Confirmation of pelitic granulite in the Altai orogen and its geological significance

The existence of pelitic granulite in the Altai orogen was confirmed for the first time by detailed petrographic research and P-Tpseudosection modeling. The pelitic granulite has the assemblage of garnet ＋ cordierite ＋ K-feldspar ＋ biotite ＋ sillimanite ＋ plagioclase ＋ quartz with some samples containing the paragenesis of cordierite ＋ spinel. Peak conditions of the pelitic granuUte determined from the P-T pseudosection involved P = 0.5-0.6 GPa, T= 780-800℃ belonging to medium- to low-pressure type. SHRIMP U-Pb dating of zircon presented a metamorphic age of 292.8 ± 2.3 Ma. The discovery of pelitic granulite reflects an extensional environment with high heat flow in the southern margin of the Altai orogen during the Early Permian, which provides an important petrological constraint on the evolution of the Altai orogen.     

An experimental study of dehydration melting of phengite-bearing eclogite at 1.5―3.0 GPa

Dehydration melting experiments were performed on ultrahigh-pressure eclogite from Bixiling in the Dabie orogen at 1.5--3.0 GPa and 800--950℃ using piston cylinder apparatus. The results show that （1） eclogite with -5% phengite started to melt at T≤800--850℃ and P = 1.5--2.0 GPa and produced about 3% granitic melt; （2） the products of dehydration melting of phengite-bearing eclogite vary with temperature and pressure. Fluid released from dehydration of phengite and zoisite leads to partial melting of eclogite and formation of plagioclase reaction rim around kyanite at pressures of 1.5--2.0 GPa and temperatures of 800--850℃; （3） phengite reacted with omphacite and quartz and produced oligoclase, kyanite and melt at elevated temperatures. Oligoclase is the primary reaction product produced by partial melting of phengite in the eclogite; and （4） the dehydration melting of phengite-bearing eclogite at pressures of 1.5--3.0 GPa and temperatures ≥900℃ results in formation of garnets with higher molar fraction of pyrope （37.67 wt.%--45.94 wt.%）. Potassium feldspar and jadeite occur at P = 2.4--3.0 GPa and T≥900℃, indicating higher pressure and fluid-absent conditions. Our results constrain the solidus for dehydration melting of phengite-bearing eclogite at pressures of 1.5--3.0 GPa. Combining experi- mental results with field observations of partial melting in natural eclogites, we concluded that phengite-bearing eclogites from the Dabie-Sulu orogen were able to partially molten at P= 1.5--2.0 GPa and T= 800--850℃ during exhumation. The ultrahigh-high pressure eclogites would have experienced partial melting in association with metamorphic phase transformation under different fluid conditions.     

The subducted slab of Yangtze continental block beneath the Tethyan orogen in western Yunnan

The western Yunnan area is a natural laboratory with fully developed and best preserved Tethyan orogen in the world. Seismic tomography reveals a slab-like high velocity anomaly down to 250 km beneath the western Yunnan Tethyan orogen, to its west there is a low-velocity column about 300 km wide. In the region from Lancangjiang to Mojiang an obvious low velocity in the lower crust and uppermost mantle overlies on the slab. Synthesizing the available geological and geochemical results, the present paper demonstrates that this slab-like high velocity anomaly is a part of the subducted plate of Yangtze continental segment after the closure of Paleotethys. The collision of India and Eurasia continent starting from 50–60 MaBP might trigger thermal disturbance in the upper mantle and cause the uprising of asthenosphere, in that case the subducted Yangtze plate could be broken off, causing Cenozoic magmatic activities and underplating in the Lancangjiang-Mojiang region.     

An experimental study of dehydration melting of phengite-bearing eclogite at 1.5―3.0 GPa

Dehydration melting experiments were performed on ultrahigh-pressure eclogite from Bixiling in the Dabie orogen at 1.5―3.0 GPa and 800―950℃ using piston cylinder apparatus. The results show that (1) eclogite with ~5% phengite started to melt at T≤800―850℃ and P = 1.5―2.0 GPa and produced about 3% granitic melt; (2) the products of dehydration melting of phengite-bearing eclogite vary with temperature and pressure. Fluid released from dehydration of phengite and zoisite leads to partial melting of eclogite a...     

苏北双湖晶质石墨矿找矿预测模型

为了使苏北地区晶质石墨矿勘查取得新突破,研究苏鲁造山带(江苏段)典型石墨矿床成矿规律及找矿模型具有重要意义。通过总结双湖石墨矿床地质、物探等综合特征,结合研究其成矿模式及关键找矿要素,总结了找矿预测模型。研究表明,双湖石墨矿体呈似层状、透镜状产于东海杂岩斜长角闪岩大理岩组一套大理岩-变粒岩-石英岩中,含矿岩性为石墨石英岩、含石墨大理岩,系多期区域变质作用形成。双湖石墨矿属区域沉积变质型晶质石墨矿,矿(化)体的产状、规模、形态均受大理岩控制,大理岩既是含矿母岩,又是赋矿围岩。石墨矿化体与低阻高极化异常基本吻合。据此建立了地质-地球物理找矿预测模型。可见,在含矿地层附近采用激电测量是快速确定找矿远景区的方法。     

造山运动与秦岭造山

对造山运动概念的演变进行了讨论，提出了分析秦岭造山作用的现实原则基础。根据秦岭造山带区域地质构造演化和不同时期、不同类型造山作用的研究，划分出俯冲、碰撞和陆内造山作用3个主要阶段。其中碰撞造山作用可进一步分为弧—陆碰撞和陆—陆碰撞阶段。研究认为：秦岭地区古生代以来随着板块构造体制向陆内构造体制的复杂转化，经历了多次、多种类型造山作用的复合叠加，仅仅根据经典板块造山模式不能对秦岭演化历史作出完整解释；受古特提斯东部构造城独特的构造背景控制，即使在古生代—早中生代板块构造体制阶段，秦岭造山作用的细节过程也表现出与传统板块作用明显不同的特征。     

桐柏造山带岩石分形几何学特征及其意义

变质变形岩石中动态重结晶石英颗粒边界分维数是很好的地质温压计,能够恰当地反映岩石的变质变形环境.文章运用分形几何学的方法对桐柏造山带内岩石中动态重结晶石英颗粒进行了研究,探讨其对桐柏山造山带构造变形指示意义.结果显示,桐柏造山带从南到北动态重结晶石英颗粒分维数为1.17-1.29-1.16,反映角闪岩相—绿片岩相—角闪...