苏鲁高压-超高压带的结构、变形特征及形成背景探讨

苏鲁高压-超高压变质带由不同层次、不同级别、不同变质岩石组合的构造岩片堆叠而成,自北向南可分别为9个构造岩片.这种复杂的结构的形成和发展主要受早期的变质变形作用控制,并被晚期构造作用改造.本文重点对高压-超高压变质带的构造变形进行了分析,自元古宙-中生代韧性改造事件可分为4期.最后在以上工作的基础上对其形成的地质背景进行了探讨,指出了两次高压-超高压变质事件存在的可能,而且其新元古代的构造事件可与全球Rodinian超大陆的形成与裂解相对比.     

祁漫塔格地区晋宁期变质侵入岩(体)的发现及其地质意义

东昆仑西段祁漫塔格地区首次发现的晋宁期变质侵入岩(体),侵入于古元古代金水口岩群中,铀-铅同位素年龄值为831±51Ma,时代为新元古代,岩浆成因属地壳物质重熔的MPG型,是同碰撞构造环境下形成。该套变质侵入岩的发现,对于东昆仑西段前震旦纪基底的深入研究及更进一步恢复和确定祁漫塔格构造岩浆带发展演化史具有重要意义。     

一种刚玉夕线钾长片麻岩的岩石学矿物学特征及形成环境

刚玉夕线钾长片麻岩是产于新太古代迭布斯格岩群中的一种低Si、高Al、高K的特殊岩石,主要包括刚玉钾长金红石片麻岩、黑云夕线钾长金红石片麻岩2种岩石组合,呈互层状产出。刚玉、夕线石和钾长石是通过白云母的变质分解和白云母 SiO2的变质反应而生成的。形成温度约为720～760℃,压力约为0.6～0.8GPa。由于温度和压力稍高,岩石中已开始出现重熔钾长石细脉。环带状次生白云母的出现属退变质反应。变质程度为区域中高温变质作用,达高角闪岩相,与围岩的变质程度一致。其原岩是在较短的稳定条件下由富K、富Al的花岗质岩石经强烈风化搬运进入大陆边缘沉积盆地,再经化学分解和沉积作用而形成的不同的原岩组合。     

五台山区甘泉一带变质砾岩特征及地质意义

山西五台山区甘泉一带呈层状夹于五台岩群中的变质砾岩,曾作为五台岩群划分为中、下亚群的重要标志.该变质砾岩层布丁状,沿着五台岩群大型复式向斜核部呈"之"字形断续出露,区域上呈一强变形带.砾岩胶结物为强烈糜棱岩化、构造片岩化的中基性火山熔岩.砾石成分为强烈塑性变形的五台岩群不同层位的滚圆度好、分选性差的复杂成分陆源物及构造、热液成因的假砾石.研究确认,在这套变质砾岩层的两侧分别存在以五台岩群不同层位为底界、以该砾岩为底砾岩的甘泉不整合和宽滩不整合,变质砾岩层分别切割所谓五台岩群下亚群和中亚群的地层.因此,甘泉变质砾岩为叠置于五台岩群之上的地层单元,不能作为五台岩群中、下亚群的界限标志,甘泉变质砾岩应从五台岩群剔除,归属于滹沱群四集庄组.     

中国大陆科学钻探100-2000m超高压变质岩普通Pb同位素地球化学初步研究——俯冲陆壳内脱耦的证据

本文首次对中国大陆科学钻探工程100～2000m榴辉岩中的绿辉石和片麻岩中的长石进行了普通Pb同位素研究。钻孔上部岩段（0-800m）样品放射成因Pb同位素含量比较高且变化幅度较小（^206Pb／^204Pb=16．81-17．29,^207Pb／^204Pb=15．37-15．45,^208Pb／^204Pb=37．20-37．66）,说明其原岩的U／Pb和Th／Pb或者初始Pb同位素比值比较高。钻孔中部岩段（800-1600m）发育有韧性剪切带,相应的Pb同位素比值开始降低且有起伏（^206Pb／^204Pb=16．26-16．72,^207Pb／^204Pb=15．27～15．38,^208Pb／^204Pb=36．73～37．40）、钻孔下部岩段（800～1600m）样品放射成因Ph同位素含量低但变化幅度较小（^206Pb／^204Pb=16.05～16．46,^207Pb／^204Pb：15．22～15.29,^208Pb／^204Pb=36．68～37．48）,说明其原岩的U／Pb和Th／Pb或者初始Ph同位素比值比较低。实测数据同模拟数据对比表明,钻孔上、下两岩段样品普通Ph同位素不同一方面是由于继承了原岩初始Pb同位素不同,另一方面是由它们的μ值不同所致。结合氧同位素研究,本文认为800m以上和1600m以下分属上地壳和中地壳．前者是从俯冲大陆岩石圈解耦的上地壳,在大陆岩石圈俯冲过程中,上部岩片同俯冲的大陆岩石圈发生挤离,率先沿着这一个挤离面逆冲折返至浅部。下岩片是随后从俯冲岩石圈解耦的中地壳岩片,并折返至浅部下伏在先期折返的上部岩片之下。考虑到中部岩段（800～1600m）既发育有韧性剪切带又具有异常低^18O峰值（Xiao et al．,2006）,挤离面是在地壳内部晚元古代的断裂带及冷水活动通道基础上发育起来的。     

渤海海域变质岩风化壳发育特征及其储层定量预测

随着渤海油田锦州25-1南、锦州20-2以及渤中26-2等风化壳型油气田的相继发现,以及近两年渤中19-6千亿方大气田的重大勘探突破,元古—太古宇变质岩逐步成为渤海海域潜山勘探层系的重点之一。为了研究渤海变质岩潜山风化壳的发育特征并建立其储层预测方法,通过对典型潜山取心、薄片、测井、常量元素以及物性资料分析,划分了变质岩潜山的风化壳纵向结构,明确了风化壳发育差异的控制因素,并以5项因素灰关联系数为介质,采用Q型聚类法对储层级别进行了优劣排序。研究结果表明：变质岩风化壳可以划分为5个纵向结构,其发育程度明显受岩性、构造和保存条件等因素的影响,其中,被前人忽视的上覆沉积环境作为风化壳的保存条件意义重大。对11口已钻井风化壳进行变量因子归类,由好到差划分了Ⅰ—Ⅳ 4个储层级别。利用该方法在渤中19-6风化壳预测中的应用效果较好。     

宜阳地区罗圈组水下岸坡冲积扇的沉积特征

罗圈组作为冰川沉积物,已为地学界所重视。作者从地层层序、粒组分析和沉积环境等沉积学角度分析,初步认为它不管是冰川沉积物或是冰川—重力流改造沉积物,均应属水下岸坡冲积扇的沉积物。     

DRY/WET CLIMATE CHANGE SINCE 960 A.D.IN TAIHU DRAINAGE BASIN OF CHINA

IINTRODUCTION climate chang巳 divided d叮／wet penodS and discussed itsrelationships with cold／warm vanatlon and solar activityRecords ofellmate dlsasterhave been abundantly（CHEN198飞 1989）．IOund In Chinese historical literature．Previous works The present study tends to establish the dry／wethave collected such records to study the historical elf－series since 960 A．D．ofTal…     

Deformation-induced reconstitution and local resetting of mineral equilibria in polymetamorphic gneisses: tectonic and metamorphic implications

A sequence of at least three Al₂SiO₅-bearing mineral assemblages are preserved in successively overprinted ductile shear zones in the Willimantic window, Connecticut. The ductile deformation, localized at and near the boundary between the Putnam-Nashoba terrane and underlying Avalon terrane is characterized by a network of anastomozing shear zones that outline metre-scale tectonic blocks of migmatitic Kfs + Sil + Gt + Bi + Pg + Qtz + Ilm + Ru gneiss. These assemblages record Acadian or older metamorphic conditions of 6 kbar, 700d? C. Mylonitic gneisses in shear zones that define block margins were formed by reconstitution and recrystallization of the migmatitic gneiss. The reconstituted rocks exhibit relict Ky + St + Grt (+Pl + Bt + Qtz + Rt + Ilm) assemblages and require a minimum pressure for the Ky-Str grade metamorphism of 8.5 kbar. Kyanite in block margins is widely replaced by sillimanite, and locally by andalusite, during a period of post-Alleghanian ductile deformation. The interiors of blocks do not record this sequence of polymorphs. The pattern of reconstitution is accounted for by localization of strain along block margins within a regionally extensive terrane-bounding fault zone. Strain provided the activation energy for recrystallization and retrograde mineral reactions. The P-T conditions of post-Alleghanian ductile deformation evolved from 600d? C and 6 kbar to 550d? C and 3 kbar. The occurrence of Ky + Str-bearing assemblages, overprinting Acadian Kfs + Sil-bearing assemblages and subsequently overprinted by Alleghanian sillimanite- and andalusite-bearing assemblages, along with reset hornblende ⁴⁰Ar/³⁹ Ar mineral ages from Mississippian to Permian, requires a prograde Alleghanian metamorphism of rocks previously metamorphosed during the Acadian. Thus, mineral assemblages from gneisses in the Willimantic fault zone retain evidence of a protracted tectonothermal evolution that included high-grade Acadian orogenesis, tectonic loading resulting from Alleghanian collision of Avalon with North America, and tectonic exhumation in Permo-Triassic time. The c.3-kbar pressure decrease between prograde and retrograde Alleghanian metamorphic conditions corresponds to 10 km of crust that must have been tectonically excised from the base of the Putnam-Nashoba terrane cover sequence following Alleghanian orogenesis in south-eastern New England.     

Garnet Sm–Nd data from the Saualpe and the Koralpe (Eastern Alps, Austria): chronological and P–T constraints on the thermal and tectonic history

Garnets from recrystallized, staurolite- and kyanite-bearing mica schists from the central Saualpe basement, representing the host rocks of the type-locality eclogites, give concordant Sm–Nd garnet–whole-rock isochron ages between 88.5±1.7 and 90.9±0.7 Ma. The millimetre-sized, mostly inclusion-free grains show fairly homogeneous element profiles with pyrope contents of 25–27%. Narrow rims with an increase in Fe and Mn and a decrease in Mg document minor local re-equilibration during cooling. According to phengite geothermobarometry, peak metamorphic conditions at 90 Ma were close to 20  kbar and 680  °C and similar to those recorded by the eclogites. The garnet rims record about 575  °C/7  kbar for the final stages of metamorphism. A phengitic garnet–mica schist, sampled at the immediate contact with the Gertrusk eclogite, gave a garnet–whole-rock Sm–Nd age of 94.0±2.7 Ma.
Garnet porphyroclasts separated from a pegmatite–mylonite of the Koralpe plattengneiss near Stainz are unzoned and show spessartine contents of 15%. Composition and Sm–Nd ages of close to 260 Ma point to a magmatic origin for these garnets.
The garnet data from the Saualpe document an intense Alpine metamorphism for this part of the Austroalpine basement. The mica schists recrystallized during decompression and rapid exhumation, at the final stages of and immediately following a high- P event. The Koralpe data show that high Alpine temperatures did not reopen the Sm–Nd isotope system, implying a closure temperature in excess of c . 600  °C for this isotopic system in garnet.