巧妙的“替代”(初二)

用天平量筒测密度的方法常用,然而若只有天平或只有量筒,要测密度,怎么办呢?我们来看下面几例. 1.利用天平、烧杯、水、细线,怎样测出一石块的密度? 分析可用天平测出石块的质量,因为没有量筒没办法直接测出石块的体积,所以就需要利用天平、烧杯、水等想办法测出与石块体积相等的那部分水的质量。

Forming Proterozoic basement within eastern Central Asian Orogenic Belt:Evidence from zircon U-Pb-Hf-O isotopes

As part of the mosaic of micro-continents within the Central Asian Orogenic Belt(CAOB), the Xing’anAirgin Sum Block(XAB) features increasingly-recognized Meso-Neoproterozoic geological records. However, the origin, temporal-spatial distribution of ancient materials, and their roles in crust evolution remain to debate. This paper presents an integrated study of zircon U-Pb ages and Hf-O isotopes for Mesoproterozoic and Paleozoic granites from the Erenhot region of central Inner Mongolia, along eastern CAOB. The intrusion of 1450 Ma syenogranite denotes that the Precambrian basement of XAB extends from Sonid Zuoqi westward to Erenhot. The 384 and 281 Ma monzogranites containing Mesoproterozoic xenocrystic zircons possess Proterozoic-dominant two-stage Hf model ages, further suggesting the wide existence of Proterozoic crust beneath western XAB. Cyclic Proterozoic crustal growth and reworking seem to show close linkages with the orogenesis during relevant supercontinent cycles. 1450-1360 Ma juvenile crustal growth at Erenhot and synchronous ancient crust reworking at Sonid Zuoqi and Abagaqi were likely resulted from retreating subduction involved in Columbia breakup, while 1.2-1.0 Ga reworking and 0.9-0.7 Ga growth events within the Erenhot basement might respond to assembly and breakup of Rodinia, respectively. Besides, our work confirms that reworking of Neoproterozoic crust played important roles during Paleozoic multi-stage accretion of CAOB.

Transitional geology and its effects on development and longwall mining in Pittsburgh Seam

This paper presents the geologic and ground control challenges that were encountered by Consol Energy＇s coal mining operations in southwestem Pennsylvania, USA. Geologic encounters, such as sandstone- to-limestone geology transition, massive sandstone channels, shale channels, pyritic rich green claystone, laminated roof, and soft floor, have significantly impacted the development and longwall mining in Consol＇s Pittsburgh Seam coal mines. Experience from different mines shows that, in the sandstone-to-limestone geology transition zone, 1.83 m high-tension, fully-grouted primary bolts employed along with 4.88 m cen- ter cable bolts at every other strap greatly improved beam building and ensured proper anchorage into the competent roof. Hydraulic fracturing of the massive sandstone was often necessary to enhance caving of the massive sandstone behind the shields to relieve pressure at the face. The presence of soft floor coupled with presence of thick floor coal and deep cover, induced excessive headgate convergence during retreat of the first right hand longwall panel. In all, it is important to explore the roof and in-seam geology in detail to delineate normal and anomalous geologic conditions prior to and during development. With diligent geologic reconnaissance, geotechnical monitoring, and assessment, site-specific geotechnical solutions have been provided to mine operations to improve safety and productivity.

Characterization of Pegmatoid from Dimension Stones Tailings for Application as Ceramic Raw Material

Exploitation and processing of pegmatoids at Brazil＇s northeast （Serido region-RN State） aiming further use as dimension stone produces mass losses ranging between 30%-90%. The tailings are predominantly composed by feldspar, quartz, muscovite and other Fe-bearing silicates such as biotite and amphiboles, suitable for ceramic production. The recovery of these elements depends on mica＇s remotion to levels under 2.0%, preferentially by dry methods due the scarce amount of water prevailing at Serido region. This paper presents results from pegmatite tailings characterization from Serido region showing the potentially application as raw material for ceramic production. To do it, a new technological route must be developed to fit it as main component to white ceramic industry, considering the properties required by ceramic industries.

Discovery of late Paleozoic fossils in tectonic blocks of the Dabao Formation in the South Qinling Orogenic Belt and their significance

The Dabao Formation in the South Qinling Orogenic Belt was previously regarded as Ordovician in age and consists of clastic matrix and blocks of siltstone,limestone,chert,and volcanic rocks.However,some Middle Devonian corals,conodonts,and other fossil fragments within the limestone blocks were discovered in recent field investigations,indicating that the Dabao Formation was formed during late Paleozoic.Combined with other regional geological data,the Dabao Formation in the Southern Qinling Orogenic Belt is considered to be a late Paleozoic or early Mesozoic accretionary complex.

Material transportation and fluid-melt activity in the subduction channel: Numerical modeling

The subduction channel is defined as a planar to wedge-like area of variable size,internal structure and composition,which forms between the upper and lower plates during slab subduction into the mantle.The materials in the channel may experience complex pressure,temperature,stress and strain evolution,as well as strong fluid and melt activity.A certain amount of these materials may subduct to and later exhume from>100 km depth,forming high to ultra-high pressure rocks on the surface as widely discovered in nature.Rock deformation in the channel is strongly assisted by metamorphic fluids activities,which change composition and mechanical properties of rocks and thus affect their subduction and exhumation histories.In this study,we investigate the detailed structure and dynamics of both oceanic and continental subduction channels,by conducting highresolution petrological-thermomechanical numerical simulations taking into account fluid and melt activities.The numerical results demonstrate that subduction channels are composed of a tectonic rock melange formed by crustal rocks detached from the subducting slab and the hydrated mantle rocks scratched from the overriding plate.These rocks may either extrude sub-vertically upward through the mantle wedge to the crust of the upper plate,or exhume along the subduction channel to the surface near the suture zone.Based on our numerical results,we first analyze similarities and differences between oceanic and continental subduction channels.We further compare numerical models with and without fluid and melt activity and demonstrate that this activity results in strong weakening and deformation of overriding lithosphere.Finally,we show that fast convergence of orogens subjected to fluid and melt activity leads to strong deformation of the overriding lithosphere and the topography builds up mainly on the overriding plate.In contrast,slow convergence of such orogens leads to very limited deformation of the overriding lithosphere and the mountain building mainly occurs on the subducting plate.

Wedge tectonics in South China:constraints from new seismic data

Collisional orogens form when tectonic forces amalgamte fragments of Earth’s continental lithosphere.The sutures between individual fragments,or terranes,are potential sites of weakness that facilitate subsequent continental breakup.Therefore,the lithospheric architecture of collisional orogens provides key information for evaluating the long-term evolution of the continental interior:for example,the South China Block(SCB),where the tectonic history is severely obscured by extensive surface deformation,magmatism,and metamorphism.Using new passive-source seismic models,we show a contrasting seismic architecture across the SCB,with three prominent crustal dipping structures across the Jiangnan Orogen.Combined with constraints from multi-disciplinary regional geophysical datasets,these pronounced dipping patterns are interpreted as relict wedge-like lithospheric deformation zones initiated in the fossil collisions that assembled the Yangtze Block and the SCB.The overall trend of these tectonic wedges implies successive crustal growth along paleo-continental margins and is indicative of northward subduction and docking of accretional terranes.In contrast,no such dipping structures are preserved in the Cathaysia Block,indicating a weak and reorganized lithosphere.The variations in the deformation responses across the SCB reflect the long-term modifications of the lithosphere caused by prolonged collision and extension events throughout the tectonic history of the SCB.Our results demonstrate the critical roles that suture zones played in the successive growth and evolution of the continental lithosphere.