Prediction of engineering properties of rocks from microscopic data

The purpose of this study is to develop the empirical equations for the prediction of the physical and mechanical properties of limestone and marble from microscopic data including their mineralogical and petrographical properties and to test the validity of model equations by using multivariate statistical methods. This study was performed on 15 different rocks, composed of six limestone and nine marble samples. Stepwise multiple regression analysis was applied to predict the engineering properties of both the marble and limestone rock samples considering petrographical properties as inputs. In order to determine the overall significance of the empirical equations for prediction of the physical and mechanical properties of marble and limestone samples, the F test was also performed. As a result of this study, it is found that the empirical equations developed in this study are statistically significant.     

内蒙古西部额济纳旗及邻区上石炭统—下二叠统 阿木山组的沉积特征和时代

额济纳旗地区是阿木山组分布的最西端,产出于伸展背景下的裂谷环境,火山岩比较发育,从下到上可分为火山岩段、灰岩段和碎屑岩段。火山岩段和灰岩段产丰富 的 类化石,灰岩段下部产丰富的珊瑚化石。珊瑚化石的时代主要为晚石炭世, 类从下到上分别属于Triticites组合和Pseudoschwagerina组合,从而确定阿木山组的3个岩性段之间以叠覆关系为主,地质时代为晚石炭世至早二叠世,其中火山岩段为晚石炭世小独山期或更早;灰岩段下部为小独山期,上部为紫松期;碎屑岩段为早二叠世紫松期或更晚一些至隆林期。     

Estimation of the Shale Oil/Gas Potential of a Paleocene–Eocene Succession: A Case Study from the Meyal Area, Potwar Basin, Pakistan

The successful exploration and production of shale-gas resources in the United States and Canada sets a new possible solution towards the energy crisis presently affecting most countries of Asia. This study focuses on the use of well log and 2D seismic data for the characterization of the shale oil/gas potential of a Paleocene–Eocene succession — the Meyal area in the Potwar Basin of Pakistan. Two shaly plays are identified in Paleocene–Eocene strata in well logs using ΔLogR and modified ΔLogR cross-plot techniques. The results indicate that Paleocene shale(the Patala Formation) and the lower shaly part of Eocene limestone(Sakesar Formation) can be potentially mature source rocks. However, the thermal maturity modelling proves that only the Paleocene shale is mature. Our results also suggest that the maturity responses on ΔLogR models for the lower shaly part of the Eocene limestone are due to trapped hydrocarbons in the intra-formational fractures. Petroelastic/petrophysical analysis of the Patala Formation reveals two potential shale oil/gas zones on the basis of Young's modulus, Poisson's ratio, Brittleness index and Total Organic Content at an exploitation depth of 3980–3988 m. This work can provide valuable insight for estimating shale oil/gas potential in highly deformed basins not only in Asia but in other parts of the world.     

浙江西部晚奥陶世五峰期沉积及奥陶系—志留系的分界

浙江西部晚奥陶世五峰期沉积包括三种相:(一)笔石页岩相:由二部分组成,上部堰口组有笔石Diplograptus bohemicus带及三叶虫Dalmanitina sp.,下部于潜组有四个笔石带:(4)Paraorthograptus yuqianensis,(3)Climacograptus venstus,(2)Dicellograptus szechuanensis,(1)Pseudoclimacograptus anhutensis(二)混合相:上部为文昌组,下部为长坞组,(三)壳灰岩相:上部为文昌组，下部为三巨山组，有Toeniolites, Proheliolites等。本区的Dralmdnitina-Hrrnantio层出露清楚，且Da.和H.与Diplograptus bohemicus共生，时代属晚奥陶世晚期。     

内蒙古西部额济纳旗及邻区上石炭统—下二叠统阿木山组的沉积特征和时代

额济纳旗地区是阿木山组分布的最西端,产出于伸展背景下的裂谷环境,火山岩比较发育,从下到上可分为火山岩段、灰岩段和碎屑岩段。火山岩段和灰岩段产丰富的类化石,灰岩段下部产丰富的珊瑚化石。珊瑚化石的时代主要为晚石炭世,类从下到上分别属于Triticites组合和Pseudoschwagerina组合,从而确定阿木山组的3个岩性段之间以叠覆关系为主,地质时代为晚石炭世至早二叠世,其中火山岩段为晚石炭世小独山期或更早;灰岩段下部为小独山期,上部为紫松期;碎屑岩段为早二叠世紫松期或更晚一些至隆林期。     

Age of the Purported Zhanjin Formation in Gêrzê County,Tibet: A New Understanding and Its Significance

The Upper Carboniferous Zhanjin Formation has attracted much attention from geoscientists for containing glacial–marine diamictite and cold-water fauna typified by the bivalve Eurydesma.The presence of this Formation has provided important evidence for determining the northern border of Gondwana.Previous researchers have classified those strata north of Niangrong Co in the Gêrzê region as part of the Zhanjin Formation based on the presence of glacial–marine diamictite, although the absence of biological fossil evidence has defied clear age determination.Our field investigations first discovered large quantities of corals, sponges and bryozoans.All coral fossils were identified as belonging to the Hexacorallia subclass including 13 genera and 25 species, primarily including Conophyllia guiyangensis Deng et Kong, Coryphyllia regularis Cuif, Cuifia columnaris Roniewicz, Distichophyllia norica Frech, Distichophyllia gigas Vinassa de Regny, Pamiroseris rectilamellosa Winkler, Retiophyllia clathrata Emmrich, and Retiophyllia paraclathrata Roniewicz.Extensive biostratigraphic correlations show that the hexacorallia should belong to the Late Triassic, thereby negating the presence of the Zhanjin Formation in the study area.Based on analyses of sedimentary facies and detailed study of the glacial–marine diamictite as supposed by earlier researchers, the limestone blocks and gravels within the facies are slope facies olistostromes and waterway sediments from lime slurry debris flows in the submarine fan rather than primary sedimentary products.Among them, lenticular sandstone should be sequentially distributed waterway sand bodies, indicating that the strata have no glacial–marine diamictite.In addition, the rocks containing the mentioned fossils are just limestone blocks from olistostromes, and limestone gravels from waterways of submarine fans.Such a result further negates the presence of the Zhanjin Formation in the study area, and indicates that the age of the studied strata should be youner than the Late Triassic.Through regional stratigraphic comparisons and the study of tectonic settings of the strata, the sedimentary characteristics of the subject strata, including lithology, lithofacies and fossils, are confirmed to be similar to the widely distributed Sêwa Formation in this region.We thus infer that the strata belong to the Middle–Lower Jurassic Sêwa Formation.This finding is important for both studying paleogeography of Tibet and determining the northern boundary of Gondwana.     

Biostratigraphy,microfacies and depositional environments of upper Viséan limestones from the Burren region,County Clare,Ireland

The Burren region in western Ireland contains an almost continuous record of Viséan (Middle Mississippian) carbonate deposition extending from Chadian to Brigantian times, represented by three formations: the Chadian to Holkerian Tubber Formation, the Asbian Burren Formation and the Brigantian Slievenaglasha Formation. The upper Viséan (Holkerian–Brigantian) platform carbonate succession of the Burren can be subdivided into six distinct depositional units outlined below. (1) An Holkerian to lower Asbian unit of skeletal peloidal and bryozoan bedded limestone. (2) Lower Asbian unit of massive light grey Koninckopora‐rich limestone, representing a shallower marine facies. (3) Upper Asbian terraced limestone unit with minor shallowing‐upward cycles of poorly bedded Kamaenella‐rich limestone with shell bands and palaeokarst features. This unit is very similar to other cyclic sequences of late Asbian age in southern Ireland and western Europe, suggesting a glacio‐eustatic origin for this fourth‐order cyclicity. (4) Lower Brigantian unit with cyclic alternations of crinoidal/bryozoan limestone and peloidal limestone with coral thickets. These cycles lack evidence of subaerial exposure. (5) Lower Brigantian bedded cherty dark grey limestone unit, deposited during the maximum transgressive phase of the Brigantian. (6) Lower to upper Brigantian unit mostly comprising cyclic bryozoan/crinoidal cherty limestone. In most areas this youngest unit is truncated and unconformably overlain by Serpukhovian siliciclastic rocks. Deepening enhanced by platform‐wide subsidence strongly influenced later Brigantian cycle development in Ireland, but localized rapid shallowing led to emergence at the end of the Brigantian. A Cf5 Zone (Holkerian) assemblage of microfossils is recorded from the Tubber Formation at Black Head, but in the Ballard Bridge section the top of the formation has Cf6 Zone (Asbian) foraminiferans. A typical upper Asbian Rugose Coral Assemblage G near the top of the Burren Formation is replaced by a lower Brigantian Rugose Coral Assemblage H in the Slievenaglasha Formation. A similar change in the foraminiferans and calcareous algae at this Asbian–Brigantian formation boundary is recognized by the presence of upper Asbian Cf6γ Subzone taxa in the Burren Formation including Cribrostomum lecomptei, Koskinobigenerina sp., Bradyina rotula and Howchinia bradyana, and in the Slievenaglasha Formation abundant Asteroarchaediscus spp., Neoarchaediscus spp. and Fasciella crustosa of the Brigantian Cf6δ Subzone. The uppermost beds of the Slievenaglasha Formation contain a rare and unusual foraminiferal assemblage containing evolved archaediscids close to tenuis stage indicating a late Brigantian age. Copyright © 2006 John Wiley & Sons, Ltd.     

Characteristics of Breccias and C-O-Sr-S Isotope Geochemistry of the Duocaima Pb-Zn Deposit in Tuotuohe, Qinghai Province: Implications for the Ore-forming Process

The Duocaima carbonate-hosted Pb-Zn deposit is a newly found large deposit in the southern area of Qinghai Province.In this paper, the characteristics, genesis, significance to Pb-Zn mineralization of the widely developed breccias, and the ore-forming process have been carefully studied based on geological documentation of drilling holes, microscopic observations of petrography and microstructure and some stable isotope measurements.Based on the compositions of the clast and matrix, the breccias can be classified into three types: limestone clasts cemented by marl; limestone clasts with fine-grained calcareous materials; and limestone clasts cemented by hydrothermal calcite.The mineralization in the first type of breccia is weak, whereas it is strong in the latter two types of breccias.According to the locations of occurrence and structural characteristics of the breccias along with the relationship between the breccias and mineralization, part of the limestone clasts that are cemented by marl and outcrop in the contact zone between the Wudaoliang Formation(Nw) and the underlying Jiushidaoban Formation(Pj) are attributed to synsedimentary fault-genetic breccia, whereas the last of the limestone clasts that are cemented by marl and developed in the Jiushidaoban Formation(Pj) are attributed to the breccia generated by karst cave collapse; the limestone clasts with fine-grained calcareous materials and the limestone clasts cemented by hydrothermal calcite are attributed to breccia formed by hydrothermal dissolution.The breccia formed by karst collapse had consistently evolved for a long period of time, while the breccias with other origins were formed around the period of mineralization(i.e., about or slightly later than 20–16 Ma).The breccia generated by karst cave collapse and hydrothermal dissolution are somewhat related; the formation of the breccia from karst cave collapse provided open space for the later mineralization and reaction between hydrothermal fluids and host rocks, and the subsequent strong dissolution by hydrothermal fluids transformed some of the breccia formed earlier by karst cave collapse.Meanwhile, carbonate host rocks with breccias and brecciaed mineralization can be a potential sign of Mississippi Valley Type(MVT) deposits and important indicators for regional mineral exploration.The δ13CV-PDB, δ18OVSMOW, and 87Sr/86 Sr values of hydrothermal calcite in the Duocaima deposit range from 4.3‰ to 7.1‰, 14.9‰ to 20.1‰, and 0.707494 to 0.708185, respectively; the δ13CV-PDB, δ18OV-SMOW, and 87Sr/86 Sr values of the host limestones of the Jiushidaoban Formation range from 3.6‰ to 5.3‰, 18.0‰ to 20.5‰, and 0.707372 to 0.707945, respectively.The δ13CV-PDB and 87Sr/86 Sr values of hydrothermal calcite and limestone are similar, indicating single sources of C and Sr in this deposit, with the likely source being the limestone of the Jiushidaoban Formation.The minor scattering of the δ18OV-SMOW values suggests that different O isotope fluids underwent the isotope exchange reaction.The C-O-Sr isotope characteristics indicate that the host limestones experienced a dissolution and precipitation process during mineralization, which is beneficial to improving the porosity of host rocks and promoting the precipitation of metal sulfides.The δ34SV-CDT value of the breccia-type mineralization sulfides ranges from-30.4‰ to-0.3‰; that is, the δ34SV-CDT value is negative with considerable variation, illustrating that during the breccia-type mineralization process, the bacteriogenic reduction of sulfates provided the vast majority of sulfur, whereas the thermochemical reduction of sulfates was relatively unimportant.The brecciation that occurred as a result of karst cave collapse was mainly generated by the dissolution of groundwater; however, the brecciation related to hydrothermal dissolution and mineralization processes were caused by mixing of different fluids.     

伊拉克HF油田上白垩统碳酸盐缓坡相储层发育特征

伊拉克HF油田上白垩统Hartha组灰岩沉积在碳酸盐缓坡环境,储层发育特征及其主控因素尚不明确。通过钻井、测井、岩芯和地震资料,并结合薄片观察、分析化验,研究了该油田Hartha组的岩石学特征、储集空间特征及物性特征,并分析了沉积相和成岩作用对储层发育的控制。结果表明,厚度约50 m的Hartha组的储层岩石类型主要为粒泥灰岩、泥粒灰岩和颗粒灰岩,孔隙度10%～22%,渗透率集中在(0.1～0.5)×10^(-3 )μm^2和(1～5)×10^(-3 )μm^2,基质物性较好。Hartha组上段储集性能相对较好,Hartha组下段发育外缓坡灰泥,储集性较差。沉积作用对储层的物性起着主要控制作用,滩相储层的物性明显好于非滩相。该套灰岩的储集空间为粒间孔、铸模孔、生物体腔孔,以及粒内溶孔和微裂缝。晚白垩世暴露剥蚀期,在表生作用下Hartha A层溶孔部分被胶结物充填,存在局部的强烈胶结带。     

Geochemistry of the limestone of Mortas Formation and related terra rossa,Seydisehir, Konya,Turkey

The purpose of this study was to determine and evaluate the geochemical characteristics of the limestone of the Upper Cretaceous Mortas Formation and related terra rossa in a 50 km² area which is located 20 km south of the city of Seydisehir, Central Anatolia, by using data obtained from the ICP-MS analysis of randomly collected 42 samples of limestone and 18 samples of the terra rossa.The limestone of the Mortas Formation is composed of fossilliferous, gray-cream colored, medium to thick bedded, partially dolomitic carbonate rocks, and generally has dismicrite, intrapelmicrite composition. It includes the largest bauxite reservior in Turkey and has many occurences of terra rossa formation on it. According to mean distance, the Ba, Be, Hg, Mo, Nb, Sb and Th concentrations in the limestones overlying and underlying the bauxite deposits are different, but the main oxides, REE and other trace elements are same. In factor analysis, the first component reflects relative enrichment of clay against to CaO contents of the limestone, the second component corresponds to the degree of dolomitization. The PAAS-normalized REEs pattern for the Mortas Formation limestone samples illustrate similar main features as seawater.The terra rossa soils in the study area are considered to be highly weathered and weakly mature soil with respect to their generally low Al₂O₃ (21%), but high CaO (2%) contents, and their alteration indices. The element ratios in the terra rossa and limestone show that in the process of the transformation from limestone to terra rossa, Ba, Si, Ti, Al and Fe were enriched together by staying in-situ. Except Ce, all lanthanides show similar behavior, but the HREE, which were richer in limestone, were consumed fast relative to the LREE during soil formation. The association and the enrichment of Co, Cu, Cr, Ni and Pb as well as Ba, Zr, Ga, Nb and Rb in soil relative to the limestone are interpreted as being resulted from eolian transportation. Ca, Au, Hg, Sr, Se, Sb, Mo, Ag, U, Cd and Na were found to be the most mobile elements during pedogenic transformation. According to main oxide composition ratios of the limestone and terra rossa, the soils were described as representing a well washed soil completing the leaching and accumulation phase, but not totally completing the silicate weathering phase. In the processes of soil formation, 97.76% of the limestone was washed away; only 2.24% of limestone was deposited as soil. Therefore, 61 times mass reduction was realized.     

南天山大山口下石炭统野云沟组碳酸盐岩岩石学特征及沉积相分析

南天山和静县大山口剖面石炭系野云沟组发育齐全,出露完好,主要由碳酸盐岩及少量碎屑岩组成,总厚度为696.8 m.岩石类型以碳酸盐岩为主,主要包括砾屑灰岩、含陆源碎屑鲕粒灰岩、生物碎屑微晶灰岩、含陆源碎屑砂屑灰岩、微晶灰岩及泥晶灰岩等.野云沟组主要为斜坡相和盆地相沉积,少量为碳酸盐台地相沉积.斜坡相主要发育砾屑灰岩、薄层...     

西藏北部班戈地层分区下白垩统郎山组、康曲组和余穷组地层层序研究

在西藏自治区北部区域地质调查过程中 ,在班戈地层分区的下白垩统郎山组之上发现一套厚约 180 0 m的滨海—浅海相碳酸盐岩、陆源细碎屑岩岩石组合 ,该套组合不属于郎山组定义之内 ,且出露良好、层序稳定、标志清楚、厚度巨大、化石丰富 ,并具有很强的可填图性。因此 ,我们将整合于郎山组之上 ,岩性以杂色微—薄层状钙质泥岩、钙质 (粉 )砂岩与泥质生物灰岩的韵律产出为特征 ,产圆笠虫、腹足类、双壳类等化石的地层命名为康曲组 ;将整合于康曲组之上 ,下部以灰—深灰色中薄层状泥质生物灰岩、圆笠虫泥晶灰岩、钙质泥岩等韵律出现为特征 ,上部以灰色中—厚层状含硅质结核圆笠虫泥晶灰岩、圆笠虫泥晶灰岩夹灰绿色薄层状钙质砂岩为特征 ,富含圆笠虫、腕足类、腹足类、双壳类及海胆等化石的地层定名为余穷组。时代均置于早白垩世晚期     

本溪组-岩石地层和年代地层与穿时性

本溪组指中国北方奥陶系灰岩不整合面之上、石炭-二叠纪含煤岩系之下,由碎屑岩夹灰岩或灰岩凸镜体所组成的一套海陆交互相地层。随着研究的深入,特别是地层学理论的发展及认识的不同,对本溪组岩石地层和年代地层的划分形成了多种争议。本文按地层多重划分的观点和方法认为组是一个岩石地层的自然实体,并有区别于相邻自然实体单位的岩石内容和反映其发育的某一特定过程。为此,建议以层型剖面(本溪市新洞沟与蚂蚁村沟间的牛毛岭)为准,将本溪组岩石地层单位定义到《全国地层多重划分对比研究》的成果上来。即奥陶系灰岩顶部不整合面之上、下蚂蚁沟灰岩底界之下的一套碎屑岩层。从该灰岩层(即华北各地下部第一层灰岩)始,到最上部一层灰岩顶界(如山西太原的东大窑灰岩、河南禹州L8灰岩)为上覆太原组。该组下部产G、F两层铝土页岩,称为湖田段;上部为紫色-杂色富碳岩系(夹一薄煤层或碳质页岩)称为新洞沟段。本溪组的地质时代或年代地层,依据各地所产化石及上覆太原组第一层灰岩(即顶界)所产化石,不同地区时限不同,在吉南-辽东地区为大塘阶-德呜阶;在晋冀鲁为罗苏阶-滑石板阶;而在河南禹州其顶界进入逍遥阶(或小独山阶)-阿瑟尔阶;明显地反映出岩石地层单位穿时的普遍性规律。     

Metallic mineral deposits

Except for the fringing reef, the limestones of Christmas Island in the Indian Ocean are of Late Eocene (Tertiary “b") and Early Miocene (Tertiary “e” to “f") age. The Upper Eocene limestone is an algal limestone containing Discocyclina, Nummulites, and Heterostegina. The Lower Miocene limestone is an algal limestone containing in its lower part species of Lepidocyclina (Eulepidina) followed by Miogypsinoides dehaarti. Miogypsinoides dehaarti extends into the zone of Flosculinella bontangensis. No rocks younger than Burdigalian were identified other than on the fringing reef which contains an assemblage of Pliocene‐Pleistocene Foraminifera.     

Detrital provenance,depositional environment,and palaeogeographic implications of Lower Triassic marine sediments in central Tibet

We present our new investigation into the depositional environment and provenance of the Yingshuiquan Formation in the central Qiangtang region of northern Tibet, in order to further our understanding of the environment of the Longmu Co–Shuanghu Palaeo–Tethys during the Early Triassic. The Yingshuiquan Formation is composed of oolitic limestone, calcareous sandstone, calcarenite, thin-bedded ribbon limestone, bioclastic limestone, and coarse oolite limestone that were deposited in a shallow-marine basin and contain abundant Lower Triassic conodont fossils (e.g. Hadrodontina anceps, Pachycladina sp., gen. et sp, Pachyclaina oblique, Hibbardelloides sp). We selected detrital zircons from four calcareous sandstone samples for U–Pb dating, yielding minimum age peaks of 263, 269, 275, and 280 Ma, respectively, and a minimum age of 249 Ma, based on several zircons around the same age. Analysis of the conodont biofacies and zircon LA-ICP-MS dating of calcareous sandstone indicates that the data is consistent with deposition in the Early Triassic. The Yingshuiquan Formation records Early Triassic shallow-water sediment in the Longmu Co–Shuanghu Palaeo–Tethys, and has a Southern Qiangtang and Northern Qiangtang terranes provenance. During the Early Triassic, the carbonate sediments of the Yingshuiquan Formation were deposited in an active environment around the Longmu Co–Shuanghu Palaeo–Tethys, which has became a residual sea basin.     

The Late Ordovician Wufengian Sediments and the Ordovician-Silurian Boundary in Western Zhejiang Province

The Late Ordovician Wufengian sediments in western Zhejiang include three facies: 1) graptolite shale facies, composed of two parts--the upper part the Yankou Formation, with the Diplograplus bohemicus(graptolite) zone and Dalmanitina sp.(trilobite), and the lower part the yuqian Formation with four graptolite zones:(4) the Paraorthograptus yuqianensis zone,(3) the Climacograptus venustus zone,(2) the Dicellograptus szechuanensis zone and(1) the Pseudoclimacograptus anhuiensis zone; 2) mixed facies, consisting of the Wenchang Formation in its upper part and the Changwu Formation in its lower; and 3) shelly limestone facies, whose upper and lower parts are separately the Wenchang Formation and Sanjushan Formation, containing Taeniolites, Proheliolites, etc. In this region the Dalmanitina-Hirnantia bed is well exposed,and Da. and H. are associated with Diplograptus bohemicus, belonging to the late Late Ordovician.The Ordovician-Silurian boundary is drawn as follows:(1) for the graptolite facies, it lies between the Diplograptus bohemicus zone and Glyptograptus persculptus zone;(2) for the graptolite-sheny limestone facies(brachiopod fauna), it is placed between the top of the Diplograptus bohemicus zone and the base of the horizon with the Eospirifer fauna; and 3) for the shelly facies(brachiopod fauna), it is drawn between the top of the horizon with the Dalmanitina-Hirnantia fauna and thebase of the horizon with the Eospirifer fauna.     

重庆南川地区中二叠统茅口组眼球状灰岩成因

中二叠世茅口组中-下部发育一种特殊的眼球状灰岩, 眼球部分通常为颜色较浅, 富含生屑颗粒的灰岩; 而眼皮部分通常为颜色较暗的泥灰岩。其成因一直存在分歧。本文通过对重庆南川大铺子剖面茅口组底部眼球状灰岩的野外观察和室内研究, 认为陆源输入的改变导致眼球和眼皮部分泥质含量的差异; 在成岩过程中, 碳酸盐沉积物为主的眼球部分因为胶结作用而没有被机械和压实作用破坏, 泥质含量较多的眼皮部分则受到强烈的压实。因此, 该地区眼球状灰岩的形成是沉积和成岩过程相互作用的结果, 为浅海陆棚沉积环境。     

滇西南昌宁—孟连构造带火山岩地层学研究

昌宁—孟连构造带火山岩非常发育,是重要的含矿岩系。在构造带南段,火山岩统称为依柳组,北段统称为平掌组下段,以往时代均归属早石炭世。本文工作表明,该区火山岩可分为两套:一套为早石炭世火山岩,分布于该构造带西部,以拉斑玄武岩系列为主,代表大洋中脊、洋岛残留物,仍称为依柳组;另一套为晚二叠世火山岩,分布于构造带中、东部,以碱性玄武岩系列为主,可能属亚速尔型洋岛火山岩范畴,而非大洋蛇绿岩套,新命名为老厂组。     

东准噶尔巴塔玛依内山组火成岩锆石U-Pb年龄及其地质意义

以东准噶尔双井子地区巴塔玛依内山组和石钱滩组剖面为研究对象,通过岩矿鉴定、地球化学分析、锆石U-Pb定年和牙形刺挑选等方法,对巴塔玛依内山组和石钱滩组的年代学特征进行了研究。结果表明,巴塔玛依内山组火山岩的形成时间始于348. 7±2. 9Ma,318. 7±4. 2Ma之后结束,侵入岩的形成时间为255. 9±3. 5Ma,这些样品中普遍含有捕获锆石,这些锆石具有岩浆锆石的特征,年龄介于早石炭世杜内期和前寒武纪之间(354. 7～971. 2Ma),与盆地周边发育的岛弧火成岩和蛇绿岩年龄相仿,此外在石钱滩组灰岩内得到4颗牙形刺化石,分属于2个属,分别为Idiognathodus和Streptognathodus。以此为基础,通过搜集整理前人数据,得到如下结论:(1)巴塔玛依内山组火山岩地层是穿时的,从早石炭世到晚石炭世连续发育,形成时间介于348. 7±2. 9Ma～300. 4±1. 3Ma之间;(2)巴塔玛依内山组上部的石钱滩组形成于318. 7±4. 2Ma之后的晚石炭世;(3)卡拉麦里蛇绿岩所代表的准噶尔洋盆闭合时间在晚泥盆世法门期和348. 7Ma之间;(4)准噶尔盆地基底可能由岛弧和洋壳组成,且存在前寒武纪基底。本研究旨在确定巴塔玛依内山组和石钱滩组地层时代,并为卡拉麦里洋闭合时限以及盆地基底性质等问题的解决提供依据。