩为富钾准铝质S型花岗岩,是砂泥质沉积岩在温度约750℃,压力0.8 Gpa的条件下,经白云母脱水引发部分熔融形成,形成于伸展背景下,时代为(437.2±1.5)Ma。结合前人的研究成果,认为柴达木山复式岩体是一个挤压到伸展等多种构造体制下形成的岩体。     

大别地块中的非镁铁质超高压变质岩石及其地质意义

报道并描述了大别地块东南部几种新的非镁铁质超高压变质岩石，这些岩石的存在为区域规模的超高压变质作用提供了颇具说服力的证据。     

哈尔滨黄土的粒度与地球化学特征及其对粉尘物源的指示

哈尔滨黄土位于欧亚黄土带的最东端，对它的风尘物源研究是深层次理解风尘堆积与区域构造-地貌-气候变化耦合关系的关键。然而，对哈尔滨黄土地球化学组成的研究尚未开展，对其性质还存在认识上的不统一。为此，我们研究了哈尔滨天恒山剖面L₁黄土层的粒度和地球化学组成，并对其化学风化和物源等展开讨论。为了示踪哈尔滨黄土的物源，我们还对东北沙地（浑善达克沙地、科尔沁沙地、呼伦贝尔沙地和松嫩沙地）进行了表土采样和地球化学分析。结果表明：哈尔滨黄土不含细砂组分（125~250 μm），含有极细砂组分（63~125 μm，4.8%~10.5%），粉砂（4~63 μm）和黏土组分（<4 μm）占绝对优势，分别占73%~82%和12%~18%；粒度模式为三峰态分布（众数分别为36~40、8~10 μm和0.8 μm），与黄土高原典型黄土的粒度分布模式一致，但明显粗于黄土高原中部黄土。哈尔滨黄土经历了初级的化学风化过程，具有较低的成熟度和再循环历史。单靠地球化学方法不能很好地确定哈尔滨黄土的物源，但整合的方法（包括粒度、元素和同位素组成、MDS和PCA统计方法以及自然地理要素等）很好确定了哈尔滨黄土有一个混合源，松嫩沙地松花江水系沉积物为哈尔滨黄土提供了主要的粉尘贡献，浑善达克沙地和科尔沁沙地为哈尔滨黄土提供了部分细颗粒粉尘。     

松嫩平原含水层沉积物特征及其对砷赋存态分布的影响

松嫩平原西部地区为中国砷中毒区域,含水层沉积物特征及砷赋存态对地下水砷迁移、转化的影响并不清楚。在对研究区高砷区与低砷区钻孔沉积物进行取样的基础上,运用激光粒度分析、Tessier五步提取法和Keon分步提取法分别确定了不同深度沉积物的粒度分布和不同赋存态砷含量,系统研究了沉积物的水力传导系数、不同赋存态砷的分布及其与高砷地下水形成的关系。结果表明:沉积物5种赋存态砷(包括可交换态、碳酸盐吸附态、铁/锰氧化物吸附态、有机物或硫化物吸附态和基质态)中,铁/锰氧化物吸附态砷含量最高,并且砷含量与铁、锰含量呈明显正相关性;高砷区钻孔沉积物铁/锰氧化物吸附态砷质量分数为(1.18~6.11)×10-6,低砷区为(0.67~2.60)×10-6;高砷区钻孔沉积物以粉砂、黏土为主,水力传导系数介于0.004~0.027m·d-1,低砷区钻孔沉积物以细砂、中砂为主,水力传导系数介于0.005~0.2m·d-1;沉积物中粉砂或黏土含量越多,则沉积物颗粒越小,其水力传导系数越低,各赋存态砷含量越高,因此,高砷区低水力传导系数有利于还原环境的形成。通过地下水的循环,高砷含水层沉积物的淋滤作用和铁/锰氧化物的还原性溶解形成了研究区高砷地下水。     

柴达木地块北缘南北沟岩体地球化学特征及成矿前景

南北沟岩体位于柴达木地块北缘,出露面积4.5km2。岩石主要类型有淡色辉长岩、辉长岩、暗色辉长岩,各岩石类型之间多为过渡关系,局部呈侵入接触。主量元素化学组成属拉斑玄武岩系列。岩石相对富集大离子亲石元素,亏损高场强元素,明显亏损Nb、Ta。岩体原生岩浆属于高镁拉斑玄武岩(MgO质量分数为11.1%),在岩浆演化过程中遭受了一定程度中—上地壳物质的同化混染作用。岩体形成于古岛弧环境,是早古生代柴达木地块向祁连地块俯冲过程的产物。从岩浆分异程度、原生岩浆性质、同化混染等方面综合评价认为,南北沟岩体具有较好的铜镍硫化物矿床成矿潜力。     

Paleomagnetism of the middle Cretaceous Iritono granite in the Abukuma region, northeast Japan

We have studied the paleomagnetism of the middle Cretaceous Iritono granite of the Abukuma massif in northeast Japan together with ⁴⁰Ar–³⁹Ar dating. Paleomagnetic samples were collected from ten sites of the Iritono granite (102 Ma ⁴⁰Ar–³⁹Ar age) and two sites of its associated gabbroic dikes. The samples were carefully subjected to alternating field and thermal demagnetizations and to rock magnetic analyses. Most of natural remanent magnetizations show mixtures of two components: (1) H component, high coercivity (B_c > 50–90 mT) or high blocking temperature (T_b > 350–560 °C) component and (2) L component, relatively low B_c or low T_b component. H component was obtained from all the 12 sites to give a mean direction of shallow inclination and northwesterly declination (I = 29.9°, D = 311.0°, α₉₅ = 2.7°, N = 12). This direction is different from the geocentric axial dipole field at the present latitude (I = 56.5°) and the typical direction of the Cenozoic remagnetization in northeast Japan. Since rock magnetic properties indicate that the H component of the Iritono granite is carried mainly by magnetite inclusions in plagioclase, this component probably retains a primary one. Thus the shallow inclination indicates that the Abukuma massif was located at a low latitude (16.1 ± 1.6°N) about 100 Ma and then drifted northward by about 20° in latitude. The northwesterly deflection is attributed mostly to the counterclockwise rotation of northeast Japan due to Miocene opening of the Japan Sea. According to this model, the low-pressure and high-temperature (low-P/high-T) metamorphism of the Abukuma massif, which has been well known as a typical location, would have not occurred in the present location. On the other hand, the L component is carried mainly by pyrrhotite and its mean direction shows a moderate inclination and a northwesterly declination (I = 42.8°, D = 311.5°, α₉₅ = 3.3°, N = 9). Since this direction is intermediate between the H component and early Cenozoic remagnetization in northeast Japan, some thermal event would have occurred at lower temperature than pyrrhotite Curie point ( 320 °C) during the middle Cretaceous to early Cenozoic time to have resulted in partial remagnetization.     

Remobilisation of deep Na-Cl waters by a regional flow system in the Alps: Case study of Saint-Gervais-les-Bains (France)

The hydrothermal system of Saint-Gervais-les-Bains, France is located in a south western low-elevation point of the Aiguilles Rouges crystalline Massif. The crystalline rocks are not directly outcropping in the studied area but certainly exist beyond 300 m depth. Uprising waters are pumped from two different aquifers below the Quaternary deposits of the Bon Nant Valley. In the Lower Trias-Permian aquifer crossed by De Mey boreholes (27–36 °C), the ascending Na-SO₄ and high-Cl thermal water from the basement (4.8 g/L) is mostly mixed by a Ca-SO₄ and low-Cl cold water circulating in the autochthonous cover of the Aiguilles Rouges Basement. The origin of the saline thermal water probably results from infiltration and circulation in the basement until it reaches deep thrust faults with leaching of residual brines or fluid inclusions at depth (Cl/Br molar ratio lower than 655). The dissolution of Triassic halite (Cl/Br > 1000) is not possible at Saint-Gervais-les-Bains because the Triassic cold waters have a low-Cl concentration (< 20 mg/L). Water–rock interactions occur during the upflow via north–south strike-slip faults in the basement and later on in the autochthonous cover. For the De Mey Est borehole, gypsum dissolution is occurring with cationic exchanges involving Na, as well as low-temperature Mg dissolution from dolomite in the Triassic formations. The aquifer of imbricated structures (Upper-Middle Trias) crossed by the Lépinay well (39 °C) contains thermal waters, which are strongly mixed with a low-Cl water, where gypsum dissolution also occurs. The infiltration area for the thermal end-member is in the range 1700–2100 m, close to the Lavey-les-Bains hydrothermal system corresponding to the Aiguilles Rouges Massif. For the Ca-SO₄ and low-Cl end-member, the infiltration area is lower (1100–1300 m) showing circulation from the Mont Joly Massif. The geothermometry method indicates a reservoir temperature of probably up to 65 °C but not exceeding 100 °C.     

佳木斯地块南缘牡丹江地区高压变质作用：黑龙江杂岩的岩石学和地质年代学

牡丹江地区出露的黑龙江杂岩是由变质基性岩、泥质片岩、大理岩和变硅质岩系列组成的类似于蛇绿岩层序的构造混杂岩,代表了佳木斯地块西南缘碰撞增生的产物。钠长石和绿帘石变斑晶中共生的矿物组合(钠云母+蓝闪石+多硅白云母+绿帘石)的地质温压计估算结果表明,黑龙江杂岩的峰期变质的温压条件为 T=320~480℃, p=800~1600MPa,为典型的绿帘-蓝片岩相高压变质作用。黑龙江杂岩带中泥质片岩所含的多硅白云母单矿物给出的40Ar/39Ar坪年龄为164.9Ma±0.5Ma。根据白云母中K-Ar同位素体系的封闭温度(350~430℃)接近于得到的黑龙江杂岩的峰期变质温度,可以认为40Ar/39Ar坪年龄指示了这期高压变质事件的年龄,也证实了黑龙江杂岩带中普遍存在一期中侏罗世末期的变质-热事件。