# Block matrices with LaTeX

Does anyone know how I could write this block matrix with a LaTeX code ? For now, this is a figure I did on photoshop... And I would like it to be an equation to have a better resolution.

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}

\newcommand{\mymatrix}{
\left(\begin{gathered}
\tikzpicture[every node/.style={anchor=south west}]
\node[minimum width=2cm,minimum height=.6cm] at (0,0) {$C_2$};
\node[minimum width=2cm,minimum height=.6cm] at (0,.6) {$B_2$};
\node[minimum width=4cm,minimum height=1.2cm] at (2,0) {$M_{3,7}^{[1,2]}$};
\node[minimum width=1.5cm,minimum height=1.2cm] at (0,1.2) {$A_4$};
\node[minimum width=4.5cm,minimum height=1.2cm] at (1.5,1.2) {$M_{3,7}^{[1]}$};
\draw[dashed] (0,1.2) -- (6,1.2);
\draw[dashed] (0,0.6) -- (2,0.6);
\draw[dashed] (2,0) -- (2,1.2);
\draw[dashed] (1.5,1.2) -- (1.5,2.4);
\endtikzpicture
\end{gathered}\right)
}

\begin{document}
$M_{3,9} = \mymatrix$
\end{document}