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11.
青藏高原东北缘(94°E—105°E,32°N-40°N)是高原北东向扩张的前沿地带,亦是研究高原生长过程的重要区域.本文利用青海省数字地震台网(2008-2014年)共7年的地震目录和波形数据,首先使用双差定位获取精定位震源位置,在此基础上,挑选位于S波窗口内(射线入射角≤45°)的地震事件,依据S波分裂分析方法(SAM),获取研究区域内共26个台站的S波分裂参数.研究结果表明:地处多个块体交汇部位的西宁及其周缘,地壳各向异性呈现两个优势偏振方向,表明该区中上地壳应力环境由区域主压应力场和活动断层共同约束;玉树地震序列的地壳各向异性优势偏振方向与区域主压应力场一致. 相似文献
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Pentti Hölttä Hannu Huhma Yann Lahaye Irmeli Mänttäri Sari Lukkari Hugh O’Brien 《International Geology Review》2020,62(3):360-387
ABSTRACTWe have identified two contrasting styles of Paleoproterozoic metamorphism in the northern part of the Fennoscandian Shield. The Karelia and Lapland-Kola Provinces, comprising Archean and overlying Paleoproterozoic supracrustal rocks, show a typical medium pressure Barrovian-style metamorphism with commonly found kyanite-bearing mineral assemblages and ITD (isothermal decompression) PT paths. In the juxtaposed Svecofennia Province metamorphism represents low pressure-high temperature Buchan style with garnet-cordierite migmatites and intercalated andalusite-cordierite and andalusite-staurolite schists and sillimanite-muscovite gneisses. The retrograde PT paths show only a moderate uplift during cooling.U-Pb age determinations on monazite were made using the LA-ICP-MS from more than 80 samples from metasedimentary rocks. The sampling covered most parts of the Paleoproterozoic bedrock in Finland. The analyses reveal three peaks at c. 1.91 Ga, 1.86–1.88 Ga and at 1.79–1.81 Ga. The oldest, c. 1.91 Ga monazites are mostly found in the Lapland-Kola Province which is located in the northernmost Finland. In the Karelia Province where the Paleoproterozoic is underlain by Archean bedrock monazite yielded ages of 1.76?1.81 Ga with only a few older exceptions in samples showing a spread of 207Pb/206Pb ages from c. 1.92–1.81 Ga. The Karelia Province underwent tectonic thickening, where monazite ages of around 1.80 Ga mostly represent exhumation near the temperature maximum.In the Svecofennia Province monazite ages vary from c. 1.89 to 1.78 Ga. In the Western Finland Subprovince the monazite ages in high-grade migmatites are mostly 1.86?1.88 Ga but within the older migmatite areas there are lower grade zones where monazite yields ages of c. 1.80 Ga. Some samples also show a spread of 207Pb/206Pb ages from 1.89?1.86 Ga to c. 1.78 Ga. In the Southern Finland Subprovince most ages are either 1.80?1.78 Ga, especially in the andalusite grade schists, or the sample shows a spread of 207Pb/206Pb ages from c. 1.88 to 1.78 Ga. Only in the eastern part of the Southern Finland Subprovince there are rocks which yield merely 1.86?1.89 Ga ages. Low pressure-high temperature metamorphism and lack of high or medium P/T rocks in the Svecofennia Province refers rather to accretionary than collisional processes. 相似文献
14.
依据不同构造岩浆区单元，江西中南部中新元古代－晚三叠世的侵入岩可划分为武夷山构造岩浆区、赣西南构造岩浆区。其中武夷山构造岩浆区共划分了43个单元，归并为11个超单元；赣西南构造岩浆区共划分为34个单元，归并为10个超单元。这样较系统地建立了江西省中南部中新元古代－晚三叠世岩石谱系单位和等级体制，为今后开展全省侵入岩谱系单位划分奠定了基础。 相似文献
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华北北部中、上元古界具大陆裂谷沉积特征，地层自下而上分三种沉积类型，反映大陆裂谷的三个发展阶段。１．碎屑岩一火山岩活动沉积类型，反映裂谷早期拉张和火山活动阶段的沉积特征，包括常州沟组、串岭沟组、团山子组、大红峪组。２．碳酸盐岩活动沉积类型，反映裂谷强烈下陷、拓宽、广泛海侵阶段的沉积特征，包括高于庄组、杨庄组、雾迷山组。３．碎屑岩一碳酸盐岩稳定沉积类型，反映裂谷活动期后，稳定残余凹陷的沉积特征，包括洪水庄组、铁岭组、下马岭组、龙山组和景儿峪组。根据裂谷发展阶段及其沉积类型，华北北部中、上元古界可划分为：长城群（常州沟组、串岭沟组、团山子组、大红峪组）；蓟县群（高于庄组、杨庄组、雾迷山组）；青白口群（洪水庄组、铁岭组、下马岭组、龙山组、景儿峪组）。 相似文献
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This chapter introduces the chronological and interdisciplinary “frieze” which presents the main events relevant (in our opinion) to the problem of the emergence of life on Earth. This selection of events is directly connected to the previous chapters of this book.The frieze may be found in print as an insert at the back of the print publication. This supplementary material is also available in the online version of this article at and is accesssible for authorized users. 相似文献
17.
张维吉 《地球科学与环境学报》1987,(1)
宽坪群被划分为三个部分,下部以基性火山岩为主,中部以碎屑岩为主,上部以碳酸盐岩为主。以蟒岭地区的层序,由下而上分为广东坪组、四岔口组和谢湾组,其它各地均可对比。根据同位素年龄及其它证据,宽坪群应属于早—中元古代,具体时限应老于17亿年。 相似文献
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辽北地区中,上元古宙凡河群,据其总的构造样式;近万 m 厚的沉积—火山建造;厚度巨大的细碧岩及其与硅质岩、英安岩、凝灰岩和火山角砾岩组合;非补偿性和补偿性堆积的双层结构;平行裂陷槽延伸方向的生长性断裂和重力梯级带,以及拉伸角砾岩带、滑塌构造、碳酸盐岩的浊积岩系等,表明凡河群为中、晚元古宙分布于华北地台北缘的坳拉谷沉积。其形成作用可据 Ramberg(1972)的重力不稳定模式来阐明。该坳拉谷构造作用的早期阶段控制了关门山铅—锌矿田的成矿和分布。对该坳拉谷构造及成矿作用的研究无疑对关门山矿田新一轮找矿和靶区分析是有稗益的,同时对整个华北地台北缘构造演化研究也具有一定意义。 相似文献
19.
In this article we summarize the petrological, geochemical and tectonic processes involved in the evolution of the Proterozoic
intracratonic Cuddapah basin. We use new and available ages of Cuddapah igneous rocks, together with field, stratigraphic,
geophysical and other criteria, to arrive at a plausible model for the timing of these processes during basin evolution. We
present petrological and geochronological evidence of dike emplacement along preferred lineament directions around the basin
in response to stresses, which may have been responsible for the evolution of the basin itself. Basaltic dike intrusion started
on the south Indian shield around 2400 Ma and continued throughout the Cuddapah basin evolution and sedimentation. A deep
mantle perturbation, currently manifested by a lopolithic cupola-like intrusion under the southwestern part of the basin,
may have occurred at the onset of basin evolution and played an important role in its development. Paleomagnetic, gravity
and geochronological evidence indicates that it was a constant thermal source responsible for dike and sill emplacement between
1500 and 1200 Ma both inside and out-side the basin. Lineament reactivation in the NW-SE and NE-SW directions, in response
to the mantle perturbation, intensified between 1400 and 1200 Ma, leading to the emplacement of several cross cutting dikes.
Fe-Mg partition coefficients of olivine and augite and Ca-Na partition coefficient of plagioclase, calculated from the composition
of these minerals and bulk composition of their host rocks, indicate that the dikes outside the Cuddapah basin are cumulates.
The contemporary dikes may be related by fractional crystallization as indicated by a positive correlation between their plagioclase
Ca# (atomic Ca/[Ca+Na]) and augite Mg# (atomic Mg/[Mg+Fe]). A few NW-SE and NE-SW cross cutting dikes of the period between
1400 and 1200 Ma, preserve petrographic evidence of episodic magmatic intrusive activity along preferred directions. Petrological
reasoning indicates that a magmatic liquid reacted with a set of cross cutting dikes, intruding into one that was already
solidified and altering the composition of the magma that produced the other dike.
The Cuddapah basin tholeiites may be related by fractional crystallization at 5 kb and 1019-1154‡ C, which occurred in the
lopolithic cupola near the southwestern margin of the basin. Xenolith bearing picrites, which occur near the periphery of
the cupola, originated by the accumulation of xenoliths in the tholeiites. This is indicated by the composition of the olivine
in the xenoliths (Fo78.7-81.9), which are closely similar to calculated olivine compositions (Fo77.8-78.3) in equilibrium with the tholeiites under the sameP-T conditions. It is inferred that fractionation in the cupola resulted in crystals settling on its walls. Hence, the xenolith-bearing
sills occur at the periphery of the lopolithic body.
The tholeiites both inside and outside the basin are enriched in incompatible elements compared to mid oceanic ridge basalts.
The Ba, Rb and K contents of the Cuddapah and other Proterozoic Gondwana tholeiites indicate that a widespread metasomatic
enrichment of the mantle source may have occurred between R∼2.9 and R∼2.7Ga. There may be local heterogeneity in the source
of the Cuddapah tholeiites as indicated by different Ba/Rb, Ti/Zr, Ti/Y, Zr/Nb and Y/Nb in samples inside and outside the
basin. Large-scale differences such as the low P2O5-TiO2 and high P2O5-TiO2 basaltic domains of the Jurassic Gondwana basalts, however, did not exist during the Proterozoic time period under consideration.
Although we are beginning to understand the tectono-magmatic processes involved in the evolution of the Cuddapah basin, much
work remains to be done to obtain a complete picture. Future research in the Cuddapah basin should focus on obtaining accurate
ages of the igneous rocks associated with the evolution of the basin. 相似文献
20.
Age determinations mostly by Rb/Sr whole rock isochrons of the Precambrian rocks of Rajasthan in northwest India are summarized
and discussed. On present sampling and subject to its possible bias, the following conclusions can be made. The Untala Granite
believed to be intrusive into the gneissic terrain (bgc) east of Udaipur has the oldest age, 2.95 b.y. yet measured for a granite in Rajasthan. This, coupled with the lead isochron
age of 3.5 b.y. for detrital zircon from the Aravalli schists by Vinogradov and others extends the basement of Rajasthan well
into the Archaean. The time equivalence of thebgc east of Udaipur with the Berach Granite dated only at 2.55 b.y. is not tenable. No satisfactory radiometric age control exists
for the onset and duration of the Aravalli Supergroup, believed to be an early Proterozoic linear belt.
Heron’s original Delhi Supergroup has recorded acid magmatism widely separate in space and time. The earliest activity between
1700 and 1500 m.y. is recorded mainly in the Alwar basin in northeastern Rajasthan while the younger activity between 850
and 750 m.y. is represented by the ‘Erinpura type’ granites in the central and southern Aravalli sector. This younger event
not only has let its thermal overprinting on the older Alwar rocks but also marks the onset of emplacement of the Malani Igneous
suite in the trans-Aravalli terrain. This raises the new possibility that the Delhi rocks of Heron represent atleast two chronologically
independent sequences with varying geographical extent. The trans-Aravalli terrain is most probably floored by partly reworked,
crystalline basement and developed along linear rift zones which acted as loci for high heat flow and igneous activity since
about 800 m.y. ago. 相似文献