Orientation-based Continuum Damage Models for Rocks

A general formulation of the Helmholtz free energy used in thermodynamics of damage process of rocks is derived within a multi-scale framework. Such a physically-based thermodynamic state potential has a hybrid, discrete/continuum, nature in the sense tha

Geochemical and isotopic characteristics of volcanic rocks from the northern East China Sea shelf margin and the Okinawa Trough

Volcanic rocks both from the northern East China Sea (NECS) shelf margin and the northern Okinawa Trough are subalkaline less aluminous, and lower in High Field Strength Elements (HFSE). These rocks are higher in Large Ion Lithophile Elements (LILE), thorium and uranium contents, positive lead anomalies, negative Nb-Ta anomalies, and enrichment in Light Rare Earth Elements (LREE). Basalts from the NECS shelf margin are akin to Indian Ocean Mid-Ocean Ridge Basalt (MORB), and rhyolites from the northern Okinawa Trough have the highest Pb-207/Pb-208 and Pb-208/Pb-204 ratios. The NECS shelf margin basalts have lower Sr-87/Sr-86 ratios, epsilon(Nd) and sigma O-18 than the northern Okinawa Trough silicic rocks. According to K-40-Ar-40 isotopic ages of basalts from the NECS shelf margin, rifting of the Okinawa Trough may have been active since at least 3.65-3.86 Ma. The origin of the NECS shelf margin basalt can be explained by the interaction of melt derived from Indian Ocean MORB-like mantle with enriched subcontinental lithosphere. The basalts from both sides of the Okinawa Trough may have a similar origin during the initial rifting of the Okinawa Trough, and the formation of basaltic magmas closely relates to the thinning of continental crust. The source of the formation of the northern Okinawa Trough silicic rocks was different from that of the middle Okinawa Trough, which could have been generated by the interaction of basaltic melt with an enriched crustal component. From the Ryukyu island arc to East China, the Cenozoic basalts have apparently increasing trends of MgO contents and ratios of LREE to Heavy Rare Earth Elements (HREE), suggesting that the trace element variabilities of basalts may have been influenced by the subduction of the Philippine Sea plate, and that the effects of subduction of the Philippine Sea plate on the chemical composition of basaltic melts have had a decreasing effect from the Ryukyu island arc to East China.

Isotopic feature and uranium dating of the volcanic rocks in the Okinawa Trough

Volcanic rocks from the northern and middle Okinawa Trough were dated by uranium-series dating method. Differential fractions using magnetic procedure were designed to separate samples. New report on the ages and isotopic data of rocks in the northern trough (especially black pumice) was discussed. Based on the uranium dates and Sr-Nd isotopic ratio, magmatic evolution process of the Okinawa Trough was noted. Firstly, there have been wide silicic volcanic activities in the Okinawa Trough from late Pleistocene to present, and the volcanic rocks can be divided into three subgroups. Secondly, magma generally came from PREMA source area under the Okinawa Trough. Magmatic evolution in the northern trough was similar to the middle, but different to the south. Finally, volcanic activities indicated that opening of the southern Okinawa Trough did not happen due to the collision between Luson Arc and Eurasian Plate until the early Pleistocene.

博兴洼陷新生代构造-沉积演化及其对鲁西隆起的响应

The West Shandong Uplift and its adjacent basins, with same evolutional history before Mesozoic, are an important basin-orogenic systems in North China. After late Mesozoic, tectonic differentiation between basin and orogenic belt gradually displayed in the study area. The Boxing sag is a part of Jiyang Depression near to West Shandong Uplift, in which the whole Mesozoic and Cenozoic strata are preserved. Based on the analysis of sedimentary records in the Boxing sag, the Cenozoic structural and sedimentary evolutions in Boxing Sag and its response to Western Shandong uplift are discussed in this dissertation. The main conclusions in this research are presented as follows. Based on Seismic and well logging profile interpretation, fault growth index, thickness difference between bottom wall and top wall and fault activity rate from Eocene to Pliocene are studied. Boxing sag had three main faults, NE, NW and NEE trending faults. Research shows that the activity of the NW trending fault in the Boxing sag became weaken from E1-2S4 to N2m gradually. The evolution of NE and the NEE trending fault can be divided into three episodes, from E1-2k to E2s4, from E2s3 to E3s1, from N2m to E3d. The analysis of Paleogene samples of heavy mineral assemblages shows that metamorphic rocks represented by garnet, intermediate-acid igneous rocks represented by the assemblage of apatite, zircon and tourmaline became less from E1-2k to N2g, and sedimentary rocks represented by the assemblage of pyrite, barite and limonite also became less. Intermediate-basic igneous rocks represented by the assemblage of leucoxene, rutile and ilmenite and metamorphic rocks represented by epidote became more and more. Electronic microprobe analysis shows that glaucophane and barroisite are existed in Kongdian Formation and the 4th member of Shahejie Formation, and they demonstrate that Western Shandong and Eastern Shandong are all the source regions of the Boxing Sag, and they also indicate that oceanic crust existed before the collision between the Yangtze and North China continent. The fact that Eastern Shandong is the source region of Boxing Sag also indicates that Western Shandong was not high enough to prevent sediment from Eastern Shandong at E1-2k and E2s4. The results of the dating of five detrital zircons of Boxing Sag show Kongdian Formation and the 4th member of Shahejie Formation have the age peaks of 2800Ma and 700-800. It means that Eastern Shandong is the source region of Boxing Sag at early Paleogene and Western Shandong is not high enough to prevent the sediment from Eastern Shandong. The ages of 160-180 and 220-260 Ma, which exist in the Guantao Formation and Paleogene, are common in Eastern Shandong and rare in Western Shandong,and it implied that Western Shandong is a low uplift at 24Ma. The Paleogene strata have almost same age groups, while the Guantao Formation has significant variations of age groups, and this indicates that Boxing Sag and Western Shandong uplift had taken place tremendous changes. The results of apatite fission track in Boxing sag show that three times uplifts happened at the source region at 60 Ma, 45Ma and 15Ma respectively, and the Boxing sag experienced two subsidences at 60Ma, 45Ma and one uplift at 20Ma.

塔里木盆地塔中—巴楚地区早二叠世岩浆岩地球化学特征及其成因

Tazhong-Bachu region is located in the Western Tarim basin.The early Permian magmatic rocks occur in the earth surface of Tazhong-Bachu region are mainly distributed in Kepintag,Mazhartag and Wajilitag region. There are a lot of wells, in which researchers found the early Permian magmatic rocks,in desert cover area.Most magmatic rocks are basic rocks, a few of which are ultrabasic rocks and intermediate-acid magmatic rocks.The ultrabasic rocks are are mainly occur in the Cryptoexplosive Breccia Pipes ,which is located in the volcanic complex body of Wajilitag region.The basic rocks can be divided into three rock types：The first type of the magmatic rocks in Tazhong-Bachu region is volcanic rock ,which occurs in the Lower Permian Kupukuziman Formation and Kaipaizileike Formation. Most Volcanic rocks are basalts,a few of which are volcanic breccias and pyroclastic rocks.The basalts are distributed in stratiform occurrences and interbeded the clastic rocks in Kepintag region.The attitudes of the basalts are nearly horizontal.Columnar Joints, gas pore textures and amygdaloidal structure are to develop in basalts.The second type of the magmatic rocks in Tazhong-Bachu region is diabase,which occurs in Mazhartag region.Diabase dike swarms occur in the stratums of Silurian, Devonian, Carboniferous and Lower Permian.They make from NNW direction to SSE direction, the obliquity of stratum is greater than 60°, and the dike thickness is form several cm to several meters. Diabasic texture is found in the rocks .The first type of the magmatic rocks in Tazhong-Bachu region are gabbro- pyroxenite rocks ,which occur in the Wajilitag igneous complex body. The intermediate-acid magmatic rocks, which are mainly syenites, are located in Mazhartag and Wajiltag region. But they are small in the whole Tazhong-Bachu region.There are intermediate-acid magmatic rocks,which are mainly dacite,in the northeast part of the wells in Tazhong-Bachu region.But ,it is not found in earth surface.Through systematical geochemical research of early Permian magmatic rocks,which are distributed in Kepintag,Mazhartag, Wajilitag region and the wells such as F1 well、Z1 well、Z13 well、TZ18 well、H3 well、H4 well et al., the focus on the geochronologic characteristics, the main element,trace element and REE geochemistry, the mineralogic characteristics, the Sr-Nd and Pb isotopic characteristics are put forward. The main points are: 1、A combined study of CL imaging and LA-ICP-MS U-Pb dating were carried out for zircon grains of the magmatic rocks in the Tazhong-Bachu region from the Tarim basin.The results of the systematic zircon LA-ICP-MS U-Pb dating reveal 272±6Ma to 291±10Ma for the magamatic rocks. It indicated that Early Permian is an important period of magmatic acvivity in the Tazhong-Bachu region. 2、There are a big hunch in the curves of primitive mantle-normalized trace element concentrations in the early Permian magmatic rocks from Kepintag, Mazhartag, Wajilitag region and the 14 wells. Light rare earth elements are comparatively rich and heavy rare earth elements are comparatively poor. The slope rates are same between light rare erath elements and heavy rare earth elements. It is not like the curves of the basalts in the convergent margin of plate , in which the slope rates of light rare erath elements is bigger than the alope rates of heavy rare erath elements, and the curves of heavy rare earth elements are comparatively flat. The magmatic rocks of Tazhong-Bachu region rarely have the characteristics of the basalts in the convergent margin of plate, which is that Tantalum, Niobium and Titanium are much poor, and Zirconium, Hafnium and Phosphorus are moderately poor. The magamatic rocks are mostly alkaline, which is indicated by the dots of the (Na2O+K2O)-SiO2 identification diagram. All of these indicate that the early Permian magmatic rocks were formed in an extension environment of intraplate. 3、The Thorium abundance is high and Tantalum abundance is low in most magmatic rocks from Tazhong-Bachu reguion, which is formed for crustal contamination.In the Th/Yb-Ta/Yb identification diagram，most dots are in the region, which means active continental margin, but a few dots are in the region, which means mantle source. It indicated the feeding of continental crust materials. 4、The magnesium content of the olvines from Wagilitag region is richest, and the olvines from Kepintag region is poorest in the tree region. 5、Through the the Sr-Nd and Pb isotopic study of the basalts and diabases from the F1 well core, Z1 well core, Z13 well core,TZ18 well core, and the basalts，gabbros, diabases(diabase-prophyrites) and pl-peridotites from Kepintag,Mazhartag, Wajilitag region , it indicated that all isotopic data is similar and close to enriched mantle.