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51.
北阿尔金巴什考供盆地南缘花岗杂岩体特征及锆石SHRIMP定年 总被引：18，自引：11，他引：18
北阿尔金巴什考供盆地南缘花岗杂岩体呈近东西向分布,长约49公里,出露面积约90平方公里,与围岩之间为明显的侵入接触关系,接触界线为不规则的渡状、锯齿状。围岩为前寒武纪砂岩、片岩、泥岩及凝灰质砂岩。该杂岩体主要由巨斑花岗岩、红色花岗岩、灰白色似斑状花岗岩和粉红色似斑状花岗岩组成。杂岩体的主元素含量变化不大,SiO2为65．14％- 75．66％,全碱含量为7．49-8．96％,K2O／Na2O比值为1．12-2．68,岩石的里特曼指数平均为2．34,CIPW标准矿物计算均出现刚玉(AC)(平均为1．78),说明岩石铝过饱和;杂岩体的稀土总量变化于89．44×10-6-335．28×10-6之间,不同岩石类型均有负铕异常,且从巨斑花岗岩→灰白色似斑状花岗岩→红色似斑状花岗岩→红色花岗岩,负铕异常越来越明显,表现在Eu／ Eu+值由0．65→0．51→0．48→0．30。在微量元素蛛网图上,所有样品的微量元素丰度均高于原始地幔值,并具有相似的配分模式,即在Ba、Nb、Sr、P、Ti处呈明显的低谷,显示出S型花岗岩的特征。锆石SHRIMP U-Pb定年得出,巨斑花岗岩、红色中细粒花岗岩、灰白色和粉红色似斑状花岗岩的年龄分别为474．3±6．8Ma、446．6±5．2Ma、434．5±3．8Ma和431．1±3．8Ma。结合区域地质特征,我们认为,该杂岩体形成于同碰撞-碰撞后的构造环境。 相似文献
52.
We examined spatial variations in benthic remineralisation (measured as sediment oxygen consumption (SOC)) and sediment properties on the northeastern New Zealand continental shelf and slope to assess the importance of benthic mineralisation in this ecosystem and to provide data for more complete global carbon budgets. SOC measured in dark incubations conducted in early summer ranged from 128 μmol m−2 h−1 at the deepest (360 m) to 1222 μmol m−2 h−1 at the shallowest (4.2 m) site and decreased significantly with water depth (p<0.001, r2=0.78, SOC=1222.8−456.3×log10[water depth], n=14 sites). These rates were in the range found on continental shelves elsewhere (64–1750 μmol m−2 h−1, n=30 studies) and had a very similar distribution with water depth. SOC was also measured in light incubations at seven sites (4.2–35 m water depth) to examine the effects of microphytobenthos and accounted for 42–106% of rates measured in the dark. Measurements of near-bed light intensities suggested that microphytobenthos production was not solely regulated by light intensity but evidently influenced by other factors. A two-dimensional PCA ordination of surface sediment properties accounted for 83.3% of the total variance in the data and divided the study area into three clusters that corresponded well to its spatial division into the shallow (<30 m) Firth of Thames, the Hauraki Gulf (30–50 m) and the northern shelf-slope region. In the Firth of Thames sediments were very fine-grained with low CaCO3 and high total organic matter and pigment content, and low C:N ratios. The northern shelf-slope sediments showed the opposite trends to the Firth of Thames and those in the Hauraki Gulf had mostly intermediate values. Dark SOC was significantly correlated with sediment organic matter, carbon, nitrogen, pigments and silt/clay content (p<0.05, r=0.55–0.85) but a multiple linear regression revealed that water depth was the only significant predictor. Calculations suggest that approximately 13%, 10% and 34% of primary production is remineralised in the sediments of the northern shelf-slope region, Hauraki Gulf and Firth of Thames, respectively, indicating a strong benthic–pelagic coupling on the northeastern New Zealand continental shelf that was particularly pronounced in the Firth of Thames due to its shallow depth and significant terrestrial and riverine inputs. 相似文献
53.
接触交代夕卡岩型矿床中石榴子石和辉石成分特点及其与矿化的关系 总被引：1，自引：0，他引：1
本文对中国十四个接触交代钙夕卡岩矿床和钙-镁夕卡岩矿床中的三百多个样品的石榴子石和辉石成分进行了电子探针分析。不同矿床类型的石榴子石和辉石成分代表着钙夕卡岩矿床的十个矿种(Fe、Fe-Cu、Pb-Zn、W、Sn、Sn-Mo-Bi-W、、W-Bi-Cu-Mo、Cu-Zn、Cu-Sn、W-Zn-Cu)和钙-镁夕卡岩矿床的三个矿种(Fe-Cu、Mo、Pb-Zn)。石榴子石和辉石成分变化范围大,大多数石榴子石是含锰铝榴石+铁铝榴石+镁铝榴石小于15％(摩尔百分数)的钙铝榴石-钙铁榴石固溶体;大多数辉石是含小于5％的锰钙辉石的透辉石-钙铁辉石固溶体。有些Pb-Zn钙-镁夕卡岩矿床中的辉石显示出Mn含量有所增加。只有Sn和W钙夕卡岩矿床及Pb-Zn钙-镁夕卡岩矿床含(Sps+Alm+Pyr)总量大于15％的石榴子石。石榴子石和辉石成分与夕卡岩矿床金属矿化类型之间有某些联系。 相似文献
54.
Pleistocene climatic and oceanographic changes have influenced the distribution of marine biodiversity in southern Africa. Most evidence, however, has been derived from rocky shore or demersal taxa; data on sandy shore species are limited, despite severe threats to many sandy beach ecosystems. To test the effects of past climatic changes on sandy shore species, we sampled 140 smooth plough shell Bullia rhodostoma individuals from eight localities and generated phylogeographic data derived from the mtDNA cytochrome c oxidase subunit 1 (COI) marker. Nuclear markers (ATPSα, ATPSβ, ANT, SRPS4, TBP, LTRS and ZMP) showed no sequence variation. Bullia rhodostoma exhibited shallow genetic differentiation (ΦST = 0.07, p < 0.05) across its range. Isolation-by-distance suggests a stepping-stone model of migration, which is expected given the species’ direct-development life-history strategy. Demographic reconstruction suggests a post-LGM (Last Glacial Maximum) range expansion, concordant with the signal of shallow genetic differentiation. Phylogeographic patterns obtained suggest that, during lower sea levels than current, B. rhodostoma could have been restricted to the South-West Coast, the central Agulhas Bioregion and probably also the East Coast. When climatic conditions changed and temperatures began to rise after the LGM, the species began a rapid westward range expansion from these refugial regions. 相似文献