岩浆热场：它的基本特征及其与地热场的区别

Magma-thermal field: Its basic characteristics,and differences with geothermal field

"岩浆热场"指的是由岩浆引发的瞬间热场。热场的热主要来自未固结的岩浆,岩浆加热了围岩,使下地壳、中地壳和上地壳的下部在一个短暂的时间内保持一种高热状态。岩浆热场与地热场有许多不同:(1)热的来源不同。地热场的热主要来自地壳物质放射性生成的热;岩浆热场的热来自岩浆。(2)热的分布不同。地热场的等温面总体上呈水平分布,温度随深度增加而增加;岩浆热场的等温面则围绕岩体分布,靠近岩体温度高,远离岩体温度低,故岩浆热场的等温面是大体垂直于地热场等温面分布的。(3)热场的规模不同。地热场是全球性的,岩浆热场是局部性的,只在有岩浆的地方才出现。岩体小则规模小(热场宽度仅几米或几十米),岩体大则规模大(宽约几千米);如果存在大规模岩浆活动,岩浆热场的长宽均可达几百或上千千米,如在中国东部中生代大规模岩浆活动期间。(4)热持续的时间不同。地热场可以持续很长的时间(几十、几百或几千个百万年);岩浆热场是瞬间的突发性事件,持续的时间从几年到几个百万年。岩浆热场最重要的意义是,它是热液赖以上升的通道,它有利于来自下地壳底部和壳幔过渡带的流体(热液)的活动,使含矿热液得以顺利上升,并在热场范围内进行充分的活动、对流循环、萃取围岩中的成矿金属元素,并在地壳浅部岩浆热场之上合适的部位沉淀富集成矿。"岩浆热场"的概念依赖于对岩浆物理性质和过程的深入了解,由于我们这方面的知识相对贫乏,所以目前对岩浆热场的了解还是很肤浅的。

The magma-thermal field indicates the instantaneous thermal field caused by magma. The heat in the thermal field mainly from unconsolidated magma has heated the surrounding rock. The lower crust,middle crust and the lower part of the upper crust maintains a high temperature state in a short time. There are many differences between a magma-thermal field and a geothermal field：（ 1） The different heat source. The heat in geothermal field is generated by the crustal radioactive material of the overlay rocks; otherwise the heat in a magma-thermal field comes from the magma.（ 2） The different distribution. The isotherm of the geothermal field was of horizontal,and it increases with increasing depth; the temperature contour of magma thermal fields is of surrounding about the intrusions,it is of high temperature close to intrusion,and lower one away from the intrusions,the isotherm of the magma thermal fields is perpendicular to the geothermal field isotherm.（ 3） The different scales of thermal field. The geothermal field is global; the magma thermal field is localized only where the magma exists,small scale with smaller intrusion（ only a few meters or tens of meters in the width）,large scale with larger intrusion（ a few kilometers in the width）. The magma thermal field is of up to hundreds or thousands of kilometers in the length and width if there is large-scale magmatic activity,such as large-scale magmatic activity in eastern China during the Mesozoic era.（ 4） The different duration of heat maintain. The geothermal field can last for a very long time（ tens, hundreds or thousands of millions of years）; the magma thermal field is instantaneous event,last from a few years to a few million years. It is the most important implication that the magma thermal field supplies the hydrothermal rise channel on which it is fever to fluid（ hydrothermal） activities under the crust bottom and crust-mantle transition zone,so that the ore-bearing hydrothermal rise smoothly,active fully,convect,and extract mineralization metal elements in the surrounding rock,and precipitation enrichment and mineralization in a suitable site on the shallow crust within the thermal field scope. The concept ‘Magma-thermal field＇relies on the deep understanding of the physical properties and processes of magma,and is still very superficial due to our relative lack of knowledge.