Structural and metamorphic evolution of the Moornambool Metamorphic Complex,western Lachlan Fold Belt,southeastern Australia

The wedge‐shaped Moornambool Metamorphic Complex is bounded by the Coongee Fault to the east and the Moyston Fault to the west. This complex was juxtaposed between stable Delamerian crust to the west and the eastward migrating deformation that occurred in the western Lachlan Fold Belt during the Ordovician and Silurian. The complex comprises Cambrian turbidites and mafic volcanics and is subdivided into a lower greenschist eastern zone and a higher grade amphibolite facies western zone, with sub‐greenschist rocks occurring on either side of the complex. The boundary between the two zones is defined by steeply dipping L‐S tectonites of the Mt Ararat ductile high‐strain zone. Deformation reflects marked structural thickening that produced garnet‐bearing amphibolites followed by exhumation via ductile shearing and brittle faulting. Pressure‐temperature estimates on garnet‐bearing amphibolites in the western zone suggest metamorphic pressures of ～0.7–0.8 GPa and temperatures of ～540–590°C. Metamorphic grade variations suggest that between 15 and 20 km of vertical offset occurs across the east‐dipping Moyston Fault. Bounding fault structures show evidence for early ductile deformation followed by later brittle deformation/reactivation. Ductile deformation within the complex is initially marked by early bedding‐parallel cleavages. Later deformation produced tight to isoclinal D₂ folds and steeply dipping ductile high‐strain zones. The S₂ foliation is the dominant fabric in the complex and is shallowly west‐dipping to flat‐lying in the western zone and steeply west‐dipping in the eastern zone. Peak metamorphism is pre‐ to syn‐D₂. Later ductile deformation reoriented the S₂ foliation, produced S₃ crenulation cleavages across both zones and localised S₄ fabrics. The transition to brittle deformation is defined by the development of east‐ and west‐dipping reverse faults that produce a neutral vergence and not the predominant east‐vergent transport observed throughout the rest of the western Lachlan Fold Belt. Later north‐dipping thrusts overprint these fault structures. The majority of fault transport along ductile and brittle structures occurred prior to the intrusion of the Early Devonian Ararat Granodiorite. Late west‐ and east‐dipping faults represent the final stages of major brittle deformation: these are post plutonism.     

Response of detrital zircon and monazite,and their U–Pb isotopic systems,to regional metamorphism and host‐rock partial melting,Cooma Complex,southeastern Australia

Progressive Early Silurian low‐pressure greenschist to granulite facies regional metamorphism of Ordovician flysch at Cooma, southeastern Australia, had different effects on detrital zircon and monazite and their U–Pb isotopic systems. Monazite began to dissolve at lower amphibolite facies, virtually disappearing by upper amphibolite facies, above which it began to regrow, becoming most coarsely grained in migmatite leucosome and the anatectic Cooma Granodiorite. Detrital monazite U–Pb ages survived through mid‐amphibolite facies, but not to higher grade. Monazite in the migmatite and granodiorite records only metamorphism and granite genesis at 432.8 ± 3.5 Ma. Detrital zircon was unaffected by metamorphism until the inception of partial melting, when platelets of new zircon precipitated in preferred orientations on the surface of the grains. These amalgamated to wholly enclose the grains in new growth, characterised by the development of {211} crystal faces, in the migmatite and granodiorite. New growth, although maximum in the leucosome, was best dated in the granodiorite at 435.2 ± 6.3 Ma. The combined best estimate for the age of metamorphism and granite genesis is 433.4 ± 3.1 Ma. Detrital zircon U–Pb ages were preserved unmodified throughout metamorphism and magma genesis and indicate derivation of the Cooma Granodiorite from Lower Palaeozoic source rocks with the same protolith as the Ordovician sediments, not Precambrian basement. Cooling of the metamorphic complex was relatively slow (average ～12°C/10⁶y from ～730 to ～170°C), more consistent with the unroofing of a regional thermal high than cooling of an igneous intrusion. The ages of detrital zircon and monazite from the Ordovician flysch (dominantly composite populations 600–500 Ma and 1.2–0.9 Ga old) indicate its derivation from a source remote from the Australian craton.     

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.     

7614铀矿床断裂构造的地球化学研究

本文以西北一个铀矿床为例,介绍了一种进行矿床断裂构造地球化学研究的方法,包括了以断裂构造的倾角和倾向为座标的微量元素含量的等值线圆形曲线图;断裂构造的元素频数分布图;断裂构造中元素的多元统计分析。据此,讨论了热液作用和其它地质作用有关的断裂构造中微量元素的相互关系,并进而讨论了它们的铀成矿作用过程以及对找矿勘探的意义。     

沂沭断裂带断层泥中 K-Ar、FT 和 TL 体系年代学含义的初步研究

本文报道了利用K-Ar法、TL法和FT法,分别测定断层泥中1Md伊利石(<1μ粒级组份)、石英(2-10μ粒级组份)和磷灰石单矿物的年龄结果;给出了沂沭断裂带三次强烈活动的年龄区间及强度逐渐减弱的变化趋势。首先提出了利用这三种测年手段,测定断层泥中三种不同物质的年龄,进而研究断层活动(强度和时间)的新方法     

粤北新洲逆冲推覆断裂系统中断层岩的地球化学特征

粤北新洲逆冲推覆断裂系统由Ⅰ，Ⅱ，Ⅲ－Ⅳ级推覆断层带组成，断层带中形成一套复杂的断层岩系，断层岩中Ａｕ，Ｐｂ，Ｗ，Ｓｂ，Ｂｉ，Ｈｇ，普遍富集，由此引起不同程度的金矿化，分别形成石英碳酸盐糜棱岩型金矿，碎裂钠长石岩型金矿和石英脉型金矿，成矿时期为印支晚期到燕山期，通过系统的微量元素，同位素和流体包裹体研究表明，１级推覆断层带断层岩中的成矿物质主要来自下地壳或上地幔，ＩＩ级推覆断层带断层岩中的成矿物质     

滇西昌宁─孟连带南部地层地质问题

滇西孟连以南，整合于南段组浊积岩之上的拉巴群硅质岩含晚二叠世早期放射虫化石，南段组时代不仅限于石炭纪，可能延入二叠纪。二者为晚古生代思茅地块的外陆坡沉积。其西面的南基河杂岩（新名）由层序混乱的晚古生代硅质岩、泥岩和少量砂岩、玄武岩构成。放射虫化石证据表明，硅质岩时代不仅限于晚泥盆世－早二叠世，还延入晚二叠世，而有的砂岩时代为早石炭世，它们是经过强烈构造变动的古特提斯洋的沉积记录。昌宁－孟连带向南可能延至泰国北部的清迈带，而非东北部的难河带。     

Mineral composition variation in Alpine Schist, Southern Alps, New Zealand: Implications for recrystallization and exhumation

Abstract Compositional variation of silicates (plagioclase, K-feldspar, epidote, titanite, garnet, white mica, biotite, chlorite), ilmenite, carbonates (calcite, ankerite) and apatite, in quartzofeldspathic lithologies of the Alpine Schist, New Zealand, is discussed in terms of increasing metamorphic grade and possible isograd-producing reactions. The mineral data, in conjunction with geological considerations, are used to determine polychronous P-T arrays of an early high P/T event (c. 16°C/kb; 5°C/km) overprinted by a lower P/T event (c. 50°C/kb; 15°C/km) that provides an estimation of Mesozoic and Cenozoic exhumation of schist of 11 to 13 km and 19 to 22 km respectively. The effects of possible shear heating and recrystallization to form K-feldspar zone schist near the Alpine Fault is consistent with movement along a mid to lower crustal detachment surface during Cenozoic shortening, and near isothermal exhumation of the schists to form the Southern Alps.     

Frictional heat generation and seismic radiation in a foam rubber model of earthquakes

Results from a study of stick-slip particle motion at the interface between two stressed foam rubber blocks indicate that normal vibrations and interface separation are an important part of the stick-slip process in foam rubber. The dimension of the dynamic slip pulse is small compared to the dimension of the model (approximately 10 cm vs. 200 cm) consistent with the abrupt-locking slip pulse model ofBrune (1970, 1976), andHeaton (1990). A comparison of frictional heat generation between stable-sliding and stick-slip foam rubber models indicates a linear relation between the temperature increase on the fault surface (for a given distance of slip) and the driving shear force for the stable-sliding model, while for the stick-slip model there is essentially no variation in frictional heat generation with an increase in shear stress. We performed experiments to investigate the ratio of normal motion to shear motion at different levels of normal stress in the stick-slip foam rubber model. Preliminary result indicate that the normal component of the particle motion increases more rapidly with increasing normal stress than the shear component. The phenomenon of interface separation and normal vibrations may thus explain some of the most frustrating problems in earthquake mechanics, e.g., the heat flow paradox, the long-term weakness of major active faults, and anomalousP-wave radiation.     

三山岛金矿控矿断层F1的力学性质及补强措施

作者以正在开采中的三山岛金矿采场为研究对象，分析矿区开采过程中的岩体结构特征及重力方向矿柱、护顶矿柱与控矿断层F1断层泥及其上覆岩体之间的关系和力学机制。通过试验研究了断层泥的物质成分和力学性质，总结了力学特性与断层泥厚度及含水量之间的关系。在此基础上提出锚固大于中倾角的结构面，提高结构面的抗滑阻力；增加含有高、陡倾角结构面矿柱的刚度等对矿柱的补强措施。对护顶矿柱提出预先锚固；分阶段开采的补强方法。在裂隙密集带设置排水设施，改善断层泥的赋存条件，提高它的力学性能。