Luminescence-dated aeolian deposits of late Quaternary age in the southern Tibetan Plateau and their implications for landscape history

Aeolian deposits are widely distributed in the interior of the Tibetan Plateau, and their chronology is poorly known. It is not yet clear whether they accumulated only after the last deglaciation, or over a longer time. We applied quartz OSL dating to aeolian samples from the Lhasa area with OSL ages ranging from 2.9 ± 0.2 to at least 118 ± 11 ka. The probability density frequency (PDF) distribution of 24 ages reveals age clusters at about 3, 8, 16–21, 33, and 79–83 ka, indicating enhanced sediment accumulation then. The results show that aeolian deposition occurred throughout most of the last 100 ka. This implies that: 1) an ice sheet covering the whole Tibetan Plateau during the last glacial maximum (LGM) could not have existed; and 2) erosion during the last deglaciation was not as strong as previously proposed, such that not all pre-Holocene loess was removed. The age distribution shown in the PDF indicates that aeolian accumulation is episodic. Sand-formation events revealed by age clusters at 3, 8, and 16–21 ka imply roughly synchronous environmental responses to corresponding global-scale arid events.     

Interpretation of charging on fracture or frictional slip surface of rocks

Fracturing and frictional sliding of quartz and granite under dry condition generates fractoluminescence, charged particle emission and electromagnetic radiation. Various kinds of experiments indicate that surface charge density on fracture or frictional slip surface of quartz and granite is 10⁻⁴ to 10⁻² C/m² which is larger than bound charges induced by the disappearance of piezoelectricity due to the release of stress. Hole and electron trapping centers, which is found in semiconductor devices with the Si–SiO₂ system, are causes of surface charging on fracture or frictional slip surface of quartz crystal. The quantity of the surface charge is enough to cause corona discharge that can generate earthquake lights. The mechanism considering the hole and electron trapping centers has a probability to explain why non-piezoelectric minerals or rocks generate electromagnetic phenomena. It can be one of origins of seismo-electromagnetic phenomena (SEP).     

东天山双龙铜矿石英闪长岩锆石U-Pb定年、Hf同位素分析及对构造环境的制约

通过对新疆东天山雅满苏岛弧带双龙铜矿成岩地质特征、岩石地球化学特征及Hf同位素分析,认为赋矿岩体为一套形成于后碰撞环境下的准铝质高钾钙碱性岩石系列的石英闪长岩,LA-ICP-MS锆石U-Pb同位素年龄为(300.9±1.2)Ma。岩石地球化学显示,赋矿岩石具富集大离子亲石元素(LILE)K,Rb等及高场强元素(HFSE)Th,U,Zr和Hf,贫Nb,Ta,Ti,Sr,P特征,可能形成于后碰撞构造环境。石英闪长岩锆石176Hf/177Hf变化范围0.282949~0.283002,平均值0.282979,εHf(t)值为12.32~14.40,平均13.40,tDM2(Hf)为375~482Ma,平均429Ma,表明岩浆物源可能来自志留纪新生地壳的部分熔融。     

大春河—一朵云断裂断层泥中石英表面 SEM 特征的分析研究

大春河—一朵云断裂位于昆明市的东南侧,沿断层线断错水系、土林地貌发育,河流的最大左旋扭动距离达两公里。断层泥中石英碎砾的SEM研究表明:断层的强烈活动时期为早更新世晚期和晚更新世,全新世断层的活动有所减弱;晚更新世以来断裂的活动方式以蠕滑为主。     

羌塘盆地最大规模沥青脉的发现及其意义

在羌塘盆地已经发现了190余处油气显示。近年笔者在盆地北部晚侏罗世地层中发现了迄今最大规模的沥青脉。研究结果表明,该沥青脉产出于上侏罗统索瓦组地层之中,地层下部系与沥青脉的形成有一定关系的中侏罗统夏里组局部含油气显示的盐丘。沥青族组分(%)为:饱和烃5.72、芳烃18.46、沥青质52.37、非烃23.45,说明该沥青脉经过了运移、氧化的过程。同时,沥青脉产出于复背斜范围内,利于油气聚集成藏。这一发现对于羌塘盆地的油气地质的作用具有现实意义。     

Middle to early Late Ordovician hydrothermal veining in the Molong Volcanic Belt,northeastern Lachlan Fold Belt: Sedimentological evidence

Detrital volcanic and vein quartz, accompanied by felsic volcanic debris, occur as minor constituents in the Ordovician subduction‐related mafic volcanics of the Molong Volcanic Belt. In the western province of the Molong Volcanic Belt, detrital quartz is present in the three episodes of the mafic Volcanics. Volcanic quartz occurs in allochthonous limestone blocks in the Bendigonian Hensleigh Siltstone overlying the Mitchell Formation. The second volcanic episode (the Fairbridge Volcanics) commenced after a hiatus of approximately 20 million years and lasted around 10 million years from Darriwilian to Gisbornian time. Locally derived vein quartz, volcanic quartz and felsic detritus are concentrated at the bases of autochthonous Wahringa and Yuranigh Limestone Members of the volcanics and are extensive and abundant in basal beds of the regional Eastonian limestone body that transgressed over an eroded volcanic centre at Cargo. This early Eastonian debris, deposited early in an 8 million‐year volcanic hiatus preceding the final Ordovician Bolindian volcanism, establishes a pre‐Eastonian age for mineralisation at Cargo. It is inferred that the pauses in volcanism were preceded by magmatic fractionation, intrusion and hydrothermal activity and followed by erosion, subsidence and deposition of autochthonous limestones. Minor occurrences of vein and volcanic quartz are found in Bolindian volcanogenic sediments of the third volcanic phase. It is concluded that hydrothermal vein formation (and mineralisation by inference) was associated with pauses in volcanic activity throughout the Middle to early Late Ordovician over a wide area in the western province, culminating in the mineralisation at Cargo and Copper Hill near Molong. Volcanism in the eastern province of the Molong Volcanic Belt was continuous from at least Darriwilian to latest Ordovician time. Here, detrital hydrothermal vein quartz and volcanic quartz and felsic detritus are distributed through late Middle and early Late Ordovician turbidites of the Weemalla Formation. The possible existence of cycles in the source area like those of the Fairbridge Volcanics is masked by the distal nature of these deposits. Vein formation occurred in both provinces from late Middle Ordovician to early Late Ordovician, long before the formation of the world‐class mineral deposit at Cadia associated with the latest Ordovician Cadia Monzonite.     

载金石英的阳离子效应及其对含矿性的指示意义

石英的阳离子效应指石英结构中Al~(3+)与Si~(4+)的置换作用.在分析海南戈枕断裂金成矿带石英中普遍存在的这一作用,以及由此造成的石英粉末红外谱(IR)、顺磁共振谱(EPR)及热释光曲线(TL)特征,进而讨论了这些特征与金成矿的关系.     

云南东川新山含金剪切带型金矿

新山金矿属构造剪切带控制的典型金矿床,产于中元古界昆阳群美党组(Pt2m)中部变质石英砂板岩中。规模大、品位富、易采易选。矿区构造——含金剪切带与土壤地球化学金异常,是寻找该类金矿的重要标志。     

Syntectonic Mobility of Supergene Nickel Ores of New Caledonia (Southwest Pacific). Evidence from Garnierite Veins and Faulted Regolith

Supergene nickel deposits of New Caledonia that have been formed in the Neogene by weathering of obducted ultramafic rocks are controlled by fracture development. The relationship of tropical weathering and tectonic structures, faults and tension gashes, have been investigated in order to determine whether fractures play a passive role only, as previously thought; or alternatively, if brittle tectonics was acting together with alteration. Observation of time‐relationship, textures, and mineralogy of various fracture fills and fault gouges shows that active faulting has played a prominent role not only in facilitating drainage and providing room for synkinematic crystallization of supergene nickel silicate, but also in mobilizing already formed sparse nickel ore, producing the very high grade ore nicknamed “green gold”.     

内蒙古白乃庙金矿含金石英脉LA-ICP-MS锆石U-Pb测年及其地质意义

为了厘定内蒙古白乃庙金矿床的成矿时代,对矿区主要含金石英脉中热液蚀变锆石进行了LA-ICP-MS U-Pb测年。结果表明,锆石热液蚀变特征明显,具有清晰的核—幔—边结构,锆石核、幔均为岩浆锆石或变质锆石,热液蚀变增生边呈自形—半自形结构,Th/U值集中于0.2~0.5之间,测年数据为421.4~447.6Ma,认为金矿形成时代为志留纪。从区域成矿规律分析,初步认为白乃庙金矿床的形成与早古生代古亚洲板块向华北地块强烈俯冲引起的构造—岩浆活动密切相关。