塔里木盆地中北部断裂体系划分及形成机制探讨

基于地震地质解释,刻画了塔里木盆地中北部断裂体系的平、剖面特征,分析了不同断裂体系的结构模式、形成机制及演化历史。结果表明,该区分为4个断裂体系:(1)托普台"X"型走滑断裂体系,下古生界主要发育NNE、NNW向"X"型共轭剪切破裂及"1"字形直立构造、正花状构造,而中新生界多表现为NNE向雁列式张性正断裂及负花状、堑垒构造;(2)塔中NW向逆冲断裂体系,以近NW向基底卷入式或滑脱式逆冲断裂为主,发育"y"字形构造;(3)顺托NE向走滑断裂体系,奥陶系及以下层系表现为近NE向左旋走滑及"1"字形直立、正花状构造,而志留-泥盆系主要发育近NE向雁列式张性正断裂及负花状、堑垒构造;(4)塔河盐下"T"型断裂体系,下古生界层系由近EW向逆冲断裂与近SN、NNE向走滑断裂组成,中新生界层系主要发育NEE向、近SN向雁列式张性正断裂组。断裂体系的研究明确了研究区压扭走滑和张扭走滑作用的叠加改造过程,认为主要受控于盆缘古洋盆5期的消减闭合及碰撞造山作用。结合研究区构造动力学背景分析,将该区断裂体系的演化过程划分为中晚奥陶世的强挤压弱走滑期、晚志留—中泥盆世的强挤压强走滑期、晚石炭—早中二叠世的强拉张弱走滑期、晚二叠世—三叠纪的强挤压弱走滑期和侏罗纪—新近纪的弱挤压弱走滑期。

Sediment record of environmental change at Lake Lop Nur (Xinjiang, NW China) from 13.0 to 5.6 cal ka BP

Lake Lop Nur is located in the eastern part of the Tarim Basin in Xinjiang,northwestern China.A 220-cm-long sediment core was collected from the center of the ear-shaped depression forming the basin and dated with AMS^(14)C.Grain size,total organic matter(TOC),total nitrogen(TN),and TOC/TN(C/N)analyses were used to reconstruct climatic conditions from 13.0 to 5.6 cal ka BP.The results showed fi ve main climatic stages.Zone I(13.0–11.3 cal ka BP)was a wet–dry environment,whereas Zone II(11.3–8.9 cal ka BP)consisted of a primarily wet environment.Zone III(8.9–7.7 cal ka BP)was subdivided into Zone IIIa(8.9–8.2 cal ka BP)that indicated lake constriction and dry climate,and Zone IIIb(8.2–7.7 cal ka BP)in which the proxies indicated wet conditions.In Zone IV(7.7–6.6 cal ka BP),the climate presented a bit wet conditions.In Zone V(6.6–5.6 cal ka BP),abundant glauberite is present in the sediment and silt dominates the lithology;these results indicate the lake shrank and the overall climate was dry.Abrupt environmental events were also identifi ed,including six dry events at 11.0,10.5,9.3,8.6,8.2,and 7.6 cal ka BP and one fl ood event from 7.8 to 7.7 cal ka BP in the Early–Middle Holocene.

Early Permian Tarim Large Igneous Province in northwest China

Tarim Large Igneous Province （TLIP） is the second Late Paleozoic LIPs in China after the recognition of Emeishan LIP, and is a hot research topic in geosciences. On the basis of the analysis of research history about TLIP, this paper summarizes the re- search result during last twenty years and suggests the key research area in the future. The residual distribution range of TLIP is up to 250000 km2, and the largest residual thickness is 780 m. The eruption of basalt happened during 290-288 Ma and be- longs to LIPs magmatic event with fast eruption of magma. The lithological units of the TLIP include basalt, diabase, layered intrusive rock, breccia pipe mica-olivine pyroxenite, olivine pyroxenite, gabbro, ultramafic dyke, quartz syenite, quartz syenite porphyry and bimodal dyke. The basalt and diabase of TLIP exhibit OIB-like trace element patterns and enrichment of LILE and HFSE, and mainly belong to high TiO2 series. There is an obvious difference in isotope among the basalt from Keping and the basalt and dibase from the northern Tarim Basin. The basalt from Keping with negative eNa and high REE value derives from enriched mantle, and the diabase and basalt from the northern Tarim Basin with positive ENa and low REE value axe re- lated to depleted mantle. The crust uplifting in the Early Permian and the development of picrite and large scale dyke and for- mation of large scale V-Ti-Magnetite deposit in Wajilitag area support the view that the TLIP is related to mantle plume. The TLIP has a temporal-spatial relationship with Permian basic to ultra-basic igneous rock, which is distributed widely in Central Asia, and they represent a tectono-magmatic event with very important geodynamic setting. This paper also suggests that the deep geological process, the relation with mantle plume, mineralization, the relation with environmental change and biological evolution, and the geodynamics of the TLIP will be the key research topics in the future.

Early dolomitisation of the Lower-Middle Ordovician cyclic carbonates in northern Tarim Basin, NW China

High-frequency metre-scale cycles are present within the Lower-Middle Ordovician carbonate successions in northern Tarim Basin, NW China. These metre-scale cycles were variably dolomitised from top to bottom. Three types of replacive dolomites were recognised, including dololaminite(very finely to finely crystalline, planar-s to nonplanar-a dolomite;type-1), patterned dolomite(finely crystalline, planar-s dolomite; type-2), and mottled dolomite(finely to medium crystalline,nonplanar-a(s) dolomite; type-3). Petrographic evidence indicate these dolomites were primarily deposited in supratidal to restricted subtidal environments, and formed in near-surface to shallow burial realms. Geochemically, all types of dolomites have similar δ13C and 87Sr/86 Sr ratios comparable to calcite precipitated in equilibrium with the Early-Middle Ordovician seawater. These geochemical attributes indicate that these dolomites were genetically associated and likely formed from connate seawater-derived brines. Of these, type-1 dolomite has δ18O values(.4.97‰ to.4.04‰ VPDB) slightly higher than those of normal seawater dolomite of the Early-Middle Ordovician age. Considering the absence of associated evaporites within type-1 dolomite, its parental fluids were likely represented by slightly evaporated(i.e., mesosaline to penesaline) seawater with salinity below that of gypsum precipitation. More depleted δ18O values(.7.74‰ to.5.20‰ VPDB) of type-2 dolomite and its stratigraphic position below type-1 dolomite indicate the generation of this dolomite from mesosaline to penesaline brines at higher temperatures in near-surface to shallow burial domains. Type-3 dolomite yields the most depleted δ18O values(–9.30‰to –7.28‰ VPDB), pointing to that it was most likely formed from coeval seawater-derived brines at highest temperatures in a shallow burial setting. There is a downward decreasing trend in δ18O values from type-1 through type-2 to type-3 dolomites, and in abundance of dolomites, indicating that the dolomitising fluids probably migrated downward from above and persisted into shallow burial conditions.