基于地球物理方法预测二连盆地及邻区晚古生代潜在烃源岩分布

二连盆地及邻区是我国油气勘探的重点区域之一,普遍认为烃源岩层主要分布在中生代地层,对其晚古生代地层的烃源岩潜力研究较少,本文对研究区内晚古生代碳酸盐岩及泥岩进行了有机地球化学实验并分析其烃源岩潜力,评价结果表明二连盆地及邻区内晚古生代地层具有一定的生烃潜力,受高成熟度的影响,剩余潜力以生气能力为主.依据研究区内电法剖面、布格重力异常特征及磁性资料认为晚古生代潜在烃源岩层具有"低电阻、高密度、弱磁性"的地球物理性质,并初步预测了二连盆地及邻区晚古生代的深度大致分布在3～5km的范围内,进一步利用优化后的小子域滤波重力异常分离技术对晚古生代地层进行了厚度预测,刻画其平面分布特征,认为研究区内的晚古生代地层具有两个分布中心,其中心区厚度范围为1000～2000m之间,与野外地质剖面的厚度基本一致,晚古生代潜在烃源岩的平面预测可以为二连盆地油气勘探工作提供新方向.     

The Permian seamount stratigraphic sequence in Chiang Mai,North Thailand and its tectogeographic significance

The widespread Permian carbonate strata outcropped in northwestern Thailand are considered as the evidence for the Late Paleozoic shallow Tethys. Our investigation, however, shows that basalt can be discovered usually under the Permian carbonate sequence in Chiang Mai-Fang area, northwestern Thailand. The basalt belongs to subalkalic basalt and potassic trachybasalt. They are characterized by high P and Ti in major elements, by high content, enriching LREE, lacking δEu anomaly in rare earth elements, and by enrichment of the large ion lithophile element (LILE) (K, Rb, Ba) and high field strength element (HFSE) (Nb, Ta, Zr) in trace elements, which can be compared with the characters of the oceanic island basalt in Three Rivers (Jinsha River, Lancang River, and Nujiang River) area, southwestern China. Therefore, the Permian carbonate in the studied area was deposited on a sea-mount, rather than on a stable carbonate platform. The oceanic basin is correlated to the Late Paleozoic ocean represented by the Changning-Menglian Belt in southwestern China and they are a major basin of the Paleo-Tethyan Archipelagoes Ocean. The result indicates nonexistence of a Shan-Thai Block in the Late Paleozoic.     

Paleomagnetic constraints on the tectonic history of the major blocks of China duing the Phanerozoic

Paleomagnetic study of China and its constraints on Asia tectonics has been a hot spot. Some new paleomagnetic data from three major blocks of China. North China Block (NCB), Yangtze Block (YZB) and Tarim Block (TRM) are first reported, and then available published Phanerozoic paleomagnetic poles from these blocks with the goal of placing constraints on the drift history and paleocontinental reconstruction are critically reviewed. It was found that all three major blocks were located at the mid-low latitude in the Southern Hemisphere during the Early Paleozoic. The NCB was probably independent in terms of dynamics. its drift history was dominant by latitudinal placement accompanying rotation in the Early Paleozoic. The YZB was close to Gondwanaland in Cambrian, and separated from Gondwanaland during the Late-Middle Ordovician. The TRM was part of Gondwanaland, and might be close to the YZB and Australia in the Early Paleozoic. Paleomagnetic data show that the TRM was separated from Gondwanaland during the Late-Middle Ordovician, and then drifted northward. The TRM was sutured to Siberia and Kazakstan blocks during the Permian, however, the composite Mongolia-NCB block did not collide with Siberia till Late Jurassic. During Late Permian to Late Triassic, the NCB and YZB were characterized by northern latitudinal placement and rotation on the pivot in the Dabie area. The NCB and YZB collided first in the eastern part where they were located at northern latitude of about 6°—8°, and a triangular oceanic basin remained in the Late Permian. The suturing zone was located at northern latitude of 25° where the two blocks collided at the western part in the Late Triassic. The collision between the two blocks propagated westward after the YZB rotated about 70° relative to the NCB during the Late Permian to Middle Jurassic. Then two blocks were northward drifting (about 5°) together with relative rotating and crust shortening. It was such scissors-like collision procedure that produced intensive compression in the eastern part of suturing zone between the NCB and YZB, in which continental crust subducted into the upper mantle in the Late Permian, and then the ultrahigh-pressure rocks extruded in the Late Triassic. Paleomagnetic data also indicate that three major blocks have been together clockwise rotating about 20° relative to present-day rotation axis since the Late Jurassic. It was proposed that Lahsa Block and India subcontinent successively northward subducted and collided with Eurasia or collision between Pacific/Philippines plates and Eurasia might be responsible for this clockwise rotating of Chinese continent.     

Paleomagnetic poles and polarity zonation from Cambrian and Devonian strata of Arizona

Basal Paleozoic Tapeats Sandstone (Early and Middle Cambrian) in northern and central Arizona exhibits mixed polarity and a low-latitude paleomagnetic pole. Carbonates of Middle and early Late Cambrian age, and directly superposed carbonate and carbonate-cemented strata of latest Middle(?) and early Late Devonian age, are characterized by reversed polarity and high-latitude poles. The high-latitude Middle Cambrian pole, which appears to record a large but brief excursion of the polar wandering path, is considered provisional pending additional work. The Devonian data from Arizona indicate that a shift of the pole to a “late Paleozoic” position had occurred by Middle Devonian time.     

鄂尔多斯盆地晚古生代以来古地磁研究

在鄂尔多斯盆地的韩城、铜川等7条剖面144个采样点上,采集了下二叠统至下白垩统的样品约1500个.分别在中国、英国、法国的4个古地磁实验室中进行测试和实验研究.样品均经系统热退磁或交变退磁处理.数据经主向量分析、部分线性谱分析,以分离剩磁成分和选取特征剩磁方向.全部特征剩磁方向通过了倒转检验,晚二叠世和早、中三叠世的结果还通过了广义褶皱检验.并做了大量磁化率、等湿剩磁、薄片岩矿鉴定和少量居里温度测定的实验研究. 所得数据以世（统）为单位计算了古地磁极位置和采样地区古纬度,绘制了鄂尔多斯盆地晚古生代以来视极移曲线和地块古方位变化图,提出了华北地块运动模式,并通过与现有的华南地块资料的综合对比分析,提出华北地块与华南地块的碰撞在东部始于晚三叠世之前,全部拼合完成于中侏罗世末.     

Long-lived Paleotethyan pelagic remnant inside Shan-Thai Block: Evidence from radiolarian biostratigraphy

The Shan-Thai Block, regarded traditionally as awhole geotectonic unit by the geologists engaged inthe study of geotectonic evolution of Southeast Asia, issituated to the west of the Ailaoshan and Nan-UttaraditSutures and to the east of the Shan Boundary Faults,and covers southwestern Yunnan, eastern Myanmar,most of Thailand, northwestern Laos, western Malay-sia, and Sumatra[1,2] (fig. 1). However, recent researchshows that it consists of two continental terranes fromGondwana and Cathay…     

Paleozoic sedimentation and tectonics in Korea: A review

Abstract The geological history of the Korean Paleozoic is recorded in lower and upper Paleozoic strata, mostly distributed in two relatively large sedimentary basins, the Taebaeksan and Pyeongnam basins. The lower Paleozoic sedimentary rocks are exclusively of marine origin, dominated by shallow platform carbonate rocks with minor interbedded siliciclastic rocks. The development of the lower Paleozoic sequence was mostly controlled by eustatic changes, having cyclic sedimentation of various temporal scales. During the early Paleozoic the Korean Peninsula was located in a low‐latitude tropical region and experienced frequent storm activities. The upper Paleozoic sequence comprises paralic to non‐marine rocks with minor limestone intercalations in the lower part of the sequence. Upsection changes in sandstone composition and mudrock geochemistry of the upper Paleozoic Pyeongan Supergroup in the Samcheok coalfield indicate that sediments may have been derived from the continued uplift and unroofing of a collisional orogen source. There exists a great unconformity between the lower and upper Paleozoic strata, which spans the geological time from the Late Ordovician to Early Carboniferous. The unconformity period is conventionally thought to be of non‐deposition, but a recent study suggests that it is characterized by continuous sedimentation and significant removal (>1 km thick) of sediments by erosion. No Paleozoic tectonic history has been addressed so far, and thus it needs further study to elucidate geological events during the middle–late Paleozoic in the Korean Peninsula. Tectonostratigraphic correlation of the Korean Peninsula with neighboring Chinese blocks has been a hot issue for a long time. Although the eastward extension of the Chinese collision belt has been recently suggested to be the Imjingang belt located in the middle of the peninsula, further studies are needed to test this hypothesis because results of recent paleontological, sedimentological and stratigraphic studies on Paleozoic sediments are not in agreement with this possibility.     

Lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt

Swarms of mafic-intermediate volcaniclastic bodies occur in the Minggang region of Henan Province, a tectonic boundary between the North Qinling and the North China Block, and emplaced at (178.31±3.77) Ma. These volcanic rocks are subalkaline basaltic andesites and contain abundance of lower crust and mantle xenoliths. Thus this area is an ideal place to reveal the lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt. Geochemical data indicate that these mafic granulites, eclogites and metagabbros have trace elemental and Pb isotopic characteristics very similar to those rocks from the South Qinling Block, representing the lower part of lower crust of the South Qinling which subducted beneath the North China Block. Talcic peridotites represent the overlying mantle wedge materials of the North China Block, which underwent the metasomatism of the acidic melt/fluid released from the underlying lower crust of the South Qinling Block. Deep tectonic model proposed in this paper is that after the Late Paleozoic South Qinling lithosphere subducted northward and decoupled, the upper part of the lithosphere emplaced under the North Qinling and the lower part continuously subducted northward under the North China Block. In Early Mesozoic, the North Qinling Block obducted northward and the North China Block inserted into the Qinling orogenic belt in a crocodile-mouth shape.     

Lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt——On deep-seated xenoliths in Minggang region of Henan Province

Swarms of mafic-intermediate volcaniclastic bodies occur in the Minggang region of Henan Province, a tectonic boundary between the North Qinling and the North China Block, and emplaced at (178.31±3.77) Ma. These volcanic rocks are subalkaline basaltic andesites and contain abundance of lower crust and mantle xenoliths. Thus this area is an ideal place to reveal the lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt. Geochemical data indicate that these mafic granulites, eclogites and metagabbros have trace elemental and Pb isotopic characteristics very similar to those rocks from the South Qinling Block, representing the lower part of lower crust of the South Qinling which subducted beneath the North China Block. Talcic peridotites represent the overlying mantle wedge materials of the North China Block, which underwent the metasomatism of the acidic melt/fluid released from the underlying lower crust of the South Qinling Block. Deep tectonic model proposed i     

宁夏卫宁北山南缘断层探测与活动性初步鉴定

宁夏卫宁北山位于青藏高原、阿拉善和鄂尔多斯3大活动地块的交汇地带,查清该地区的活断层对厘清活动地块边界和规划中卫工业园区布局均具有重要意义。采用浅层地震勘探、钻孔联合剖面探测及槽探等手段,针对卫宁北山南缘推测断层开展综合探测,以便查清该断层展布情况和地层断错特征,并结合区域地层时代对比,初步鉴定已探明断层的活动性。结果表明：前人推测的地貌陡坎之下的卫宁北山南缘正断层并不存在,而在卫宁北山南缘地貌陡坎偏北基岩内发育一条逆冲断层,浅层地震勘探剖面揭示该断层上断点埋深35～40 m,钻孔联合剖面探测和槽探发现断层错断了石炭系和新近系,但未错断上覆的上更新统,表明该断层不是活动断层;另外,浅层地震剖面揭示在中卫盆地内部还发育一条北西西向的隐伏正断层,上断点埋深约60 m,但也未错动晚更新世以来地层,因而推测该断层不存在晚第四纪活动性。     

Remelting of subducted continental lithosphere: Petrogenesis of Mesozoic magmatic rocks in the Dabie-Sulu orogenic belt

The Dabie-Sulu orogenic belt was formed by the Triassic continental collision between the South China Block and the North China Block. There is a large area of Mesozoic magmatic rocks along this orogenic belt, with emplacement ages mainly at Late Triassic, Late Jurassic and Early Cretaceous. The Late Triassic alkaline rocks and the Late Jurassic granitoids only crop out in the eastern part of the Sulu orogen, whereas the Early Cretaceous magmatic rocks occur as massive granitoids, sporadic intermedi- ate-ma...     

Ancient volcanic glasses of the Urals

The existing data on findings of unaltered volcanic glasses in the Paleozoic (from Late Ordovician to Late Devonian inclusive) volcanic strata of the Ural fold belt are systematized. These glasses have compositions that correspond to tholeiitic basalts, potassic alkaline basaltoids, andesites, and rhyolites. Relic portions of glasses of cenotypal appearance are preserved in thick glassy crusts of pillow lava flows, in fragments among hyaloclastites, in bombs from tuffs, and in extrusive bodies and dykes. Chemical analysis showed that the amount of dissolved water was low (1–1.3 wt %) in the primary tholeiitic magma and higher (8–10 wt %) in the magma that formed island-arc hyalobasalts, potassic alkaline basaltoids, andesites and rhyolites.     

The Langjiexue Group is an in situ sedimentary sequence rather than an exotic block: Constraints from coeval Upper Triassic strata of the Tethys Himalaya(Qulonggongba Formation)

The Upper Triassic Langjiexue Group in southeastern Tibet has long been an enigmatic geological unit. It belongs tectonically to the northern Tethys Himalayan zone, but provenance signatures of the detritus it contains are significantly different from those of typical Tethys Himalayan sandstones. Because the Langjiexue Group is everywhere in fault contact with Tethys Himalayan strata, its original paleogeographic position has remained controversial for a long time. According to some researchers, the Langjiexue Group was deposited onto the northern edge of the Indian passive continental margin, whereas others interpreted it as an independent block accreted to the northern Indian margin only during final India-Asia convergence and collision in the Paleocene. This study compares the Langjiexue Group and coeval Upper Triassic strata of the southern Tethys Himalayan zone(Qulonggongba Formation). Our new provenance data indicate that Qulonggongba Formation sandstones contain common felsic volcanic rock fragments, minor plagioclase, and euhedral to subhedral zircon grains yielding Late Paleozoic to Triassic ages. These provenance features compare well with those of the Langjiexue Group. Because the Qulonggongba Formation certainly belongs to the Tethys Himalayan zone, the provenance similarity with the Langjiexue Group indicates that the latter is also an in situ Tethys Himalayan sedimentary sequence rather than part of an exotic block. Volcanic detritus including Late Paleozoic to Triassic zircon grains in both Langjiexue Group and Qulonggongba Formation are interpreted to have been derived from the distant Gondwanide orogen generated by Pan-Pacific subduction beneath the southeastern margin of Gondwana. The Qulonggongba Formation, deposited above marlstones of the lower Upper Triassic Tulong Group, is overlain by India-derived coastal quartzose sandstones of the uppermost Triassic Derirong Formation. Deposition of both the Qulonggongba Formation and the Langjiexue Group were most likely controlled by regional tectonism, possibly a rifting event along the northern margin of Gondwana.     

Characteristics of magnetic carriers responsible for Late Paleozoic remagnetization in carbonate strata of the mid-continent, U.S.A.

Magnetic analysis of carbonate strata of the mid-continent region of the United States indicates that the Late Paleozoic remagnetization already recognized in the Appalachians also affects almost the entire mid-continent. Magnetic intensity is regionally variable, with more intense magnetizations occurring on intracratonic arches. Magnetization is carried predominately by magnetite, which often occurs in tiny hollow spheroids composed of well formed octahedral microcrysts. Spheroid chemistry and morphology suggests that the magnetite is authigenic, composed of iron extracted from pre-existing pyrite or clay. The timing of the remagnetization, the character of the magnetite, and the regional variation in magnetic intensity support the idea that the remagnetization is a diagenetic consequence of tectonically-driven brine migration.     

Absolute reconstructions of the Paleozoic oceans

The orientation of three intraplate magmatic belts—the Mongolian (from 130 to 280 m.y.), South Siberian (from 320 to 400 m.y.) and Baltic (from 365 to 400 m.y.) belts—which can be considered as hot spot tracks, are used together with apparent paleomagnetic pole wander paths to reconstruct true motions of continents during Paleozoic times. The reconstructions obtained show that the old, Late Precambrian Pangea continued to exist in the Early Paleozoic with an inner arrangement of constituent continents strongly different from that of the Late Paleozoic Pangea. The continents were constantly located in the eastern hemisphere only. The western hemisphere was occupied by the Paleo-Pacific oceans. Four oceans existed in Paleozoic times between the continents in the eastern hemisphere: (1) the Iapetus which originated in the Late Precambrian and closed before Devonian times (400 m.y.), (2) the Asiatic paleo-ocean which originated in the Late Precambrian and closed 450 m.y. ago, (3) the Uralian paleo-ocean which opened around 500 m.y. ago and closed in the latest Permian (240–230 m.y.), (4) the Paleo-Tethys which opened in the Ordovician (480–450 m.y.) and became the Mesozoic Tethys. Life duration of the oceans was 200–400 m.y. The main trend in the Earth's evolution during the Paleozoic was a break up of the old, Precambrian Supercontinent and construction of the new, Late Paleozoic Pangea.     

从沉积特征研究格尔木－额济纳旗地学断面走廊域地体的构造演化史

将格尔木－额济纳旗地学断面走廊域及其邻区划分为１４个地体，分属扬子－华南、华北－柴达木、塔里木和哈萨克斯坦－准噶尔４个板块，其间为规模不等的洋盆所分隔．从中元古代以来，上述板块经历了开裂到碰撞、拼合的复杂过程．主要的事件包括：早古生代时期祁连小洋盆的闭合、柴达木－祁连重新和华北拼合；石板井－小黄山洋盆闭合，塔里木和哈萨克斯坦－准噶尔板块拼合；晚古生代时期阿尔金洋盆和古亚洲洋闭合，柴达木－华北、塔里木－准噶尔和西伯利亚拼合成一个完整陆块；中新生代时期，除了受南侧特提斯洋盆活动及陆块碰撞的影响以外，一系列陆相盆地沉积、陆内构造变动及青藏高原隆升成为该区构造演化中的主要事件．     

Tectonic setting of the Helong Block: Implications for the northern boundary of the eastern North China Craton

The Helong block, located in southeastern Jilin Province, was thought to be an Archean geological unit in the most northeast part of the North China Craton (NCC)[1,2]. Previous geological survey sug-gested that this block is mainly composed of two parts: Jinchengdong Archean metamorphic supracrustal rocks intruded by Archean TTG complex[3―5], and the Bailiping granite[6,7] distributed in the Shiliping-Bai- liping-Guangping area. Both of them were thought as the Jinchengdong (or Helong…     

Classification of the Sibumasu and Paleo-Tethys tectonic division in Thailand using chert lithofacies

Two types of chert are defined in Thailand based on lithology, faunal content, and stratigraphy. 'Pelagic chert' consists of densely packed radiolarian tests in a microcrystalline quartz matrix with no terrigenous material and is found as blocks embedded within sheared matrix. 'Hemipelagic chert' also has a microcrystalline quartz matrix, and contains not only scattered radiolarian tests, but also calcareous organisms such as foraminifers. The pelagic cherts range in age from Devonian to Middle Triassic, whereas hemipelagic chert is only from the Early to the Late Triassic. Lithological and stratigraphic characteristics indicate that the pelagic chert originated in the Paleo-Tethys, whereas the hemipelagic chert accumulated on the eastern margin of the Sibumasu Block. The hemipelagic and pelagic chert are exposed in two north-trending belt-like zones. The western zone includes the hemipelagic chert, as well as glaciomarine and other Paleozoic to Mesozoic successions, overlying a Precambrian basement that consists exclusively of Sibumasu elements. The eastern zone contains pelagic chert and limestone and should be correlated to the Inthanon Zone. The Inthanon Zone is characterized by the presence not only of Paleo-Tethyan sedimentary rocks, but also of Sibumasu Block elements that structurally underlie the Paleo-Tethyan rocks. The boundary between the Sibumasu and Paleo-Tethys zones is a north-trending, low-angle thrust that resulted from the collision of the Sibumasu and Indochina blocks.     

Changhsingian sea level changes and brachiopod diversity in the upper Yangtze region

Sedimentary environment and distribution of brachiopods during the Changhsingian in Xingwen, Si-chuan Province of the upper Yangtze region, are statistically analyzed. Changing regularity in diversity of brachiopod is synthetically investigated based on qualitative and quantitative analysis of transgres-sion-regression cycles. The results show that the diversity of brachiopods in this region in the trans-gression (aggradation) sequence is higher than that in the regression (progradation) sequence. The brachiopods in this area began to diversify in the early Changhsingian. And the species diversity had four peak stages which are respectively in the middle Early Changhsingian, late Early Changhsingian, early Late Changhsingian and late Late Changhsingian. The species diversity reached its highest in the late Late Changhsingian but this is followed by a sharp decrease at the end-hanghsingian, indicating the mass extinction of most brachiopod species which were prosperous in the Late Paleozoic.     

塔里木地块奥陶纪古地磁新结果及其构造意义

本文报道塔里木地块阿克苏—柯坪—巴楚地区奥陶纪古地磁研究新结果.对采自44个采点的灰岩、泥灰岩及泥质砂岩样品的系统岩石磁学和古地磁学研究表明,所有样品可分成两组：第一类样品以赤铁矿和少量磁铁矿为主要载磁矿物,该类样品通常可分离出特征剩磁组分A;第二类样品以磁铁矿为主要载磁矿物,系统退磁揭示出这类样品中存在特征剩磁组分B.特征剩磁组分A分布于绝大多数奥陶纪样品中,具有双极性,但褶皱检验结果为负,推测其可能为新生代重磁化.特征剩磁组分B仅能从少部分中晚奥陶世样品中分离出,但褶皱检验结果为正,且其所对应古地磁极位置（40.7°S,183.3°E,dp/dm=4.8°/6.9°）与塔里木地块古生代中期以来的古地磁极位置显著差别,表明其很可能为岩石形成时期所获得的原生剩磁.古地磁结果表明塔里木地块中晚奥陶世位于南半球中低纬度地区,很可能与扬子地块一起位于冈瓦纳古大陆的边缘;中晚奥陶世之后,塔里木地块通过大幅度北向漂移和顺时针旋转,逐步与冈瓦纳大陆分离、并越过古赤道;至晚石炭世,塔里木地块已到达古亚洲洋构造域的南缘.