牡丹江地区新生代火山岩初步研究

牡丹江地区上新世至全新世玄武质火山岩基本属于钠质碱性系列岩石。随时代变新,岩石的硅酸不饱和程度和碱含量增高,出现不同的岩石组合。岩石具轻稀土富集的特点,普遍富集大离子亲石元素(K、Rb、Ba、Th等)。据估算,橄榄玄武岩、碱性橄榄玄武岩和响碧玄岩分别为上地幔14.4％及3.2—3.5％部分熔融生成的。这是在库拉板块俯冲作用下,地幔上隆引起的弧后扩张使敦化-密山断裂复活,上地幔发生部分熔融的结果。     

地幔交代作用

地幔交代作用是地球内部的一种化学变化。从200公里深处由高速喷发带上来的地幔岩块的研究表明,在熔融之前某些含挥发组分的交代矿物已经存在。地幔交代作用的提出,是用以解释硷性岩浆的化学组成和同位素体系变化的原因。硷性岩浆作用广泛的时空分布表明,地幔交代作用是广泛的,并且是长期的一种地质作用。它不仅是引起地幔化学上和氧化还原条件变化的主要因素之一,而且是产生硷性岩浆的理想源区和引起克拉通地区陆壳抬升的动因之一。     

幔汁(ACOHNS)流体的重大意义

详细探讨了幔汁及幔汁活动对地壳中各种地质作用的重大影响,分析幔汁的成分结构,运动方式和对地质作用的控制。     

攀西裂谷构造─岩浆活动及其成因探讨

本文主要讨论弯窿一火山型攀西裂谷的成因，岩浆深成作用与火山作用过程;弩窿梅 造的发生、发展的演化历史，岩浆分异趋势及双峰式岩浆演化系列及其成因。 攀西裂谷曾经历了岩石圈弯窿一除壳弯窿一次火山弯窿三个发展演化阶段。碱性岩浆作用与 地壳隆开、地慢去气、热流汇聚作用有着密切的成因联系，成弯作用最盛，岩浆碱度最高。随着 陆壳破裂、开放、挥发分散逸，岩浆性质从强碱质一弱碱质一碱酸性转化。 弯窿构造的发展演化阶段有机地控制了岩浆源和二次岩浆房的深度和岩浆演化特点，随着弯 窿构造的发展演化，岩浆活动由深成慢源→中浅成慢源加嵌轻微混染→超浅成壳慢混合源逐渐 演化，因而可以认为:弯窿一火山型裂谷发育的各个阶段，存在有低位→中位→高位的二次岩浆 房. 攀西裂谷属不发育的夭折裂谷，以演化时间长为特点，有利于岩浆深源(二次岩浆房内)结 晶分异、液体不混容性分离作用和陆壳的同化混染作用等得以彻底进行，最终形成“双峰式”岩 浆组合。     

MTS studies on the upper mantle conductivity in China

Based on the data from more than 200 MTS sites distributed within different areas of the Chinese continent, general characteristics of upper mantle conductivity have been described. At least two conductive layers have been found in the upper mantle of some areas. The first is thin with a resistivity of a modicum to few tens m; the second one is thicker with a resistivity of one to m. Nearly 300 heat-flow values indicate that there exists an exponential correspondent relationship between a depth of the upper mantle conductive layer with a thickness and an average value of heat flow. Based on the above results, the top depth map of this upper mantle conductive layer has been outlined for parts of the Chinese continent. This conductive layer is basically consistent with the low velocity zone in the upper mantle, and Cenozoic tectonism and current seismicity are significantly related to the variation of depth of the conductive layer in the upper mantle. The possible origins of the conductive layers in the upper mantle have been discussed here.     

Substitute conductors for electromagnetic response estimates

Various concepts exist to define substitute conductors for empirical response estimates at singular frequencies: Chapman's shell-core model, the Cagniard-Tikhonov apparent resistivity, the Niblett-Bostick and Molochnov transformation, thep ^* —z ^* transformation. They are all interrelated and assign comparable resistivities to the substitute conductor at a given frequency. Applications to synthetic response data of plane and spherical conductors show under which conditions these substitutions come closest to the model and which influence of source dimensions and Earth's sphericity can be expected.p ^* —z ^* transformed global response data forS andDst variations demonstrate how substitute conductors may serve as useful guides in inverse procedures.     

Temperature profiles in the earth of importance to deep electrical conductivity models

Deep in the Earth, the electrical conductivity of geological material is extremely dependent on temperature. The knowledge of temperature is thus essential for any interpretation of magnetotelluric data in projecting lithospheric structural models. The measured values of the terrestrial heat flow, radiogenic heat production and thermal conductivity of rocks allow the extrapolation of surface observations to a greater depth and the calculation of the temperature field within the lithosphere. Various methods of deep temperature calculations are presented and discussed. Characteristic geotherms are proposed for major tectonic provinces of Europe and it is shown that the existing temperatures on the crust-upper mantle boundary may vary in a broad interval of 350–1,000°C. The present work is completed with a survey of the temperature dependence of electrical conductivity for selected crustal and upper mantle rocks within the interval 200–1,000°C. It is shown how the knowledge of the temperature field can be used in the evaluation of the deep electrical conductivity pattern by converting the conductivity-versustemperature data into the conductivity-versus-depth data.     

Crustal Growth Rate of the North China Platform：a Method of Estimating Mass Equilibrium between Crust and Mantle

The following equation is proposed in this paper to estimate the crustal growth rate of the North China Platform on the basis of mass equilibrium between the crust and the mantle:

The trace element composition of silicate inclusions in diamonds: a review

On a global scale, peridotitic garnet inclusions in diamonds from the subcratonic lithosphere indicate an evolution from strongly sinusoidal REE_N, typical for harzburgitic garnets, to mildly sinusoidal or “normal” patterns (positive slope from LREE_N to MREE_N, fairly flat MREE_N–HREE_N), typical for lherzolitic garnets. Using the Cr-number of garnet as a proxy for the bulk rock major element composition it becomes apparent that strong LREE enrichment in garnet is restricted to highly depleted lithologies, whereas flat or positive LREE–MREE slopes are limited to less depleted rocks. For lherzolitic garnet inclusions, there is a positive relation between equilibration temperature, enrichment in MREE, HREE and other HFSE (Ti, Zr, Y), and decreasing depletion in major elements. For harzburgitic garnets, relations are not linear, but it appears that lherzolite style enrichment in MREE–HREE only occurs at temperatures above 1150–1200 °C, whereas strong enrichment in Sr is absent at these high temperatures. These observations suggest a transition from melt metasomatism (typical for the lherzolitic sources) characterized by fairly unfractionated trace and major element compositions to metasomatism by CHO fluids carrying primarily incompatible trace elements. Melt and fluid metasomatism are viewed as a compositional continuum, with residual CHO fluids resulting from primary silicate or carbonate melts in the course of fractional crystallization and equilibration with lithospheric host rocks.

Eclogitic garnet inclusions show “normal” REE_N patterns, with LREE at about 1× and HREE at about 30× chondritic abundance. Clinopyroxenes approximately mirror the garnet patterns, being enriched in LREE and having chondritic HREE abundances. Positive and negative Eu anomalies are observed for both garnet and clinopyroxene inclusions. Such anomalies are strong evidence for crustal precursors for the eclogitic diamond sources. The trace element composition of an “average eclogitic diamond source” based on garnet and clinopyroxene inclusions is consistent with derivation from former oceanic crust that lost about 10% of a partial melt in the garnet stability field and that subsequently experienced only minor reenrichment in the most incompatible trace elements. Based on individual diamonds, this simplistic picture becomes more complex, with evidence for both strong enrichment and depletion in LREE.

Trace element data for sublithospheric inclusions in diamonds are less abundant. REE in majoritic garnets indicate source compositions that range from being similar to lithospheric eclogitic sources to strongly LREE enriched. Lower mantle sources, assessed based on CaSi–perovskite as the principal host for REE, are not primitive in composition but show moderate to strong LREE enrichment. The bulk rock LREE_N–HREE_N slope cannot be determined from CaSi–perovskites alone, as garnet may be present in these shallow lower mantle sources and then would act as an important host for HREE. Positive and negative Eu anomalies are widespread in CaSi–perovskites and negative anomalies have also been observed for a majoritic garnet and a coexisting clinopyroxene inclusion. This suggests that sublithospheric diamond sources may be linked to old oceanic slabs, possibly because only former crustal rocks can provide the redox gradients necessary for diamond precipitation in an otherwise reduced sublithospheric mantle.