中国三北地区荒漠化区域分类与发展趋势综合研究

中国北方土地荒漠化主要受青藏高原隆升以来形成的构造－沉积特征、水文地质条件、全球气候变化、尤其是亚洲季风等地质背景控制。本文仅对北方沙质荒漠化、水蚀荒漠化两种主要的荒漠化类型的区域地质分布、成因及其发展趋势进行探讨。三北地区沙质荒漠化依成因可分为：就地起沙型、风沙侵入型和土地粗粒化型等。就地起沙型沙质荒漠化主要分布在西部内陆盆地周缘冲洪积扇上，中东部高原、冲积平原上的沙漠边缘地带、沙地内部和流经这些沙漠和沙地的古河道，以及河湖相砂质沉积物和以砂质沉积物为母质的土壤分布区；风沙侵入型沙质荒漠化主要分布在上述沙漠、沙地边缘的下风地带，如巴丹吉林沙漠和腾格里沙漠的东南缘、毛乌素沙地以南的覆沙黄土区、科尔沁沙地以东的辽河平原等；土地粗化主要分布在西部盆地沙漠与戈壁的过渡地带、中东部高原砾质沙草原。沙质荒漠化在毛乌素、科尔沁和浑善达克等沙地、河西走廊的局部地区有所逆转，但三北地区总体上仍呈恶化趋势，尤其是以地表土壤粗化为主的沙质荒漠化的发展更应引起人们的关注。水蚀荒漠化依地质背景之不同可分为土漠化和岩漠化两类，前者主要分布在北方中部黄土高原地区、内蒙古科尔沁沙地南侧的黄土分布区等；后者主要分布于太行山北部、辽宁西北部的基岩山区。晋陕蒙交界地带、甘肃平凉北部、定西地区和科尔沁沙地东南的蒙辽交界处等地水蚀荒漠化形势严峻；以小流域水土流失为主的治理工程使陕西的吴旗、延安、洛川等地和朝阳河中上游地区水蚀荒漠化有所好转。总之，第四纪以来的构造－沉积特征控制着不同类型荒漠化的区域分布，气候变化和水文地质条件控制着漠化的进程，人类不合理的经济活动则更是荒漠化过程的催化剂，尽管在局部、在一定的时间段内可使这一过程得以缓解甚至逆转。     

苏鲁变质带北部的岩石构造单元及结晶块体推覆构造

虽然苏鲁变质带北部的超高压变质岩石的类型及其特征与大别山超高压带相似,但是要划出与大别山相对应的岩石构造单元是困难的。详细的区域地质、岩石学、同位素年代学及地球化学的研究已将超高压带的西界大致圈定在牟平断裂至米山断裂的范围内。特别需要提出的是,在荣成超高压变质岩石分布区的南北两侧,出露有3 种不同成因的麻粒岩,即榴辉岩化的麻粒岩;由超高压变质岩经高压升温变质作用生成的麻粒岩;以及未经过榴辉岩相变质的麻粒岩。它们有规律地成带分布。这些麻粒岩带以及在荣成地区出露的未经过麻粒岩相叠加变质的超高压变质带,各自都有着完全不同的变质历史,并且都以深大韧性剪切带为其边界。由此笔者将苏鲁变质带北部由南向北划分为海阳所变质地块(榴辉岩化扬子陆块基底变质单元)、荣成变质地块(超高压变质单元)、威海变质地块(麻粒岩相叠加变质的超高压构造岩片)、昆嵛山边界杂岩带。这些来源于地壳深层的结晶块体是超高压带形成和演化的产物,在后来的进一步碰撞挤压中,这些来源于深层而就位于中上地壳水平的结晶块体,有可能发生了与薄皮构造机制(thin-skin thrust)类似的构造过程。它们有如一系列的推覆体挤压叠置,使华北和华南陆块最后挤压在一起。     

黔西北地区铜炉上铅锌矿床地质特征及找矿方向

论述了黔西北地区铜炉上铅锌矿床产出的地质背景、铅锌矿床地质地球物理、地球化学及遥感影像特征,结合区内开展深部工程验证发现富厚铅锌矿体的成功经验,指出今后在该区深部及外围的找矿方向。     

THE PALEOCURRENT PATTERN OF EARLY TERTIARY REDBEDS IN THE HOH XIL BASIN,NORTHERN TIBET PLATEAU:IMPLICATIONS FOR AN EARLY UPLIFT AND UNROOFING

THE PALEOCURRENT PATTERN OF EARLY TERTIARY REDBEDS IN THE HOH XIL BASIN,NORTHERN TIBET PLATEAU:IMPLICATIONS FOR AN EARLY UPLIFT AND UNROOFING     

天山北麓活动构造基本特征

在近ＳＮ向强烈挤压下,天山北麓发育了两个不同类型的大型逆冲推覆构造,一是乌鲁木齐以西具有典型断裂扩展褶皱特征的依连哈比尔尕山山前推覆构造,二是乌鲁木齐以东博格达山前弧形推覆构造;同时水平剪切作用成了大型斜切天山的右旋走滑断裂。ＮＷ－ＮＮＷ向的博罗科努一阿齐克库都克断裂切割天山,右旋走滑特征非常清楚。天山北麓的应变分配特征在内陆造山带中具有典型性。     

南海北部深水区油气勘探的关键地质问题

南海北部深水区已经获得了重大的天然气发现,正逐渐成为全球深水勘探的热点区之一。通过与相邻陆架区以及世界上典型深水盆地的类比发现,南海北部深水区具有独特的石油地质特征。南海北部大陆边缘经历了从燕山期主动陆缘向新生代边缘海被动陆缘的转变,其演化过程和成盆机制复杂;陆坡深水区具“热盆”特征,凹陷普遍发育超压,其生烃机制不明;深水区距离物源区较远,缺乏世界级大河系的注入,具远源沉积特征,未发现盐层及其相关构造,其油气成藏条件具有特殊性。此外,南海北部深水区海底地形崎岖、多火山,还面临着地震采集、处理等地球物理难题。因此,南海北部深水油气勘探需要在借鉴相邻陆架区和世界其他深水区成功经验的基础上,一方面深入研究其独特的油气地质特征,另一方面研发适应于我国深水环境的地球物理新技术,切实推动深水勘探的进程。     

Revised Mesozoic–Cenozoic orogenic architecture and gold metallogeny in the northern Circum-Pacific

The orogenic collages of the northern Circum-Pacific between Japan and Alaska revealed an endowment of about 450 Moz Au in various deposit types and diverse Mesozoic–Cenozoic tectonic settings. The area consists of predominantly late Paleozoic to Cenozoic turbidite to island arc terranes as well as Precambrian cratonic terranes that can be grouped into the Kolyma–Alaska, Kamchatka–Aleutian, and Nipponide collages. The latter can be linked via the Mongol–Okhotsk suture with the late Paleozoic to early Mesozoic terranes in the Mongolides.The early Yanshanian magmatic arc terranes in the fossil Kolyma–Alaska collage host copper–gold porphyry deposits, which have only recently received much attention. Exploration has revealed a large and growing gold endowment of more than 30 Moz Au in some individual deposits, with smaller role of epithermal deposits. This mineralization, formed at 140–125 Ma, is partly coeval with the collisions of magmatic arcs with the passive margin sequences of the Siberian craton and related granitoid magmatism. About 200 Moz of gold is known in the Kolyma–Alaska collage in the Mesozoic orogenic gold deposits and related Quaternary placers. The Central Kolyma, Indigirka, South Verkhoyansk, and North Chukotka subprovinces of the collage revealed an endowment of more than 10 Moz Au each. A similar and coeval event in the Mongolides in relation to the collision between Siberia and North China is largely reflected in still poorly dated intrusion-related gold deposits clustered along the Mongol–Okhotsk suture.The overlapping Yanshanian magmatic arcs in Transbaikalia and northeast China and the Okhotsk–Chukotka magmatic arc in the Russian Far East stitch the Kolyma–Alaska collage with the Paleozoic Central Asian supercollage and adjacent cratons. While the Okhotsk–Chukotka arc reveals a relatively simple and broad oroclinal pattern, the Yanshanian arcs in Mongolia, and NE China form a tightly deformed giant Z-shaped feature that was bent in response to the southward movement of the Siberian craton and northward translation of the Nipponides and North China craton to close the Mongol–Okhotsk suture in late Jurassic to Cretaceous times. The Yanshanian arcs host mostly small to medium-sized 100–70 Ma Au–Ag deposits, with the largest endowment discovered in the Baley district in Transbaikalia and at Kupol in the northern part of the Okhotsk–Chukotka arc. Some intrusion-related gold deposits were formed synchronously with this arc magmatism, with the largest known examples in the Tintina belt in Alaska formed at 104 and 93–91 Ma.The Kamchatka–Aleutian collage is still evolving in front of the westward-subducting Pacific plate. It's late Cretaceous to Paleogene magmatic arc rocks form immature island arc terranes, extending from the Aleutian islands towards the Nipponides via Kamchatka peninsula, Kuril islands and eastern Sakhalin. However, in the Nipponides, the Sikhote–Alin portion of the magmatic arc overlaps the Mesozoic turbidite terranes. The oroclinal pattern of this more than 8000 km-long magmatic arc indicates its westward translation in agreement with the movement of the Pacific plate so that the arc is presently colliding with itself along the island of Sakhalin, a seismically active intraplate lineament and a boundary between the Nipponide and Kamchatka–Aleutian collages. This magmatic arc is usually interpreted to be of intra-oceanic origin, with subsequent docking to Asia from the south; however, presence of the Sea of Okhotsk cratonic terrane between Sakhalin and Kamchatka suggests that it may be rather considered as an external arc system that separated from the rest of Asia due to backarc spreading events, therefore, forming the most external arc system at the active margin with the Pacific plate. The subduction-related events in the collage produced numerous late Mesozoic to Cenozoic 1–3 Moz gold epithermal deposit in Kamchatka and Sikhote–Alin as well as Au–Cu porphyry deposits, with currently largest gold endowment in the pre-Tertiary Pebble Copper deposit in Alaska. The westward translation of the Kamchatka–Aleutian collage might have controlled the emplacement of this porphyry deposit, as well as up to 30 Moz into intrusion-related gold deposits at 70–65 Ma in the Kuskokwim belt, immediately north from the porphyry cluster.     

新疆希勒库都克铜钼矿床硫同位素特征及成矿物质来源探讨

位于东准噶尔北缘的希勒库都克铜钼矿床是一个以钼为主的斑岩型矿床,形成于早石炭世。希勒库都克铜钼矿床硫化物δ34S值介于+0.4‰~+7.6‰之间,平均为+4.1‰,其中黄铁矿δ34S值为+0.4‰~+7.6‰(平均+4.2‰)、辉钼矿δ34S值为+3.2‰~+4.7‰(平均+4.2‰)、黄铜矿δ34S值为+1.6‰~+2.5‰(平均+2.1‰),均显示出岩浆硫的组成特征。硫化物稀土元素特征与含矿斑岩类似,暗示成矿物质可能来源于含矿斑岩;流体包裹体地球化学及H-O同位素特征也表明成矿流体主要来自岩浆热液。而含矿斑岩高的正εNd(t)值、低的87Sr/86Sr初始比值表明含矿岩浆可能主要来自于地幔源区。综合研究区硫化物硫同位素、稀土元素及流体包裹体地球化学特征等分析,本文认为希勒库都克铜钼矿床成矿物质主要来自地幔源区,且含矿岩浆可能经历了地壳深部壳幔物质混合均一化的过程。     

大别山北缘西段双桥中生代火山岩地球化学及锆石U-Pb同位素年代学

首次对大别山北缘西段(河南省境内)中生代火山岩进行了锆石原位U-Pb同位素测年。结果表明,罗山县双桥火山岩集中区石英安山岩锆石LA-ICP-MS U/Pb年龄为133.1±1.5 Ma,与大别东段中生代火山岩主体毛坦厂组的时代一致,属早白垩世,稍早于或与大别山区大规模花岗岩岩基侵位时代相同;与长江中下游地区的宁芜和庐枞盆地火山岩喷发时间同步,可能同属中国东部中生代巨量岩浆活动的重要组成部分,与太平洋板块斜向俯冲引起的大陆岩石圈重力不稳而产生的拆沉导致岩石圈强烈减薄深部动力学过程相联系。大别山西段早白垩世火山岩属高钾钙碱性系列粗安岩-英安岩-流纹岩组合。中酸性火山岩显示轻稀土元素富集、重稀土元素强烈亏损、弱或基本无负Eu异常的稀土元素配分模式以及高Sr低Yb特征,反映岩浆部分熔融源区残余有石榴石,说明当时存在加厚的成熟陆壳。高(87Sr/86Sr)i(0.707 56)、极低的εNd(t)(-20.1)和大离子亲石元素富集、高场强元素Nb、Ta明显亏损,显示岩浆源区的壳源性质。以上特征反映大别山地区该时期岩石圈伸展程度和软流圈上涌规模远不如长江中下游同时期以幔源为主的中基性火山岩发育的宁芜和庐枞地区。     

桐柏山造山带南麓随州群变沉积岩中碎屑锆石的年代学及其地质意义

扬子克拉通北缘的随州——枣阳地区是整个秦岭——桐柏山——大别山——苏鲁造山带及其前陆地区受晚三叠世(印支期)扬子板块向华北板块深俯冲并发生高压——超高压变质作用影响最小的地区,因而扬子克拉通北缘的前寒武纪基底在这里得到了较多的保存。它们不仅为研究扬子克拉通北缘新元古代构造环境提供了难得的样品,也为研究造山带内变质杂岩的原岩性质提供了参照物。出露的前寒武纪基底包括新元古代的变质火山——沉积岩系(随州群)以及大量的超镁铁质——镁铁质岩床群。本文用LA-ICP-MS锆石U-Pb法对随州群中变质沉积岩中的碎屑锆石进行了系统的年代学研究,结果表明:①随州群变质沉积岩中最年轻碎屑锆石的年龄约为720Ma,表明随州群的主要沉积作用应晚于该时间;②年龄介于700～1000Ma时间段的锆石颗粒构成了随州群变质沉积岩中最大的碎屑锆石群体,峰值在800Ma左右,说明新元古代,尤其是新元古代中、晚期形成的岩浆岩是随州群沉积岩最重要的一个物源;③随州群变质沉积岩中也出现了较多1700～2100Ma年龄段的锆石颗粒,说明古元古代中、晚期形成的岩浆岩也是随州群沉积岩的重要物源之一;④随州群沉积岩具有古元古代早期,甚至太古代年龄的碎屑锆石,说明扬子克拉通北缘可能存在层位相当的物源。