Heavy minerals refer to terrigenous detrital minerals with a relative density of more than 2.9 in sedimentary rocks. They are usually accessory minerals in parent rocks, and generally contain less than 1% in sedimentary rocks.It is used to infer the terrigenous source area and the composition of parent rock, and to divide and contrast strata.It plays a certain role, but it can be dissolved in the diagenetic epigenetic stage, and can also produce authigenic heavy minerals, so it should be used carefully.[1]
influence factor
Announce
edit
Hydrodynamic conditions and burial diagenesis are two main factors that affect source information.Therefore, under similar hydrodynamic conditions and diagenesis, the mass ratios of stable heavy minerals can better reflect the source characteristics. These ratios are called heavy mineral characteristic indexes, such as ATi (apatite tourmaline index), RZi (containing TiOtwoMineral zircon index), MZi (monazite -zirconIndex), CZi (chrome spinel zircon index) and other heavy mineral characteristic indexes are used to indicate the source characteristics.[2]
Analysis process
Announce
edit
Using heavy mineral analysis (HMA) to determine the source can be divided into three steps:
① The traditional heavy mineral analysis method is used to identify the rock type and limit the location of the source area;
② Select one or more single particle minerals and source mineralsGeochemistryComparison to further obtain the information of source rocks;
③ Isotopic dating is used to further determine the age of the source area.
The comprehensive utilization of the three methods will provide accurate information for the correct evaluation of source areas.[2]
application
Announce
edit
Material source analysis
Heavy minerals are important signs of provenance.Geologists have long judged the provenance of heavy minerals based on their physical characteristics (such as color, morphology, grain size, hardness, stability, etc.) and their combination relationship.However, due to the diversity of mineral species, it is often difficult to distinguish them only by their physical properties.For example, optical features can be easily distinguishedOrthopyroxeneAnd clinopyroxene, but it is still difficult to use it to distinguish various species of clinopyroxene.With the application of electronic analysis technology, the geochemical differentiation characteristics of single grain heavy minerals have been fully utilized. Many scholars have proposed indicators and end element diagrams to determine the source of materials by analyzing different heavy minerals (such as zircon, tourmaline, garnet, pyroxene, hornblende, spinel, etc.).Although the geochemical characteristics of heavy minerals are sensitive to provenance analysisabundanceIn the process of transportation, sedimentation and diagenesis, it is often affected by many factors, such as physical sorting, mechanical crushing, interlayer dissolution, etc., which will inevitably affect the accuracy of provenance identification.[2]
Tectonic evolution
Tectonic activity determines the type andbasinAnd thus affect the combination and characteristics of heavy minerals.On the contrary, the information fed back by heavy minerals in sedimentary basins can be used to study the tectonic evolution and the relationship between basins and orogenic belts.Unstable minerals (such as pyroxene, hornblende, etc.) in heavy minerals that are sensitive to tectonic activity and weathering conditions can be used to reflect the structural information of orogenic belts and sedimentary basins.However, when using heavy minerals to study tectonic evolution, attention should also be paid to the source of heavy minerals, that is, whether it is provided by the decapitation of peripheral orogenic belts or syntectonicvolcanic activityAt this time, isotopic dating is particularly important.[2]
Stratum analysis and correlation
stayFlyschIn the basins and molasse basins, due to the lack of fossils, single lithology, and often diachronic phenomenon, stratigraphic analysis and correlation are very difficult. At this time, the establishment of heavy mineral strata is an effective way to solve this problem, because each layer has a special combination of heavy minerals.The heavy minerals in different strata come from different tectonic backgrounds.Basin mountain conversion is one of the hot spots in modern geology, and correct division and correlation of heavy mineral strata in sedimentary basins is the basis for inversion of tectonic evolution of basin margin orogenic belts.[2]
Lithofacies paleogeography
The distribution of heavy minerals is restricted by geographical environment.The flume experiment results show that the distribution of heavy minerals is obviously different in different geographical environments.In the straight channel, sorting results in the increase of coarse mineral content in the surface sediment.The enrichment capacity of heavy minerals is different in different river sections. On the plane, deep troughs and shoals are the enrichment areas of heavy minerals.[2]
In a word, with the application of advanced testing techniques and analytical methods in heavy mineral analysis, heavy minerals are increasingly used in basin analysis.However, heavy mineral analysis is only one method, and the geological environment is often complex, so it is inevitable that deviation will occur only by one method.Therefore, when heavy minerals are used for basin analysis, different methods should be combined for overall evaluation and comprehensive research to obtain more practical conclusions.[2]
