黑龙江省漠河县富源沟林场含电气石 花岗岩的形成时代及地质意义

本文对额尔古纳地块北段的富源沟林场含电气石花岗岩体进行了LA-ICP-MS锆石U-Pb同位素定年和岩石地球化学研究。含电气石花岗岩的锆石²⁰⁶Pb/²³⁸U年龄加权平均值为458±4 Ma（MSWD = 1.8）,表明含电气石花岗岩形成于晚奥陶世初期。岩石地球化学特征表明该花岗岩应为高钾钙碱性系列（K₂O = 3.45%～4.83%）,铝饱和指数A/CNK＞1.1（1.11～1.28）,属强过铝质的S型花岗岩,富集Th、U、Rb、K等元素,相对亏损Sr、Ba、 Nb、Ti、 P、Eu等元素,是同碰撞构造背景下地壳部分熔融的产物。结合前人研究资料和本文数据提出,富源沟林场含电气石花岗岩的形成与额尔古纳地块和兴安地块的碰撞拼贴有关,形成于额尔古纳地块与兴安地块碰撞拼贴作用所引发的碰撞构造背景,由于地缘因素,构造岩浆作用滞后于额尔古纳地块东缘的碰撞拼贴时限,是额尔古纳地块和兴安地块碰撞拼贴的远程效应。     

大兴安岭北部塔河花岗杂岩体的地球化学特征及成因

塔河杂岩体位于塔源-喜桂图缝合带北侧的额尔古纳地块东部,是早古生代侵入的花岗杂岩体。该杂岩体的主要岩石类型为正长花岗岩、二长花岗岩,少量碱长花岗岩和花岗闪长岩,辉长岩以包体存在于花岗岩中。岩石成因类型为典型的Ⅰ型后造山侵入体。岩体在野外地质特征、矿物组合、显微结构、化学成分及锆石Hf同位素特征等方面都表现出岩浆混合成因。在早古生代额尔古纳地块与兴安地块拼合后的后造山伸展拉张背景下,地壳和地幔都发生部分熔融,直接起源于亏损地幔的玄武质岩浆侵入到下地壳熔融的花岗质岩浆房,经结晶分异作用,形成了塔河杂岩体不同的岩石类型。花岗岩的εHf(t)为-0.8~+5.6之间,Hf模式年龄在0.9~1.5Ga之间,反映塔河花岗岩的源岩应该是在中-新元古代时期由亏损地幔起源的新生地壳物质。结合额尔古纳地块早古生代和中生代花岗岩锆石Hf同位素资料,我们认为额尔古纳地块在中-新元古代时曾发生过一次重要的地壳增生事件。     

大兴安岭北部察哈彦岩体的Hf同位素特征及其地质意义

察哈彦岩体位于大兴安岭东北部额尔古纳地块之上,主要岩性为斑状黑云母正长花岗岩.岩体中锆石呈自形晶,发育细微振荡生长环带,显示高的Th/U值(0.32～1.12),表明锆石的岩浆成因.锆石LA-ICP-MS U-Pb 定年结果为(236±1)Ma,属中三叠世岩浆活动的产物.察哈彦岩体未见变形,具有块状构造,地球化学显示为弱过铝质、高钾钙碱性系列,富集LREE和Rb、K等元素,亏损Nb、Ta、P、Ti等元素,与后造山I型花岗岩特征相似,应形成于引张的构造环境.结合区域构造研究成果,其成因应与华北板块和西伯利亚板块碰撞造山后岩石圈伸展环境有关.察哈彦岩体的 Hf(t)值为-3.94～2.19,其模式年龄为1.1～1.5 Ga,与额尔古纳地块早古生代花岗岩和中生代花岗岩基本相同,表明额尔古纳地块地壳增生的时间主要发生在中-新元古代.     

黑河市五道沟地区早二叠世A型花岗岩成因

根据岩石学、岩石化学、地球化学及同位素等特征,对黑河市五道沟地区早二叠世碱长花岗岩进行了构造成因研究。该套岩石具高硅、富碱、低钙镁、偏铝质-过铝质特点,且富Rb、Th、K等大离子亲石元素,相对亏损Ba、Sr、P、Ti、Nb等元素,稀土元素具有典型的海鸥式分配样式,总体具有典型A型花岗岩特征;其形成于额尔古纳—兴安地块与松嫩—张广才岭地块挤压拼贴后的伸展环境。黑河市五道沟地区A型花岗岩的最新厘定对该地区晚古生代构造演化的研究及区域成矿规律的探讨具有重要意义。     

黑龙江塔溪地区晚古生代后造山花岗岩特征及其地质意义

摘要：位于兴蒙造山带东端的黑龙江塔溪地区花岗岩主要岩石类型为二长花岗岩和正长花岗岩,锆石U Pb( LA ICP MS)同位素测年结果为295～285 Ma,表明形成于晚古生代。岩石地球化学以弱过铝质、中—高钾为特征,总体表现为：高钾钙碱性系列,轻稀土元素富集,重稀土元素相对亏损,弱—中等δEu负异常,大离子亲石元素(LILE)Rb、La富集,Ba、Sr亏损,高场强元素(HFSE)Ce、Zr、Hf、Th富集,Nb、Ta亏损。推测花岗质岩浆曾发生壳幔混染作用,有更多壳源物质参与,显示后造山I型花岗岩特征。认为花岗岩形成于挤压向伸展转换的后造山环境,为兴安地块与松嫩地块碰撞拼合的后造山阶段产物。     

大兴安岭北段漠河地区早古生代花岗质岩体:对额尔古纳-兴安地块碰撞后伸展过程的响应SCIEI北大核心CSCD

本文报道了大兴安岭北段漠河地区早古生代二长花岗岩的岩相学、锆石U-Pb年龄、Hf同位素组成以及全岩主-微量元素地球化学数据,以揭示古亚洲洋构造域早古生代期间的构造-岩浆演化过程。漠河地区花岗岩中锆石发育典型的岩浆振荡生长环带和高Th/U比值,表明为岩浆成因锆石,其LA-ICP-MS U-Pb同位素测试结果显示漠河地区花岗岩形成于482~456Ma,代表奥陶纪-志留纪岩浆活动的产物。花岗岩主体为二长花岗岩,主要矿物组成为石英、斜长石和碱性长石,及少量黑云母。全岩主-微量元素地球化学分析结果显示,花岗岩具有高SiO_(2)、Al_(2)O_(3)和全碱(Na_(2)O+K_(2)O)含量,低MgO、Mg^(#)、Cr和Ni含量,并显示高钾钙碱性的属性;结合花岗岩准铝质特征,表明其属于高钾钙碱性I型花岗岩。此外,花岗岩样品富集大离子亲石元素(Rb、Ba、K、Sr等)和轻稀土元素,亏损高场强元素(Nb、Ta、P、Ti等)和重稀土元素,显示明显Eu负异常,与地壳组分的地球化学特征较为相似。花岗岩的锆石ε_(Hf)(t)值大多为正值,结合它们相应的Hf同位素二阶段模式年龄(1487~1106Ma),表明花岗岩的岩浆源区以中-新元古代期间新增生的年轻地壳组分为主,并且存在少量古老地壳物质的贡献。结合部分花岗岩样品重稀土元素亏损的特征,表明漠河地区早古生代花岗岩可能起源于石榴石角闪岩相和角闪岩相地壳物质的部分熔融作用,岩浆演化后期的分离结晶作用对岩浆成分的变化影响并不显著。结合额尔古纳地块广泛发育的同时期造山后岩石组合(A型花岗岩,双峰式岩石组合和碱性侵入体),本文认为漠河地区早古生代花岗岩是地幔物质底侵导致下地壳物质重熔的产物,与额尔古纳地块和兴安地块碰撞后的伸展环境下地幔物质上涌密切相关。     

内蒙赤峰楼子店拆离断层带下盘变形花岗质岩石的时代、成因及其地质意义——锆石U-Pb年龄和Hf同位素证据

对内蒙赤峰楼子店拆离断层带下盘前人划为前寒武纪岩石的糜棱状花岗质岩石中锆石进行了U-Pb年龄测定和Hf同位素测试,结果显示其时代为晚古生代至中生代。楼子店扎兰营子片麻状花岗岩的锆石206Pb/238U年龄为253.6±1.2Ma,锆石εHf(t)值为-8.6～-14.6,锆石Hf同位素地壳模式年龄为1.8～2.2Ga;朝阳沟糜棱岩化片麻状花岗岩的锆石206Pb/238U年龄为150.43±0.79Ma,锆石εHf(t)值为-5.6～-14.9,锆石Hf同位素地壳模式年龄为1.6～2.1Ga;莫里海沟片麻状闪长岩的锆石206Pb/238U年龄为127.6±3.1Ma,锆石εHf(t)值为-5.1～-13.9,锆石Hf同位素地壳模式年龄为1.5～2.1Ga。不同岩性、不同形成年龄的3个样品的εHf(t)值主要为负值,说明这些岩石主要来自地壳岩石的部分熔融。2.2～1.5Ga的锆石Hf同位素两阶段模式年龄表明它们可能主要来源于华北克拉通下地壳物质的部分熔融。结合该区已经获得的锆石U-Pb年龄,将该区古生代至中生代花岗质岩浆作用划分为4个时期:早石炭世(327Ma)、二叠纪(285～252Ma)、中三叠世—早侏罗世(241～184Ma)、中侏罗世—早白垩世(163～125Ma)。早石炭世喇嘛洞混合花岗岩的产出对应于古亚洲洋古生代向南俯冲于华北板块的时期,二叠纪花岗岩是古亚洲洋最后闭合、蒙古弧与华北陆块北缘拼合与伸展有关的岩浆活动的产物,大面积的中三叠世—早侏罗世的花岗岩是西伯利亚与华北陆块碰撞后地壳伸展的记录,中侏罗世—早白垩世(163～125Ma)岩浆活动则发育在伸展构造背景中,与岩石圈减薄存在密切的成因联系。这些新年龄资料将为华北陆块北缘古生代—中生代的地质构造演化提供重要的年代学制约。     

黑龙江霍龙门地区早古生代花岗岩的锆石U-Pb年龄、地球化学特征及构造意义

黑龙江霍龙门地区位于兴蒙造山带东部的兴安地块和松嫩地块接触带上,区内发育有早古生代花岗岩,岩性主要为二长闪长岩、石英二长闪长岩。对研究区内的2个二长闪长岩进行SHRIMP锆石U—Pb定年,结果分别为(440.6±5.8)Ma、(471.3±8.7)Ma,表明其形成于中—晚奥陶世。该时代花岗岩的主量元素具有高钠、中-高钾、略富铝、富镁、钙的特征;微量元素表现出K、Ba、Rb明显富集,而Nb、Ta、P、Ti明显亏损的特征;稀土元素具有明显的轻稀土元素富集、重稀土元素相对亏损的特征,呈弱的负Eu异常,轻重稀土元素分馏程度较弱,稀土配分曲线较为平缓。花岗岩的R_1-R_2构造环境判别图解与微量元素(Yb+Nb)-Rb、Y-Nb构造环境判别图解显示,该期发育的早古生代花岗岩为后造山或碰撞后环境,结合本区所处的构造环境推测研究区内早古生代花岗岩应为兴安地块向北移动拼贴额尔古纳地块俯冲、挤压过程中形成的后造山或碰撞后阶段的产物。     

大兴安岭东北部早古生代花岗岩锆石U-Pb年龄、Hf同位素特征及地质意义

大兴安岭东北部早古生代花岗岩属于Ⅰ型花岗岩。锆石的LA-ICPMS U-Pb年代学研究表明,十八站岩体、内河岩体、白银纳岩体的形成年龄分别为499±1、500±1和460±1Ma,而查拉班河岩体为一多次侵入的杂岩体,其形成年龄在465～481Ma。结合本区和邻区其它早古生代花岗岩体的锆石U-Pb年龄,限定了大兴安岭东北部地区早古生代花岗岩浆活动的时限为460～500Ma。锆石的LA-MC-ICPMS Hf同位素研究显示,本区早古生代花岗岩的锆石ε_(Hf)(t)多数介于 1.5～ 3.8之间,二阶段模式年龄介于1.1～1.4Ga,表明其主要起源于中-新元古代增生的地壳物质。结合兴安地块其它花岗岩的锆石Hf同位素资料,认为额尔古纳地块在中-新元古代时期曾发生一次重要的地壳增生事件,与兴安地块主要为显生宙地壳的特点明显不同。     

大兴安岭中段突泉地区早白垩世碱性流纹岩锆石U-Pb定年及岩石成因

LA-ICP-MS锆石U-Pb年龄表明,突泉地区碱性流纹岩锆石的~(206)Pb/~(238)U年龄分别为135±1Ma、133±1Ma,属于早白垩世岩浆活动的产物。岩石地球化学资料表明,碱性流纹岩具富SiO_2、K_2O和高TFeO/MgO值,低Al_2O_3、CaO和MgO的特征,属于高钾钙碱性系列岩石,稀土元素总量较高,轻、重稀土元素分馏明显,具右倾的稀土元素分布模式,负Eu异常明显,相对富集Rb、U、Zr、Hf,亏损Sr、Ti、Nb、Ta等元素,花岗岩判别图解上,样品分布在A型花岗岩区;在Nb-Y-3Ga图解上,显示拉张构造环境的A_2型花岗岩的特征;元素地球化学示踪指出,突泉地区碱性流纹岩可能起源于下地壳的部分熔融,结合区域上分布的同时代火山岩及A型花岗岩类,可以限定碱性流纹岩形成于伸展构造背景,并可能与北部蒙古-鄂霍茨克缝合带的演化有关。锆石Hf同位素研究显示,本区早白垩世流纹岩ε_(Hf)(t)值为+4.2～+10.7,其二阶模式年龄平均为0.74～0.76Ga,结合松嫩地块、兴安地块Hf同位素资料,表明兴安地块与松嫩地块具有相似的地壳增生过程。     

Wavelength-dispersive X-ray fluorescence spectrometric determination of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites

Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours.     

高压微波消解法测定醋酸纤维过滤器采集的微尘粒子中的砷镉钴铬铜铁锰镍铅钒锌

最新的流行病学研究表明,空气中较高浓度的悬浮细颗粒可能对人类的健康有不利的影响。根据该项研究显示,由于心脏病、慢性呼吸问题和肺功能指标恶化而导致死亡率的升高与细尘粒子有关。这些研究结果已经促使欧盟于1999年4月出台了限制空气中二氧化硫、二氧化氮、氧化氮、铅和颗粒物含量的法案(1999/30/EC),对各项指标包括对可吸入PM10颗粒的浓度提出了新的限制性指标。PM10颗粒是指可以通过预分级器分离采集的气体动力学直径小于10μm的细颗粒。目前研究的兴趣重点逐步偏向PM2.5这些更细微颗粒物,PM2.5这种颗粒物对健康有明显的不利影响。在欧盟指令2008/50/EC中,对PM10和PM2.5都提     

硅酸盐类样品中硅、铁、铝、钛、锰、钙、镁、钾、钠和磷的x射线荧光光谱测定

本文拟定了一种以熔融法制备样片,用X射线荧光光谱测定硅酸盐类样品中Si、Fe、Al、Tj、Mn、Ca、Mg、K、Na、P等元素的分析方法。在对不同靶材X光管和分光晶体实验对比的基础上,选择了最佳的测量条件。该法具有快速、准确,测量范围广,检测限低,价格便宜等优点。经过近百个各种类型标样或管理样品的分析对比表明,本法不仅适用于硅酸盐类岩石样品的分析,还适用于铁矿、铝土矿、碳酸盐类岩矿样品以及水泥、耐火材料等样品的分析。     

Isotopic systematics of He,Ar, S,Cu, Ni,Re, Os,Pb, U,Sm, Nd,Rb, Sr,Lu, and Hf in the rocks and ores of the Norilsk deposits

This paper reports the first results of a study of 11 isotope systems (³He/⁴He, ⁴⁰Ar/³⁶Ar, ³⁴S/³²S, ⁶⁵Cu/⁶³Cu, ⁶²Ni/⁶⁰Ni, ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ^206–208Pb/²⁰⁴Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.     

Viscous, cohesive, non-Newtonian, depositing, radial slurry flow

Mining induced subsidence can significantly affect mining costs where major surface facilities and natural environment need to be protected. Overburden grout injection is a technology used to control coal mine subsidence by injecting the mine waste material extracted from the coal back into the inter-burden rock during longwall mining. The flowing slurry is here categorised as a nonlinear viscous cohesive (Bingham plastic) fluid. During longwall mining the grout slurry is pumped into the separated beds of the rock mass through a central vertical borehole, which is drilled deep into the inter-burden rock strata above the coal seam. However, a blockage can occur in the injection system when the slurry velocity falls below a certain critical threshold velocity, indicating a material phase change from cohesive-viscous to cohesive-frictional. In situ field injection tests through boreholes have been simulated at a smaller scale at the CSIRO laboratory in Brisbane by pumping the slurry through a radial disk (gap = 4 mm) from its centre. Laboratory experiments indicate a general, nonlinear, cohesive, viscous, frictional model for shear behaviour of the slurry, in which the material shear parameters are functions of the disk radial distance. Complete dimensional and dimensionless analytical solutions have been developed based on an approach related to Bingham–Herschel–Bulkley fluid mechanics. The derived formulae include relations for minimum pump pressure, local pressure and pressure gradient, wall shear stress, volume rate, velocity and velocity gradient. The theoretical results match the experimental measurements. The experiments covered slurries with maximum particle sizes of 0.5 to 2 mm with about 50% being larger than 100 µm. The viscosities at the various solids concentrations were measured with a standard torsion viscometer. This study differs from the previous research in several distinct aspects, namely, consideration of the variable shear parameters rather than fixed values, inclusion of total nonlinear behaviour, and implementation of a friction function to mimic behaviour of the deposited and consolidating stiff slurry, which can cause a significant pressure rise as a result of the increased shear resistance.     

硅酸盐中铁、锰、钛、钙、钾、磷、硅、铝、镁、钠、锶、铷、钡的X-射线荧光光谱定量测定

本文介绍样品经四硼酸锂熔融制成玻璃小饼。采用Lachance模式和理论a系数来校正元素间的效应,由3080E型X-射线荧光谱仪和DF-350B数据处理系统完成硅酸盐中十三个项目的测定。     

Bellechester,Minnesota, USA,lagoon collapses

Bellechester, Minnesota, is a small community of approximately 155 residents located on the county line between Goodhue and Wabasha counties in southeast Minnesota's karst region. Bellechester is served by a 21-year-old wastewater treatment facility (WWTF) consisting of three waste-stabilization ponds. On 28 April 1992 six sinkholes were discovered to have drained cell 2 of the WWTF resulting in the loss of approximately 8.7×10⁶ 1 of partially treated effluent and about 600 m³ of soil into previously undetected subsurface voids of unknown dimensions. In the week following the collapse, approximately 200 water wells located within a 5-km radius of the WWTF were sampled in an after-the-fact, emergency sampling program. Twelve samples with elevated fecal coliform levels, 18 samples with nitrate-nitrogen greater than the 10 mg/1 standard, and no samples with elevated chlorides were found. However, the elevated levels could not be unambiguously attributed to the WWTF collapse. This is the third WWTF to fail by sinkhole collapse in southeast Minnesota since 1974. All three collapsed lagoons have been located in similar geomorphic and stratigraphic settings. However, at least two lagoons have collapsed in the adjacent area in northeast Iowa, and these lagoons are located at different stratigraphic positions. Twenty-two WWTFs constructed in southeast Minnesota's karst region in the last 25 years have been identified as subject to potential sinkhole collapse. An unknown but significant number of manure storage lagoons, flood control structures, etc., have also been constructed in the karst region and are at risk. Public agencies are beginning to develop plans to deal with the risk associated with existing and future waste lagoons in this environment. The critical hydrogeologic parameters that can be used to prioritize the risk of collapse at existing facilities include: (1) the lithology of the first bedrock beneath each lagoon, (2) the thickness of surficial materials between the lagoon and the bedrock surface, (3) the presence and construction of liners (seepage rate), and (4) the proximity to existing sinkholes.     

Mercury,arsenic, antimony,and selenium contents of sediment from the Kuskokwim River,Bethel, Alaska,USA

The Kuskokwim River at Bethel, Alaska, drains a major mercury-antimony metallogenic province in its upper reaches and tributaries. Bethel (population 4000) is situated on the Kuskokwim floodplain and also draws its water supply from wells located in river-deposited sediment. A boring through overbank and floodplain sediment has provided material to establish a baseline datum for sediment-hosted heavy metals. Mercury (total), arsenic, antimony, and selenium contents were determined; aluminum was also determined and used as normalizing factor. The contents of the heavy metals were relatively constant with depth and do not reflect any potential enrichment from upstream contaminant sources.     

滇东南花岗岩与锡、银、铜、铅、锌多金属矿床的成因关系

滇东南锡、银、铅、锌多金属矿床主要分布在个旧、白牛厂、都龙3个矿区,而滇东南较大的3个花岗岩体又分别出露在3个矿区或附近.花岗岩体均形成于燕山晚期,岩石化学、矿物成分相似,富含锡、银、铅、锌、钨、铜等成矿元素.矿床主金属元素组合与岩体之间的距离由远而近出现由锡、钨、(铍、铌、钽)→锡、钨、(铁)、铜、铟→锡、铅、锌、银、铟、(锑)有规律的变化.花岗岩浆是成矿物质来源和成矿热源.岩浆侵入初期使上覆地层隆起产生背斜(凹陷部位成向斜);同时使地层产生一系列裂隙、压性断层或层间断裂;岩浆侵入晚期,这些断层再次活动,表现为张性,岩浆产生的含矿热液沿由其活动所造成的断裂迁移、充填、交代、沉淀而形成矿床.     

岩石密度和超高压岩石折返速率

在常温常压条件下对中国大陆科学钻CCSD主孔100-3000米岩心样品进行了密度测量,建立了密度连续剖面,并界定了不同超高压岩石的密度值。通过对比高温高压物性实验资料,岩石密度随着退变程度增强而降低,榴辉岩密度变化序列为3.52g/cm3→3.49g/cm3→3.07g/cm3→2.93g/cm3。超高压长英质岩石密度变化序列为3.00g/cm→2.80g/cm3→2.65g/cm3。上述实验资料是讨论不同折返阶段岩石所受浮力的基础,为研究折返速率大小提供了基本参数。本文通过折返板块运动平衡时,上浮力与粘滞力平衡这一关系式,定量研究了大陆俯冲板块的折返速率,认为密度差产生上浮力从而引起折返,温度对板块折返速率的影响最为显著;密度差大小、折返角度、折返板块大小对折返速率也有直接的影响。定量模拟分析表明,在温度高于850℃时,板块的折返速率可以超过100mm/a;当温度降至700℃时,折返速率则低于1.5mm/a。作者认为在折返早期,温度较高,板块快速折返至60-70km榴辉岩相深度;随着传导散热,温度降低,板块以较慢的速率折返至中下地壳。折返速率的估算表明,浮力是板块折返第一阶段(从>100km深部折返至<40km的中下地壳)的主要驱动力。