Evidence for the thrust emplacement of the ‘Lesser Himalaya’ Chur granite,Himachal Pradesh

Numerous peraluminous and porphyritic granitic bodies and augen gneisses of granitic compositions occur in the nappe sequences of the Lower Himalaya. They are Proterozoic-to-lower Paleozoic in age and have been grouped into the ‘Lesser Himalaya granite belt’. The mode of emplacement and tectonic significance of these granites are as yet uncertain but they are generally considered to be sheet-like intrusions into the surrounding rocks. The small and isolated granite body (the Chur granite) that crops out around the Chur peak in the Himachal Himalaya is one of the more famous of these granites. Several lines of evidence have been adduced to show that the Chur granite has a thrust (the Chur thrust) contact with the underlying metasedimentary sequence (locally called the Jutogh Group). The Chur granite with restricted occurrence at the highest topographic and structural levels represents an erosional remnant of a much larger sub-horizontal thrust sheet. The contact relations between the country rocks and many of the other granite and granitic augen gneisses in the Lesser Himalaya belt are apparently similar to that of the Chur granite suggesting that at least some of them may also represent thrust sheets.     

大兴安岭中生代火山岩地层时空分布与蒙古—鄂霍茨克洋、古太平洋板块俯冲作用响应

为了提高大兴安岭中生代火山岩地层的区域可对比性、深入研究大兴安岭中生代火山岩与古太平洋和蒙古—鄂霍茨克洋的构造关系,本文在大兴安岭地区1: 1 000 000地质图编图的基础上,依据岩石组合、古生物、接触关系、区域对比以及最新的年代学(锆石U-Pb、⁴⁰Ar/³⁹Ar测年)资料,对大兴安岭中生代火山岩地层重新进行了厘定。进一步界定了塔木兰沟组(172~161 Ma)、满克头鄂博组(162~148 Ma)、玛尼吐组(158~145 Ma)、白音高老组(145~129 Ma)、梅勒图组(143~128 Ma)、龙江组(128~120 Ma)、光华组(128~118 Ma)、甘河组(120~113 Ma)和孤山镇组(118~110 Ma)的形成时代。结合古太平洋、蒙古—鄂霍茨克洋板块对东亚大陆边缘的俯冲作用,解析了中生代火山岩形成的构造背景,认为中—晚侏罗世NE向展布的火山岩主要形成于蒙古—鄂霍茨克洋板块向南东俯冲的伸展背景,早白垩世NNE向展布的火山岩主要形成于伊泽奈岐板块向东亚大陆俯冲的伸展背景。晚侏罗世与早白垩世火山岩地层之间发育的开库康组、木瑞组等类磨拉石建造,是两个构造体系转换阶段的主要沉积记录。     

Early Devonian synorogenic alluvial-fan deposits of the Maccullochs Range,western New South Wales

The Early Devonian, Maccullochs Range beds (new) of the Winduck Interval largely comprise non-marine fine-grained sheet-flood-deposited sandstones which lie in the southeast sector of the Darling Basin Conjugate Fault System. Deposition of the >2.5 km-thick sequence occurred on the Wilcannia, Towers and Coolabah Bore alluvial fans, that were sourced largely from lightly indurated sandstone caps overlying a large basement high lying north of the Darling River Lineament, and also from west of Maccullochs Range (Coolabah Bore Fan). Four lithofacies are recognised. Lithofacies 1, massive sandstone, is proximal and was deposited from hyperconcentrated sheet floods. The more distal lithofacies 2 is partly massive, partly laminated and partly affected by soft sediment slumping during its deposition. It contains 1.3 – 3.5 m-thick sheet-flood successions that rarely show cross-bedding. Lithofacies 3 and 4 are minor: lithofacies 3, stream-flood deposited, comprises coarse-grained, pebbly sandstone and lithofacies 4, transient playa lake deposits that are locally intercalated with lithofacies 2. In lithofacies 2, thick massive fine-grained sandstone is commonly overlain by laminated sandstone that was deformed when soft. Incised channel deposits in lithofacies 2 deposits are rare and palaeosols were not discovered. Permanency of the positions of two of the alluvial fans, and by inference their feeder streams, remained unchanged for ～9 million years. The fans overlie probable floodplain deposits observed in a quarry in the easternmost part of the study area. Marine fossils are very minor in the range—the brachiopod Howellella jaqueti at one locality indicates an Early Devonian age for one of the brief marine incursions into what was normally an alluvial-fan environment. Very brief marine incursions elsewhere in the group are deduced from the presence of very rare fossil gastropods.     

福建华安玉的矿物学特征及成因研究

通过福建华安玉野外地质观察、室内显微镜下观察、矿物电子探针分析和X射线粉末衍射分析,研究了华安玉的结构构造和矿物组成,结果表明: 华安玉显示出不同艳丽的条带,实质上是不同矿物分带的体现,绿-墨绿色条带主要由铁次透辉石组成,红色或淡肉红色条带主要由钾长石组成,灰白色或乳白色条带主要由石英、方解石等矿物组成。并对华安玉的形成构造环境和成因进行了初步研究,认为其形成于被动大陆边缘的潮坪泻湖环境,原岩主要是钙质粉砂岩、泥灰岩、硅质岩等,燕山期强烈的构造岩浆活动对其进行了多期热接触变质或交代作用,钙质粉砂岩、泥灰岩、硅质岩等经变质成为透辉石角岩。     

The role of fluids in the formation of talc deposits of Rema area,Kumaun Lesser Himalaya

Talc deposits of Rema area in the Kumaun Inner Lesser Himalaya are hosted within high magnesium carbonates of the Proterozoic Deoban Formation. These deposits occur as irregular patches or pockets mainly within magnesite bodies, along with impurities of magnesite, dolomite and clinochlore. Textures represent different phases of reactions between magnesite and silica to produce talc. Petrography, XRD and geochemistry reveal that the talc has primarily developed at the expense of magnesite and silica, leaving dolomite largely un-reacted. Early fluid inclusions in magnesite and dolomite associated with talc are filled with H₂O+NaCl+KCl ± MgCl₂ ± CaCl₂ fluids, which represent basin fluid system during diagenesis of carbonates. Their varied degree of re-equilibration was although not pervasive but points to increased burial, and hence requires careful interpretation. H₂O-CO₂ fluid with XCO₂ between 0.06 and 0.12 was equilibrated with talc formation. The reaction dolomite+quartz → talc was not extensive because T-X_CO2 was not favourable, and talc was developed principally after magnesite+quartz.     

晚震旦世陡山沱期后生生物群的古生态环境探讨

早期后生生物群是当前古生物学研究热点之一。我国上扬子区的庙河生物群和瓮安生物群是震旦纪的重要生物群,而生物群是怎样繁盛和埋藏保存是研究早期后生生物群的一个重要方面。作者研究认为翁安生物群是由于洋流上升提供了大量的ＳｉＯ２和Ｐ２Ｏ５等养分,使生物在台地边缘大规模繁盛,其海水由于富ＳｉＯ２和Ｐ２Ｏ５所引起强烈的磷酸岩化及硅化作用,使大量的生物尸体被快速矿化,形成具有抗水动力强的骨架,避免水动力和氧化作     

Influence of underground space development mode on the groundwater flow field in Xiong’an new area

The degree and scale of underground space development are growing with the continuous advancement of urbanization in China. The lack of research on the change of the groundwater flow field before and after the development of underground space has led to various problems in the process of underground space development and operation. This paper took the key development zone of the Xiong’an New Area as the study area, and used the Groundwater modeling system software (GMS) to analyse the influence on the groundwater flow field under the point, line, and surface development modes. The main results showed that the underground space development would lead to the expansion and deepening of the cone of depression in the aquifer. The groundwater level on the upstream face of the underground structure would rise, while the water level on the downstream face would drop. The “line” concurrent development has the least impact on the groundwater flow field, and the maximum rise of water level on the upstream side of the underground structure is expected to be approximately 3.05 m. The “surface” development has the greatest impact on the groundwater flow field, and the maximum rise of water level is expected to be 7.17 m.     

Géomorphologie de Tromelin,océan Indien

Tromelin is a small coral reef island (1 km²) located in the Indian Ocean, approximately 440 km east of Madagascar and 580 km north of La Réunion. Despite the presence of a permanent Météo France weather station on Tromelin since the 1950 s, a detailed geomorhological study of the island has never been undertaken. In this paper, we describe results from the 2008 field season, which enabled us to map and describe seven geomorphological zones on the atoll. (1) Tromelin's bathymetry is characterised by a pronounced submarine slope, which attains depths of 1000 m at only 2.5 km from the island's coastline. This geomorphology is typical of volcanic hotspots. (2) A coral platform borders the emerged crown of the island. This platform is exposed at low tide and has been fashioned in an ancient Pleistocene substratum. The substratum has been eroded by abrasive marine action to its present shape since the stabilisation of relative sea level around 6000 years ago. Erosion of the reef yields most of the biogenic sediment supply to the island. (3) The upper foreshore is characterised by outcrops of beachrock. These formations show a stratfication in slabs and dip gently towards the sea in the same manner as the contemporary clastic sediments. (4) Tromelin's beaches are divided into three sub-units, which reflect the different energy dynamics around the island, in addition to the transfer of sediment from the windward to the leeward side: (i) the southern storm beaches are characterised by coral blocks reworked during episodic high-energy events; they form boulder ramparts. Four perched rampart ridges have been recorded at ∼1 m, ∼3 m, ∼4.5 m and ∼7 m above mean sea level; (ii) transitional beaches are observed between the south and the north, constituting storm blocks and coarse sands and gravels; and (iii) sandy beaches are noted on the northern leeward side, comprising rounded gravels and coarse sands. The northern tip of the island is characterised by a sand spit (∼125 × ∼225 m), whose geometry varies based on the seasonal and meteo-marine contexts. (5) On Tromelin, a number of dune formations are observed. These are best developed in the north of the island due to the south-north translation of clastic sediments by aeolian wind action, and the trapping of sands by the well-developed vegetation. The height of the dunes varies between 10 cm (the southern micro-dunes) to 250 cm in the Northeast of Tromelin. (6) Exceptional waves have deposited storm tracts up to 250 m from the foreshore zone, comprising coarse gravels and coral blocks. The storm tract deposits are most prevalent on the windward side of the island, due not only to the high-energy dynamics, but also to the absence of vegetation cover in this area. (7) The southern depression covers an area of ∼40,000 m². At its lowest point it is only 1.2 m above sea level.     

Provenance of lateritic bauxite deposits in the Wuchuan–Zheng’an–Daozhen area,Northern Guizhou Province,China: LA-ICP-MS and SIMS U–Pb dating of detrital zircons

The provenance of the large and super-large scale bauxite deposits developed in the Wuchuan–Zheng’an–Daozhen (WZD) alumina metallogenic province in the Yangtze Block of South China is poorly understood. LA-ICP-MS and SIMS U–Pb dating of detrital zircons from bauxite ores and the underlying Hanjiadian Group in the WZD area provide new constrains on the provenance of the WZD bauxite and provide new insight on the bauxite ore-forming process. The ages of the detrital zircons in the bauxites and the zircons in the Hanjiadian Group are similar suggesting that the bauxites are genetically related to the Hanjiadian sediments. The detrital zircon populations of the four samples studied show four primary age peaks: 2600–2400 Ma, 1900–1700 Ma, 1300–700 Ma and 700–400 Ma. The age distribution of detrital zircons indicates that they are probably derived from various sources including Neoproterozoic, Mesoproterozoic, Paleoproterozoic, Archean and some minor Paleozoic sources. The most abundant age population contains a continuous range of ages from 1300 to 700 Ma, ages consistent with subduction-related magmatic activities (1000–740 Ma) along the western margin of the Yangtze Block and the worldwide Grenville orogenic events (1300–1000 Ma). Thus, it is suggested that the main provenances of the WZD bauxite and the Hanjiadian Group are the Neoproterozoic igneous rocks in the western Yangtze Block and the Grenville-age igneous rocks in the southern Cathaysia Block. In addition, this work verifies that the global Grenville orogenic events and subduction-related magmatic activities associated with the Yangtze Block had a significant influence on the formation of the WZD bauxite deposits.     

福建永安小磉调查区推覆构造及煤炭资源远景评价

永安小磉调查区大面积出露外来推覆体即寒武系中一下统林田组、上统东坑口组,泥盆系上统天瓦崃组、桃子坑组,石炭系下统林地组、中统黄龙组、上统船山组,利用推覆构造理论,并结合深部钻探验证,推覆体下保存较厚煤系（童子岩组）和可采煤层,找煤潜力大,推覆构造理论对指导深部找煤具有重要意义。